University of Virginia

Moore’s Creek Stormwater Management

Master Plan

Volume I

Prepared by

Judith Nitsch Engineering, Inc. 186 Lincoln Street, Suite 200

Boston, Massachusetts 02111

JNEI Project #3534

November 5, 2002 Final December 31, 2002

Moore’s Creek Stormwater Management Master Plan Final Report December 31, 2002

A Draft Moore’s Creek Stormwater Management Master Plan was issued on November 5, 2002. In response to an e-mail from Robert Cooper (Virginia Department of Conservation and Recreation, VADCR) to Stephen Benz (Judith Nitsch Engineering, Inc.) dated December 19, 2002, the following changes were made to the Draft Moore’s Creek Stormwater Management Master Plan and are incorporated in the Final Report dated December 31, 2002:

1. A summary sheet for the Baseline Conditions vs. Proposed Conditions was compiled based upon data found in Volume II. This summary table has been added to a new Appendix section, Appendix E in Volume I. The Table of Contents was also revised to include Appendix E.

2. The text on Page 1 of Volume I has been revised to state that the University of Virginia

will check all projects for compliance with the Stormwater Master Plan and will issue a letter to VADCR for their final approval.

VOLUME I

TABLE OF CONTENTS

SECTION TITLE PAGE EXECUTIVE SUMMARY .......................................................................................... v I. INTRODUCTION .............................................................................................. 1 II. GOALS, PRINCIPLES, AND OBJECTIVES.................................................... 1 III. HYDROLOGY ................................................................................................... 2 A. Existing Conditions ................................................................................... 2 1. Watershed Characteristics ............................................................... 2 2. Moore’s Creek Tributaries .............................................................. 3 3. Land Cover ...................................................................................... 4 4. Soils ................................................................................................. 5 B. Former Studies .......................................................................................... 5 1. University of Virginia Strategic Plan for Water Resources

Management .............................................................................. 6 2. Moore’s Creek Watershed Study..................................................... 7

3. Moore’s Creek Watershed Assessment Letter................................. 8 4. West Grounds Stormwater Pond Improvements ............................. 8 5. Rock Creek Stream Valley Master Plan .......................................... 8 6. East Precinct Parking Garage and Infrastructure Project-The University of Virginia Health Sciences Center ............................... 8

C. Hydrologic Modeling Approach ............................................................... 9 1. Methodology.................................................................................... 9 2. Hydrologic Models.......................................................................... 10 D. Baseline Conditions Model ....................................................................... 10 1. Analysis ........................................................................................... 10 E. Unmitigated Hydrologic Model ................................................................ 11 1. Analysis ........................................................................................... 11 2. Watershed Sensitivity ...................................................................... 14

3. Watershed Response to Development ............................................. 14 F. Proposed Conditions Model ...................................................................... 14

1. Mitigation Analysis ......................................................................... 14 2. Buildout Analysis ............................................................................ 19

3. Selected Mitigation Measures ......................................................... 20 G. Mitigation for Future Development .......................................................... 28

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TABLE OF CONTENTS (continued)

SECTION TITLE PAGE IV. WATER QUALITY APPROACH ..................................................................... 30 A. Introduction to Water Quality ................................................................... 30 1. Pollutants in Stormwater ................................................................. 30

2. Water Quality Control on a Site-by-Site Basis................................ 30 3. Water Quality Control on a Regional Basis .................................... 31

B. Natural Processes ...................................................................................... 31 1. Ecosystems ...................................................................................... 31 2. Characteristics of Streams, Ponds, and Wetlands............................ 31 3. The Benefits of Streams, Ponds and Wetlands................................ 32 C. Watershed Restoration .............................................................................. 32 1. Impacts to the Natural Drainage System ......................................... 33 2. Reestablishing Natural Ecological Processes .................................. 33 3. Benefits of Watershed Restoration .................................................. 34 D. Pollutant Removal Mechanisms................................................................ 35 1. Physical Mechanisms ...................................................................... 35 2. Chemical Mechanisms..................................................................... 35 3. Biological Mechanisms ................................................................... 36 E. Regional Watershed Restoration Opportunities ........................................ 36 1. Daylighting Streams ........................................................................ 37 2. Creating Wetlands ........................................................................... 37 3. Creating Ponds................................................................................. 37 4. Planting Native Wetland Species .................................................... 37 5. Creating Floodplains ....................................................................... 37 6. Incorporating Aquatic Benches ....................................................... 37 7. Incorporating Vegetated Buffers ..................................................... 38 F. Proposed Watershed Restoration............................................................... 38 1. Stadium Drainage Basin .................................................................. 38 2. Brandon Drainage Basin.................................................................. 38 3. Health Sciences Center and University Hospital............................. 39 V. WATER QUALITY............................................................................................ 40

A. Pollutant Removal Efficiencies for Existing BMP’s................................. 40 1. West Grounds Stormwater Management Pond (Gilmer Pond) ....... 40 2. Gooch/Dillard Stormwater Pond ..................................................... 40 3. Health Sciences Center Stormwater Management Pond ................. 41

B. Water Quality for Identified Future Development Projects ...................... 41

1. Water Quality Volumes ................................................................... 41 2. Pollutant Runoff Loads.................................................................... 42

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TABLE OF CONTENTS (continued) SECTION TITLE PAGE

C. Best Management Practices Strategies...................................................... 44 1. Stadium Drainage Basin .................................................................. 44 2. Brandon Drainage Basin.................................................................. 45 3. Health Sciences Center.................................................................... 46

D. Water Quality Treatment Volumes ........................................................... 47

E. Water Quality for Future Development..................................................... 48

F. Site-Specific Water Quality Management................................................. 49 VI. COMPLIANCE WITH VIRGINIA STORMWATER MANAGEMENT

REGULATIONS ............................................................................................. 50 VII. CONCLUSION................................................................................................... 52 VIII. REFERENCES.................................................................................................... 54

LIST OF FIGURES FIGURE TITLE PAGE 1 Watershed Rating Curve for 2-year Storm Design ............................. 17 2 Watershed Rating Curve for 100-year Storm Design ......................... 17 3 Hydrologic Criteria for the Modified Gooch/Dillard Pond ................ 21 4 Hydrologic Criteria for the Enhanced Extended Detention Basin...... 22 5 Hydrologic Criteria for the Rainstore Unit ......................................... 24 6 Hydrologic Criteria for the Extended Detention Basin....................... 26

LIST OF TABLES TABLE TITLE PAGE 1 University Property within Drainage Areas........................................ 2 2 Baseline Conditions Data.................................................................... 11 3 Proposed Impervious Planning Areas within “Changed” Sub-basins 12 4 Unmitigated Model Data .................................................................... 13 5 Analysis Areas and Discharge Points ................................................. 15 6 Health Services Projects ..................................................................... 18 7 Peak Flow Rate from Sub-basin MO-3C with Gooch/Dillard Pond

Modifications...................................................................................... 21 8 Peak Flow Rate from Sub-basin MO-3A with proposed Enhanced

Extended Detention Basin .................................................................. 22

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LIST OF TABLES (continued) TABLE TITLE PAGE 9 Peak Flow Rate at the Stadium Drainage Basin Design Point............ 23 10 Peak Outflow from South Lawn Development Site ........................... 24 11 Peak Flow Rate from Sub-basin MO-5B............................................ 24 12 Peak Flow Rate at the Brandon Drainage Basin Design Point ........... 25 13 Peak Flow Rate from Sub-basin MO-6B with proposed Extended

Detention Basin .................................................................................. 26 14 Peak Flow Rate at the Health Sciences/University Hospital Design

Point.................................................................................................... 27 15 Peak Flow Rate at the MO-6A (Unmitigated) Design Point .............. 28 16 Sample Water Quantity Tracking Table ............................................. 29 17 Water Quality Volumes ...................................................................... 42 18 Pollutant Runoff Loads and Pollutant Removal Requirements ......... 43 19 Water Quality Treatment Volumes..................................................... 47 20 Sample Water Quality Tracking Table……………… ....................... 49

LIST OF APPENDICES APPENDIX TITLE A Tracking Table A.1 – Stadium Drainage Basin Water Quantity Tracking Table

Tracking Table A.2 – Brandon Drainage Basin Water Quantity Tracking Table Tracking Table A.3 – Health Sciences Center/University Hospital Area Water Quantity Tracking Table Tracking Table A.4 – Stadium Drainage Basin Water Quality Tracking Table Tracking Table A.5 – Brandon Drainage Basin Water Quality Tracking Table Tracking Table A.6 – Health Sciences Center/University Hospital Area Water Quality Tracking Table

B Exhibit 1 Moore’s Creek – University Property Map Exhibit 2 Moore’s Creek Drainage Area C Stormwater Management Facilities Maintenance Guidelines D Cox Report – Stormwater Management Calculations for Health Sciences Center Pond E Summary Tables for Baseline Conditions vs. Proposed Conditions

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EXECUTIVE SUMMARY Judith Nitsch Engineering, Inc. (JNEI) has prepared this Stormwater Master Plan (SWMP) to support the growth and development of the University of Virginia within the watershed of Moore’s Creek. The University of Virginia lies in the headwaters of many small creeks that drain in a southerly direction to join Moore’s Creek en route to the Rivanna River. Through this SWMP, the University is attempting to improve the downstream erosion and flooding problems in Moore’s Creek and its tributaries by implementing measures to reduce the peak rate of stormwater discharge – both within UVA property and at the point where the Moore’s Creek tributary branches exit UVA property. In addition, the incorporation of enhanced stormwater treatment measures will serve to improve the quality of stormwater both within the University property, as well as in the downstream receiving systems. The extent of future development identified by the University of Virginia is located along the southern portion of the University property where stormwater is collected and conveyed to Moore’s Creek via one of three waterways. These include Rock Creek, a tributary of Rock Creek, and a city drainage pipe. JNEI has strategically planned stormwater mitigation and treatment strategies in three basin areas, each of which conveys stormwater to one of these three collection waterways. For the purposes of this SWMP, the three basin areas are referred to as the Brandon Drainage Basin, the Stadium Drainage Basin, and the Health Sciences/University Hospital Area. In order to evaluate the condition and to make recommendations regarding the University Basin Areas within the Moore’s Creek Watershed, JNEI has undertaken a two-pronged approach. First, a comprehensive stormwater hydrology model was developed to assess the existing hydrologic condition of Moore’s Creek. Using this baseline conditions model, JNEI was able to develop an understanding of this complex watershed under today’s conditions. To evaluate the effects of future development, JNEI modeled development conditions based on future development projects identified by the University of Virginia in their current Master Plan. Through a series of workshop meetings held at the UVA, JNEI has presented the results and recommendations to the UVA in an effort to promote workable and realistic implementation strategies. The selected mitigation strategies intended to improve the flooding and erosion of downstream Moore’s Creek include: Stadium Drainage Basin

1. Taking advantage of “banked” storage capacity remaining in the existing Gilmer Pond.

2. Increasing the Storage Capacity of Gooch/Dillard Pond and modifying the outlet. 3. Creating an enhanced extended detention basin upstream from existing Gilmer

Pond. Brandon Drainage Basin

1. Promoting the “greening” approach at the South Lawn Development, where the post-development condition will contain less impervious area than the pre-development condition.

2. Creating an underground detention basin to reduce the peak flow rate and volume for small storm events.

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Health Sciences/University Hospital Area 1. Taking advantage of “banked” storage capacity remaining in the existing Health

Sciences Center Pond. 2. Creating an extended detention basin in the University Hospital Area.

Stormwater quality measures within the basin areas include: Stadium Drainage Basin

1. Taking advantage of “banked” storage capacity for water quality treatment in existing Gilmer Pond.

2. Providing for water quality treatment through the increased storage in Gooch/Dillard Pond, as well as providing enhanced treatment through the addition of native vegetation, aquatic benches, and floodplains.

3. Creating a new enhanced extended detention basin associated with the Observatory Hill/Alderman Road Residence Cluster that incorporates a shallow marsh system – providing additional pollutant removal through wetland plant uptake, absorption, filtration, decomposition, and settling.

Brandon Drainage Basin

1. Promoting the “greening” approach to development for the South Lawn Project. 2. Providing vegetated filter strips, grassed swales, and/or biofiltration areas.

Health Sciences/University Hospital Area

1. Taking advantage of “banked” permanent pool storage remaining for water quality treatment in the existing Health Sciences Center Pond.

2. Creating an extended detention basin upon development of areas outside the current Health Sciences Master Plan to provide pollutant removal through gravitational settling.

All Development Projects

1. Providing pretreatment at development sites. This SWMP is intended to satisfy the Virginia Department of Conservation and Recreation’s (DCR) requirements for stormwater management. As such, the level of development that has been identified and modeled in the SWMP should be acknowledged by the DCR upon their approval and review of site-specific project plans for sound engineering practices and consistency with the SWMP. Within this SWMP, JNEI has provided a simple methodology to track the projects that were anticipated and modeled within the basin areas. Thus, the University and the DCR will easily be able to compare the scopes and sizes of specific projects as they materialize and make certain the projects are consistent with the assumptions made in the SWMP.

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I. INTRODUCTION Judith Nitsch Engineering, Inc. (JNEI) has prepared this Stormwater Master Plan (SWMP) for the University of Virginia (UVA). In order to support the growth and development of the University of Virginia within the watershed of Moore’s Creek, the UVA seeks to develop its projects within the guidance parameters established by this SWMP. JNEI’s Scope of Work for this SWMP consisted of stormwater modeling of existing conditions, modeling of future development, assessment of potential impacts on stormwater peak rate and stormwater quality, and determining stormwater mitigation and treatment measures. This SWMP will become the “blueprint” for stormwater management of the development projects the UVA has planned now and in the near future. As such, certain assumptions have been made regarding the scopes and sizes of developments within the Moore’s Creek Watershed. As projects approach the completion of the design stage, they will be checked by the University of Virginia for compliance with the assumptions made in this SWMP. UVA will send a letter to the Virginia Department of Conservation and Recreation (DCR) stating the project’s compliance with the SWMP. DCR will review each project and grant approval upon acceptance of the design with the objectives of the SWMP and their current design standards. II. GOALS, PRINCIPLES, AND OBJECTIVES The goals and objectives of this Master Plan include:

To develop workable solutions to relieve the existing “stressed” stream condition of the Moore’s Creek and its tributaries;

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To understand the “baseline” conditions associated with the existing conditions within the watershed;

To evaluate the hydrologic sensitivity of the watershed;

To model the development conditions associated with the UVA’s build-out plans for the Southern portion of Campus;

To support the UVA’s desire to be responsible to the environment and to its downstream neighbors;

To ensure compatibility with previous stormwater management planning;

To implement realistic hydrologic mitigation and water quality treatment measures in support of the plans for development within the watershed, thus creating a blueprint for development of the UVA grounds;

To develop onsite and/or local-type management approaches to stormwater quantity and quality, and

To develop a stormwater management plan in accordance with the Virginia Stormwater Management Regulations addressing hydrologic and water quality issues associated with the UVA’s development within the watershed.

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III. HYDROLOGY A. Existing Conditions The existing conditions of the Moore’s Creek Watershed within the UVA property were discussed in a report entitled University of Virginia Strategic Plan for Watershed Management by Andropogon Associates. Judith Nitsch Engineering Inc. (JNEI) used the information set forth in the Andropogon report as a basis for determining the existing conditions of the watershed for the hydrological analysis discussed in this report. In addition, JNEI used City of Charlottesville watershed maps and recent topographic information to refine the existing conditions assumptions set forth by Andropogon. 1. Watershed Characteristics The University of Virginia is within the headwaters of two major tributaries that drain to the Rivanna River and, ultimately, to the Chesapeake Bay. Located on the south of the UVA campus, one of the tributaries, Moore’s Creek, is fed by many small creeks, which drain from the steep hills within the University of Virginia property. Between Ivy Road and Fontaine Road, small creeks flow down Lewis Mountain and Observatory Hill where they are collected in Morey Creek. Morey Creek flows in a southeasterly direction and joins Moore’s Creek shortly after passing beneath the railroad tracks. Along Jefferson Park Avenue and the railroad, University storm drain systems and small creeks flow south and collect in Rock Creek, which joins Moore’s Creek at the Charlottesville/Albemarle County line. For the purposes of stormwater management planning, Andropogon delineated the University property into 11 sub-basins that form the headwaters of Moore’s Creek. Using the City of Charlottesville watershed map and recent topographic information, JNEI refined the Moore’s Creek sub-basins identified by Andropogon and delineated 15 sub-basins as the Moore’s Creek Watershed. The Moore’s Creek Watershed sub-basin delineations are illustrated in Exhibit 2 of Appendix A. The Moore’s Creek Watershed consists of University property, as well as City and County property. Many of the 15 sub-basins consist of land owned by the University, as well as residential neighborhoods adjacent to University property. As part of this study, JNEI determined the portion of the various sub-basins within the watershed that are University property. A summary of the findings is shown in Table 1. See also Exhibit 1 of Appendix A of this report for a plan summarizing these findings. Table 1 University Property within Drainage Areas

SUB-BASIN IDENTIFICATION

TOTAL DRAINAGE AREA (ACRES)

TOTAL UVA AREA WITHIN

DRAINAGE AREA (ACRES)

PERCENTAGE OF DRAINAGE AREA

ATTRIBUTED TO UVA

MO-1A 73.04 67.07 92% MO-1B 10.71 2.92 27% MO-2B 23.97 0 0% MO-3A 36.13 36.13 100% MO-3B 78.76 45.57 58% MO-3C 25.13 22.78 91% MO-5A 51.89 16.69 32% MO-5B 45.90 28.33 62% MO-6A 65.66 28.50 43%

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SUB-BASIN IDENTIFICATION

TOTAL DRAINAGE AREA (ACRES)

TOTAL UVA AREA WITHIN

DRAINAGE AREA (ACRES)

PERCENTAGE OF DRAINAGE AREA

ATTRIBUTED TO UVA

MO-6B 18.50 3.33 18% MO-7 99.19 48.51 49%

MO-8A 89.18 59.85 67% TOTAL 618.06 359.68 58%

2. Moore’s Creek Tributaries The University of Virginia lies within the headwaters of two Moore’s Creek tributaries, which flow in a southerly direction from the University where they join Moore’s Creek. These tributaries include Morey Creek and Rock Creek. Although a stream channel survey was not part of the scope of this study, JNEI compiled the information regarding the properties of these collection tributaries from United States Geological Survey (USGS) Maps and a report entitled “Moore’s Creek Watershed Study” by Dewberry and Davis (1996). Stormwater runoff from the western portion of the University of Virginia campus (UVA sub-basins MO-1A, MO-1B, MO-7, MO-8A, MO-8B, MO-8C, and MO-9) is collected in drainage systems and small tributaries where it is conveyed beneath Route 29 and discharged into Morey Creek. Morey Creek travels in a south-to-southeasterly direction where it joins Moore’s Creek just as it passes beneath the Southern Railroad. According to the analysis performed by Dewberry & Davis (1996) and as interpreted by the City of Charlottesville Engineering Department, stormwater from the southern portion of the University contributes to two primary waterways within the Moore’s Creek Watershed – namely Rock Creek and a tributary of Rock Creek. The area identified as the city’s Brandon drainage basin (UVA Sub-basins MO-5A and MO-5B) conveys and discharges stormwater runoff to Rock Creek. Stormwater from this basin is conveyed under the railroad tracks south of Valley Road and into the Rock Creek basin. Rock Creek begins near the intersection of Jefferson Park Avenue (JPA) and Valley Road, travels southeast under the railroad tracks, under Cherry Avenue, and along Rock Creek Road to 5th Street near Cleveland Avenue. Stormwater runoff from the City’s Stadium Drainage Basin (UVA Sub-basins MO-3A, MO-3B, and MO-3C) is conveyed and discharged to a tributary of Rock Creek. The Rock Creek Tributary begins at the intersection of Stadium Road and Shamrock Road, travels under the railroad tracks, under Center Avenue, under Cherry Avenue, and along Mosely Drive and Cleveland Avenue to 5th Street where it joins Rock Creek. At this point, Rock Creek travels in a southeasterly direction where it joins Moore’s Creek just south of the Charlottesville City/Albemarle County line. Stormwater runoff from the University’s Hospital/Health Sciences Area is conveyed through two large-diameter pipes beneath the railroad tracks and is also discharged into the Rock Creek basin where it flows along the boundary of the Orangedale and Nalle Street Basins, and crosses beneath the 5th Street Extended (at the confluence of Rock Creek and the Rock Creek Tributary) and subsequently joins Moore’s Creek. The Dewberry & Davis Report also documents the severe flooding and stream channel erosion problems that occur in Rock Creek and its tributary. Although some improvements have been made to this system, the report indicates there is still a

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significant concern regarding the impacts of stormwater runoff of the existing Rock Creek stream channels. 3. Land Cover The existing land features of the sub-basins that contribute to the Moore’s Creek Watershed vary greatly. Large portions of the watershed have been developed by the University and by residential development with houses, academic buildings, residence halls, paved parking lots, and driveways. Other areas have been cleared for the creation of grass lawns and landscaped areas. The land cover of the 15 sub-basins within the Moore’s Creek Watershed is described below. The sub-basins are described first along the western portion of campus- from north to south, then along the southern portion of campus –from west to east (Refer to Exhibit 2 of Appendix A). Sub-basin MO-7 lies at the northern foothills of Lewis Mountain. As the mountain itself is undeveloped, the majority of the sub-basin is developed with University Research and Industrial Facilities, as well as a residential development north of Ivy Road. Sub-basin MO-8A lies at the western foothills of Lewis Mountain. This sub-basin is largely wooded and undeveloped, with the exception of a small portion of the Aerospace Research Center. Sub-basins MO-8B, MO-8C, and MO-9 lie at the western foothills of Observatory Hill. Within these sub-basins, a small amount of development is found near the peak of Observatory Hill with the McCormick Observatory Buildings; however, the remainder of these sub-basins are largely wooded and undeveloped. Sub-basin MO-1A lies in the southeastern foothills of Observatory Hill. The sloping hill is wooded and undeveloped. The eastern portion of Sub-basin MO-1A, however, is developed with University Housing, as well as a residential neighborhood of approximately one-third-acre lots along Mimosa Drive. This residential district extends east into Sub-basins MO-1B and MO-2B where it becomes denser (one-quarter-acre lot) neighborhoods along Appletree Road, Pierce Avenue, and Maury Avenue. The southern portion of Sub-basin MO-3C is developed with University Housing areas, the largest being the Gooch/Dillard Dormitory, and associated walkways, driveways, etc. The northern portion is also developed with the water towers and water plant along Observatory Road. The middle portion of Sub-basin MO-3C, between the water plant and the Gooch/Dillard Dormitory, consists of a large area of woods. Sub-basin MO-3B is an extensively developed sub-basin. The northern portion of the sub-basin consists of the University Stadium, associated parking areas, University Engineering Buildings, University Housing, and the water plant. The southern portion of the sub-basin, south of Stadium Road, consists of residential neighborhoods with lots that are approximately one-quarter acre in size. The residential neighborhoods are less than half impervious as they contain houses, roads, and driveways, but also contain pervious grassed yards and landscaped areas. Sub-basin MO-3A is also a developed sub-basin as a large area consists of the Alderman Road Residence Cluster, Gilmer Hall, and the Aquatic and Fitness Center. Portions of MO-3A remain pervious as grassed lawns, landscaped areas, and a stormwater management pond.

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The upper portion of Sub-basin MO-5A contains University Housing buildings and associated impervious areas, such as Olsson Hall, Thompson Hall, and Clark Hall. The remainder of the sub-basin consists of dense residential communities along Jefferson Park Avenue and Valley Road. These neighborhoods consist of houses and driveways on approximately one-quarter-acre lots with lawns and other pervious areas. The northern portion of Sub-basin MO-5B consists of hotels, pavilions, an amphitheater, University Housing, and other buildings, as well as associated walkways, driveways, roadways, and parking lots. However, the northern portion of this sub-basin also consists of large pervious areas such as The Lawn and other grassed and landscaped areas between walks and buildings. The southern portion of Sub-basin MO-5B is also developed with a University parking lot, the Student Nurses Dorm Area, and dense residential neighborhoods. Pervious areas within this sub-basin consist of grassed lawns and landscaped areas. The development of hotels, pavilions, and University Housing and other buildings also extends east into the northern portion of Sub-basin MO-6A, as well as The Lawn area. The northern portion of MO-6A also consists of University Health Sciences Buildings and a Heating Plant. The southern portion of Sub-basin MO-6A and all of MO-6B is also extensively developed with the University Hospital, parking facilities, research buildings and other impervious areas. A small portion of Sub-basin MO-6A also consists of a residential housing development along Monroe Lane and 15th Street. 4. Soils The soils within the University property were classified in the report by Andropogon Associates. Andropogon Associates used the USDA Natural Resources Conservation Service (NRCS) soil classifications to analyze the soils that exist on the University Campus. The NRCS categorizes soils in one of four hydrologic soil groups: type A, B, C, or D according to the soil’s ability to absorb water into the ground. Type A soils are the most permeable and Type D soils are the least. The soil classification determined by Andropogon Associates is summarized as follows: “At the University, the Albemarle fine sandy loam and the Louisburg very stony sandy loam (Hydrologic Group B) are fairly well-drained and are located in the upland areas. The Culpeper fine sandy loam (Hydrologic Group C) have somewhat poorer drainage properties and are found in low-lying areas such as along stream channels. The report also suggested that undistributed soils will allow satisfactory infiltration, but developed sub-basins that have experienced a high degree of disturbance and excavation, will produce a soil condition that is less than suitable for infiltration.” B. Former Studies Former studies have been performed within the Moore’s Creek Watershed that provided useful information for the purposes of this hydrological analysis. The reports include the following:

University of Virginia Strategic Plan for Water Resources Management, prepared by Andropogon

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Moore’s Creek Watershed Study, prepared by Dewberry and Davis (August, 1996)

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Moore’s Creek Watershed Assessment Letter, prepared by the City of Charlottesville (May 7, 2002)

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West Grounds Stormwater Pond Improvements, prepared by CEGG Associates (January 2000)

Rock Creek Stream Valley Master Plan, prepared by the Cox Company (December 2, 1997)

East Precinct Parking Garage and Infrastructure Project-The University of Virginia Health Sciences Center, prepared by the Cox Company (August 27, 1997 – revised May 4, 1998)

1. University of Virginia Strategic Plan for Water Resources Management The Andropogon report illustrates the effects of University development on the natural drainage system of the University of Virginia. It states that the large increase in impervious area over time has resulted in a greater volume of stormwater runoff downstream and a lesser volume of stormwater able to infiltrate into the ground. Along with the historical development, large portions of the natural drainage system have been altered or destroyed as streams have been placed in pipes and wetlands have been eliminated. The common mitigation practice associated with the historical development of the University has been to “build earthen detention basins at the lowest point of a project site.” However, the report concludes, “this practice has done little to compensate for the total increase in stormwater runoff volume and to prevent pollutants…from reaching the stream(s).” The Andropogon report proposes a new sustainable approach to stormwater management through the concept of a “Water Balance” model. The Water Balance model uses the concepts of the hydrologic cycle to measure the amount of water both before and after development to evaluate how impervious surfaces and manmade drainage structures alter the natural cycle. In the first part of the model, Andropogon developed a predevelopment water balance that accounted for the natural cycle of water on an undeveloped segment of land for an average year. The second part of the model demonstrated the effects of development on the natural hydrological cycle in the post-development water balance. The major effect is due to the fact that a large portion of rainfall landing on developed land is unable to infiltrate into the ground. Instead, rainfall is converted directly into runoff. The effect of development, therefore, causes erosion and flooding due to the increased volume of stormwater runoff. In addition, the loss of baseflow to the streams causes drought to occur during storm events. Andropogon concludes that one way to mitigate the drought and flood effects of land development is to restore the water balance so it replicates the natural hydrologic cycle. It was determined that “solutions to stormwater problems must go beyond simply fulfilling regulatory requirements…when the natural hydrologic cycle is significantly changed by development, only solutions that replicate the pre-development water balance can solve the broad-range of stormwater management issues.” The report proposes a stormwater management plan that combines land use and development strategies with the restoration of the natural drainage system and the use of better management practices for the sustainable future of the University. Land use strategies include the protection of stream headwaters, stream channels, associated riparian corridors, wetlands, and floodplains. Land development strategies include

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providing recharge in the uplands, minimizing impervious and semi-pervious surfaces in new development, and minimizing grading and removal of natural vegetation. The proposed restoration strategies include “daylighting” streams and establishing wetlands, floodplains, and vegetated corridors. The proposed Better Management Practices include the use of recharge beds underneath pavement, porous pavement, infiltration trenches, vegetated swales, and detention basins retrofit in streams. Specifically, Andropogon explored several areas within the University to manage stormwater according to their proposed plan. Although the report did not conclude with a single solution, case studies were performed in order to demonstrate how the various principles of the stormwater management plan could be incorporated within the University. It was proposed that the stormwater management solution should vary depending on the level of development, but, in all cases, the goal should be to restore the natural drainage system to the greatest extent possible. A large portion of the Case Studies Section involved plans to restore Meadow Creek. One Case Study, however, involved the retrofit of a detention basin in the Valley below Gilmer Hall in order to control stormwater flows from the largely developed Sub-basin MO-3 and to provide additional water quality enhancement. The Andropogon report finally touches upon the treatment of the management of stormwater as a “University-wide concern” rather than on a site-by-site basis. The report recommends the University integrate “sustainable water resources management into the University Master Plan and in strategies for future University growth.” 2. Moore’s Creek Watershed Study In the Moore’s Creek Watershed Study, Dewberry & Davis performed a detailed hydrologic, hydraulic, and water quality analysis of the entire Moore’s Creek Watershed. The report provided the City of Charlottesville and the County of Albemarle with a Stormwater Management Feasibility Study and a Watershed Plan for Moore’s Creek. The important aspects of the Dewberry & Davis Report included the analysis of the flooding and erosion problems in the major tributaries of Moore’s Creek. The report identified the two primary waterways that serve the southern portion of the City adjacent to the University of Virginia as the City of Charlottesville’s Brandon (MO-5A & MO-5B) and Stadium Drainage Basins (MO-3A, MO-3B & MO-3C). These waterways were identified as Rock Creek and a Tributary to Rock Creek, respectively; whereby a detailed Channel Capacity Analysis was performed along various reaches. Through this analysis, the study provided an idea of the severe flooding and erosion in Rock Creek and the Tributary to Rock Creek downstream from the University of Virginia. The document also noted several large culvert replacement projects and stream stabilization projects that have been completed. The report proposes several alternative approaches to Stormwater Management to address existing and future drainage, flooding, and water quality problems in the Moore’s Creek Watershed. Dewberry & Davis recommended an approach that involves implementing a regional approach to Stormwater Management that also includes onsite Stormwater Management controls. The report recommended that Albemarle County and the City of Charlottesville develop Stormwater Management Practices and Policies to prevent further stormwater impacts to the existing stream channels.

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3. Moore’s Creek Watershed Assessment Letter On May 7, 2002, the City of Charlottesville Neighborhood Development Services (Engineering Division) issued a letter to Judith Nitsch Engineering, Inc. for the purposes of the Stormwater Management Master Plan for the Moore’s Creek Watershed. The letter used information compiled from two sources, which included the Dewberry & Davis Report and a report entitled City of Charlottesville Storm Drainage Study completed in 1979 by Huffman & Associates and William Roudabush, Inc. This letter synopsized the City of Charlottesville stormwater system as it relates to three areas adjacent to the University of Virginia property and proposed future projects within these areas. The three areas included the following:

• MO-5A & MO-5B Area including JPA and the South Lawn • MO-3A, MO-3B, & MO-3C Area including Alderman Rd. and Scott

Stadium • MO-6A & MO-6B Area including the University Hospital

The letter identified various pipe systems and culverts where the previous studies recommended pipe and culvert upgrades. The letter also addressed current erosion and flooding problems observed in the southern portion of the University and the downstream tributaries. The letter also provided a summary of the Stream Crossing and Channel Capacity Analysis performed by Dewberry & Davis. 4. West Grounds Stormwater Pond Improvements CEGG Associates prepared a report in January 2000 for the West Grounds Stormwater Management Pond (or Gilmer Pond) entitled West Grounds Stormwater Pond Improvements. This report included an erosion and sediment control narrative, a stormwater management narrative, TR-20 pre-development and post-development stormwater calculations, and detailed pond-routing calculations. In addition, the report included a comparison of the impervious area anticipated in the design of the pond to the impervious area actually constructed. Through this comparison, CEGG Associates calculated the impervious area “banked” for water quantity mitigation and water quality treatment in the existing pond. The “banked” impervious area for water quantity mitigation in the pond is 1.46 acres and the “banked” impervious area for water quality treatment in the pond is 4.74 acres. 5. Rock Creek Stream Valley Master Plan The Rock Creek Stream Valley Master Plan prepared by the Cox Company in December 1997 presented a summary of stream rehabilitation and storm drainage improvements in the Rock Creek Stream Valley. This plan proposed a series of improvements to the existing stream and drainage system in response to functional aesthetic and environmental quality objectives of the Stream Valley. This report was part of a comprehensive Master Plan by the University of Virginia and the City of Charlottesville and provided JNEI with an overview of the goals and recommendations for the improvement of the Rock Creek Drainage Basin downstream from the University of Virginia. 6. East Precinct Parking Garage and Infrastructure Project-The University of Virginia

Health Sciences Center The Cox Company prepared Stormwater Management Calculations for the Stormwater Management Pond at the Health Sciences Center, with a final revision issued in May 1998. This report presented stormwater management and pond routing calculations for the stormwater retention pond in Sub-basin MO-6A. According to the Cox Company,

8

the pond was designed to accommodate the Full Development Scenario identified in Phases 1 through 4 of the 1996 Master Plan. The report concluded that the pond was designed to mitigate the Full Development scenario of 15.7 acres of impervious development. Based on the permanent pool storage capacity, the pond was designed to treat 20.88 acres of impervious area for water quality treatment, an area greater than the Full Development scenario. Based on the level of development that has occurred since the issuance of the report, JNEI was able to determine the amount of impervious area that was considered in the Full Development scenario that has not been constructed at this time. JNEI concluded that there is impervious area “banked” in the existing pond for water quantity mitigation and water quality treatment. JNEI determined that there is approximately 3.43 acres of development area planned in the Cox Company report remains “banked” for water quantity mitigation of future development in the Health Sciences/University Hospital Area. In addition, approximately 8.61 acres remains “banked” for water quality treatment of future development projects within the Health Sciences/University Hospital Area. A summary of JNEI’s determination of “banked” impervious areas for water quantity and quality is found in Section III.F.1.c and V.A.3 respectively. C. Hydrologic Modeling Approach 1. Methodology Using the Hydrologic Analysis from the Andropogon report, JNEI divided the Moore’s Creek Watershed into 15 sub-basins. Each sub-basin is defined as an area where the runoff from that area flows to a particular design point. In this case, each sub-basin produces stormwater runoff that is collected by Moore’s Creek through a creek or small tributary. All stormwater runoff from the Watershed is conveyed through various creeks and tributaries where they exit University property en route to Moore’s Creek. Exhibit 2 of Appendix A illustrates the division of the 15 sub-basins in the Moore’s Creek Watershed for the purposes of the hydrologic model in this report. The rate of runoff that reaches each point is determined by a number of factors: the slope and flow lengths of the sub-basin, the soil type of the sub-basin area, and the type of surface cover in the sub-basin area. The slope of the sub-basin area affects the amount of runoff and rate of runoff, as steep slopes produce more runoff and transport it at a faster rate than a flat site. This is due to the fact that, at a flat site, stormwater flows slowly and, therefore, has a greater opportunity to infiltrate into the ground before it flows away as runoff. The flow length of a sub-basin area is the longest hydraulic distance that runoff would have to travel to the design point. Flow length is an important factor in determining time of concentration (Tc). Tc influences the volume and rate of runoff. A low Tc will result in more runoff with a higher peak rate than a high Tc. The type of soil on a site also affects the volume and rate of runoff generated. The soil type found on a site determines the volume and rate at which water can be absorbed into the ground. The more water infiltrating into the soil, the greater the reduction in runoff volume and rate. The surface cover on a site refers to what is on the surface of a site, whether it is lawn, asphalt, brush, etc. Surface cover affects the rate and volume of runoff as certain covers

9

allow for more of an opportunity for water to be absorbed into the ground. A site covered with impermeable asphalt will not allow for any water to be absorbed into the ground, yet a site covered by vegetation will. Almost all the rain that falls onto asphalt or other impermeable covers will be converted to runoff. In addition, different vegetative covers have different properties with regard to producing runoff. Once JNEI determined drainage flow path lengths, slopes of the flow path, and surface cover types, the information was used to determine the Tc for the area. Based on the soil type, ground cover, and other factors, a weighted Curve Number (CN) was determined for each sub-basin. The peak runoff rates for various storm events were determined by inputting the weighted CN, Tc, drainage areas, and drainage information into the HydroCAD Version 6.00 stormwater modeling system computer program. The storm events were based on the 24-hour duration storm with a NRCS Type II storm distribution curve. The HydroCAD computer program uses the NRCS TR-20 method to model drainage systems. TR-20 (Technical Release 20) was developed by the Natural Resources Conservation Service to estimate runoff and peak discharges in small watersheds. TR-20 is generally accepted by engineers and reviewing authorities as the standard method for estimating runoff and peak discharges. HydroCAD Version 6.00 uses up to four structure types to analyze the hydrology of a given watershed. These structures are subcatchments (sub-basins), reaches, basins, and links. Subcatchments are areas of land that produce surface runoff. They are characterized by their area and weighted CNs. Reaches are generally uniform streams, channels, or pipes that convey water from one point to another. A basin is any impoundment that fills with water from one or more sources and empties via an outlet structure. Links are used to introduce hydrographs into a project from another source. 2. Hydrologic Models In order to develop a hydrologic analysis of the Moore’s Creek Watershed, JNEI developed three separate model scenarios:

1. Baseline Conditions Model – Baseline, or pre-developed, current conditions model

2. Unmitigated Hydrologic Model – Post-development conditions model,

without mitigation measures

3. Proposed Conditions Model – Post-development conditions model, with mitigation measures

D. Baseline Conditions Model 1. Analysis JNEI established the pre-development “snapshot” of existing conditions by determining watershed characteristics for the Moore’s Creek Watershed. The baseline data documented the existing conditions of the Moore’s Creek Watershed at the time the study began. JNEI used the CADD-based 100-scale mapping provided by the University as well as similar City of Charlottesville mapping to determine physical features and assess watershed characteristics.

10

Data developed for this Baseline Model scenario included:

• Existing soil types and land cover

• Delineation of Moore’s Creek watershed and sub-basin areas (See Exhibit 2 of Appendix A)

• Flow paths and times of concentration for sub-basins

• Runoff “Curve Numbers” for sub-basins

Due to the developed nature of some of the sub-basins and the completion of recent drainage modifications, JNEI found it necessary to further divide four sub-basins for the purposes of a more accurate hydrologic model. For example, a portion of Sub-basin MO-6A bypasses the stormwater management pond and, therefore, should be separated from the remaining area of Sub-basin MO-6A that is mitigated by the pond. The following table summarizes the data documented in the Baseline Model: Table 2 Baseline Conditions Data

SUB-BASIN IDENTIFICATION

DRAINAGE AREA

(ACRES)

PERCENT PERVIOUS

(%)

PERCENT IMPERVIOUS

(%)

PERCENT WOODED

(%)

SOIL TYPE

TIME OF CONCENTRATION

(Tc)

WEIGHTED CURVE

NUMBER (CN)

MO-1A 73.04 17% 36% 47% C 15 minutes 81

MO-1B 10.71 62% 38% 0% C 14 minutes 83

MO-2B 23.97 62% 38% 0% C 17 minutes 83

MO-3A 36.13 14% 79% 7% C 11 minutes 92

MO-3B north 45.47 15% 85% 0% C 10 minutes 94

MO-3B south 33.29 62% 38% 0% C 11 minutes 83

MO-3C 15.13 53% 33% 14% C 10 minutes 82

MO-3C bypass 10.00 58% 10% 32% C 10 minutes 76

MO-5A 17.45 15% 85% 0% C 12 minutes 94

MO-5A south 34.44 62% 38% 0% C 13 minutes 83

MO-5B 45.90 55% 45% 0% C 22 minutes 87

MO-6A mitigated 27.29 15% 85% 0% C 12 minutes 94

MO-6A unmitigated 38.37 15% 85% 0% C 12 minutes 94

MO-6B 18.50 15% 85% 0% C 11 minutes 94

JNEI input these data into HydroCAD to generate a series of watershed conditions for four different design storm conditions. JNEI ran runoff models for the 2-, 10-, 25-, and 100-year storm events. The HydroCAD report for the Baseline Conditions Model can be found in Volume II of this report. The baseline conditions scenarios formed a basis from which to compare the watershed response to the proposed conditions models. E. Unmitigated Hydrologic Model 1. Analysis JNEI analyzed all sub-basins where the University of Virginia has identified potential future development projects at the time this study began. These future development projects are illustrated in the Master Plan in Appendix A, Exhibit 2. Within these sub-basins, a net change due to a developed area was determined and identified as a

11

“changed” drainage area in the Unmitigated Model. JNEI used a conservative approach to model these changed drainage areas, as each future development project and associated impact area was estimated and assumed to be completely impervious (Curve Number 98). The proposed impervious development areas and the associated impervious impact areas within a sub-basin are collectively referred to as “planning areas” for the purposes of this report. The following table summarizes development projects within these identified sub-basins and the impervious planning area determined for the purposes of this Stormwater Management Master Plan (SWMP). Table 3 Proposed Impervious Planning Areas within “Changed” Sub-basins

“Changed” Sub-basin Proposed Development Projects Identified by University

Proposed Impervious

Planning Area (acres)

MO-3A

Gilmer Hall Addition Aquatic & Fitness Center Addition

Observatory Hall Addition 25% Additional Residential Housing

4.65

MO-3B

Chemistry Building Additions Mechanical Engineering Addition

Material Science Building Addition Chemical Engineering Research Addition

Additional Unidentified

9.47

MO-3C Unidentified 2.78

MO-5A Olsson Hall Addition Additional Housing near Halsey Hall 1.56

MO-5B South Lawn Phase I South Lawn Phase II

Parking Garage 15.51

MO-6A mitigated

McCleod Hall Expansion Health Science Library Expansion South Parking Addition Phase III

University Hospital Expansion Phase I and II Medical Research near McLeod MR-6, MR-7, MR-8

Additional Residential Housing Additional Medical Research

4.76

MO-6A unmitigated McKim Hall Addition 1.06

MO-6B University Hospital Addition Additional Unidentified 7.61

The hydrologic properties of the planning areas, such as land cover, flow paths, and times of concentration, were estimated based on JNEI’s determination of the size of the project and the conservative impervious development Curve Numbers of these “changed” areas. The “unchanged” portions of the developed sub-basins were modeled using the same hydrologic characteristics as in the Baseline Model. JNEI created an Unmitigated Hydrologic Model in order to determine the characteristics of the future developed watershed without incorporating mitigation measures. Data developed for the Unmitigated Model scenario included: 12

• All information developed in the Baseline Conditions Model for unchanged sub-basins

• Land cover for sub-basins where proposed University development will

occur

• Flow paths and times of concentration for sub-basins containing proposed development

• Runoff CNs for sub-basins containing proposed development

The following table summarizes the data documented in the Unmitigated Model: Table 4 Unmitigated Model Data

SUB-BASIN IDENTIFICATION

DRAINAGE AREA

(ACRES)

PERCENT PERVIOUS

(%)

PERCENT IMPERVIOUS

(%)

PERCENT WOODED

(%)

SOIL TYPE

TIME OF CONCENTRATION

(Tc)

WEIGHTED CURVE

NUMBER (CN)

MO-1A 73.04 17% 36% 47% C 15 minutes 81

MO-1B 10.71 62% 38% 0% C 14 minutes 83

MO-2B 23.97 62% 38% 0% C 17 minutes 83

MO-3A 31.48 14% 78% 8% C 11 minutes 92

MO-3A change 4.65 0% 100% 0% C 10 minutes 98

MO-3B north 36.00 15% 85% 0% C 10 minutes 94 MO-3B north

change 9.47 0% 100% 0% C 10 minutes 98

MO-3B south 33.29 62% 38% 0% C 11 minutes 83

MO-3C 12.35 59% 41% 0% C 10 minutes 83

MO-3C change 2.78 0% 100% 0% C 10 minutes 98

MO-3C bypass 10.00 58% 10% 32% C 10 minutes 77

MO-5A 16.45 15% 85% 0% C 12 minutes 94

MO-5A change 1.56 0% 100% 0% C 10 minutes 98

MO-5A south 34.44 62% 38% 0% C 13 minutes 83

MO-5B* 45.90 55% 45% 0% C 22 minutes 87

MO-6A mitigated 22.76 15% 85% 0% C 12 minutes 94 MO-6A mitigated

change 4.76 0% 100% 0% C 10 minutes 98

MO-6A unmitigated 37.31 15% 85% 0% C 18 minutes 94 MO-6A unmitigated

change 1.06 0% 100% 0% C 10 minutes 98

MO-6B 10.66 15% 85% 0% C 11 minutes 94

MO-6B change 7.61 0% 100% 0% C 10 minutes 98

* Includes Changed Area – Refer to Section III.F.1.b JNEI input these data into HydroCAD to generate a series of watershed response scenarios for four different design storm conditions including the 2-, 10-, 25-, and 100-year storm events. The runoff model enabled JNEI to perform a thorough analysis of the watershed’s sensitivity and natural response to the proposed development during the various storm events. The unmitigated model also created a baseline from which to compare the response to development for individual reach segments throughout the Moore’s Creek Watershed.

13

2. Watershed Sensitivity JNEI used the results from the unmitigated model to develop an idea of the sensitivity of the watershed to development. JNEI concluded that certain areas within the watershed were more sensitive to development than others. For example, the area referred to by the City of Charlottesville as the Stadium Drainage Basin (Sub-Basins MO-3A, MO-3B, and MO-3C) appears to be especially sensitive to development. JNEI concluded that this is due to the fact that the existing drainage system within this sub-basin is currently stressed and operating under full capacity. On the other hand, Sub-basins MO-6A and MO-6B were less sensitive to development, as the existing stormwater management pond appeared to mitigate the majority of the increases in stormwater runoff. JNEI was able to locate components of the drainage system that would be more affected by development than others. For example, some existing drainage pipes that were operating at or near capacity for large storm events could not accommodate the additional runoff due to development. However, other drainage features, such as small creeks and swales, had the capacity to accommodate the increase in stormwater runoff. Knowledge of sensitive areas within the watershed was an important factor in the selection of mitigation measures in the post-developed model. 3. Watershed Response to Development The results of the unmitigated model also provided an opportunity to analyze the watershed’s natural response to the development, as well as the response of various reaches within the watershed to the development. In general, the downstream segments (design points) saw only a minimal increase in peak stormwater flow in response to the development. However, negative effects to development were most apparent in various upstream drain pipes (reaches), especially those that were stressed in the pre-development condition. Therefore, JNEI concluded that the effects of proposed mitigation measures should be analyzed in these upstream reaches, as well as at the design points. F. Proposed Conditions Model 1. Mitigation Analysis In sub-basins where the University has identified future development, JNEI performed a mitigation analysis in order to determine the most effective means of controlling stormwater runoff. As development areas were identified in Sub-basins MO-3A, MO-3B, MO-3C, MO-5A, MO-5B, MO-6A, and MO-6B, the mitigation analysis was performed only in these areas. The first step in performing this analysis was to identify strategic design points throughout the watershed. Throughout the southern portion of the University of Virginia where future development is anticipated, existing stormwater runoff is conveyed to Moore’s Creek via one of three collection tributaries. These tributaries collect runoff from multiple sub-basins and convey the stormwater to Moore’s Creek. Therefore, sub-basins contributing to each discharge point have been combined for the purposes of the mitigation analysis. The following table summarizes the three analysis areas associated with each discharge point.

14

Table 5 Analysis Areas and Discharge Points Analysis Area Discharge Point Collection

Tributary Contributing Sub-basins

Stadium Drainage Basin (City of Charlottesville)

Box Culvert beneath Jefferson Park Avenue at Harmon Street

Rock Creek Tributary

MO-3A, MO-3B, MO-3C

Brandon Drainage Basin (City of Charlottesville)

Rock Creek Culvert beneath Railroad Rock Creek MO-5A, MO-

5B

Health Sciences/ University Hospital Area

84” Storm Drain Beneath Railroad from Stormwater

Management Pond

City Storm Drains to Rock

Creek

MO-6A*, MO-6B

* Not including the portion of MO-6A that bypasses the existing stormwater management pond Once these discharge points were selected, JNEI analyzed how incorporating various mitigation measures in each of the three analysis areas would affect the downstream design points and upstream reaches of the Moore’s Creek Watershed. a. Stadium Drainage Basin At present, two existing stormwater management ponds function to control stormwater runoff from Sub-basins MO-3A and MO-3C before conveying it to the University drainage system. The former pond is referred to as the West Grounds Stormwater Management Pond, or Gilmer Pond, and is between the Aquatic Fitness Center and Gilmer Hall. This pond is currently fed by a small open-mouth stream, which collects stormwater from the existing sub-basin. JNEI obtained design information for the pond from a report issued in January 2000 by CEGG Associates entitled “West Grounds Stormwater Pond Improvements.” According to the report, the West Grounds Stormwater Management Pond was designed to accommodate 5.02 acres of impervious area due to the development of the Chemistry Building Addition, the Aquatic and Fitness Center, the Student Housing Facility, and a Proposed Residence Hall. CEGG Associates determined that only 3.56 acres of this proposed impervious development has been constructed, and, therefore, 1.46 acres of impervious development has been “banked” for the water quantity mitigation of future development projects. The second existing stormwater pond is referred to as the Gooch/Dillard Pond as it is south of Alderman Road near the Gooch and Dillard Dormitories. Although an engineering report was not available, JNEI used recent topographic information to determine the hydrologic characteristics of the existing pond. However, due to the lack of detailed information, JNEI assumed the pond was designed to treat stormwater runoff only from the contributing Gooch and Dillard Dormitory areas. JNEI concluded that the Gooch Dillard Stormwater Pond could not accommodate additional impervious areas associated with future development for stormwater mitigation without modifications or enhancement to the existing pond. As the primary strategy to mitigate stormwater runoff from future development sites within the Stadium Drainage Basin, JNEI attempted to take advantage of the existing stormwater management ponds (Gilmer Pond and Gooch/Dillard Pond). Although it is not desirable to make future modifications to Gilmer Pond, the “banked” impervious area was an important factor for the purposes of the analysis, as it decreased the amount of total (16.90 acres) impervious area requiring water quantity mitigation by 1.46 acres. As part of the primary strategy to take advantage of the existing Gooch/Dillard Pond, JNEI analyzed increasing the storage capacity of the existing Pond and modifying the existing outlet structure. The goal of this modification was to improve the existing

15

inadequacies of the Gooch/Dillard Pond as well as to control increased flow rates associated with a significant amount of future impervious development. JNEI analyzed increasing the storage of the existing pond throughout the entire depth to provide for stormwater mitigation, as well as to provide for upper stage storage areas for additional erosion and flood control benefits. The final stormwater mitigation analysis within the Stadium Drainage Basin occurred at the site of the existing Observatory Dining Hall in the Alderman Road Residence Cluster, which was identified by the University of Virginia as a potential site for a stormwater management facility. JNEI analyzed various stormwater mitigation measures that would mitigate and control the increased stormwater runoff produced from the future impervious development that would not be accommodated in either the existing Gilmer Pond or the modified Gooch Pond. b. Brandon Drainage Basin As the “conservative” approach to modeling identified future development within the Moore’s Creek Watershed is to assume the entire planning or impact area to be completely impervious (Curve Number 98), JNEI was able to incorporate a more accurate approach within the Brandon Drainage Basin. This was due to the fact that the South Lawn Development Project Area was in the conceptual design phase by Polshek Partnership and SMBW Architects. In coordination with the design team, JNEI promoted the “greening” approach at the South Lawn Development Project. This approach involved decreasing the amount of impervious area from pre-development to post-development condition to the greatest extent possible. Besides the South Lawn Development Project, the University has also identified the future development of a garage within this Sub-basin; however, since the project was less defined than the South Lawn Project, JNEI followed the conservative approach and assumed the entire impact area to be completely impervious. Impact areas associated with projects in Sub-basin MO-5A were also considered to be completely impervious. Through analysis of the Unmitigated Hydrologic Model, JNEI was able to determine that the “greening” approach could be used to improve the overall condition of the watershed. Using various weighted Curve Numbers for the South Lawn Development Project Area, JNEI analyzed the peak outflow from Sub-basin MO-5B based on the proposed development. This peak outflow was then compared to the peak outflow from the baseline (or pre-development) conditions model. JNEI created Watershed Rating Curves using a 2-year and a 100-year storm event to illustrate this exercise.

16

Figure 1 Watershed Rating Curve for 2-year Storm Design

Watershed Rating Curve for 2-year Storm Design

80859095100105110115120125130135

72 74 76 78 80 82 84 86 88 90 92 94 96 98 100

Anticipated South Lawn Development Curve Number

Peak

Out

flow

(cfs

)

Baseline Conditions Peak Outflow

Watershed Rating Curve

Figure 2 Watershed Rating Curve for 100-year Storm Design

Watershed Rating Curve for 100-year Storm Design

250

260

270

280

290

300

310

320

330

340

70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100

Anticipated South Lawn Development Curve Number

Peak

Out

flow

(cfs

)

Baseline Conditions Peak Outflow

Watershed Rating Curve

From the Watershed Rating Curves, JNEI determined that, when the South Lawn Development area has a Curve Number of 86 (50% impervious and 50% pervious), the post-development peak rate of runoff from Sub-basin MO-5B would be equal to the pre-development peak rate of runoff – as seen in Figure 1 and 2 above. Developing the South Lawn Development area at any Curve Number less than 86 would result in a post-development peak rate of runoff that is less than the pre-development peak rate of runoff and the resultant improvement in the peak rate of discharge. Developing the South Lawn Development area at any Curve Number greater than 86 would result in a post-development peak rate of runoff that is greater than the pre-development peak rate of runoff and the resultant increase in the peak rate of discharge. The assumed South Lawn Development Project Area is illustrated in Exhibit 2 of Appendix A.

17

The current Proposed South Lawn Development (Scheme C) has a Curve Number of 85 (approximately 45% impervious and 55% pervious). The peak rate of runoff at the design point will, therefore, be less in the post-development condition than in the pre-development condition. According to Virginia Stormwater Regulations, mitigation measures would not be required to control the quantity of stormwater runoff due to the decrease in the post-development condition. However, due to the erosion and flooding problems in this Moore’s Creek tributary area, the DCR is requiring compliance with the Virginia Erosion and Sediment Control Regulations (Minimum Standards Section 4VAC50-30-40). Compliance with the Minimum Standard 19 ensures the protection of downstream properties, which result from increases in volume, velocity, and peak flow rate for small storm events. Therefore, JNEI has performed an analysis of incorporating a stormwater detention structure at the South Lawn site in order to decrease the overall peak flow rate, volume, and velocity of stormwater runoff from the sub-basin in small storm events to improve the downstream condition. c. Health Sciences/University Hospital Area At present, a large retention pond located south of the South Parking Garage and north of the Railroad Tracks mitigates stormwater runoff from a large portion of Sub-basins MO-6A and MO-6B, which is referred to, for the purposes of this report, as the Health Sciences/University Hospital Area. Stormwater runoff from the Health Sciences and University Hospital Area is collected in University drainage pipes and conveyed to this Health Sciences Stormwater Management Pond for mitigation. Stormwater is then released from the basin to an 84-inch drainage pipe, which eventually joins Rock Creek. JNEI used the technical design data provided by the Cox Company, with a final revision date May 4, 1998, in order to understand the mitigation capacity of the existing pond. According to the report, the retention basin was designed to mitigate stormwater runoff from the “Full Development Scenario,” which included up to 15.7 acres of additional impervious development identified in Phases 1-4 of the Master Plan updated in July 11, 1996. As part of this mitigation analysis, JNEI compared the Full Development Scenario of 1996 to the development condition that exists today within the Health Sciences Center and University Hospital area. JNEI has identified impervious development projects that have been completed since the 1996 report. Some of these projects included “greening”, or the replacement of existing impervious areas with pervious areas, resulting-in some cases-with a net decrease in impervious area. The following table summarizes completed development projects within the Health Sciences/University Hospital Area that JNEI determined to be completed at the time this study began. Table 6 Health Sciences Project

Proposed Development Projects Completed since the 1996 Master Plan

Proposed Impervious Area (acres)

South Parking Garage 1.18 McLeod Hall 0.35

Medical Research Lab 0.75 University Hospital 4.32

Pedestrian walkway over Jefferson Park Avenue 0.29 Jordan Hall 1.17

Health Sciences Library 0.83

18

Proposed Development Projects Completed since the 1996 Master Plan

Proposed Impervious Area (acres)

Barringer Mansion 0.12 Spanish House 0.06

Gildersleeve Apartments 0.07 412 Monroe Lane 0.04

Other Buildings along Monroe Lane 0.23 McKim Hall 0.53

Telephone Exchange 0.13 Cobb Hall 0.42

Elson Student Health Center and Expansion 0.53 Medical Research near McLeod (MR-5) 0.66

MR-5 Plaza (Green Space) -0.30 South Chiller Plant 0.30

Cavalier Substation Parking 0.25 Multistory Entry Court (greening) -0.17

Jordan Loading Dock Parking Area 0.02 Demolition of Houses of 15th Street -0.03 Monroe Lane Apartment Complex 0.012

Additional Impervious 0.51

Total 12.27 JNEI determined that approximately 3.43 acres of impervious development that was factored into the design of this pond is, in fact, still not developed at this time. This was determined by subtracting the total impervious development (12.27 acres) from the total mitigation capacity designed into the pond (15.70 acres). Therefore, JNEI has concluded that 3.43 acres is “banked” for water quantity mitigation of future impervious development within the Health Sciences and University Hospital area, as anticipated by the current Master Plan. A second part of this mitigation analysis was to determine the amount of future impervious development area within Sub-basins MO-6A and MO-6B that would require mitigation in a facility other than the existing pond. JNEI performed a preliminary analysis of various stormwater management measures that would accommodate the level of development anticipated. Although the University has not proposed a site for this facility, JNEI also performed a preliminary sizing of the various facilities – assuming the chosen mitigation measure will be coordinated with a future development project(s). 2. Buildout Analysis JNEI used all information obtained in the Unmitigated Model and input the data into HydroCAD (See Table 3). JNEI also incorporated selected mitigation measures in the model and generated the watershed model for the 2-, 10-, 25-, and 100-year storm events. The results of these model runs were compared to the Baseline Conditions and Unmitigated Model in order to determine the effectiveness of the mitigation measures for each design storm. 19

3. Selected Mitigation Measures Analysis of the peak runoff rate at the three design points for various mitigation measures enabled JNEI to determine the most effective mitigation strategies within the sub-basin areas contributing to these points. The selected mitigation measures would be most effective in controlling runoff for all ranges of storm events at the design points, as well as within various reaches within the University property. The selected mitigation measures are discussed below. a. Stadium Drainage Basin Within the Stadium Drainage Basin, JNEI proposes three strategies to mitigate stormwater runoff from the full-extent of future impervious development. In addition, these opportunities will serve to improve the quality of Moore’s Creek in downstream areas by decreasing flooding and erosion caused by increased stormwater runoff from these upstream areas. The three mitigation strategies within this sub-basin include the following:

• Using the 1.46-acre “banked” impervious area for mitigation within Gilmer Pond;

• Providing additional storage capacity within the Gooch/Dillard Pond and

modify the existing outlet structure; and

• Designing a new stormwater management facility at the site of the Observatory Dining Hall, in the Alderman Road Residence Cluster.

(1) West Grounds Stormwater Pond (Gilmer Pond) As previously discussed, the West Grounds Stormwater Pond has been designed to accommodate water quantity mitigation for future impervious development. Therefore, the first mitigation strategy within the Stadium Drainage Basin is to take advantage of this “banked” area. This can be accomplished by tracking impervious development area for future development projects within sub-basins MO-3A, MO-3B, and/or MO-3C up to 1.46 acres. (2) Gooch/Dillard Pond JNEI also recommends the cumulative storage volume of the Gooch/Dillard Pond be increased from 0.38 acre-feet to 0.88 acre-feet for the purposes of water quantity mitigation. This proposed increase in cumulative storage can be accomplished by increasing the Pond’s surface area by 25% and making the pond approximately 1.6 feet deeper, for a total pond depth of 6.0 feet. The increase in cumulative storage will provide an additional 0.50 acre-feet of pool storage that will serve to detain the stormwater runoff from future developed areas and mitigate the existing deficiency. In addition, JNEI recommends modifying the existing outlet structure in order to hydraulically control the outflow of stormwater runoff from the modified pond. In order to control small storm events, JNEI proposes an 18-inch orifice at the bottom elevation, a rectangular weir structure to accommodate the larger storm events, and an overflow weir to accommodate severe flood events. JNEI has determined that the modifications to the Gooch/Dillard pond will provide mitigation for 6.00 acres of future impervious development within the entire Stadium Drainage Basin. The hydrologic design criteria for the modified Gooch/Dillard Pond is illustrated in the following Stage-Storage and Stage-Discharge Charts.

20

Figure 3 Hydrologic Criteria for the Modified Gooch/Dillard Pond

Modified Gooch/Dillard Pond - Stage-Discharge Curve

523.00524.00525.00526.00527.00528.00529.00530.00531.00

0.00 5.00 10.00 15.00 20.00 25.00 30.00

Discharge (cubic feet per second)

Elev

atio

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Future development projects within sub-basins MO-3A, MO-3B, and/or MO-3C up to 6.00 acres, which will be mitigated by the Gooch/Dillard Pond after the modifications the Pond have been completed. The following table illustrates the peak stormwater flow from Sub-basin MO-3C with the modified Gooch/Dillard Pond compared to the pre-development peak outflow. Table 7 Peak Flow Rate from Sub-basin MO-3C with Gooch/Dillard Pond Modifications

Peak Inflow to Reach R3C-2 (18” Pipe from Gooch/Dillard Pond) with Modifications to Gooch Pond (Overall Sub-basin MO-3C)

Storm

Peak Flow Pre-development

(cubic feet per second)

Peak Flow Post-development

(cubic feet per second)

Percent Reduction in Flow Rate

(%) 2-year (3.60”) 44.63 36.29 19%

10-year (5.50”) 100.40 79.10 21% 25-year (6.00”) 114.84 93.11 19%

100-year (8.00”) 172.34 148.13 14% (3) Observatory Hill Enhanced Extended Detention Basin The final strategy for the Stadium Drainage Basin is to design a stormwater management facility to accommodate the additional stormwater runoff associated with 9.44 acres of future impervious development. JNEI recommends an enhanced extended detention basin be sited upstream from existing Gilmer Pond, at the site of the existing Observatory Dining Hall. An enhanced extended detention basin would serve to temporarily store stormwater runoff and control heavy flows to downstream areas. The enhanced extended basin was also selected due to its enhanced water quality benefits, which will be discussed later in this report. JNEI has sized the proposed basin to accommodate the additional stormwater runoff associated with 9.44 acres of future impervious development. Using the Virginia Stormwater Management Regulations for an Enhanced Extended Detention Basin, JNEI preliminarily sized this basin to have a cumulative storage volume (including marsh areas and a 5-foot deep pool) of approximately 50,000 cubic feet (1.1 acre-foot) with a 4-inch orifice at the bottom elevation and a larger overflow weir to control large storm events. The hydrologic criteria for design of the enhanced extended detention basin at the site of the existing Observatory Dining Hall is illustrated in the following Stage-Storage and Stage-Discharge diagrams.

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Figure 4 Hydrologic Criteria for the Enhanced Extended Detention Basin

Enhanced Extended Detention Basin - Stage-Storage Chart

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The enhanced extended detention basin will significantly alleviate the heavy flows passing through Gilmer Pond and reduce the peak flow rate of stormwater from the entire sub-basin, especially during a 100-year flood event. The following table illustrates the peak flow rate from Sub-basin MO-3A with the proposed basin compared to the pre-development basin. Table 8 Peak Flow Rate from Sub-basin MO-3A with proposed Observatory Hill Enhanced Extended Detention Basin

Peak Inflow to Reach 3A-1 (36” Pipe from Gilmer Pond) with New Basin Upstream (Overall Sub-basin MO-3A)

Storm

Peak Outflow Pre-development

(cubic feet per second)

Peak Outflow Post-development

(cubic feet per second)

Percent Reduction in Flow Rate

(%) 2-year (3.60”) 17.84 16.97 5%

10-year (5.50”) 22.00 21.30 3% 25-year (6.00”) 22.92 22.28 3% 100-year (8.00”) 63.34 51.18 19%

Given that all three mitigation strategies are completed according to this SWMP, the full 16.90 acres of anticipated future development within the Stadium Drainage Basin can be mitigated. This is due to the fact that the stormwater mitigation strategies within Sub-basins MO-3A and MO-3C provided a “cushion” for proposed projects within Sub-basin MO-3B. The anticipated impervious development within Sub-basin MO-3B has been accounted for in either the bank at Gilmer Pond, the modifications to the Gooch/Dillard Pond, or the proposed basin upstream from Gilmer. At the design point (the box culvert beneath Jefferson Park Avenue) the post-development peak flow rate will be equal to or less than the pre-development peak rate, given all mitigation measures and all anticipated impervious development are in place. Although the peak flow rate will be greatly decreased in the upstream reaches due to the mitigation measures, existing pipes that are flowing at maximum capacity in the pre-developed condition will also restrict flow in the post-developed condition, and, therefore, the peak flow rate in both conditions, pre- and post-development, will be nearly the same.

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The following table illustrates the peak flow rate at the Design Point in the post-development condition (with all mitigation measures and full development assumed) compared to the peak flow rate in the pre-development condition. Table 9 Peak Flow Rate at the Stadium Drainage Basin Design Point

Peak Inflow to Watershed Design Point (Box Culvert beneath JPA) (Overall Stadium Drainage Basin – MO-3A, MO-3B, MO-3C)

Storm

Peak Outflow Pre-development

(cubic feet per second)

Peak Outflow Post-development

(cubic feet per second)

Percent Reduction in Flow Rate

(%) 2-year (3.60”) 78.38 77.75 1%

10-year (5.50”) 81.84 77.75 5% 25-year (6.00”) 77.75 77.75 0%

100-year (8.00”) 82.57 79.79 3% b. Brandon Drainage Basin In order to protect properties and waterways downstream from the Brandon Drainage Basin, in compliance with Virginia Erosion and Sediment Control Regulations (MS-19), JNEI proposes incorporating an underground detention structure at the South Lawn Project Site. JNEI recommends an underground detention basin using a product called Rainstore3 by Invisible Structures, Inc. who describes this product as the following:

“Rainstore3 is a plastic structure used to store stormwater underground. Made from injection molded plastic, a single panel contains 36 vertical columns and supports H-20 loading, allowing the construction of driving areas, parking lots, or other small structures above the system. Built-in compression fittings allow units to be easily stacked to a variety of depths up to 8'4". Rainstore3 provides 94% open water storage, virtually eliminating crushed stone requirements.

JNEI has chosen a standard Rainstore unit that is 1 meter long by 1 meter wide by 1.2 meters tall (3.28 feet x 3.28 feet x 3.94 feet). The detention area, as modeled by JNEI, will consist of a total of 312 Rainstore units. These units will be placed in a rectangular formation – 13 Rainstore units long and 12 Rainstore units wide, stacked 2 units high. The footprint of this unit will be approximately 45 feet long and 40 feet wide. The stacking of 2 Rainstore units results in a detention structure that is 7.87 feet in height. Since the Rainstore units have 94% open water storage, the water storage available within the proposed stormwater detention structure will be 12,429 feet3. The purpose of this structure will be to detain stormwater runoff from the proposed South Lawn Development Site for small storm events and release stormwater to the 36-inch UVA Storm Drain at a controlled rate. This structure will not detain stormwater runoff from large storm events. Stormwater from 1-year and 2-year storm events will be detained within the detention structure and be released via a 20-inch outlet to the existing 36-inch drain. Stormwater runoff from the 10-year and larger storm events will overflow the detention system via a large weir or bypass the structure entirely. The hydrologic criteria for design of the Rainstore unit at the South Lawn Development site is illustrated in the following Stage-Storage and Stage-Discharge diagrams.

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Figure 5 Hydrologic Criteria for the Rainstore Unit

Rainstore Unit - Stage-Storage Curve

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The following table illustrates the effects of this detention structure on the peak outflow from the South Lawn Development Site (or Planning Area) for the 1-year and 2-year storm events: Table 10 Peak Outflow from South Lawn Development Site

Peak Outflow from South Lawn Development Site with Proposed Stormwater Detention

Storm

Outflow from South Lawn Project Area

(Inflow to Detention) (cubic feet per second)

Outflow from Stormwater Detention (cubic feet per second)

Percent Reduction in Flow Rate

(%)

1-year (3.30”) 35.5 25.5 28% 2-year (3.60”) 40.4 30.1 26%

Despite the fact that the detention structure only reduces the peak flow rate from the South Lawn Development Site for small storm events, the peak flow rate reaching the 36-inch UVA storm drain the entire downstream system from sub-basin MO-5B will be reduced during all storm events. This will be due to the fact that the proposed underground stormwater detention structure is detaining and slowly releasing stormwater for small storm events and altering the time the peak flow rate reaches the design point during large storm events for an overall reduction. The reduction in the peak flow rate from Sub-basin MO-5B contributing to the 36-inch Storm Drain will, in effect, improve the downstream erosion and flooding problems in accordance with the Virginia Erosion and Sediment Control Regulations Minimum Standard-19. The following table illustrates the effects of this detention structure on the peak outflow from Sub-basin MO-5B into the 36-inch UVA Storm Drain: Table 11 Peak Flow Rate from Sub-basin MO-5B

Peak Inflow to 36” UVA Storm Drain with Proposed Stormwater Detention (Overall Watershed MO-5B)

Storm

Inflow Pre-development

(cubic feet per second)

Inflow Post-development

(cubic feet per second)

Percent Reduction in Flow Rate

(%) 1-year (3.30”) 97.4 90.6 7% 2-year (3.60”) 110.2 103.7 6%

10-year (5.50”) 192.7 188.3 2% 25-year (6.60”) 214.5 210.3 2%

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Peak Inflow to 36” UVA Storm Drain with Proposed Stormwater Detention (Overall Watershed MO-5B)

Storm

Inflow Pre-development

(cubic feet per second)

Inflow Post-development

(cubic feet per second)

Percent Reduction in Flow Rate

(%) 100-year (8.00”) 301.1 293.3 3%

The reduction in peak flow rate from Sub-basin MO-5B will improve the downstream condition, as well as to provide a “cushion” for mitigating the small area of impervious development (1.56 acres) proposed within Sub-basin MO-5A. In other words, the peak flow rate at the design point for the Brandon Drainage Basin will be reduced for all storm events. The following table summarizes the peak flow rate at the Rock Creek Culvert Design Point from Sub-basins MO-5A and MO-5B: Table 12 Peak Flow Rate at the Brandon Drainage Basin Design Point

Peak Inflow to Watershed Design Point (Rock Creek Culvert) (Overall Brandon Drainage Basin – MO-5A, MO-5B)

Storm

Peak Flow Pre-development

(cubic feet per second)

Peak Flow Post-development

(cubic feet per second)

Percent Reduction in Flow Rate

(%) 2-year (3.60”) 242.66 241.43 0.5%

10-year (5.50”) 382.85 380.38 0.6% 25-year (6.00”) 406.83 404.26 0.6%

100-year (8.00”) 489.09 484.75 0.8% c. Health Sciences Center/University Hospital Area Within Sub-basins MO-6A and MO-6B, JNEI proposes two strategies to mitigate stormwater runoff from the full extent of future impervious development. These opportunities will also serve to improve the downstream condition of Rock Creek and Moore’s Creek by decreasing flooding and erosion caused by increased stormwater runoff from these upstream areas. The two mitigation strategies within this sub-basin include the following:

• Using the 3.43-acre “banked” impervious area for mitigation within Health Sciences Center Pond

• Designing a new extended detention basin in coordination with a future

development project within Sub-basin MO-6B. (1) Health Sciences Center Stormwater Management Pond As previously discussed, the Health Sciences Center Stormwater Management Pond has been designed to accommodate water quantity mitigation for future impervious development. Therefore, the first mitigation strategy within the Health Sciences/ University Hospital area is to take advantage of the 3.43 acres of “banked” impervious development area. The future anticipated development within sub-basin MO-6A was conservatively estimated to be 4.76-acres as it includes a “cushion” by assuming that all potential impact areas associated with future development projects are impervious(See Section III.E.1). However, the current master plans for Near Term and Long Term Potential Construction within the University/Health Sciences area actually only accounts for 3.30-acres of impervious development (assuming 0.50-acres of impervious area is converted to pervious area is coordination with the MR-6 project). Therefore, it appears that the anticipated future development within Sub-basin MO-6A could be mitigated by

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the existing pond’s “banked” capacity. JNEI proposes tracking impervious development within Sub-basin MO-6A up to 3.43 acres without requiring mitigation measures. (2) Proposed Extended Detention Basin The second strategy for the Health Sciences Center and University Hospital area is to design an extended detention basin within Sub-basin MO-6B, in coordination with a future development project. JNEI proposes an extended detention basin in order to temporarily store stormwater runoff and control heavy flows to downstream areas. JNEI has sized the proposed basin to accommodate the additional stormwater runoff associated with 8.94 acres of future impervious development. This is the amount of impervious area conservatively assumed for the full future development of Sub-basin MO-6B (7.61 acres) as well as the additional impervious area in Sub-basin MO-6A that could not be mitigated in the existing pond (4.76-3.43). Using the Virginia Stormwater Management Regulations for an Extended Detention Basin, JNEI preliminarily sized this basin to be 6-feet deep, having a cumulative storage volume of approximately 32,800 cubic feet (0.74 acre-foot) with a 12-inch orifice at the bottom elevation, an 8-inch orifice to accommodate larger storm events, and an rectangular overflow weir to accommodate severe flood events. The hydrologic criteria for design of the extended detention basin is illustrated in the following Stage-Storage and Stage-Discharge diagrams. Figure 6 Hydrologic Criteria for the Extended Detention Basin

Extended Detention Basin - Stage-Discharge Curve

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The extended detention basin will significantly alleviate the small storm flows from developed Sub-basin MO-6B that pass through the University drainage pipes to the existing pond. The detention basin will also detain stormwater runoff from the developed sub-basin in large storm events and discharge at a rate slightly less than the pre-development condition. The following table illustrates the peak flow rate from Sub-basin MO-6B with the proposed extended detention basin compared to the pre-development condition: Table 13 Peak Flow Rate from Sub-basin MO-6B with proposed Extended Detention Basin

Peak Inflow to Reach 6B-1 (36” University pipe) with Proposed Detention Basin (Overall Sub-basin MO-6B)

Storm

Peak Outflow Pre-development

(cubic feet per second)

Peak Outflow Post-development

(cubic feet per second)

Percent Reduction in Flow Rate

(%) 2-year (3.60”) 74.64 50.72 32%

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Peak Inflow to Reach 6B-1 (36” University pipe) with Proposed Detention Basin (Overall Sub-basin MO-6B)

Storm

Peak Outflow Pre-development

(cubic feet per second)

Peak Outflow Post-development

(cubic feet per second)

Percent Reduction in Flow Rate

(%) 10-year (5.50”) 118.64 111.42 6% 25-year (6.00”) 130.13 125.63 3%

100-year (8.00”) 175.82 175.30 0.3% Given that all mitigation strategies are completed according to this SWMP, a total of 12.37 acres of anticipated future development within the Health Sciences Center and University Hospital area can be mitigated. The majority of the anticipated impervious development within Sub-basin MO-6A will be accounted for in the existing Health Sciences Center Pond, the remaining impervious development from Sub-basin MO-6A and the anticipated impervious development in Sub-basin MO-6B will be mitigated in the proposed extended detention basin. At the design point, where the 84-inch pipe from the existing pond passes beneath the railroad tracks, the post-development peak flow rate will be less than the pre-development peak rate given that all mitigation measures and all anticipated impervious development are in place. Although the peak flow rate will be significantly decreased in the upstream reaches due to the mitigation measures, existing pipes that are flowing at maximum capacity for large storm events in the pre-developed condition will also restrict flow in the post-developed condition, and, therefore, the peak flow rate will, in both conditions, be nearly the same for these large events. The following table illustrates the peak flow rate at the Design Point in the post-development condition (with all mitigation measures and full development assumed) compared to the peak flow rate in the pre-development condition: Table 14 Peak Flow Rate at the Health Sciences/University Hospital Design Point

Peak Inflow to Watershed Design Point (84” pipe beneath Railroad) (Overall Health Sciences/University Hospital Area – Sub-basins MO-6A and MO-6B)

Storm

Peak Inflow Pre-development

(cubic feet per second)

Peak Inflow Post-development

(cubic feet per second)

Percent Reduction in Flow Rate

(%) 2-year (3.60”) 76.26 70.04 8%

10-year (5.50”) 145.02 143.47 1% 25-year (6.00”) 154.09 153.42 <1%

100-year (8.00”) 160.34 160.28 <1% d. Unmitigated Sub-basin MO-6A As previously discussed, the northern and western portions of Sub-basin MO-6A bypass the existing stormwater management pond entirely. At present, the University has identified two small future development projects within Sub-basin MO-6A that would contribute to this bypass system. These include a development between McKim Hall and Cobb Hall, north of Jefferson Park Avenue, and an academic research building between Brandon Avenue and Monroe Lane. The total impervious future development from these two projects is approximately 1.06 acres. JNEI proposes that these two project areas contribute to the existing 72-inch bypass system without the incorporation of mitigation measures, as in the pre-development condition. Due to the fact that these impervious developments will have a low time of

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concentration, the peak flow rate from the project areas will reach the downstream design point (where a 72-inch drain pipe passes beneath the railroad) before the peak flow rate from the entire unmitigated portion of Sub-basin MO-6A. Therefore, the peak flow rate at the design point in the post-development condition will be less than the pre-development condition, as demonstrated in the following table. Table 15 Peak Flow Rate at the MO-6A (Unmitigated) Design Point

Peak Inflow to Watershed Design Point (72” pipe beneath Railroad) (Overall Sub-basin MO-6A not contributing to existing pond)

Storm

Peak Inflow Pre-development

(cubic feet per second)

Peak Inflow Post-development

(cubic feet per second)

Percent Reduction in Flow Rate

(%) 2-year (3.60”) 127.37 127.18 0.1%

10-year (5.50”) 202.91 202.47 0.2% 25-year (6.00”) 222.62 222.12 0.2%

100-year (8.00”) 301.04 300.29 0.2% G. Mitigation for Future Development As previously discussed, the mitigation strategies presented in the SWMP have accounted for a significant amount of impervious development within the Stadium Drainage Basin (Sub-basins MO-3A, MO-3B, and MO-3C) and the Health Sciences/University Hospital area (Sub-basins MO-6A and MO-6B). JNEI has prepared a Water Quantity Tracking Table for each of these two areas in order to enable the University to plan future development within these University sub-basins. Each mitigation strategy can accommodate for impervious area due to development up to a certain value. Therefore, it is necessary to know when additional stormwater mitigation strategies must be added to accommodate additional development, as well as when the overall development limit has been reached. When the impervious limit has been reached in a given sub-basin, the hydrologic model must be re-evaluated to determine if the mitigation measures can accommodate the additional development. It must be realized that only sub-basins where projects have been identified within the Stadium Drainage Basin (Sub-basins MO-3A, MO-3B, and MO-3C) and the Health Sciences Center/University Hospital Area (Sub-basins MO-6A and MO-6B) have been incorporated into the model, and, therefore, only these sub-basins have been modeled to accommodate additional development. Therefore, projects outside the areas identified have not been anticipated and would require revising the model or incorporating a project-specific mitigation plan to control the rate and volume of stormwater runoff from the site. The Water Quantity Tracking Table is presented in Appendix B of this report. The following table demonstrates a sample of how the tracking table is used.

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Table 16 Sample Water Quantity Tracking Table

*** The Impervious development area can also be divided among multiple mitigation strategies as long as impervious area remains banked within that selected measure.

Water Quantity Tracking Table for Stadium Drainage Basin

Sample Water Quantity

Treatment Measure

Project within Sub-basins MO-3A, MO-

3B, and MO-3C

Project Impervious

Area (acres)

Impervious Area Remaining (acres)

"Banked at Gilmer Pond

1.46

Sample Project A 1.00 0.46 Sample Project B 0.30 0.16 Sample Project C 1.00*

*Because 0.16 – 1.00 would be less than zero, another BMP

strategy must be selected in order to complete Project C.

JNEI’s model has taken into account up to 1.46 acres of

allowable impervious area due to the “banked” area at Gilmer

Pond.

Proposed

modification to Gooch Pond

6.00

Sample Project C 1.00 5.00 Sample Project D 4.50 0.50 Sample Project E 1.00**

**Because 0.50-1.00 would be less than zero, another BMP Strategy must be selected in order to Complete Project E.

Once most or all the impervious area has been accounted for due to the

“banked” area at Gilmer, the proposed modifications to

Gooch Pond were completed, therefore impervious

development can be accounted for up to 6.00 acres.

Proposed Basin at site of Observatory

Dining 9.44

Sample Project E 1.00 8.44 Sample Project F 7.44 1.00

Once the enhanced extended detention basin has been

constructed, up to 9.44 acres of impervious development area can be accounted for.

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IV. WATER QUALITY APPROACH A. Introduction to Water Quality When it rains, stormwater runoff that flows across developed land collects numerous pollutants along its way and discharges them into receiving waters. The accumulation of these pollutants in receiving water bodies ultimately degrades the quality of the receiving water and affects the habitat of biological resources. In an attempt to protect the health of the public and to preserve the natural environment, local, state, and federal regulations have been enacted to maintain and improve the quality of our nation’s waters. 1. Pollutants in Stormwater Stormwater runoff from developed areas carries pollutants that are potentially harmful to the quality of receiving waters. Typical harmful contaminants carried by stormwater runoff include the following (Best Management Practices 4-11 through 4-18):

• Solids, Sediments, and Floatables – including dust, litter, and particles

• Oxygen-Demanding Substances and Dissolved Oxygen – measured by Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), and Total Organic Carbon (TOC)

• Nitrogen and Phosphorus – characteristic of fertilizers, detergents, plant

debris, and animal waste

• Petroleum hydrocarbons – including oil and grease

• Metals – including copper, lead, and zinc

• Synthetic organics – including pesticides, solvents, and household and industrial chemicals

• Bacteria – sources include livestock operations and failing septic systems

Pollutant discharges in stormwater runoff are attributed to negatively impacting the quality of water, the aesthetics of the polluted areas, and the integrity of aquatic ecosystems (Best Management Practices 4-2). 2. Water Quality Control on a Site-by-Site Basis Over time, large increases in development have resulted in a corresponding increase in typical pollutant accumulations that have, resultantly, degraded the quality of the receiving water bodies. As a result, stormwater management regulations were developed to require the use of Best Management Practices (BMPs) to efficiently reduce pollutant loads carried by stormwater runoff before discharging to the natural environment. Traditionally, the removal of harmful pollutants carried by stormwater runoff is controlled on a site-by-site basis whereby each developed site is required to use BMPs to achieve target pollutant removal efficiencies set by state regulations. Similarly, the Virginia Stormwater Management Regulations require the use of water quality BMPs at developed sites to effectively meet target removal efficiency levels for the discharge of the pollutant phosphorus.

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3. Water Quality Control on a Regional Basis The Virginia Stormwater Management Regulations encourage “large tracts of land such as campuses…to develop regional (stormwater management) plans where practical” (10). A regional stormwater management plan enables stormwater concerns to be addressed over an entire region or watershed rather than on the traditional site-by-site basis. Presently, a unique situation exists at the UVA, as it lies in the headwaters of Moore’s Creek where it enters the City of Charlottesville. Stormwater quality improvements made within the upstream tributaries will serve to provide water quality benefits the entire downstream “region.” In other words, the opportunity to improve the quality of stormwater runoff from many existing and future developed sites within the University would also improve the quality of Moore’s Creek downstream. B. Natural Processes “Natural processes have always cleansed water as it flowed through rivers, lakes, streams, and wetlands” (Constructed Wetlands 5). Wetlands, ponds, and streams provide habitat for ecosystems where a stable interaction between plants, animals, and microorganisms can occur. Prior to human interference, these watershed ecosystems flourished with a healthy and diverse population of plants and animals, as well as an abundance of clean water. 1. Ecosystems An ecosystem can be thought of as a natural unit consisting of living and non-living components (i.e., plants, animals, soil chemistry, temperature, nutrients, etc.) that interact to form a stable system. The natural ecosystem is a well-balanced system supporting a diverse structure of plants, animals, and microorganisms. Energy flows through an ecosystem as higher groups of organisms efficiently feed on lower organisms in the food web, and the chain recycles itself continuously. Ecosystems are likely to continue to recycle and maintain a balanced situation, as long as they are not induced by some outside form of intervention (Lessons on the Lake). 2. Characteristics of Streams, Ponds, and Wetlands Streams, ponds, and wetlands provide habitat for natural ecological processes to occur. These wetland systems are characterized by unique hydrologic, soil, and biotic conditions, which set them apart from other systems. The unique characteristics of the stream, pond, and wetland system are described below (Wetland Restoration 76-81):

• Hydrology and Water Quality – The hydrologic characteristics of wetlands, ponds, or streams are characterized in terms of water depths over time, flow patterns, and duration and frequency of flooding or saturation. These systems fluctuate based on seasonal precipitation, temperature, and evaporation. Water within these systems naturally contains a number of dissolved and suspended nutrients, contaminants, and other constituents. When the chemistry of these water systems is typical of the ecosystem and region, healthy populations of native plants and animals are able to flourish, resulting in good water quality.

• Soils – The hydric soils within a wetland, pond, or stream are waterlogged

for all or part of the year, resulting in anaerobic conditions that support survival of particular species of plants and animals. In addition, organic soils are characterized by relatively high amounts of organic carbon and nutrients, which drive the significant biological productivity in these areas.

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• Plants – As hydric soils are hostile to terrestrial plants, they are able to

provide a pleasant environment that supports hydrophytic vegetation (plants that are adapted to anaerobic, waterlogged environments). Species of vascular plants are regionally and locally specific and include variations of emergent plants, submerged plants, floating plants, trees, shrubs, and mosses.

• Wetland Animals – As wetland areas exist where land and water meet, they

are used by animals from both land and water environments. Wetlands are important in maintaining biodiversity; as many species of large and small animals depend on wetlands for all or part of their lives. The ecological diversity of wetlands varies by region, but may include such animals as amphibians and reptiles, invertebrates, fish, birds, and mammals.

3. The Benefits of Streams, Ponds, and Wetlands Streams, ponds, and wetlands are essential elements in a healthy environment. These areas are not only of great importance to ecosystems but also to human society. Some important benefits of streams, ponds, and wetlands include, but are not limited to, the following (Wetland Restoration 4 through 6):

• Support for birds and wildlife – wetlands, ponds, and streams provide locally diverse populations of birds and wildlife.

• Erosion control – vegetated buffers act to dissipate wave energy and stabilize

shorelines.

• Flood damage reduction – wetlands and ponds intercept and store stormwater runoff, slowing the rate of peak flows and discharging smaller amounts over longer periods of time.

• Good water quality – wetlands capture sediments and filter pollutants, which

improve water quality. Ponds allow extended detention times for the settlement of pollutants.

• Biodiversity protection – streams, ponds, and wetlands support a great

diversity of unique and rare species.

• Aesthetics and recreation – many recreation activities take place in and around streams, ponds, and wetlands, as they provide a natural habitat and open space.

C. Watershed Restoration Human interaction through development has destroyed streams, ponds, and wetlands, altering the natural ecosystem within the watershed. In effect, the occurrence of natural processes has been altered by human intervention, causing detrimental effects to the stable interaction between members of the ecosystem. As a result, plant and animal habitat has been lost, causing the chemistry of the system to be altered and the quality of the water to be degraded. Restoring natural resources such as streams, ponds, and wetlands would provide opportunity for the re-establishment of the natural ecological processes and the resultant recovery of benefits of these natural systems. Benefits can be restored through the re-

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creation of meandering streams enhanced by floodplains, wetlands, and ponds, as they once flowed through the campus. Restoration of the natural drainage system would improve the water quality of the system, additionally enhancing the environment, provide recreational areas, and recover aquatic diversity. Watershed restoration would require restoration of the natural drainage system by mimicking the natural environment of the watershed. Although some natural functions can be mimicked by engineered structures, maximum ecological benefits can only be recovered through systems that mimic the natural processes that existed before human development altered them. In order to re-establish the natural processes, the system must blend with the natural landscape and use native soils and vegetation. By mimicking the natural system, ecological processes will be able to readjust to a balanced state, thereby improving the quality of the environment. 1. Impacts to the Natural Drainage System Prior to extensive human intervention, a natural drainage system of springs, creeks, and streams flowed through the grounds of the University where they joined Moore’s Creek en route to the Rivanna River and the Chesapeake Bay. Along these creeks and streams, naturally occurring ponds and wetlands provided areas for the storage of floodwaters and a habitat for ecosystems. During a storm, rainfall either percolated into the soils on the wooded hills and pastures or was conveyed over the sloping land where it flowed through streams, flooded ponds, and wetland floodplains (Strategic Plan 1 through 5). Today, the natural drainage system has been greatly altered by the complex and extensive development of the University. Much of the original wooded areas and open space have been cleared, re-graded, and developed with impervious materials, such as buildings, parking lots, and roadways. As a result, the drainage characteristics of the watershed have been greatly altered due, in part, to the large increase of impervious material that is preventing rainfall from percolating into the soil. This has resulted in a large overall increase in stormwater runoff, as rainfall intercepted by buildings, pavement, and roadways is being converted directly to runoff. Along with the extensive development of the University, the drainage system has been further impacted as streams have been buried, low areas have been filled, wetlands have been eliminated, and large areas of naturally occurring streams have been diverted through subsurface storm sewers and culverts (Strategic Plan 1 through 5). 2. Re-establishing Natural Ecological Processes It has been demonstrated that a balanced ecosystem is a fundamental process in maintaining a healthy watershed. At present, naturally occurring streams, ponds, and wetlands have been altered and/or destroyed by human interaction and development and, as a result, the ecological processes that occur within these resources have also been destroyed. The loss of a balanced ecosystem ultimately affects the quality of the environment; as the natural interaction between all organisms in the watershed is altered, an unbalanced situation is created among the natural processes. Re-establishing the natural ecological processes within the watershed would involve the restoration of the destroyed streams, ponds, and wetlands so as to regain their natural functions. The self-adjusting nature of the plant and animal community would enable the ecosystem to re-establish itself and resulting benefits, such as clean water, could be enjoyed.

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3. Benefits of Watershed Restoration It is evident that natural streams, ponds, and wetlands maintain diverse ecosystems, exemplify unique characteristics, and offer a multiple number of benefits to the environment and the society. Watershed restoration will allow the natural functions of streams, wetlands, and ponds to re-establish themselves. The benefits gained through the re-establishment of the natural processes may include the following:

• Water quality improvement • Ecological benefits • Cycling of nutrients • Habitat for fish and wildlife • Biological diversity • Landscape enhancement • Improved aesthetics • Open space • Passive recreation • Education and research

a. Water Quality Improvement The natural physical, chemical, and biological mechanisms that occur within streams, wetlands, and ponds provide a means of removing pollutants contained in stormwater runoff. Restoring the natural resources of the drainage system will ultimately recover the efficient removal of pollutants passing through the system, and the quality of the water will be greatly improved. b. Ecological Benefits Restoring natural streams, wetlands, and ponds within the watershed will provide habitat for plants, animals, and microorganisms to interact with one another and create a balanced ecosystem. A balanced, healthy ecosystem improves the quality and health of the environment and society (Lessons on the Lake). c. Cycling of Nutrients Free-flowing water within the restored drainage system promotes the constant movement and cycling of important nutrients. Nutrients are an essential component of the health and growth of wetland plant communities. d. Habitat for Fish and Wildlife Restoring streams, ponds, and wetlands within the watershed will provide a healthy environment for fish and wildlife communities to flourish. It has been demonstrated that healthy communities of animals are an essential part of a balanced ecosystem. e. Biological Diversity The restoration of natural streams, ponds, and wetlands will provide habitat for rich and diverse plant and animal communities, which is essential for the support of a healthy ecosystem (Lessons on the Lake). f. Landscape Enhancement The native vegetation essential for healthy streams, ponds, and wetlands will enhance the landscape of the University. As the streams, ponds, and wetlands will be interwoven throughout the campus, so too will diverse plants, shrubs, and trees of the natural system.

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g. Aesthetics The restoration of natural water resources with the incorporation of native plant communities will dramatically improve aesthetics throughout the grounds of the University. h. Open Space Open areas along stream banks, floodplains, and vegetative buffer zones provide a space for the community to enjoy the benefits of the natural environment. i. Passive recreation Paths along streams and ponds provide opportunities for the community to enjoy walks and leisure activities in a clean, natural environment. j. Education and Research Recovery of the altered ecosystem through restoration of the watershed would provide an opportunity for research documenting the natural recovery of the quality of the environment. D. Pollutant Removal Mechanisms (Urban Runoff 329, Table 1) The restoration of the natural system will benefit the region as ecological processes are re-adjusted and the natural pollutant removal mechanisms can recur. The complex assemblage of soils, plants, animals, and microorganisms contributing to the natural system will function to perform various mechanisms that remove pollutants from water (Constructed Wetlands 17). Numerous physical, chemical, and biological mechanisms can occur within the system to trap and transform pollutants as they pass. 1. Physical Mechanisms The most dominant pollutant removal mechanism in the natural system is sedimentation (Pollution Control 311). Sedimentation is the removal of suspended particles using gravitational settling. Sedimentation occurs within wetlands and ponds between storm events where detention time allows solid particles to undergo settling. Sedimentation can be effective in removing high concentrations of nutrients, metals, oxygen-demanding substances, and hydrocarbons that can become adsorbed to particulate matter (Best Management Practices 5-4). Another mechanism effective in the removal of particulates is filtration. The dense vegetation characteristic of a natural system can act like a filter to remove pollutants and sediments. In addition, as water infiltrates into the soil matrix, filtration can also take place. Dense vegetation can also be effective in removing floatables and litter from stormwater through the process of filtration (Pollution Control 312). 2. Chemical Mechanisms “Adsorption of pollutants onto the surfaces of suspended particulates, sediments, vegetation, and organic matter is a principal mechanism for removing dissolved or floatable pollutants” (Pollution Control 311). Phosphorus and other dissolved metals absorbed onto surfaces of particulates are then able to settle to the bottom of ponds or wetlands through sedimentation (Pollution Control 311). The unique chemical conditions of a wetland environment cause many metals to dissolve or precipitate. Precipitation can be effective in removing metals such as copper, lead, and zinc, as well as dissolved phosphorus (Pollution Control 312). Ion exchange is also effective in removing dissolved metals from the natural environment.

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Volatilization (or evaporation) is also a natural process that occurs within wetland areas that can be effective in removing volatile pollutants and hydrocarbons (Pollution Control 312). 3. Biological Mechanisms The dense populations of plant communities incorporated within the natural system can be effective in the uptake of significant concentrations of nutrients. Nutrients such as nitrogen and phosphorus are removed from water by aquatic plants, algae, and microorganisms through biological uptake necessary for their growth (Best Management Practices 5-6). Plants also remove metals as they uptake them into their tissues. Microbial communities within the natural system can function to break down complex and toxic organic compounds into less harmful compounds (Best Management Practices 5-6). In addition, microbes are capable of decomposing oxygen-demanding substances and hydrocarbons through their natural processes. E. Regional Watershed Restoration Opportunities This Stormwater Management Master Plan uses the guiding principles of watershed restoration as a basis for the regional plan for the Moore’s Creek Watershed. Although the extensive development within the Moore’s Creek Watershed is a critical constraint to watershed restoration, JNEI has strived to take advantage of any and all opportunities to restore the watershed. The primary goal of the Stormwater Management Master Plan is to re-create the naturally functioning drainage system flowing through the University in order to improve the quality of water within the region. As the University of Virginia lies in the headwaters of tributaries to Moore’s Creek, the benefits of stormwater quality improvements at the University will be seen throughout the entire downstream Moore’s Creek Watershed. The entire region will enjoy the benefits of the natural system that will serve to cleanse stormwater runoff from both existing and future developed areas. The regional approach to stormwater management attempts to restore the natural processes in these upstream areas in order to support a habitat for a balanced ecosystem, ultimately functioning to improve the quality of water within the entire downstream “region.” In order to accomplish the goals of the plan, the University must take advantage of any and all opportunities that exist to re-create the natural drainage system that has been altered by extensive University development. Such restoration opportunities throughout the University that will serve to improve the water quality of the Moore’s Creek Watershed may include the following:

• Daylighting streams • Creating wetlands • Creating ponds • Planting native wetland species • Creating floodplains • Incorporating aquatic benches • Creating vegetated buffers

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1. Daylighting Streams With the widespread development of the University, large segments of the natural-flowing streams were placed in underground pipes and culverts. In doing so, biological communities and plant and animal habitats were destroyed. As previously demonstrated, the effects of lost habitat are detrimental to the balance of the ecosystem and, resultantly, negatively affect the quality of water. Daylighting streams would begin to reverse the negative effects caused by development and begin to restore the natural system. 2. Creating Wetlands Throughout the phases of University expansion, wetlands were destroyed and replaced with development areas. Wetland areas are of major importance to the functioning natural system, as they not only provide a primary habitat for an ecosystem, but also function to improve the quality of water. Recreating wetlands along stream banks would provide a major benefit to the overall quality of the watershed and the environment. With the addition of native aquatic vegetation and other natural features, a sustained and healthy environment would be created within the wetland where a diverse ecosystem could flourish. In addition, the pollutant removal mechanisms of a naturally functioning wetland would serve as one of the primary water quality controls within the system. 3. Creating Ponds A pond would function to hold large volumes of water for extended periods of time, allowing for the efficient removal of pollutants and increased plant and animal habitat. In addition, a pond would add open space for recreational activities and enhance the overall quality of the natural system. 4. Planting Native Wetland Species The greatest enhancement of restoring the natural system will arise from the planting of natural and native communities of wetland plants. Healthy wetland plant communities will promote ecological activity within the system through the re-creation of habitats for animals and microbes. The opportunity to restore large populations of plants in and around streams, wetlands, and ponds will benefit the overall system by aiding in the removal of pollutants and contributing to the improved landscape enhancement of the University. Planting native wetland species is beneficial to the improvement of water quality and the environment in general. 5. Creating Floodplains In order to enhance the functioning capabilities of the restored system, the creation of floodplain areas will allow additional water quality opportunities to occur during large storm events. Gently sloping floodplain areas along the banks of wetlands and streams will act as a buffer between developed areas and water resources and create open space and recreational areas. 6. Incorporating Aquatic Benches With the restoration and re-creation of wetland areas and natural ponds, the opportunity to promote additional diversity within these systems can arise through the incorporation of aquatic benches. Aquatic benches will allow various depth zones within permanent pools that function to enhance the benefits of wetlands and ponds. The various depth zones enable many species of vegetated plants to emerge and augment pollutant removal, provide animal habitats, conceal trash and water level fluctuation, and enhance safety (Virginia Stormwater 1).

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7. Incorporating Vegetated Buffers Vegetated buffers will provide open space between components of the drainage system and the grounds of the University. The vegetated buffers are vitally important in protecting the resource areas from everyday human disturbances. The incorporation of upland plants within vegetative buffer zones will further enhance the ecological diversity of the system, as well as the landscape of the University. The vegetated buffers will provide additional habitat for animals that will benefit the ecosystem. F. Proposed Watershed Restoration The current University of Virginia Master Plan proposes a multi-phase plan for development projects within the southern portion of the University of Virginia property, or the Moore’s Creek Watershed. The stormwater runoff from these future development areas will be discharged through one of three discharge points, which each travels in a southerly direction to join Moore’s Creek, either as an open channel stream or a closed pipe system. Refer to Section III.G.1 of this report for a discussion regarding the characteristics of the existing and proposed sub-basins contributing to each of the collection tributaries. The proposed Stormwater Management Plan incorporates water quality improvements to each of the three tributary systems in order to, ultimately, benefit the downstream Moore’s Creek region. 1. Stadium Drainage Basin Watershed re-creation opportunities exist in coordination with proposed development projects within the Stadium Drainage Basin (Sub-basins MO-3A, MO-3B, and MO-3C). These opportunities will not only treat stormwater runoff from the existing and future development sites, but will also serve to improve the quality of stormwater passing downstream to Moore’s Creek. As part of this Stormwater Management Plan, JNEI recommends creating an enhanced extended detention basin upstream from the existing Gilmer Pond (within the Alderman Road Residence cluster) in order to treat stormwater runoff from development areas identified by the University in the Master Plan. Presently, discussions have taken place between JNEI and the University of Virginia regarding the future demolition of the Observatory Dining Hall as the site of this stormwater management pond. The enhanced extended detention basin should serve to temporarily store stormwater runoff and provide for water quality enhancement. The basin should be designed to include shallow marsh areas and/or aquatic bench areas for additional pollutant removal through wetland plant uptake, absorption, physical filtration, and decomposition (Virginia Stormwater Management Handbook, 3.07-1). The basin area should also be enhanced with native vegetation to promote additional pollutant removal. JNEI also recommends enhancement of the existing Gooch/Dillard Pond with aquatic benches, native vegetation, and wetlands areas along the banks. The enhancement of Gooch/Dillard Pond will promote a diverse ecosystem and a primary location for the removal of pollutants, contributing to the improvement of the quality of the system in coordination with the proposed modifications to the pond for water quantity mitigation. 2. Brandon Drainage Basin Due to the level of development within Sub-basin MO-5B, the “South Lawn Project” and other future development projects within this sub-basin will not provide for the opportunity to restore existing water quality features. However, JNEI recommends including various site-specific water quality features in order to efficiently treat

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stormwater runoff from anticipated future development projects within this sub-basin. The proposed water quality features should include the incorporation of vegetated filter strips, grassed swales, and/or biofiltration areas in order to achieve pollutant removal efficiencies greater than those required by the Virginia Stormwater Regulations. The current South Lawn Project Proposal (Scheme C) proposes to improve the existing watershed condition, as the amount of impervious area will be slightly lowered due to the “greening” approach. Therefore, the incorporation of site-specific stormwater management techniques will improve the quality of stormwater in the sub-basin and contribute to the overall improvement of the entire Moore’s Creek Watershed. 3. Health Sciences Center and University Hospital Due to the level of development within Sub-basins MO-6A and MO-6B, few opportunities exist to restore the existing Watershed condition. At present, the existing stormwater retention basin provides efficient water quality treatment for the existing developed watershed. However, as part of this Stormwater Master Plan, JNEI proposes creating an extended detention basin upstream from the existing Health Sciences Stormwater Pond in order to treat stormwater runoff from the future developed Sub-basin MO-6B.

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V. WATER QUALITY A. Pollutant Removal Efficiencies for Existing BMP’s At present, stormwater runoff from three development areas within the Moore’s Creek Watershed is treated in an existing BMP facility before discharging into a tributary of Moore’s Creek. Namely, these BMPs include the following:

• West Grounds Stormwater Management Pond (also referred to as Gilmer Pond)

• Gooch/Dillard Stormwater Pond • Health Sciences Center Stormwater Management Pond

1. West Grounds Stormwater Management Pond (Gilmer Pond) A report issued in January 2000 by CEGG Associates entitled “West Grounds Stormwater Pond Improvements” provided stormwater management design and pond improvements for the West Grounds Pond, which have since been completed. The existing West Grounds Stormwater Management Pond is between Gilmer Hall and the Aquatic and Fitness Center in Sub-basin MO-3A and is also referred to as Gilmer Pond. The pond has a volume of 10.52 acre-feet between elevations 522.3 and 542.0 and has a surface area of 0.96 acres at an elevation of 542.0. The West Grounds Stormwater Management Pond is currently fed by a small stream, which collects stormwater from the developed sub-basin. A multi-stage outlet controls the discharge from the pond into the University drainage system. The stormwater management pond, as determined from as-built studies, has a water quality volume of 0.35 acre-feet, supporting up to 8.3 acres of new impervious area for water quality treatment. According to CEGG Associates, proposed development associated with the Chemistry Building addition, Aquatic and Fitness Center, Student Housing Facility, a Proposed Residence Hall, and additional development in the sub-basin have accounted for 3.56 acres of the available impervious development area contributing to the pond. Therefore, 4.74 additional acres of impervious have been “banked” in the design of the West Grounds Stormwater Management Pond for water quality treatment of future development projects within sub-basin MO-3A. 2. Gooch/Dillard Stormwater Pond South of the existing Gooch and Dillard Dormitories, a small stream collects stormwater from the developed dormitory area and passes through a culvert beneath Alderman Road where it is collected in a small stormwater management pond. This pond is referred to as the Gooch/Dillard Stormwater Pond and is in sub-basin MO-3C. According to the most recent topographic plans by the City of Charlottesville, JNEI has estimated the pond to have a volume of 0.40 acre-feet between elevations 524.0 and 528.4 and a surface area of 0.16 acres at the flood elevation of 528.4. An engineering report is not available for the Gooch/Dillard Stormwater Pond; therefore, it is assumed the pond was designed to treat stormwater runoff only from the contributing Gooch and Dillard Dormitory areas. Therefore, JNEI has concluded that the Gooch/Dillard Stormwater Pond cannot accommodate additional impervious areas associated with future development for stormwater quality treatment without modifications or enhancement to the existing pond.

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3. Health Sciences Center Stormwater Management Pond The Cox Company prepared a report entitled “Stormwater Management Report – East Precinct Parking Garage and Infrastructure Project, The University of Virginia Health Sciences Center” with a final revision issued in May of 1998. This report presented design and performance criteria for an onsite stormwater retention basin that would provide adequate quantity and quality measures for the Phase I Parking Garage project, as well as for the Full (future) Development of the Health Sciences Center. The Health Sciences Center Stormwater Management pond is currently located south of the newly constructed South Parking Garage in Sub-basin MO-6A and collects stormwater from the developed Health Sciences/University Hospital district. The pond has a permanent pool capacity of approximately 3.56 acre-feet between elevations 436.00 and 445.00. The pond also has approximately 6.55 acre-feet of additional flood storage capacity above the permanent pool to an elevation of 452.10. A complex, multi-stage outlet discharges treated stormwater from the pond to the 84-inch City of Charlottesville storm drain system. As documented in the Cox Company report and confirmed by JNEI, the 3.56 acre-feet of permanent pool storage in the pond provide a water quality treatment volume of 0.87 acre-feet. Given the definition of the water quality volume (water quality volume based on one-half inch of runoff over new impervious area), the pond has the capacity to treat 20.88 acres of impervious development. JNEI has determined that approximately 12.27 acres of the Full Development scenario have been developed at this time (See Section III.F.1.c). Therefore, the remaining, or “banked” impervious development area is 8.61 acres for water quality treatment of future impervious development projects within the Health Sciences Center/University Hospital area. B. Water Quality for Identified Future Development Projects For the purposes if this Stormwater Management Master Plan, JNEI studied the pollutant loads and water quality volumes generated from proposed future development projects identified by the University of Virginia. 1. Water Quality Volumes The Virginia Stormwater Management Regulations require the first flush (first 0.5 inches) of runoff, or the water quality volume, be treated to enhance the water quality using BMPs. Therefore, water quality volumes have been calculated for the sub-basins within the Moore’s Creek Watershed where the University has identified future development. As a conservative approach to this analysis, JNEI has assumed that identified future development areas, as well as potential impact areas associated with the development (i.e., walkways, parking, etc.), are totally impervious. Within these sub-basins, planning areas have been assumed as either the entire sub-basin area or a portion of the sub-basin area, depending on the extent of the proposed development within the sub-basin. The following table summarizes the water quality volumes required for treatment in sub-basins where the University has identified future development.

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Table 17 Water Quality Volumes

Sub-basin

Proposed Development Projects Identified by University

Planning Area

(acres)

Proposed Impervious

Area (acres)

Water Quality Volume

(acre-feet)

MO-3A

Gilmer Hall Addition Aquatic & Fitness Center Addition

Observatory Hall Addition 25% Additional Residential Housing

36.13 * 4.65 0.19

MO-3B

Chemistry Building Additions Mechanical Engineering Addition

Material Science Building Addition Chemical Engineering Research Addition

Additional Unidentified

45.47 ** 9.47 0.39

MO-3C Unidentified 16.52 ** 2.78 0.12

MO-5A Olsson Hall Addition Additional Housing near Halsey Hall 17.45 ** 1.56 0.06

MO-5B South Lawn Phase I South Lawn Phase II

Parking Garage 15.51 ** 8.75 0.36

MO-6A pond

McCleod Hall Expansion Health Science Library Expansion South Parking Addition Phase III

University Hospital Expansion Phase I and II Medical Research near McLeod MR-6, MR-7,

MR-8 Additional Residential Housing Additional Medical Research

27.29 ** 4.76 0.20

MO-6A bypass McKim Hall Addition 38.37 ** 1.06 0.04

MO-6B University Hospital Addition Additional Unidentified 18.50 * 7.61 0.32

* Entire Sub-Basin Area is considered “Planning Area” ** Portion of Sub-Basin Area is considered “Planning Area” 2. Pollutant Runoff Loads JNEI determined the annual pollutant runoff loads generated from sub-basins where the University has identified future development. The annual pollutant loads were calculated using the Performance-based water quality criteria set forth in The Virginia Stormwater Management Regulations. These calculations were performed based on the previously defined planning areas and conservative impervious development areas. The following table summarizes the pollutant loads and pollutant removal requirements for sub-basins where the University has identified future development.

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Table 18 Pollutant Runoff Loads and Pollutant Removal Requirements (Phosphorus)

Sub-basin

Planning Area

(acres)

Proposed Impervious

Area (acres)

Post-Development Impervious

Cover (%)

Pre-Development Impervious

Cover (%)

Post-Development Pollutant Load

(pounds per year)

Pre-Development Pollutant Load

(pounds per year)

Removal Requirement

(pounds per year)

MO-3A 36.13 * 4.65 84.25 78.88 66.58 62.60 10.24

MO-3B 45.47 ** 9.47 88.12 85.00 87.40 84.49 11.36

MO-3C 16.52 ** 2.78 47.15 30.33 17.87 12.16 6.93

MO-5A 17.45 ** 1.56 89.05 84.99 33.88 32.42 4.70

MO-5B 15.51 ** 8.75 56.42 65.15 19.72 22.50 -

MO-6A pond 27.29 ** 4.76 88.35 85.01 52.59 50.72 6.94

MO-6A bypass 38.37 ** 1.06 85.41 84.99 71.62 71.29 7.46

MO-6B 18.50 * 7.61 90.11 85.03 36.32 34.39 5.37

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C. Best Management Practices Strategies It has been discussed that the southern portion of the University of Virginia property, where future development has been identified as part of this Master Plan, will discharge stormwater runoff to a Moore’s Creek tributary through one of three discharge points beneath the CSX Railroad. Sub-basins contributing to each discharge point have, therefore, been combined for the purposes of stormwater management strategies. As a result, BMP strategies will be discussed in the following three areas:

1 Stadium Drainage Basin (Sub-basins MO-3A, MO-3B, and MO-3C) 2 South Lawn Development Area (Sub-basin MO-5B) 3 Health Sciences/University Hospital Area (Sub-basins MO-6A and MO-6B)

1. Stadium Drainage Basin (Sub-basins MO-3A, MO-3B, MO-3C) Within the Stadium Drainage Basin, three opportunities exist to treat stormwater runoff from the full-extent of future impervious development. In addition, these opportunities will serve to restore the existing watershed and improve the quality of Moore’s Creek in downstream areas. The three water quality opportunities within this sub-basin include the following:

• Using the 4.74-acre “banked” impervious area for water quality treatment within Gilmer Pond.

• Provide additional water quality treatment in the Gooch/Dillard Pond by

increasing the storage capacity and enhancing the pond with additional water quality features.

• Designing a new enhanced extended detention basin at the site of the

Observatory Dining Hall, in the Alderman Road Residence Cluster. a. West Grounds Stormwater Pond (Gilmer Pond) As previously discussed, the West Grounds Stormwater Pond has been designed to accommodate water quality treatment for future impervious development. Therefore, the first BMP strategy within the Stadium Drainage Basin is to take advantage of this “banked” area. This can be accomplished by tracking impervious development area for future development projects within Sub-basins MO-3A, MO-3B, and/or MO-3C up to 4.74 acres. b. Gooch/Dillard Pond This SWMP recommends increasing the cumulative storage volume of the Gooch/Dillard Pond from 0.38 acre-feet to 0.88 acre-feet for the purposes of water quantity mitigation. The additional 0.50 acre-feet of pool storage will serve to treat the stormwater runoff from future developed areas. According to the Virginia DCR Stormwater Regulations (one-half inch of runoff over the impervious area), a water quality treatment volume of 0.50 acre-feet will treat 6.00 acres of impervious development, assuming the Gooch/ Dillard Pond is designed as an extended detention basin. Therefore, the second BMP strategy with the Stadium Drainage Basin is to track impervious development areas for future development projects within Sub-basins MO-3A, MO-3B, and/or MO-3C up to 6.00 acres after the modifications to Gooch Pond have been completed.

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JNEI also recommends that the modified Gooch/Dillard Pond be enhanced with water quality features such as native wetland vegetation, aquatic benches, and floodplains. These features will provide additional water quality treatment credits and serve to restore the natural drainage system for the overall improvement of the quality of the sub-basin and the entire Moore’s Creek Watershed. c. Observatory Hill Enhanced Extended Detention Basin As part of this SWMP, the University of Virginia and the design team have discussed the future the Observatory Dining Hall site for consideration of a stormwater management facility. In order to ensure water quantity mitigation and the conservative treatment of stormwater runoff, JNEI recommends an enhanced extended detention basin be sized according to the DCR Stormwater Regulations to treat the water quality volume for 9.44 acres of future impervious development, as discussed in Section III.G.3.a. An enhanced extended detention basin is recommended because it has a high pollutant removal efficiency because it incorporates a shallow marsh system, which provides additional pollutant removal through wetland plant uptake, absorption, filtration, decomposition, and settling. The proposed enhanced extended detention basin shall have a pool volume of 0.39 acre-feet and a marsh area volume of 0.39 acre-feet to provide adequate treatment of 9.44 acres of impervious future development area. d. Full Development within the Stadium Drainage Basin Given that all three BMP strategies are completed according to this SWMP, a total of 20.18 acres of future impervious development within the Stadium Drainage Basin can be treated. For the purposes of this SWMP, a total of 16.90 acres of impervious development have been identified by the University of Virginia. As the proposed BMPs will effectively mitigate only up to the anticipated 16.90 acres, the Stadium Drainage Basin will have the capacity to treat the quality of stormwater runoff above and beyond the extent of development anticipated at this time. Therefore, if all anticipated 16.90 acres of impervious area are developed within Sub-basins MO-3A, MO-3B, and MO-3C, an additional 3.28 acres should be “banked” for the water quality treatment of unidentified future development within this drainage area. 2. Brandon Drainage Basin (Sub-basin MO-5A and MO-5B) Within Sub-basin MO-5B, Polshek Partnership and SMBW Architects are currently in the preliminary design phase for the South Lawn Development Project (Scheme C). Within Sub-basin MO-5B, the University has also identified the future development of a garage; however, this project is less defined than the South Lawn Project. Using a conservative impervious area for this proposed garage development and the impervious area anticipated for the South Lawn Development, the overall sub-basin will see an improved condition. This is due to the “greening” approach taken in the South Lawn Development Scheme C, whereby the post-development condition will contain less impervious area than the pre-development condition. JNEI has performed water quality calculations within this sub-basin according to the DCR Stormwater Regulations and has noted that there is no pollutant removal requirement due to the decreased impervious area in the post-developed condition. However, only a small amount of impervious development area above and beyond what has been calculated for the purposes of this SWMP (i.e., 0.25 acres) would raise the pollutant load to the threshold by which water quality measures would be required. Therefore, JNEI is recommending the use of water quality measures to achieve a removal

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efficiency between 1% and 15%, such as vegetated filter strips, grassed swales, and/or biofiltration areas, as the primary BMP strategy within this sub-basin area. The use of the proposed water quality measures will serve to adequately treat the pollutant load generated from future development within Sub-basin MO-5B and ensure that even a slight increase in impervious development above what is anticipated at this time will be accounted for. The proposed water quality measures would also treat stormwater runoff to a level greater than that required by the DCR Stormwater Regulations in order to contribute to the overall improvement of the quality of the Moore’s Creek Watershed. The water quality measures should also serve as to pre-treat stormwater runoff upstream of the recommended Rainstore unit in order to prevent the accumulation of sediments. 3. Health Sciences Center/University Hospital (Sub-basins MO-6A and MO-6B) Within Sub-basins MO-6A and MO-6B, two opportunities exist to treat stormwater runoff from the full-extent of future development identified for the purposes of this SWMP. In addition, these opportunities will provide enhancement of the existing watershed for the improved quality of the downstream Moore’s Creek Watershed. The two water quality opportunities within the Health Sciences Center/University Hospital Area are as follows:

• Use the 8.61 acres banked for water quality treatment in the Health Sciences Pond.

• Incorporate an extended detention basin in coordination with a project in

Sub-basin MO-6B. a. Health Sciences Center Pond As previously discussed, the Health Sciences Center Pond has been designed to accommodate water quality treatment for future impervious development. Therefore, the first BMP strategy within the Health Sciences Center/University Hospital area is to take advantage of this “banked” impervious area. This can be accomplished by tracking impervious development area for future development projects within Sub-basin MO-6A up to 8.61 acres. b. Proposed Extended Detention Basin As part of this SWMP, JNEI recommends designing an extended detention basin in order to treat stormwater runoff from 8.94 acres of impervious development. This accounts for the full-extent of future development within Sub-basin MO-6B and additional area that could not be mitigated in the existing pond. Although the University has not selected a proposed location for this facility, the basin should be constructed in coordination with a future development project within this sub-basin. The extended detention basin will provide water quality enhancement through gravitational settling. In order to ensure the conservative treatment of stormwater runoff, JNEI sized an extended detention basin according to the DCR Stormwater Regulations to treat the water quality volume for 8.94 acres of future impervious development. Therefore, given that the required volume for an extended detention basin is two times the water quality volume, the extended detention basin shall have a volume of at least 0.74 acre-feet.

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c. Full-development within the Health Sciences/University Hospital Area Given that all BMP strategies are completed according to this SWMP, a total of 17.55 acres of future impervious development within Sub-basins MO-6A and MO-6B can be treated. As the proposed BMPs will effectively mitigate only up to the anticipated 12.37 acres, the BMPs will have the capacity to treat the quality of stormwater runoff above and beyond the extent of development anticipated at this time. Therefore, if all anticipated 12.37 acres of impervious area are developed within Sub-basins MO-6A and MO-6B, an additional 5.18 acres would be “banked” for the water quality treatment of unidentified future development within this drainage area. D. Water Quality Treatment Volumes In order to comply with the Virginia Stormwater Management Regulation requirements to adequately treat the water quality runoff, JNEI has quantified the pollutant removal efficiencies of the various components of the BMP strategies within two of the analysis areas (Stadium Drainage Basin and Health Sciences/University Hospital Area). For the purposes of the water quality calculations, the water quality treatment components of the SWMP were evaluated to determine the water quality treatment volume provided. The following table summarizes the Best Management Strategies, which provide water quality treatment, as discussed in Section V.C, and the water quality treatment volume provided by each. Table 19 Water Quality Treatment Volumes

Sub-basin

Water Quality Opportunity

Design Size Criteria (Chapter 3 Virginia Stormwater Design

Handbook)

Treatment Volume Provided

(cubic feet)

Water Quality Volume

Provided (acre-feet)

MO-3A Existing Gilmer Pond As modeled by CEGG Associates

As modeled by CEGG Associates

0.20 remaining

MO-3A

Proposed Enhanced Extended Detention Basin at Observatory

Dining Hall

Pool: 1*WQ Volume Marsh: 1*WQ Volume 33,976 0.39

MO-3C Modification to Gooch/Dillard Pond

Extended Detention Basin: Volume = 2*WQVolume 21,780 0.25

MO-6A Existing Health Sciences Pond

As modeled by Cox Company

As modeled by Cox Company

0.40 remaining

MO-6B Proposed Extended Detention Basin

Extended Detention Basin: Volume = 2*WQVolume 32,234 0.37

A subtotal of the water quality treatment volumes provided in the Stadium Drainage Basin results in a volume of 0.84 acre-feet. The water quality volume in this Drainage Basin requiring treatment, as shown in Table 16, is 0.70 acre-feet. Therefore, the water quality opportunities within the Stadium Drainage Basin will adequately satisfy the requirement to treat the water quality volume of 0.70 acre-feet. A subtotal of the water quality treatment volumes provided in the Health Sciences/University Hospital Area results in a volume of 0.77 acre-feet. The water

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quality volume requiring treatment, as shown in Table 16, is 0.52 acre-feet. Therefore, the water quality opportunities within the Stadium Drainage Basin will adequately satisfy the requirement to treat the water quality volume of 0.52 acre-feet. Water Quality Treatment provided in the Brandon Drainage Basin will be applied on a site-specific basis. Each development site must comply with the Regulations in order to adequately treat the water quality volume required. E. Water Quality for Future Development The Best Management Practices Strategies presented in the SWMP have accounted for a significant amount of impervious development within the Stadium Drainage Basin (Sub-basins MO-3A, MO-3B, and MO-3C) and the Health Sciences/University Hospital area (Sub-basins MO-6A and MO-6B). JNEI has prepared Water Quality Tracking Tables within these two areas in order to enable the University to plan future development within these University sub-basins. Each BMP strategy can accommodate for impervious area due to development up to a certain value. Therefore, it is necessary to know when additional water quality features must be added before additional development is completed, as well as when the overall development limit has been reached. When the impervious limit has been reached in a given sub-basin, the water quality calculations must be re-evaluated in order to determine if the water quality measures can accommodate the additional development. It must be realized that only projects within the Stadium Drainage Basin (Sub-basins MO-3A, MO-3B, and MO-3C) and the Health Sciences Center/University Hospital Area (Sub-basins MO-6A and MO-6B) have been included in these tracking tables. Therefore, projects outside these areas have not been anticipated and would require revising the calculations or incorporating a project specific water quality plan to accomplish the pollutant removal requirement for the given site. The Tracking Tables are presented in Appendix B of this Report. The following table demonstrates a sample of how the tracking table is used.

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Table 20 Sample Water Quality Tracking Table Water Quality Tracking Table for Stadium Drainage Basin

Sample Water Quality

Treatment Measure

Project within Sub-basins MO-3A, MO-

3B, and MO-3C

Project Impervious

Area (acres)

Impervious Area Remaining (acres)

"Banked at Gilmer Pond

4.74

Sample Project A 2.00 2.74 Sample Project B 2.00 0.74 Sample Project C 1.00*

*Because 0.74 – 1.00 would be less than zero, another BMP

strategy must be selected in order to complete Project C.

JNEI’s model has taken into account up to 4.74 acres of

allowable impervious area due to the “banked” area at Gilmer

Pond.

Proposed

modification to Gooch Pond

6.00

Sample Project C 1.00 5.00 Sample Project D 4.50 0.50 Sample Project E 1.00**

**Because 0.50-1.00 would be less than zero, another BMP Strategy must be selected in order to Complete Project E.

Once most or all the impervious area has been accounted for due to the

“banked” area at Gilmer, the proposed modifications to

Gooch Pond were completed, therefore impervious

development can be accounted for up to 6.00 acres.

Proposed Basin at site of Observatory

Dining 9.44

Sample Project E 1.00 8.44 Sample Project F 7.44 1.00

Once the enhanced extended detention basin has been

constructed, up to 9.44 acres of impervious development area can be accounted for.

*** The impervious development area can also be divided among multiple BMP strategies as

long as impervious area remains banked within that BMP. F. Site-Specific Water Quality Management Although the stormwater runoff from developed sites will be treated through one of the three BMP strategies, the incorporation of site-specific water quality management is still necessary. In order to maintain and enhance pollutant removal within each drainage system, it is necessary to develop a means of pre-treating stormwater runoff at newly developed sites.

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VI. C OMPLIANCE WITH VIRGINIA STORMWATER MANAGEMENT REGULATIONS (4 VAC 3-20)

In compliance with the Virginia Stormwater Management Regulations 4 VAC 3-20, the Moore’s Creek Stormwater Management Plan meets the Technical Criteria for water quantity mitigation, water quality treatment, stream channel erosion control, and flood prevention. This section summarizes how the components of the Stormwater Master Plan (SWMP) comply with the Virginia Stormwater Management Regulations and refers to sections of the report where compliance issues are discussed in detail. The SWMP complies with the technical criteria set forth in 4 VAC 3-20-50 through 4 VAC 3-20-86 as demonstrated by the following: 4VAC 3-20-60 General A. Three discharge points have been established whereby all flooding and erosion

impacts in the Moore’s Creek Watershed due to future development were evaluated. These discharge points are discussed in Section III.G.1 and are summarized in Table 5 of this report.

B. Hydrologic models for various storm events were based on the 24-hour storm with a

Natural Resources Conservation Service Type II Storm Distribution. Hydrologic models were developed for three model scenarios described in Section III. D.1, E.1, and G.2 and are modeled in Volume II.

C. All pervious land areas were considered to be in good condition prior to

development. Refer to Section III.D.1 for pre-development pervious areas and Volume II for hydrologic models containing these areas.

D. Individual measures described in the report will be subject to all applicable laws and

regulations governing their construction. E. Impounding structures shall be designed to withstand the 100-year flood. Individual

design plans for stormwater management facilities should be reviewed by DCR for compliance with this requirement.

F. Consistent with good engineering practices, pre-development and post-development

runoff rates were calculated using the Natural resources Conservation Service Technical Release 20 and modeled in the HydroCAD computer program. The hydrologic modeling approach is described in Section III.C.1, and the HydroCAD models containing runoff rates can be found in Volume II.

G. Outflows from stormwater management facilities shall be designed to discharge into

adequate channels with non-erosive velocity. Individual design plans for stormwater management facilities should be reviewed by DCR for compliance with this requirement.

H. The hydrologic parameters for proposed conditions situations (both unmitigated and

mitigated) reflects the ultimate land development as identified by the University at the start of the stormwater study, as described in Sections III.E.1, F.1, and F.2.

I. The University of Virginia will be the Owner and responsible party of all stormwater

management facilities. Each stormwater management facility shall have a

50

Maintenance Plan prepared by the designer of the facility, which has been prepared in accordance with Stormwater Management Facilities Maintenance Guidelines presented in this report.

J. Stormwater management impoundment structures are not located within a FEMA

designated floodplain. See FIRM Panel #5100330002C. K. The stormwater management plan will preserve the natural channel characteristics of

Moore’s Creek and its tributaries. L. Land development projects comply with the Virginia Erosion and Sediment Control

Act. Individual design plans for stormwater management facilities should be reviewed by DCR for compliance with this requirement.

4 VAC 3-20-71 Water Quality A. Compliance with the water quality criteria is achieved by comparing the water

quality treatment volume required from proposed development areas to the water quality treatment volume provided by the selected water quality strategies. This is described in Section V.A, C, and D.

B. Section V.C describes the water quality components that will be located, designed,

and maintained to achieve the effective pollutant removal requirements. C. Technology Based Criteria was not analyzed for this study. 4VAC 3-20-81 Stream Channel Erosion A. Properties and receiving waters will be protected from erosion and damage due to the

reduction of the peak flow rate and the corresponding decrease in downstream channel velocities. Refer to Section III.G.3.

B. Individual design plans for stormwater management facilities should be reviewed by

DCR for compliance with this requirement. C. This SWMP reduces the peak rate of discharge from the three collection tributaries of

Moore’s Creek, namely Rock Creek, the Rock Creek Tributary, and the City Storm Drain that joins Rock Creek. Refer to Section III.G.3.

D. Minimum Standard 19 has been applied at the South Lawn Development Site,

whereby an underground detention structure will reduce the peak rate of runoff for the 1-year and 2-year storm event before discharging to the Rock Creek Tributary. Refer to Sections III.G.1.b and 3.b.

4VAC 3-20-85 Flooding A. Downstream properties and waters will be protected from flooding as the volume and

peak flow rate of stormwater will be reduced in the proposed development condition. Refer to Section III.G.3.

B. The 10-year post-developed peak rate of runoff at the three design points will not

exceed the 10-year pre-developed peak rate of runoff. Refer to Section III.G.3 for a discussion of the reduction in the peak rate of runoff for the 10-year storm event, and Volume II for technical documentation in the hydrologic models.

51

VII. CONCLUSION JNEI has created a Stormwater Master Plan (SWMP) which models the existing and future conditions of the Moore’s Creek Watershed in order to (1) assess the potential impacts of development on the peak rate and quality of stormwater in the watershed, and (2) to determine mitigation measures that would improve the present condition of the watershed. JNEI has developed this SWMP in order to provide the University with the necessary parameters for planned projects as well as unforeseen future development projects along the southern portion of the University, all the while improving the condition of Moore’s Creek, its tributary branches, and the entire watershed. In order to create a “blueprint” for the development of the University grounds, the SWMP proposes a realistic approach to stormwater mitigation and treatment that is in keeping with the previous studies and plans for development of projects that were identified up to the point of the start of the study, and is flexible enough for the addition of future University expansion. In accordance with the Virginia Stormwater Management Regulations set forth by the Department of Conservation and Recreation, this SWMP provides control for both the quantity and quality of water contributing to the Moore’s Creek drainage systems. JNEI carefully selected a combination of mitigation measures that would be most effective in controlling the peak flow rate at each of the three design points, and improve the existing stressed stream condition of Moore’s Creek and its tributaries. With the incorporation of the proposed mitigation measures, heavy flows of stormwater flowing through the Moore’s Creek collection tributaries during all storm events will be retained and slowly discharged back into the Moore’s Creek system once the storms have subsided. The selected mitigation measures include the following: Stadium Drainage Basin

1. Taking advantage of “banked” storage capacity remaining in the existing Gilmer Pond.

2. Increasing the Storage Capacity of the Gooch/Dillard Pond and modifying the outlet.

3. Creating an enhanced extended detention basin upstream from the existing Gilmer Pond at the site of the Observatory Dining Hall.

Brandon Drainage Basin

1. Promoting the “greening” approach at the South Lawn Development, where the post-development condition will contain less impervious area than the pre-development condition.

2. Creating an underground detention basin to reduce the peak flow rate and volume for small storm events.

Health Sciences/University Hospital Area

1. Taking advantage of “banked” storage capacity remaining in the existing Health Sciences Center Pond.

2. Creating an extended detention basin in the University Hospital Area. The mitigation measures will provide the opportunity to re-create some natural functions of the drainage system and treat stormwater runoff on a local-type and/or site-specific basis. The proposed water quality measures include the following:

52

Stadium Drainage Basin 1. Taking advantage of “banked” area remaining for water quality treatment in the

existing Gilmer Pond. 2. Providing additional pool storage for water quality treatment through the

increased storage in Gooch/Dillard Pond; as well as providing enhanced treatment through the addition of native vegetation, aquatic benches, and floodplains.

3. Creating a new extended detention basin associated with the Observatory Hill/Alderman Road Residence Cluster that incorporates a shallow marsh system - providing additional pollutant removal through wetland plant uptake, absorption, filtration, decomposition, and settling.

Brandon Drainage Basin

1. Promoting the “greening” approach to development for the South Lawn Project. 2. Providing vegetated filter strips, grassed swales, and/or biofiltration areas.

Health Sciences/University Hospital Area

1. Taking advantage of “banked” permanent pool storage remaining for water quality treatment in the existing Health Sciences Center Pond.

2. Creating an extended detention basin upon development of areas outside of the current Health Sciences Master Plan to provide pollutant removal through gravitational settling.

All Development Projects

1. Providing pretreatment at development sites JNEI has developed the proposed mitigation/treatment measures using a conservative approach to the Proposed Conditions Model. Due to the lack of detailed plans available for most of the proposed development projects within these watershed areas at the time of this study, JNEI estimated a greater amount of impervious cover for development than is likely to be needed. As a result, the Model sets a conservative allowance for additional development above and beyond what is anticipated at this time. As part of this SWMP, JNEI has prepared a tracking table to enable the University to account future development in identified Sub-basin areas for water quantity mitigation and water quality treatment. The tracking tables will notify the University when the development limit has been reached and the model must be re-evaluated.

53

VII. REFERENCES Andropogon and Cahill Associates. University of Virginia Strategic Plan for Water Resources Management Brown W. and T. Schueler (1997). The Economics of Storm Water BMP’s in the Mid-Atlantic Region. The Center for Watershed Protection, Elliot City, MD. CEGG Associates, L.C. (2000). Erosion and Sediment Control Narrative; Stormwater Management Narrative; Pond Calculations. University of Virginia. Cox Company. (1997). Rock Creek Stream Valley Master Plan. University of Virginia & City of Charlottesville. Cox Company. (1997) Stormwater Management Calculations. University of Virginia Health Sciences Center. Cox Company. (1998). Stormwater Management Study. University of Virginia Health Sciences Center. Davis, Luise (2001). A Handbook of Constructed Wetlands. USDA-Natural Resources Conservation Service and United States EPA, Pennsylvania. Department of Conservation and Recreation (2001). Commonwealth of Virginia – Virginia Stormwater Management Regulations. Division of Soil and Water Conservation, Richmond, VA Department of Conservation and Recreation (1999). Virginia Stormwater Management Handbook. Division of Soil and Water Conservation Department of Conservation and Recreation (2001). Virginia Erosion and Sediment Control Law, Regulations, and Certification Regulations. Division of Soil and Water Conservation. Dewberry & Davis. (1996). Moore’s Creek Watershed Study. Albemarle County & City of Charlottesville. Horner, Richard (1993). Constructed Wetlands for Urban Runoff Water Quality Control. United States Environmental Protection Agency: National Conference on Urban Runoff Management, Chicago, IL Lake Pontchartrain Basin Foundation (1998). Lessons on the Lake: Ecosystems in Delicate Balance. United States Department of the Interior, USGS, Washington, D.C. Massachusetts Department of Environmental Protection (1997). Stormwater Management: Volume Two: Stormwater Technical Handbook. Strecker, Eric W (1993). The Use of Wetlands for Stormwater Pollution Control. United States Environmental Protection Agency: National Conference on Urban Runoff Management, Chicago, IL.

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Strecker, Eric W. et al (1992). The Use of Wetlands for Controlling Stormwater Pollution. United States Environmental Protection Agency, Washington D.C. United States Environmental Protection Agency (1999). Preliminary Data Summary of Urban Storm Water Best Management Practices. EPA Office of Water, Washington D.C. United States Environmental Protection Agency (2001). An Introduction to Wetland Restoration, Creation, and Enhancement. Interagency Workgroup on Wetland Restoration, Washington D.C.

APPENDIX A TRACKING TABLES

Water Quantity Mitigation Measure

Project within Sub-basins MO-3A, MO-3B, and MO-3C

Preliminary Design Impervious Area

Final Design Impervious Area As-built Impervious Area Impervious Area Remaining

(acres)

"Banked" at Gilmer Pond 1.46

Proposed modification to Gooch Pond

6.00

Enhanced Extended Detention

Basin at site of Observatory Dining

9.44

Note: When the impervious development area remaining for a given water quantity mitigation measure has reached a value of zero, the capacity of the mitigation measure has been reached. The next mitigation measure must be designed according to the SWMP and impervious development must be accounted for until this measure has reached a value of zero, and so on.

Water Quantity Tracking Table

Tracking Table A.1 - Stadium Drainage Basin (Sub-basins MO-3A, MO-3B, and MO-3C)

This Tracking Table accounts for both identified and unidentified future impervious area within sub-basins MO-3A, MO-3B, and MO-3C where development has been anticipated by the University for the purposes of this Stormwater Management Master Plan.

Water Quantity Mitigation Measure

Project within Sub-basins MO-5A and MO-5B

Preliminary Design Impervious Area

Final Design Impervious Area As-built Impervious Area Impervious Area Remaining

(acres)

Underground Detention 10.05

Note: When the impervious development area remaining for a given water quantity mitigation measure has reached a value of zero, the capacity of the mitigation measure has been reached. The next mitigation measure must be designed according to the SWMP and impervious development must be accounted for until this measure has reached a value of zero, and so on.

Water Quantity Tracking Table

Tracking Table A.2 - Brandon Drainage Basin (Sub-basins MO-5A and MO-5B)

This Tracking Table accounts for both identified and unidentified future impervious area within sub-basins MO-5A and MO-5B where development has been anticipated by the University for the purposes of this Stormwater Management Master Plan.

Water Quantity Mitigation Measure

Project within Sub-basins MO-6A and MO-6B

Preliminary Design Impervious Area

Final Design Impervious Area As-built Impervious Area Impervious Area Remaining

(acres)

"Banked" at Health Sciences Pond

4.30

Proposed ExtendedDetention Basin 8.07

Note: When the impervious development area remaining for a given water quantity mitigation measure has reached a value of zero, the capacity of the mitigation measure has been reached. The next mitigation measure must be designed according to the SWMP and impervious development must be accounted for until this measure has reached a value of zero, and so on.

Water Quantity Tracking Table

Tracking Table A.3 - Health Sciences Center and University Hospital Area (Sub-basins MO-6A and MO-6B)

This Tracking Table accounts for both identified and unidentified future impervious area within sub-basins MO-6A and MO-6B where development has been anticipated by the University for the purposes of this Stormwater Management Master Plan.

Water Quality Treatment Measure

Project within Sub-basins MO-3A, MO-3B, and MO-3C

Preliminary Design Impervious Area

Final Design Impervious Area As-built Impervious Area Impervious Area Remaining

(acres)

"Banked" at Gilmer Pond 4.74

Proposed modification to Gooch Pond

6.00

Enhanced Extended Detention

Basin at site of Observatory Dining

9.44

Note: When the impervious development area remaining for a given water quality treatment measure has reached a value of zero, the capacity of the water quality treatment measure has been reached. The next water quality treatment measure must be designed according to the SWMP and impervious development must be accounted for until this measure has reached a value of zero, and so on.

Water Quality Tracking Table

Tracking Table A.4 - Stadium Drainage Basin (Sub-basins MO-3A, MO-3B, and MO-3C)

This Tracking Table accounts for both identified and unidentified future impervious area within sub-basins MO-3A, MO-3B, and MO-3C where development has been anticipated by the University for the purposes of this Stormwater Management Master Plan.

Water Quality Treatment Measure

Project within Sub-basins MO-5A and MO-5B

Preliminary Design Impervious Area

Final Design Impervious Area As-built Impervious Area Impervious Area Remaining

(acres)

0.00

Note: When the impervious development area remaining for a given water quality treatment measure has reached a value of zero, the capacity of the water quality treatment measure has been reached. The next water quality treatment measure must be designed according to the SWMP and impervious development must be accounted for until this measure has reached a value of zero, and so on.

Water Quality Tracking Table

Tracking Table A.5 - Brandon Drainage Basin (Sub-basins MO-5A and MO-5B)

This Tracking Table accounts for both identified and unidentified future impervious area within sub-basins MO-5A and MO-5B where development has been anticipated by the University for the purposes of this Stormwater Management Master Plan.

Water Quality Treatment Measure

Project within Sub-basins MO-6A and MO-6B

Preliminary Design Impervious Area

Final Design Impervious Area As-built Impervious Area Impervious Area Remaining

(acres)

"Banked" at Health Scineces Pond 9.48

Proposed ExtendedDetention Basin 8.07

Note: When the impervious development area remaining for a given water quality treatment measure has reached a value of zero, the capacity of the water quality treatment measure has been reached. The next water quality treatment measure must be designed according to the SWMP and impervious development must be accounted for until this measure has reached a value of zero, and so on.

Water Quality Tracking Table

Tracking Table A.6 - Health Sciences Center and University Hospital Area (Sub-basins MO-6A and MO-6B)

This Tracking Table accounts for both identified and unidentified future impervious area within sub-basins MO-6A and MO-6B where development has been anticipated by the University for the purposes of this Stormwater Management Master Plan.

APPENDIX B EXHIBITS

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APPENDIX C STORMWATER MANAGEMENT

FACILITIES MAINTENANCE GUIDELINES

Appendix C: Stormwater Management Facilities Maintenance Guidelines Future development of the Moore’s Creek Watershed within the University of Virginia includes the creation of stormwater detention ponds enhanced by native plant species, as well as the use of traditional Best Management Practices such as Sediment Control Structures and Underground Detention Structures. In order to ensure these water quality and mitigation measures sustain adequate performance levels, Judith Nitsch Engineering, Inc. (JNEI) has developed these Maintenance Guidelines for the University of Virginia to accompany the Moore’s Creek Stormwater Management Master Plan. In order to perform as expected, stormwater treatment and mitigation areas must be maintained according to this Plan. Designers of stormwater management systems shall submit a detailed Maintenance Plan for the systems that are proposed. Maintenance of these systems shall follow these Guidelines as they relate to each of the facilities being designed. Maintenance plans shall be submitted to the Virginia Department of Conservation and Recreation (DCR) for review and approval. Inspection and Maintenance Inspection and maintenance is required for proper operation of the enhanced extended detention basin at the site of the Observatory Dining Hall, the modified Gooch/Dillard Pond, the extended detention basin in the Health Sciences/University Hospital Area, as the Sediment Control Structure(s) upstream from the Rainstore system at South Lawn. In order to ensure the stormwater management goals of the Master Plan are achieved on a long-term basis, the University of Virginia must comply with the following Inspection and Maintenance Plan for the water quality features in these proposed areas.

Inspection and Maintenance Plan for Enhanced Extended Detention Basin at the Site of the Observatory Dining Hall

Inspection Criteria Inspection Action

Inspection Schedule Sediment Management Water Management Vegetation Management

▪Check for sediment accumulations ▪Check for outlet clogging ▪Inspect erosion and sediment control functions

▪Compare depth zones and topographic features with design plan ▪Compare normal pool elevation with original design plan

▪ Take note of types dominant plants and their distributions in each zone ▪Check plant condition – look for signs of disease, pest infestations, and stunted growth ▪Take note of survival rates of plants in wetland buffer

Twice yearly (once in growing

season and once in non-

growing season) for first 3 years

after construction

If possible, inspections should be conducted during wet weather to determine if the extended-detention time is being achieved.

All conditions should be noted during these inspections and any problem should be addressed immediately

Monthly and after each

major storm

Rapid visual inspection should be made by a qualified observer to identify and take action on any problems that would damage the wetland’s functions

Maintenance Action

Maintenance Schedule Sediment Management Water Management Vegetation Management

First 3 years, often

▪Provide care to plantings and trees including watering, supporting, mulching, and removing weeds

Approximately 1 to 2 years

after construction

▪Add reinforcement plants as necessary ▪Remove undesirable species, such as species with a high potential to invade and dominate

As necessary ▪Remove sediment accumulations at outlet ▪Remove trash and debris

▪Clean and maintain inlet and outlet structures

▪ Side slopes, embankments, emergency spillways should be mowed

Every 5 to 10 years

▪Remove accumulated sediment from the basin

Inspection and Maintenance Plan for Modified Gooch/Dillard Pond

Inspection Criteria Inspection Action

Inspection Schedule Sediment Management Water Management Vegetation Management

▪Check for sediment accumulations ▪Check for outlet clogging ▪Inspect erosion and sediment control functions

▪Compare depth zones and topographic features with design plan ▪Compare normal pool elevation with original design plan

After large storm events (more than

2.0-inches of rainfall in 24-hour period) All conditions should be noted during these inspections and any problem should be

addressed immediately.

Weekly

Rapid visual inspection should be made by a qualified observer to identify and take action on any problems that would damage the wetland’s functions.

If possible, inspections should be conducted during wet weather to determine if the extended-detention time is being achieved.

Maintenance Action

Maintenance Schedule Sediment Management Water Management Vegetation Management

As necessary ▪Remove sediment accumulations at outlet ▪Remove trash and debris

▪Clean and maintain inlet and outlet structures

▪ Side slopes, embankments, emergency spillways should be mowed

As sediment accumulations reach a depth greater than 6.0-inches. (Typically every 5-10

years)

▪Remove sediment from the basin by non-intrusive means

Inspection and Maintenance Plan for Extended Detention Basin in Health Sciences/University Hospital Area

Inspection Criteria Inspection Action

Inspection Schedule Sediment Management Water Management Vegetation Management

▪Check for sediment accumulations ▪Check for outlet clogging ▪Inspect erosion and sediment control functions

▪Compare depth zones and topographic features with design plan ▪Compare normal pool elevation with original design plan

After large storm events (more than

2.0-inches of rainfall in 24-hour period) All conditions should be noted during these inspections and any problem should be

addressed immediately.

Weekly

Rapid visual inspection should be made by a qualified observer to identify and take action on any problems that would damage the wetland’s functions.

If possible, inspections should be conducted during wet weather to determine if the extended-detention time is being achieved.

Maintenance Action

Maintenance Schedule Sediment Management Water Management Vegetation Management

As necessary ▪Remove sediment accumulations at outlet ▪Remove trash and debris

▪Clean and maintain inlet and outlet structures

▪ Side slopes, embankments, emergency spillways should be mowed

As sediment accumulations reach a depth greater than 6.0-inches. (Typically every 5-10

years)

▪Remove sediment from the basin by non-intrusive means

APPENDIX D COX REPORT

APPENDIX E SUMMARY TABLES

Appendix EUniversity of Virginia Moore's Creek Stormwater Management Master PlanSummary Tables for Baseline Conditions vs. Proposed Conditions

Table E.1 Summary Table for Baseline Conditions

SUB-BASIN IDENTIFICATION

DRAINAGE AREA

(ACRES)

PERCENT PERVIOUS

(%)

PERCENT IMPERVIOUS

(%)

PERCENT WOODED

(%)SOIL TYPE

TIME OF CONCENTRATION

(Tc)

WEIGHTED CURVE

NUMBER (CN)

2-year Runoff, Q*

(cfs)

10-year Runoff, Q*

(cfs)

25-year Runoff, Q*

(cfs)

100-year Runoff, Q*

(cfs)

MO-1A 73.04 17% 36% 47% C 15 minutes 81 168.88 322.00 363.29 529.54MO-1B 10.71 62% 38% 0% C 14 minutes 83 27.46 50.67 56.88 81.73MO-2B 23.97 62% 38% 0% C 17 minutes 83 55.81 103.28 115.97 166.86MO-3A 36.13 14% 79% 7% C 11 minutes 92 138.82 225.69 248.36 338.42

MO-3B north 45.47 15% 85% 0% C 10 minutes 94 187.94 298.63 327.52 442.46

MO-3B south 33.29 62% 38% 0% C 11 minutes 83 93.47 171.74 192.62 276.25MO-3C 15.13 53% 33% 14% C 10 minutes 82 41.03 77.74 87.61 127.33

MO-3C bypass 10 58% 10% 32% C 10 minutes 76 20.26 42.50 48.69 74.03MO-5A 17.45 15% 85% 0% C 12 minutes 94 67.66 107.57 117.98 159.42

MO-5A south 34.44 62% 38% 0% C 13 minutes 83 93.11 171.39 117.98 275.97MO-5B 45.9 55% 45% 0% C 22 minutes 87 110.22 192.72 214.48 301.14

MO-6A mitigated 27.29 15% 85% 0% C 12 minutes 94 107.34 170.62 187.13 252.84

MO-6A unmitigated 38.37 15% 85% 0% C 12 minutes 94 127.37 202.91 222.62 301.04

MO-6B 18.5 15% 85% 0% C 11 minutes 94 74.64 118.64 130.13 175.82

Page 1

Baseline Conditions

* Q values refer to the runoff from the subcatchment only. These values do not reflect routing through reaches or BMP's. See Volume II of the SWMP for mitigated rates of runoff and Q at the design points.

Appendix EUniversity of Virginia Moore's Creek Stormwater Management Master PlanSummary Tables for Baseline Conditions vs. Proposed Conditions

Table E.2 Summary Table for Proposed Conditions

SUB-BASIN IDENTIFICATION

DRAINAGE AREA

(ACRES)

PERCENT PERVIOUS

(%)

PERCENT IMPERVIOUS

(%)

PERCENT WOODED

(%)SOIL TYPE

TIME OF CONCENTRATION

(Tc)

WEIGHTED CURVE

NUMBER (CN)

2-year Runoff, Q*

(cfs)

10-year Runoff, Q*

(cfs)

25-year Runoff, Q*

(cfs)

100-year Runoff, Q*

(cfs)

MO-1A 73.04 17% 36% 47% C 15 minutes 81 168.88 322.00 363.29 529.54MO-1B 10.71 62% 38% 0% C 14 minutes 83 27.46 50.67 56.88 81.73MO-2B 23.97 62% 38% 0% C 17 minutes 83 55.81 103.28 115.97 166.86MO-3A 31.48 14% 78% 8% C 11 minutes 92 120.95 196.64 216.39 294.86

MO-3A change 4.65 0% 100% 0% C 10 minutes 98 20.62 31.69 34.60 46.21MO-3B north 36 15% 85% 0% C 10 minutes 94 148.80 236.43 259.31 350.31

MO-3B north change 9.47 0% 100% 0% C 10 minutes 98 42.00 64.54 70.46 94.11

MO-3B south 33.29 62% 38% 0% C 11 minutes 83 93.47 171.74 192.62 276.25MO-3C 12.35 59% 41% 0% C 10 minutes 83 39.17 70.75 79.14 112.63

MO-3C change 2.78 0% 100% 0% C 10 minutes 98 12.33 18.95 20.68 27.63MO-3C bypass 10 58% 10% 32% C 10 minutes 77 20.26 42.50 48.69 74.03

MO-5A 16.45 15% 85% 0% C 12 minutes 94 63.78 101.40 111.22 150.29MO-5A change 1.56 0% 100% 0% C 10 minutes 98 6.92 10.63 11.61 15.50MO-5A south 34.44 62% 38% 0% C 13 minutes 83 93.11 171.39 192.28 275.97

MO-5B* 45.9 55% 45% 0% C 22 minutes 87 103.74 188.29 210.28 293.25

MO-6A mitigated 22.76 15% 85% 0% C 12 minutes 94 89.52 142.30 156.07 210.87

MO-6A mitigated change

4.76 0% 100% 0% C 10 minutes 98 20.09 30.87 33.70 45.02

MO-6A unmitigated 37.31 15% 85% 0% C 18 minutes 94 123.85 197.30 216.47 292.73

MO-6A unmitigated change

1.06 0% 100% 0% C 10 minutes 98 4.70 7.22 7.89 10.53

MO-6B 10.66 15% 85% 0% C 11 minutes 94 43.01 68.36 74.98 101.31MO-6B change 7.61 0% 100% 0% C 10 minutes 98 34.77 53.43 58.33 77.91

Page 2

Proposed Conditions

* Q values refer to the runoff from the subcatchment only. These values do not reflect routing through reaches or BMP's. See Volume II of the SWMP for mitigated rates of runoff and Q at the design points.