FINAL DESIGN REPORT/FINAL EIS/FINAL SECTION 4(F)

EVALUATION

PIN 0054.05.103NY Route 347 Safety and Mobility Improvement

Project

Northern State Parkway to NY Route 25ATowns of Smithtown, Islip & Brookhaven

Suffolk County

May 2007

Storm Water Management andRoadway Drainage Technical Report

Volume II, Appendix F

U.S. Department of TransportationFederal Highway Administration

NEW YORK STATE DEPARTMENT OF TRANSPORTATIONELIOT SPITZER, Governor ASTRID C. GLYNN, Acting Commissioner

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Table of Contents Executive Summary .......................................................................................................... 3

Compliance with NYSDEC SPDES GP-02-01 ............................................................ 3 Roadway Runoff and Stormwater Management ........................................................... 4 Roadway Runoff Collection and Conveyance .............................................................. 4

Water Quality...................................................................................................................... 4 Water Quantity.................................................................................................................... 6 Roadway Runoff and Stormwater Management ........................................................... 9

SPDES COMPLIANCE AREA.................................................................... 10 NON-SPDES COMPLIANCE AREA.......................................................... 10

Eliminate Existing MLBS..................................................................................... 11 Utilize Existing RB’s ............................................................................................... 12 Eliminate Discharge to Existing Pipe Systems ........................................................... 14

Roadway Runoff Collection and Conveyance System ........................................................ 19 Inlet Runoff Interception and Spacing ....................................................................... 19 Pipe Diameter ......................................................................................................... 24

Appendices A – Stormwater Quality Calculations B – Stormwater Quantity Calculations C – Eliminate Existing MLBS Calculations D – Utilize Existing RB’s Calculations E – Eliminate Discharge to Existing Pipe Systems Calculations F –Roadway Drainage Evaluation Inlet Runoff Interception and Spacing Calculations Pipe Diameter Calculations

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Executive Summary The Route 347 Safety and Mobility Improvement Project provides roadwy improvements that

include the two additional 3.6 meter wide lanes and a 0.612 meter wide shoulder in each direction

along both sides of the road plus turning lanes at numerous intersections, and various

interchange/intersection alternatives at the Route 454/Route 347 split, Middle Country Road and

Nicolls Road, selected pavement widening of the ramps at the Northern State Parkway, and

variable widening of cross streets.

Runoff from the portion of the project between the high point east of White Oak Drive, Station

18+757, and the high point east of Southern Boulevard, Station 27+612, discharges to the

Nissequogue River and its tributaries. The Nissequogue River is designated a waterbody of the

United States. Therefore compliance with the New York State Department of Environmental

Conservation (NYSDEC) State Pollution Discharge Elimination System (SPDES) General Permit

(GP –02-01 is required for this portion of the project.

The report is divided into three sections, NYSDEC SPDES GP-02-01 Compliance, Roadway

Drainage and Stormwater Management, and Roadway Runoff Collection and Conveyance.

Compliance with NYSDEC SPDES GP-02-01

Compliance with both the water quality requirements and the water quantity requirements of

SPDES GP-02-01, was evaluated in accordance with the procedures contained in the New York

State Stormwater Management Design Manual (NYSSMDM).

Water quality compliance is achieved with the installation of a surface water quality basin, most

likely a stormwater pond or wetland pond, near three existing waterbodies, with overflow and

discharge from each water quality basin to the nearby existing waterbody.

Water quantity compliance for discharges to the Nissequogue River is achieved in accordance

with the provisions of Section 4.7 Downstream Analysis of the NYSSMDM. The increased

runoff resulting from the project is less than five percent of the total existing runoff in the stream

at the point of roadway runoff discharge to the existing watercourses. Consequently, compliance

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with the intent of the Unified Stormwater Sizing Criteria is achieved. Therefore, stormwater

attenuation facilities are not required to address runoff rate changes.

Roadway Runoff and Stormwater Management

Roadway runoff from the portion of the project exempt from compliance with NYSDEC SPDES

GP-02-10, west of high point east of White Oak Drive and east of Southern Boulevard discharges

to either a recharge basin (RB), pipe system or multiple leaching basin system (MLBS). The

objective of the roadway runoff and stormwater management evaluation was to direct runoff to a

recharge basin and eliminate discharge to existing pipe systems and MLBS to the greatest extent

possible. Installation of the proposed 17 RB achieve this objective except for approximately 117

meters of Route 347 in the vicinity of the Route 11 intersection and approximate 697 meters of

the road east of Market Street to Route 25A.

Roadway Runoff Collection and Conveyance

The roadway runoff collection and conveyance and conveyance system was evaluated in

accordance with the requirements of Chapter 8, Highway Drainage, of the NYSDOT Highway

Design Manual (HDM). The runoff collection system evaluation identified the inlet spacing

required along each edge and the median of Route 347 and the resultant quantity of inlets

required for the project. The runoff conveyance system evaluation computed the pipe diameter

required for each pipe to convey runoff to a water quality basin, existing waterbody or recharge

basin. The evaluation also established the approximate invert elevation at each receiving facility

and potential need for use of a “bubbler “ chamber in selected cases when the invert was below

the invert of the receiving facility.

NYSDEC SPDES GP-02-01 Compliance

Compliance with the water quality and water quantity requirements of NYSDEC SPDES GP-02-

01 is described below

Water Quality

Water quality requirements are presented in Chapter 4 of the NYSSMDM. Section 4.2 includes

guidance and procedures to demonstrate compliance with the water quality requirements. The

water quality volume is directly related to the amount of impervious cover created by the project.

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Impervious cover is defined as that portion of the project that does not have permanent vegetative

or permeable cover. Roadway pavement is considered impervious cover. The impervious cover

created by the project includes two components, the additional 3.6-meter wide lane and 0.61

meter wide additional shoulder pavement in each direction for the entire length of the project and

the left turn pavement at the intersections. Proposed sidewalk replaces existing sidewalk.

Therefore, sidewalk installation does not create impervious cover on the project. The impervious

cover created by the project includes four components:

a. two additional 3. 6 meter wide lanes and 0.61 meter wide additional shoulder

pavement in each direction yields a width of 8.42 meters.

b. additional pavement at Northern State Parkway (NSP)

c. additional pavement at cross streets

d. additional turning lane pavement at intersections.

The total area made impervious by the project is 103 753 square meters. Compliance will be

achieved by providing treatment for the runoff from the portion of the roadway equal to the area

made impervious by the project. This will be accomplished by installing surface water quality

basins (WQB), at three locations in undeveloped property beyond wetland limits. The total area

made more impervious by the project of 103 753 square meters yields a required storage volume

of 3 199 cubic meters. The runoff from the portion of the roadway equal to the impervious cover

created by the project within the limits that contribute runoff to each discharge location will be

directed to its respective discharge location. The WQB location, WQB designation, contributing

pavement characteristics required storage volume and storage volume provided are summarized

in Table 1

Table 1 Water Quality Basin Characteristics WQB Contributing Pavement

Characteristics WQv (M3)

Location Designation Station Limits Area Required Provided West East (M2) East of Old Willets Path

WQ-OWP1 19+450 20+150 28 039 808 946

East of Simeon Woods Road

WQ1BR2 21+300 21+455 5 285 153 420

West of Helen Ave. WQ2B2 25+555 27+612 77 171 2 238 2 631 TOTAL 110 495 3 199 3 997

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Runoff will be delivered to each proposed WQB through a closed pipe system that

collects runoff from the portion of the roadway indicated in Table 1. Runoff that exceeds

the storage volume of each proposed WQB will breach the control spillway set an

elevation below the top of the berm for the WQB, and proceed through the adjacent

wetlands to a receiving water body with a culvert crossing at Station 20+630 for WQ-

OWP1, at Station 21+230 for WQ1B2R, and at Station 25+400 for WQ2B2.

The required pipe invert is below the GWT for WQ1BR2 and WQ2B2. Installation of the pipe

with the invert elevation below the GWT, into a drainage chamber with an open grate on top that

allows runoff to overtop the chamber and enter the WQB surrounding the chamber is a reasonable

solution.

The calculations are in Appendix A.

Water Quantity

Overland runoff from the south side of Route 347 is conveyed across Route 347 in various

tributaries of the Nissequogue River at four locations. The location of the existing culvert

crossings that discharge to the Nissequogue River or its tributaries, their configuration and their

contributing watershed roadway limits are presented in Table 2.

Table 2 Existing Culvert Crossings Culvert Crossing Location/(Station)

Culvert Crossing Configuration

Approximate Contributing Watershed Roadway Limits

East of County Center Rd./(20+630)

2-914 mm Diameter

White Oak Dr. (18+757) to H. Lee Dennison Bldg. Dr. (20+962)

East of Simeon Woods Road/(21+230)

5 791 x 1 524 Box 310 mm x 375 mm Elliptical

H. Lee Dennison Bldg. Dr.(20+962) to West of State Office Bldg. Access(21+455)

East of State Office Building Access/(21+580)

3-762 mm Diameter West of State Office Bldg. Access (21+455) to East of Rte 111(23+544)

West of Helen Avenue/(25+480)

2-914 mm Diameter 1 320 mm Diameter

to East of Rte 111 (23+544) to East of Southern Blvd.(27+612)

The increased runoff created by the project primarily results from the construction of pavement

on areas that currently have permanent vegetative or permeable cover.

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A hydrologic analysis was performed to demonstrate compliance with the intent of complying

with the ten percent rule as presented in Section 4.7 of the New York State Stormwater

Management Design Manual. The intent of the Unified Stormwater Sizing Criteria presented in

Chapter 4 of the NYSSMDM, as stated in Section 4.1 Introduction, is to “reduce channel erosion,

prevent overbank flooding and help control extreme floods”. The ten percent rule as presented in

Section 4.7, Downstream Analysis, of the NYSSMDM provides an evaluation procedure to

document that the impact of the increase in proposed project runoff is insignificant. Review of

the Central Islip, New York USGS topographic quadrangle reveals that the contributing drainage

area at each runoff discharge point to existing watercourses is substantial as compared to the

areas occupied by the road.

The hydrologic calculations were performed for the Overbank Flood (recurrence interval of once

in 10 years) and the Extreme Storm (recurrence interval of once in 100 years) using the

procedures presented in Urban Hydrology for Small Watersheds, Soil Conservation Service,

Technical Release No. 55 (TR-55).

A generic hydrologic evaluation was performed for a one meter wide strip of roadway to

determine the increase in peak runoff for the Overbank Flood (recurrence interval of once in 10

years) and the Extreme Storm (recurrence interval of once in 100 years) resulting from the

proposed roadway project. This procedure was selected for initial screening because it would

expedite the evaluation process by quickly identifying the specific conditions for which a more

detailed evaluation is warranted.

The hydrologic calculations were performed for a roadway footprint the maximum width of the

proposed roadway, Typical Section Case I, 54.6 meters. The total area used in the evaluation, as

stated in Section 4.7 of the NYSSMDM, is ten times the site area. This yields an evaluation area

of 546 square meters. The existing runoff rate was computed using the narrowest existing

pavement section within the GP-02-01 compliance limit, 31 meters in the vicinity of Sequoia

Drive, with the remainder of the 54.6-meter wide roadway section considered grass. The

comparison between the existing and proposed runoff rate for the Overbank Flood and the

Extreme Storm was computed for four development conditions adjacent to the roadway, forested

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areas, light residential (30% impervious), moderate residential (60 % impervious) and

commercial. The resultant runoff coefficients are 0.20, 0.40, 0.65 and 0.80 respectively.

A 1.2 meter wide sidewalk is to be installed along the edge of the roadway to replace an existing

sidewalk. The calculation was performed to identify the change in runoff resulting from the

project. Therefore, the calculation was simplified by disregarding the sidewalk. The calculations

are in Appendix B. The results are summarized in Tables 3 and 4.

The hydrologic evaluation was performed at the point of discharge of the roadway drainage pipe

to the existing stream at each of the four existing discharge locations. The roadway area that

contributes runoff to the stream, the total contributing area to the stream at the point where the

roadway pipe discharge to the stream, and the percent of the total contributing area represented by

the roadway runoff contributing area, are summarized for each discharge location in Table 3.

Table 3 Contributing Drainage Areas Discharge

Station Roadway Area

(acres) Total Area (acres) Roadway Percent

20+630 11.1 347 3.1 21+230 6.6 127 5.2 21+580 12.7 1,339 1.0 25+555 43.1 2,530 1.7

Table 3 demonstrates that the contributing project area is less than ten percent of the total

contributing drainage area. This appears inconsistent with the requirement that the hydrologic

evaluation be performed at the point where the project area is ten percent of the total contributing

area. However, extending the evaluation point farther downstream to the point where the project

area represents ten percent of the evaluation area will only increase the total contributing area and

consequently significantly reduce the percentage of the total area represented by the roadway

contributing area. Similarly, increasing the total contributing area reduces the percentage

increase in runoff resulting from the roadway project.

The runoff in each stream at the point of discharge from the roadway drainage system from the

roadway for the existing and proposed conditions and the resultant percent increase, based on the

hydrologic computations, are summarized in Table 4

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Table 4 Runoff Increase Discharge

Station Runoff (cms) Percent Increase

10-Year 100-Year 10-Year 100-Year

Existing Proposed Existing Proposed 20+630 11.2 11.5 22.6 23.0 2.6 1.5 21+230 4.3 4.5 8.9 9.1 4.5 2.5 21+580 29.7 29.9 58.3 58.6 0.8 0.5 25+555 20.1 20.5 39.6 40.1 2.0 1.2

The increased runoff resulting from the project is less than five percent of the total existing runoff

in the stream at the point of roadway runoff discharge to the existing watercourses.

Consequently, compliance with the intent of the Unified Stormwater Sizing Criteria is achieved.

As a result, stormwater attenuation facilities are not required to address runoff rate changes

resulting from the project.

The calculations are in Appendix B.

Roadway Runoff and Stormwater Management

The existing roadway drainage system discharges runoff to either a stream, a recharge basin (RB)

or a multiple leaching basin system (MLBS). The objectives of the project in addition to

complying with the requirements of SPDS GP-02-01 as described above, include eliminating the

existing MLBS to the greatest extent possible, utilizing existing RB’s where feasible, and

eliminating discharges to existing pipe systems on 347 east of Southern Boulevard to the greatest

extent possible by conveying runoff to a recharge basin.

The project was divided into eighteen separate watersheds, six in the SPDES compliance area

west of Southern Boulevard and twelve in the non-SPDES compliance portion of the project. The

limit of each watershed was established as the length between successive roadway high points.

The watershed designation and limits are presented in Table 5.

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Table 5 Watershed Designation and Limits Watershed Designation

West Limit East Limit

SPDES COMPLIANCE AREA

A East of White Oak Drive (Station 18+757

Grassy Pond Drive (Station 19+450)

B Grassy Pond Drive (Station 19+450)

H. Lee Dennison Bldg. Drive (Station 20+962)

C H. Lee Dennison Bldg. Drive (Station 20+962)

East of Simeon Woods Drive (Station21+455)

D East of Simeon Woods Drive (Station21+455)

East of Brooksite Drive (Station 22+883)

E East of Brooksite Drive (Station 22+883)

East of Route 111 (Station 23+544)

F East of Route 111 (Station 23+544)

East of Southern Boulevard (Station 27+612)

NON-SPDES COMPLIANCE AREA

1 East of Southern Boulevard (Station 27+612)

East of Lake Avenue South (Station 28+072),

2 East of Lake Avenue South (Station 28+072),

East of Middle Country Road (Station 29+897)

3 East of Middle Country Road (Station 29+897)

East of Hallock Avenue (Station 31+898)

4 East of Hallock Avenue (Station 31+898)

Lakeside Avenue (Station 32+531)

5 Lakeside Avenue (Station 32+531) West of Nicolls Road (Station 33+094) 6 West of Nicolls Road (Station

33+094) East of Nicolls Road (Station 33+800)

7 East of Nicolls Road (Station 33+800) West of Mark Tree Road (Station 34+508)

8 West of Mark Tree Road (Station 34+508)

East of Belle Meade Road (Station 35+531)

9 East of Belle Meade Road (Station 35+531)

Arrowhead Lane (Station 37+143)

10 Arrowhead Lane (Station 37+143) West of Woodhull Avenue (Station 38+455)

11 West of Woodhull Avenue (Station 38+455)

Rose Lane – Sylvan Lane Extension (Station 40+498)

12 Rose Lane – Sylvan Lane Extension (Station 40+498)

Route 25A (Station 41+800)

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Conveyance to each proposed WQB will be through a closed pipe system. Runoff that

exceeds the storage volume of each proposed WQB will breach the control spillway set

an elevation below the top of the berm for the WQB, and proceed through the adjacent

wetlands to a receiving water body with a culvert crossing. Runoff conveyed to each

existing water body with a stream crossing that is not delivered to a WQB will be

conveyed to the culvert crossing location in a closed pipe system. Runoff delivered to

each RB will be conveyed in a closed pipe system. The absence of a viable site for the

installation of a RB in watershed # 4 and # 5 requires the installation of a conveyance

pipe that breaches the high point between the watersheds to deliver the runoff to the RB’s

in the adjacent watershed # 6.

Eliminate Existing MLBS

Elimination of existing MLBS focused on conveying the runoff to a stream or RB. The resultant

proposed runoff disposal system is presented in Table 6. Profile constraints, primarily the

combination of the roadway elevation at the MLBS the distance and slope of the pipe to a

discharge location and the elevation of the receiving facility prevented the ability to eliminate the

existing MLBS in the vicinity of the Route 111 intersection (Station 22+883 to Station 23+00)

and east of Market Street to Route 25A (Station 41+103 to Station 41+800.

Table 6 MLBS Elimination Existing MLBS Limits (Station) Proposed Disposal Remarks

West East Grassy Pond Dr. (19+450) West of Old Willets Path

(20+150) WQ-OWP1 1

Rte. 454 Split (22+320) West of Rte 111 (22+883) Steam @ Sta. 21+580 2 West of Rte.111 (22+883) West of Rte. 111 (23+000) MLBS 3 East of Rte 111 (23+650) East of Plaisted

Ave.(24+330) Stream @ Sta. 25+500 2

East of Southern Blvd. (27+612)

East of Lake Ave. (28+072) AJR2 2

East of Lake Ave. (28+072) Grassy Pond Rd. (28+330) 209 2 East of Hallock Rd. (31+900) West of Stony Brook Rd.

(32+040) Nicolls Road 2

West of Nicolls Rd. 33+120) East of Nicolls Rd. (33+700) Nicolls Road 2 West of Belle Mead Ave. (35+000)

East of Belle Mead Ave. (35+530)

WR1 2

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Table 6 MLBS Elimination Existing MLBS Limits (Station) Proposed Disposal Remarks

West East East of Wireless Rd. (36+300) West of Arrowhead La.

(36+500) XR6 2

West of Arrowhead La. (36+940)

Arrowhead La. (37+143) XR6 2

East of Old town Rd. (38+110) West of Terryville Rd. (39+107)

15AR5 2

East of Rte. 112 (40+498) East of Market St, (41+103) 17AR4 2 East of Market St. (41+103) Route 25A(41+800) MLBS 2 Remarks:

1. Overflow proceeds overland through adjacent wetlands to the stream at Station

20+630.

2. Runoff to be discharged to an existing stream or a proposed RB will be conveyed in a

closed pipe system.

3. Provide longitudinal pipe infiltration system.

The calculations are in Appendix C

Utilize Existing RB’s

Runoff from a portion of Route 347 is currently discharged to an existing recharge basin (RB) at

five locations. These include the RB in the area between eastbound Northern State Parkway,

New Highway and Parkway Drive South, RB-08 on the eastbound side of Route 347 west of

Autumn Drive, RB-0274 on the south side of Route 111 west of the Route 347 intersection, RB-

209 on the eastbound side of Route 347 between Browns Road and Middle Country Road (Route

25) and RB-0276 on the eastbound side of Route 347 west of Stony Brook Road.

Each of the existing RB’s was evaluated to determine how each could be incorporated into the

design. The volume required to contain the storm with a recurrence interval of once in fifty

years was computed by multiplying the contributing area by 0.16 meters (6.3”) of rainfall in

accordance with DM 92 (20) Recharge Basin Design Criteria to determine the geometric

requirements of each existing RB. The results are summarized below.

1. RB at Northern State Parkway

The proposed realignment of Parkway Drive South at the intersection with New

Highway introduces fill into the exiting RB No. SP10, thereby reducing the usable

storage volume. This reduced storage volume will be replaced by increasing the

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slope between the last two contours to the standard one vertical on two horizontal.

This increases the area of the bottom contour and consequently the volume in the RB.

The fill introduced by the project causes a volume loss of approximately 430 cubic

meters as compared to the approximately 585 cubic meters resulting from re-grading

the basin.

2. RB-08, Eastbound Side of Route 347 West of Autumn Drive

Runoff from approximately between White Oak Drive (Station 18+757) and Grassy

Pond Drive (Station 19+450) is discharged to existing RB No.SP08 located on the

eastbound side of Route 347 west of Autumn Drive. The usable storage volume in

existing RB-08 is approximately 4 550 cubic meters.

The required storage volume is 11 840 cubic meters as compared to a usable storage

volume in existing RB 08 of approximately 4 550 cubic meters. Supplemental RB

SRB1B2 to be installed in the property on the eastbound side of Route 347 between

Autumn Drive and New Highway currently owned by Suffolk County provides a

usable storage volume of 12 981 cubic meters.

The surface area of supplemental RB SRB1B2 was limited by the configuration,

dimensions, ground water table elevation and topography of the candidate site. The

ground water table is approximately seven meters below the existing Route 347

elevation at the roadway centerline between Ledgewood Drive and New Highway.

The bottom will be above the ground water table elevation.

3. RB 0274 – Route 111 West of the Route 347 Intersection

Runoff from the eastbound lanes of Route 347 in the vicinity of the Route 111

intersection (approximately between Station 23+000 and Station 23+650) is discharged

to existing Recharge Basin (RB) – 0274 located on the eastbound side of Route 111 west

of the Route 347 intersection. This basin has a history of standing water because of high

groundwater. Rehabilitation to improve infiltration is highly unlikely. Runoff from the

remainder of Route 347 within these limits is conveyed in a closed pipe system to an

existing pond on the westbound side of Route 347 west of the Route 111 intersection.

Opportunity to enlarge this existing pond is limited, primarily due to the small

area of the exiting lot and encroachment of athletic fields. The apparently shallow

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depth to groundwater further restricts the ability to increase volume by increasing

the depth. Installation of a longitudinal infiltration pipe system below the

pavement box and above the groundwater table elevation may be the only

opportunity to create additional storage volume for this portion of Route 347.

Runoff from this portion of Route 347 should continue to be delivered to the

existing pond and RB 0274, supplemented by a longitudinal pipe infiltration

system to supplement the storage volume.

4. RB 209 – Eastbound Side of Route 347 between Browns Road and Route 25

The existing RB provides a usable storage volume of 5 060 cubic meters. The RB

will be re-graded using current RB design criteria to provide a usable storage volume

of 9 975 cubic meters and incorporated into the project.

5. RB-0276 – Eastbound Side of Route 347 West of Stony Brook Road

The small size of this RB and the resultant limited usable storage volume warrants

eliminating this RB from the project.

The calculations are in Appendix D.

Eliminate Discharge to Existing Pipe Systems

Eliminating the discharge of roadway runoff to existing pipe crossings of Route 347 is achieved

with the installation of RB’s also known as a dry extended detention pond, dry pond, extended

detention basin, detention pond or an extended detention pond with adequate a usable storage

volume that contains the runoff with a recurrence interval of once in fifty years.

Identification of sites for the installation of a RB focused on areas within the highway boundary.

This optimizes the use of otherwise unusable areas and minimizes the need for additional

property acquisition. Ramp infield areas at proposed grade separated interchanges are ideal

candidate RB sites. When the required storage volume could not be achieved within the highway

boundary, alternatives were considered in the following sequence:

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1. Expand an existing NYSDOT RB into adjacent vacant land

2. Utilize residual portions of parcels acquired for the roadway project

3. Acquire vacant public property with access denied to Route 347

4. Acquire vacant private property with access denied to Route 347

5. Acquire vacant private property

6. Acquire other private property

RB’s were located as close as possible to the main line low points. This procedure minimizes the

length of pipe required to convey the runoff to the RB and minimizes the depth of the RB

required to contain the required storage volume

Use of the sequential RB site identification procedure described above occasionally yielded a RB

site in some watersheds some distance from the mainline low point location. Also, no candidate

RB site was identified in watershed 4 and 5, since there is no available undeveloped parcel.

Therefore, the runoff from these watersheds is conveyed to the RB’s in the Nicolls Road

interchange area in the adjacent watershed 6.

The configuration of each proposed RB was limited by the site dimensions, ground water table

elevation and topography of the candidate site. RB configuration typically used a six-meter offset

from the property line to the edge of the berm, slopes of one vertical on two horizontal, and a 4.

2-meter wide access ramp with a maximum 12 percent grade into the bottom. The bottom

typically provided a minimum fifteen-meter by ten-meter flat area.

The designation and location of the proposed RB’s is presented in Table 7.

Table 7 Designation and Location of Proposed RBs Watershed Designation

RB Designation RB Location

1 AJR2

Westbound side of Route 347 between Lake Avenue and Gibbs Pond Road

2 MCR2 & MCR4 Middle Country Road ramp infield areas 2 RB 0209 Existing RB on eastbound side of Route 347 between

Brown’s Road and Middle Country Road to be enlarged 3 RB 9DRA Eastbound side of Route 347 between the projection of

Cambon Place (Sta. and Middle Country Road (Sta. 3 MO-3 Westbound side of Route 347 ,,behind exiting shopping

center, between Moriches Road and Hallock Road

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Table 7 Designation and Location of Proposed RBs Watershed Designation

RB Designation RB Location

4 No RB site available in this watershed. Convey runoff to

RB’s in the Nicolls Road interchange 5 No RB site available in this watershed. Convey runoff to

RB’s in the Nicolls Road interchange 6 Opt 1A SPD NR3R1 & NR4R2 Interchange Areas 6 Opt 2A Cloverleaf

Int.1R, Int. 2R, Int. 3R, Int. 4R

Interchange Ramp Infield Areas

7 VR-1 Eastbound side of Route 347 west of Emily Drive 8 WR-1 Eastbound side of Route 347 west of Mark Tree Rd. 9 XR-6 Eastbound side of Route 347 east of Belle Meade Avenue 10 15 AR5 Westbound side of Route 347 between Arrowhead Lane

and Old Town Road 11 AM Eastbound side of Route 347 between Woodhull Avenue

and Terryville Road 11 15 AR5 Westbound side of Route 347 between Arrowhead Lane

and Old Town Road (in watershed # 10) 12 17AR4 Southeast quadrant of the Route 347/Route 112

intersection The volume required to contain the storm with a recurrence interval of once in fifty years was

computed by multiplying the contributing area by 0.16 meters (6.3”) of rainfall in accordance

with DM 92 (20) Recharge Basin Design Criteria to determine the geometric requirements of

each proposed RB. The area that contributes runoff to Route 347 included the roadway and

adjacent berm area along Route 347 plus areas along cross streets, including the adjacent terrain

that slopes toward Route 347.

The contributing watershed limits, contributing drainage area and the required and usable storage

volume in each proposed RB in the non-SPDES compliance portion of the project, east of the

high point ( Station 27+612), between Southern Boulevard and Lake Avenue, are summarized in

TABLE III-8.

The usable storage volume is based on the allowable water surface (AWS) elevation in each RB.

The AWS is either 0.3 meters below the top of berm or 0.3 meters below the lowest elevation of

the roadway that contribute runoff to the RB. The lowest roadway elevation considered the cross

slope of the road and was, therefore set 0.3 meters below the TGL along the eastbound roadway.

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Site constraints, primarily limited viable sites for the installation of RB’s, and the limited usable

storage volume at several sites occasionally required conveying runoff to a RB in an adjacent

watershed as stated in the remarks column of table 8. T

Table 8 Proposed RB Characteristics

RB Designation Contributing Watershed Area

(Roadway Station Limits)

Contributing Drainage Area (M2)

Storage Volume (M3)

Remarks

West East Required Usable AJR2 27+612 28+072 64 025 10 244 10 172 209 (EB) 28+072 29+200 58 681 9 389 9 975 1 MCR2 (EB) 29+200 29+897 MCR2 (WB) 28+072 29+897 MCR4 (EB) 29+200 29+897 MCR4 (WB) 28+072 29+897 Sub-total MCR2(EB), MCR2(WB), MCR4(EB) & MCR4(WB)

185 831 29 733 27 549 2

9DRA 29+897 31+130 120 412 19 266 24 760 3 MO3 31+130 31+898 74 556 11 929 15 074 3 & 4 Sub-total 9DRA &MO3 194 968 31 193 39 834 NR3R1 31+898 33+800 86 071 NR4R2 31+898 33+800 129 794 Sub-total NR3R1 & NR4R2

657 325 105 172 215 865 5

Int1R1 31+898 33+800 71 003 Int2R1 31+898 33+800 51 032 Int3R 31+898 33+800 19 365 Int4R 31+898 33+800 17 266 Sub-total Int1R1, Int2R1, Int3R & Int4R

657 325 105 172 158 666 6

VR1 33+800 34+508 94 125 15 060 16 237 7 WR1 34+508 35+531 90 038 14 406 14 170 XR6 35+531 37+143 171 719 27 475 33 684 15AR5 (EB) 37+143 39+030 15AR5 (WB) 37+143 39+480

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Table 8 Proposed RB Characteristics RB Designation Contributing

Watershed Area (Roadway Station

Limits)

Contributing Drainage Area (M2)

Storage Volume (M3)

Remarks

West East Required Usable Sub-total 15AR5(EB) & 15AR5(WB)

239 088 38 254 41 438 8

AM (EB) 39+030 40+100 AM (WB) 39+480 40+100 Sub-total AM(EB) & AM(WB)

56 850 9 096 9 096 9

17AR4 40+100 41+103 157 130 25 141 25 188 10

Remarks:

1. Contributing area is limited by usable storage volume. Runoff from the remaining area is

conveyed to RB MCR2 and MCR4.

2. Modified existing RB 209 plus RB MCR2 and MCR4 work together to supply the

required storage volume in watershed # 2. RB MCR2 and MCR4 will be connected with

a pipe and work together to provide the usable storage volume.

3. RB DR9A and RB MO3 work together to supply the required storage volume in

watershed # 3

4. Contributing area is limited by usable storage volume. Runoff from the remaining area is

conveyed to RB 9DRA.

5. NR3R1 and NR4R2 work together to supply the required storage volume in watershed #

6 plus all the runoff from watershed # 4 (Station 31+898 to Station 32+531), watershed #

5 (Station 32+531 to Station 33+094) plus the runoff from 100 meters of watershed #7

for the SPUE interchange alignment. RB NR3R1 and NR42 will be connected with a

pipe and work together to provide the usable storage volume.

6. Int1R1, Int2R1, Int3R and Int4R work together to supply the required storage volume in

watershed # 6 plus all the runoff from watershed # 4 (Station 31+898 to Station 32+531),

watershed # 5 (Station 32+531 to Station 33+094) plus the runoff from 100 meters of

watershed #7 for the cloverleaf alignment. RB Int1R1, Int2R1, Int3R and Int4R will be

connected with a pipe and work together to provide the usable storage volume.

7. Runoff from approximately 100 meters of the Route 347 mainline contributing area is

conveyed to the RB’s in the adjacent Nicolls Road interchange.

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8. Accommodates runoff from the portion of the adjacent watershed # 11for which storage

volume cannot be a provided in RB AM.

9. Contributing area is limited by usable storage volume. Runoff from the remaining area is

conveyed to RB 15AR5.

10. Accepts runoff from portions of watershed # 11 and watershed # 12. Contributing runoff

area limits along Route 347 are from the west side of Jayne Boulevard (at approximately

Station 40+100) to the highpoint at approximately Station 401+103.

Stormwater Management Maps are in Appendix E

Roadway Runoff Collection and Conveyance System

The objective of the roadway drainage evaluation was to determine the runoff collection and

conveyance system required for the Route 347 project in accordance with the requirements of

Chapter 8, Roadway Drainage of the HDM (HDM), supplemented with the procedures in

Federal Highway Administration, Hydraulic Engineering Circular No. 22, Urban Drainage

Design Manual (HEC22). The design was performed for a ten-year design flood frequency in

compliance with Table 8-2 in Chapter 8 of the HDM.

Inlet runoff interception and spacing and pipe diameters are each discussed separately in the

following narrative.

Inlet Runoff Interception and Spacing

Inlet spacing is a function of the peak runoff contributing to the surface conveyance system,

either the gutter at each outside edge of the road or the triangular swale along the median and the

conveyance capacity in the gutter or median swale. The conveyance capacity on the gutter or

swale is a function of the geometry of each, including the component cross slopes and associated

lane/shoulder widths, allowable spread on the pavement and profile. Peak Runoff, Conveyance

Capacity and Inlet Spacing are discussed separately in the following narrative.

a. Peak Runoff - The peak runoff contributing to the gutters and the median swale was

computed based on the Case I typical section, which is the widest typical section used

on the project. The total width that contributes runoff to each gutter includes fifteen

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meters of overland area that was identified by field observation. The pavement area

that contributes runoff to each gutter or the median was based on the roadway crown

lines shown on the typical section. The widest pavement area that contributes runoff

to the gutter (15.9 meters) was used to compute the runoff to the gutter. A runoff

coefficient of 0.95 was used for pavement and 0.55 was used for the overland area.

The resultant composite runoff coefficient for the gutter sections is 0.73. A time of

concentration of five minutes was used. This yielded a rainfall intensity for the storm

with a recurrence interval of once in ten years of 168 mm/hour. The resultant peak

runoff per linear meter of roadway length for the gutter and median section is

0.000652 and 0.000750 cubic meters per second respectively.

b. Conveyance Capacity – The capacity of each conveyance configuration, including

the triangular gutter, composite gutter and symmetrical median swale, is primarily a

function of the cross slope(s), profile and allowable spread/depth. The allowable

spread is one half the width of the right most travel lane, limited in the gutter section

to a maximum depth of ten mm less than the curb height. The median section

includes a 0.7-meter wide area, sloped at six percent in both directions toward the

center of the median for the installation of beam guide rail. One side of the beam

guide rail installation area includes a 1.2-meter wide shoulder sloped at six percent

toward the beam guide rail area, flanked by a travel lane. The other side includes a

0.6-meter wide area sloped at six percent toward the beam guide rail area. The

design runoff was not allowed to encroach on the travel lane. Therefore, the

controlling depth for the symmetrical section is the 1.2-meter wide area at six percent

cross slope. This yields a maximum depth of 72 mm. The allowable spread for the

various conveyance sections evaluated is presented in Table 9.

TABLE 9

Section Shoulder Width (M)

Allowable Spread (M)

Notes

Triangular Gutter 3.0 2.4 1 & 2 Composite Gutter 1.5 4.1 1, 2, 3 &4 Symmetrical Median

2.4 5

Notes: 1 From Curb Face

2. Limited by Curb Height (depth=142 mm)

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3. Includes 2.6meters in Turn Lane

4. Encroaches into adjacent turn lane

5. Limited by 72 mm depth in 1.2-meter wide shoulder

The capacity of each conveyance configuration was determined in accordance with the

requirements of Chapter 8 of the HDM using the procedures presented in HEC22. The

flow capacity in the triangular gutter section, with a vertical curb face, was determined

from Chart 1A Flow in Triangular Gutter Sections (HEC 22 page A-2). The flow

capacity in the composite gutter section, with a vertical curb face, was determined using

Chart 1A and Chart 2A, Ratio of Frontal Flow to Gutter Flow (HEC 22 page A-4). The

flow capacity for the triangular gutter section with a vertical curb face and the composite

gutter section with a vertical curb face was limited by the allowable depth 10 mm below

the top of curb. The flow capacity in the median section was determined for a

symmetrical V-shape, 2.4 meters wide section using Chart 1A. The flow capacity for the

median swale was limited by the maximum spread of 1.2-meter wide shoulder, yielding a

total swale width of 2.4 meters. The flow velocity was computed by dividing the flow

capacity by the cross sectional area of the gutter or median swale section. The Total flow

capacity, and velocity for the various conveyance sections for selected longitudinal

grades are presented in Table 10.

TABLE 10 Profile Runoff Capacity (cms) Velocity (m/s)* Length (M)**

Triangular Gutter Area = 0.1704 M2 0.0025 0.12 0.704 100 0.0050 0.16 0.939 134 0.0100 0.23 1.35 193 0.0200 0.31 1.82 260 0.0300 0.40 2.35 336 Composite Gutter Area = 0.2143 M2 0.0025 0.12 0.56 100 0.0050 0.155 0.72 130 0.0100 0.21 1.00 176 0.0200 0.305 1.42 256 0.0300 0.395 1.84 332

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TABLE 10 Profile Runoff Capacity (cms) Velocity (m/s)* Length (M)**

Symmetrical Median

Area = 0.0864 M2 0.0025 0.040 0.46 53 0.0050 0.057 0.66 76 0.0100 0.079 0.91 105 0.0200 0.110 1.27 147 0.0300 0.140 1.62 187

* Velocity = Runoff Capacity/Area

** The length required to generate the runoff capacity is determined by dividing the

runoff capacity by the runoff contributed per linear meter of roadway to each gutter or

median swale section. The contributing rate per linear meter for the gutter sections is

0.00119 cms per meter and 0.000750 cms per meter for the median swale.

The first inlet is located the distance downstream of the high point needed to generate the

capacity of the gutter or median swale as indicated in Table 10.

Subsequent inlets are located the distance required to generate the runoff that is

intercepted by the inlet. Inlet interception was evaluated for the different lengths of the

610 mm wide reticuline grate. The lengths evaluated include G1 (699 mm), G2 (953

mm) and G3 (1 207 mm).

Inlet interception capacity is primarily a function of the velocity and grate length. The

entire portion of the flow over the grate is intercepted when the velocity is less than the

splash-over velocity. The splash-over velocity for various grate lengths, as determined

from Chart 5A (page A-10) in FHWA HEC22, is shown in Table 11.

TABLE 11

Grate Length (mm) Splash-Over Velocity (M/sec) 699 1.45 953 1.80 1 220 2.15

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The longer grate length is needed to intercept the entire frontal flow as the

capacity of the gutter or swale increases. The profile at which the splash-over

velocity is exceeded for the various grate lengths is shown in Table 12

TABLE 12

Grate Length (mm) Splash-Over Velocity (m/sec)

Maximum Profile (%)

Triangular Gutter 699 1.45 1.22 953 1.85 2.00 1 207 2.15 2.63 Composite Gutter 699 1.45 1.49 953 1.85 3.0 + 1 207 2.15 3.0 + Symmetrical Median 699 1.45 2.86 953 1.85 3.0 + 1 207 2.15 3.0 +

The appropriate grate length should be used until the maximum allowable profile is

reached so that the entire frontal flow is intercepted.

The percentage of the total flow in each conveyance section intercepted by the inlet with

an approach velocity lower than the splash-over velocity is presented in Table 13.

TABLE 13

Conveyance Section Percent of Total Intercepted Triangular Gutter 44 Composite Gutter 35 Symmetrical Median 50

The intercepted flow rate represents the quantity that can be added to the by-pass at

which point the spread will once more exceed the allowable width. Therefore, the length

of roadway that generates the intercepted flow quantity is the required inlet spacing. The

total gutter or median capacity, intercepted capacity and roadway length that generates

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the intercepted capacity for selected longitudinal grades for the gutter and median

sections evaluated are shown in Table14.

TABLE 14 Profile Total Runoff

Capacity (cms) Intercepted Runoff

(cms) Inlet Spacing Length (M)

Triangular Gutter See Note 1 See Note 4 0.0025 0.12 0.053 44 0.0050 0.16 0.070 59 0.0100 0.23 0.101 85 0.0200 0.31 0.141 118 0.0300 0.40 0.176 148 Composite Gutter See Note 2 See Note 4 0.0025 0.12 0.042 35 0.0050 0.155 0.054 45 0.0100 0.21 0.074 62 0.0200 0.305 0.107 90 0.0300 0.395 0.138 116 Symmetrical Median See Note 3 See Note 5 0.0025 0.040 0.020 26 0.0050 0.057 0.0285 38 0.0100 0.079 0.0395 53 0.0200 0.110 0.055 73 0.0300 0.140 0.070 93

Notes: 1. Total Runoff Capacity Times 40 Percent

2. Total Runoff Capacity Times 35 Percent

3. Total Runoff Capacity Times 50 Percent

4. Intercepted Runoff Divided by 0.000652 cms/Meter

5. Intercepted Runoff Divided by 0.000750 cms/Meter

The inlet runoff interception and spacing computations are contained in Appendix F.

Pipe Diameter

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Determination of the pipe diameter required to convey the design runoff to the discharge location

includes two components, computation of the design runoff and determination of the resultant

required pipe diameter as explained in the following narrative.

Design Runoff – The design runoff was computed using the rational formula. The calculation

requires determination of the rainfall intensity that is a function of the time of concentration, the

area from which runoff is contributed and the weighted runoff coefficient for the area from which

runoff is contributed. The procedures employed to determine these factors are explained below.

a. Rainfall Intensity – Determined from the charts supplied by Region 10 included in

appendix A. A recurrence interval of once in ten-years was used in compliance with

Table 8-2 in Chapter 8 of the Highway Design Manual.

b. Time of Concentration – computed using a 5 minute minimum plus the run time to

the discharge location using a velocity of three meters per second for the length of the

run to the discharge point.

c. Contributing Area – field observation revealed that, except in isolated locations, the

overland area that contributes runoff to Route 347 is limited to approximately fifteen

meters either side of the edge of the typical section. The Case I typical section was

used in the evaluation because it represents the widest proposed pavement section on

the project. Additional area contributes runoff to westbound Route 347 from

approximately Davis Avenue to Crystal Brook Hollow Road, near the east terminus

of the project.

d. Weighted Runoff Coefficient – a runoff coefficient of 0.95 was used for pavement

areas and 0.55 for adjacent unpaved areas to compute the weighted runoff coefficient.

This yielded a weighted runoff coefficient of 0.81.

Pipe Diameter - Hydraulic computations were performed using the Manning equation to

determine the diameter of the pipe needed to convey the design runoff to each proposed disposal

location. A friction factor of 0.016 was used. A minimum slope of 0.005 meters per meter was

used, including locations where grades adverse to the roadway vertical geometry were required to

reach the discharge location. The roadway grade was used when it exceeded 0.005 meters per

meter. An average slope was computed, using the TGL at the upper and lower ends of the run

divided by the length of the run, when several grades steeper than 0,005 meters per meter were

present within the proposed pipe length. The pipe diameter was computed for the runoff at the

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discharge location for each approach, both from the west and from the east, at each discharge

location.

Pipe diameters upstream of the discharge location were approximated from the computed

diameter using a proportional analysis. The analysis is valid for the typical section Case I

including the 15 meter width adjacent to each side of Route 347. This analysis was based on the

relative conveyance in different diameters of pipe related to the portion of the contributing length

that this represents. The evaluation was prepared for a slope of 0.005 meters per meter, which is

the predominant slope used on the project. The proportions are presented in Table 15.

TABLE 15

PIPE PROPORTION Diameter Capacity (meters) (cms)

1.52 5.2 100 1.37 3.9 75 100 1.22 2.9 56 74 100 1.07 2.02 39 52 70 100 0.914 1.33 26 34 46 60 100 0.762 0.83 16 21 28 40 62 100 0.610 0.45 9 12 14 22 34 55 100 0.452 0.20 4 5 7 10 15 24 44 As an example, the diameter for the pipe from Station 35+530 to the discharge point at Station

34+827, a total length of 703 meters is 1.37 meters with a capacity of 3.94 cms. The table

indicates that seventy-four percent of the design runoff is accommodated in the 1.22 meter

diameter pipe. Therefore, the 1.22-meter diameter pipe is adequate for seventy-four percent of

the total pipe length. This yields a distance twenty six percent of the total length from the

discharge location, which yields Station 35+010. The table indicates that fifty-two percent of the

design runoff is accommodated in the 1.07meter diameter pipe. Therefore, this pipe is adequate

for fifty-two percent of the total pipe length. This yields a distance forty-eight percent of the total

length from the discharge location, which yields Station .35+164. Continue to the end of the run.

The procedure provides pipe to the high point of the contributing area and disregards the flow in

the gutter until an inlet and pipe is needed. However, this simplification is consistent with the

level of detail of this evaluation.

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The absence of a viable location for the installation of a recharge basin (RB) in several

watersheds in the portion of the project that does not require compliance with the NYSDEC

SPDES requirements, east of Southern Boulevard, warranted redirecting the runoff generated in

that watershed to the RB in an adjacent watershed. These locations include the diversion of

runoff from watershed # 5 to RB’s in watershed #6 and the diversion of some of the runoff from

watershed # 12 to RB’s in watershed # 11. The pipe design was based on these diversions.

The pipe diameter computations are contained in Appendix F.