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Pursuant to Public Law 92-1h7, Phas~e I Inspection Reports are preparedtinder guidance contained in the recommended guidelines for safety

napect ion oif dasn published h'v the Office of rhier of Engineers,Washington, D. C. 20314. The purpose of a Ph&s* I Inspection is to

identfy expeditiously those dams which may pose hazards to humnan life or

prapertv. 7%0 assessment of the general conditions of trte dam Is basediipon evalI aNI c da ta 4knd vi sualI inbpi-.t Ion Detailed investigation and

4nales involving topographic mapping. stubsurface investigations,f pst Ing, and deta iled --omptattiout I evalIuat ions are beyond t he scope of aMhaseo I investigation; however, the Investigation is intended to Identify,-1 iced for t-jti~ ota-fies.

Cssed Otpon te !iel1 onditione. it the time of the field inspection Ind

4!1 4vailable engineering data, the Phase I report addresses the'idraultt, hydrologic, 1geologic, Igeotechnic, and structural tspectot of

thie Aam. 7The engineering techniques employed give a reasonably accurateasessment of 0,r .oditionu )f the Aaw. It should he realized that

c-ertain erigineeringt aspects cannot he fully analysed during a Phase II -Ispe, tilon. Assessment and reme~dia&I measures i n t he report I nc lude t he

reqoiireeents of additional Indepth sitd when necessary.

Phase 7rep~ort% In, I ide pr, Itt iwiforsAt ion I t he lam apportenoal.eb, ill

#eKibtintg engirwi~.ng lata. operational procedures, hvdrauilic'hvrdrologic

lat% af *t te .uiterahed.'J&=da %taS lit v visuali I nupe. tion report and an

Assessment :noladlng required remedial measures.

S5C iW1T' CL A966iC A OO '"V P5OI Dog* aegE

POTOMAC RIVER SASIN

NAME OF DAM: DALEY DAM

LOCATION' LOUDOUN COUNTY, VIRGINIA

INVENTORY NU1KJER: VA 10709

PNASE I INSPECTION REPORT

NATIONAL DAN SAFETY PROGRAM

DTICNational Dam Safety Program. Daley S OCT 2 D

Dam (Inventory Number VA 10709), DPotomac River Basin, Loudoun County,

Virginia. Phase I Inspection Report.

PREPARED ai

NORFOLY, DISTRICT CORPS O1 ENGINEERSg03 FRONT STR ET

NoRFOL. VIRGINIA 23510

APROW'B 1

.~/

TABLE OF CONTENTS

Preface . . . . . . . . . . . . . . . . . . . . . . . . . i

Brief Assessment of Dam ....... . . . . . . . . .

Overview of Dam

Section 1: PROJECT INFORMATION. . . . . . . . 1-1Section 2: ENGINEERING DATA ..... ............ .. 2-1Section 3: VISUAL INSPECTION. . . . ........... 3-1

Section 4: OPERATIONAL PROCEDURES ........... .. . 4-1Section 5: HYDRAULIC/HYDROLOGIC DATA . . ......... 5-1Section 6: DAN STABILITY . . . . ............ 6-1Section 7: ASSESSMENT/REMEDIAL MEASURES ......... 7-1

Appendix 1: Maps and DrawingsAppendix 11: PhotographsAppendix III: Field ObservationsAppendix IV: References

Acoession For

NTIS GT1A&IDTIC TAB 03

UtI&Ma,ounced 0just fitcat ion_

Distribution/

Avnii:,_' !l'ty Codes. a +'; nd!or

;Dir

tS

PREFACE

This report is prepared under guidance contained in the RecommendedGuidelines for Safety Inspection of Dams, for Phase I Investigations.

Copies of these guidelines may be obtained from the Office of the Chiefof Engineers, Washington. D.C. 20314. The purpose of a Phase I investi-gation is to identity expeditiously those dams which may pose hazards tohuman life or property. The assessment of the general condition of thedam is based upon available data and visual inspections. Detailed in-vestigation and analyses involving topographic sapping, subsurfaceinvestigations testing, and detailed computational evaluations are beyondthe scope of a Phase I investigation; however, the investigation isintended to identity any need for such studies.

In reviewing this report, it should be realized that the reportedcondition of the dam is based on observations of field conditions at thetime of inspection along with data available to the inspection team. Incases where the reservoir was lowered or drained prior to inspection, suchaction, while improving the stability and safety of the dam, removes thenormal load on the structure and may obscure certain conditions whichmight otherwise be detectable if inspected under the normal operatingenvironment of the structure.

It is important to note that the condition of a dam depends onnmmerous and constantly changing internal and external conditions, and isPvrlutionary in nature. It would be incorrect to assume that the presentcondition of the dam will continue to represent the condition of the damir some point in the future. Only through continued care and inspectioncan there be any chance that unsafe conditions be detected.

Phase I inspections are not intended to provide detaijed hydrologicAnu hvdraulic AnALvseq. In accordance with the established guidelines,the spilliway design flood is based on the estimated "Piobable MaxmumnF:ood" for the region (flood discharges that may be expected from themost severe combination of critical meteorologic and hydrologic conditionsthat are reasonably possible), or fractions thereof. Because of themagnit-ide and rarity of such a storm event, a finding that a spillwayw.I. not pass the design flood should not be interpreted as necessarilyp., rij a highly inadequate condition. The design flood provides am'asute ,of relative spillway capacity and serves as an aide inditermining the need for more detailed hydrolog- and hydraulic studies,.onsidering the size of the dam, its general condition and the downstream

damage potential.

PHASE I REPORT

NATIONAL DAN SAFETY PROGRAM

BRIEF ASSESSMENT OF DAN

Name of Dam: Daley DamState: VirginiaLocation: Loudoun CountyUSGS Quad Sheet: Purceville, VirginiaStream: Tributary to Catoctin CreekDate of Inspection: 30 April 1981

Daley\Dam is an earthfill structure about 800 feet long and 29.4

feet high, The dam is owned and maintained by' the Mr. John E. Sewell,Hr. James E. Heisel, and Mr. Robert M. Terry.>The dam is classified

as a small dam with a significant hazard classification. Theprincipal spillway is a drop-inlet located in the reservoir discharges

into a stilling basin below the dam. The emergency spillway is anopen channel cut in the right abutment. A reservoir drawdown gate is

attached to the bottom of the drop-inlet. The reservoir provides

recreation.

Based on criteria established by the Department of the Army,

Office of the Chief of Engineers (OC),' the Spillvay Design Flood(SDF) is the 100-Year Flood., The spillway will pass 25 percent of the

PHF or 100 percent of the SDF without overtopping the crest of the

dam. The spillways are adjudged as adequate.

The visual inspection revealed an upstream slope failure. Based

on U. S. Department of Interior, Bureau of Reclamation guidelines theupstream slope is inadequate. Therefore, the dam is assessed asunsafe, non-emergency.

The "unsafe, non-emergency" classification applied to a dam with a

structural deficiency is not meant to connote that the dam is in

danger of imminent failure. It dvsf-ean$ hmmewrX that based on an

initial screening and preliminary calculations, there appears to be a

serious deficiency in the stability of the upstream slope# This could

lead to failure of the dam significantly increasing the hazard to life

downstream from the dam.

,It is recommended that within 2 months from the date of

notification to the Governor of the Commonealth of Virginia,-,the

owners engage the services of a qualified geotechnical engineering

firm to perform a stability analysis on the dam and recommend methods

of eliminating the danger imposed by the project.

Within 6 months of the notification of the Governor, thegeotechnical engineer's report should be completed and the owners

should have an agreement with the Commonwealth of Virginia for a

reasonable time frame in which all recommendations should be

implemented. -. n the interim, a detailed emergency operations plan and

ii

6w

warning system, should be promptly developed There is no yarning

system in effect. This warning system should9u tline how to operate

the dm in an emergency and who to notify, inctuding public officials,

in case an evacuation from the downstream area is necessary. Also,

during periods of unusually heavy precipitation, around-the-clock

surveillance should be provided.

There is no maintenance operations program. It is recommended

that a regular maintenance operations program and inspection program

be instituted with provisions for accurate records of all maintenance

and inspections performed. Also, the maintenance items listed in

Section 7.2 should be accomplished as part of the regular maintenance

program within the next 12 months.

Submitted By: Approved:

Original signed by: Original signed by:

Carl S. Anderson, Jr. Ronald E. Hudson

CARL S. AN DERSON RONALD E. HUDSON

Acting Chief, Design Branch Colonel, Corps of EngineersCommander and District Engineer

Recommended By Date: SEP1 1981

OrIgInal signed by.JAMES A. WALSH

4 "'JACK G. STARRChief, Engineering Division

Li.

T 7

DAM

RESER VOIR

OVERALL VIEWS - DALEY DAM30 APRIL 1981

SECTION I

PROJECT INFORMATION

1.1 GENERAL:

1.1.1 Authority: Public Law 92-367, 8 August 1972, authorizedthe Secretary of the Army, through the Corps of Engineers to initiatea National Program of Safety Inspections of Dams throughout the UnitedStates. The Norfolk District has been assigned the responsibility ofsupervising the inspection of dams in the Commonwealth of Virginia.

1.1.2 Purpose of Inspection: The purpose is to conduct a Phase Iinspection according to the Recommended Guidelines for SafetyInspection of Dams (Reference I, Appendix IV). The mainresponsibility is to expeditiously identify those dams which may be apotential hazard to human life or property.

1.2 Project Description:

1.2.1 Dam and Appurtenances: Daley Dam is an earthfill structureapproximately 800 feet long and 29.4 feet high. The crest of the dammeasures 17 feet wide at an elevation of 508.0 feet msl. The upstreamslope measures 3 horizontal to I vertical (3H:lV) and the downstreamslope measures 2.5H:IV. A design drawing shows the crest width to be14 feet and both slopes to be 2.5H:lV. Riprap is placed along thelower portion of the upstream slope.

According to the design drawing, the dam is keyed into thefoundation with a core trench and has a toe drain. It is unknown ifthere are any foundation drains. There are no embankment orfoundation drain outlets.

The principal spillway is a 42-inch corrugated metal pipe (CMP)drop-inlet connecting to a 30-inch CMP running through the dam at lowlevel and discharging into a small stilling basin near the toe of thedam. The crest of the principal spillway is at elevation 500.0

The emergency spillway is an open channel cut into the rightabutment. The crest of the emergency spillway is 75 feet wide and atelevation 504.0.

An 12-inch slide gate, located 55 feet into the reservoir, isconnected to the drop-inlet at low level and is capable of dewateringthe reservoir.

1.2.2 Location: Daley Dam is located on a tributary of theCatoctin Creek about 2 miles northeast of Hillsboro, Virginia inLoudoun County.

1.2.3 Size Classification: The dam is classified as small dam asdefined in Reference 1 of Appendix IV.

1-1

1.2.4 Hazard Classification: The dam is located upstream ofseveral farms and State Route 611. Should a dam failure occur, the

structures on the farms may sustain property damage with a possibilityof loss of life. Therefore, a significant hazard classification isgiven for Daley Dam according to guidelines contained in Section 2.1.1of Reference 1, Appendix IV. The hazard classification used tocategorize a dam is a function of location only and has nothing to dowith its stability or probability of failure.

1.2.5 Ownership: Mr. John E. Sewell, Mr. James E. Heisel, andMr. Robert M. Terry.

1.2.6 Purpose: The reservoir provides recreation and some floodcontrol.

1.2.7 Design and Construction History: Daley Dam was designedand engineered with the assistance ol the U. S. Department ofAgriculture, Soil Conservation Service and constructed by Hope andArnold. The dam was completed in 1974.

1.2.8 Normal Operational Procedures: Tue normal operation of

Daley Dam is automatic with water passing into the drop-inlet as thereservoir rises above elevation 500.0 and passing through theemergency spillway when the reservoir reaches elevation 504.0.

1.3 Pertinent Data:

1.3.1 Drainage Area: The dam controls a drainage area of 1.38square miles.

1.3.2 Discharge at Dam Site: The maximum flood at the dam siteis unknown.

Pool level at crest of dam.

Principal Spillway ...... .................. 64 cfs

Emergency Spillway ...... .................. 1560 cfs

1.3.3 Dam and Reservoir Data: Pertinent data on the dam andreservoir are shown in the following table:

TABLE 1.1 DAH ANV RESERVOIR DATA

Rese rvoi r

Elevation _ Capac ityfeet Area Acre Watershed, Lengt h,

Item msl Acres feet Inches feet

Crest of Dam 508.0 51.5 465 6.3 ?90CEmergency Spillway Crest 504.0 37 290 3.9 650Principal Spillway Crest 500.0 25.7 193 2.0 .500Streambed at Down-

stream toe of dam 478.6. - - -

1-2

SEc.iiON 2

ENGINEERING DATA

2.1 Desiln: A design drawing was provided by the U. S.Department of Agriculture, Soil Conservation Service. The drawingprovides a typical section through the embankment at the principalspillway including details of the embankment intake structure, outletpipe, anti-seep collars, and reservoir drains. A Bill of Materials isalso provided showing perforated pipe and gravel for a toe drain (See

Plate II, Appendix I).

2.2 Construction: There are no known construction records.

2.3 Evaluation: There is insufficient information to evaluatefoundation conditions and embankment stability.

2-1

~I.

SECTION 3

VISUAL INSPECTION

3.1 Findinxs:

3.1.1 General: The results of the 30 April 1981 inspection are rrcordJ.4in Appendix Il. At the time of the inspection, the weather was overcast.The temperature was 78" F. and the ground conditions were damp. The poolelevation was 500.0 feet msi or normal pool. The tailwater was at elevation480.0 feet msl. A slight flow was passing through the principal spiliay.There are no known prior inspection reports.

3.1.2 Embankment: The embankment is in fair condition. Sketchebshowing a plan view, a profile and a cross section at the time of theinspection are provided on Plates III & IV, Appendix 1. An overall view ofthe dam is provided at the beginning of the report.

There are no signs of surface cracks, unusual movement, sloughing ormisalignment on the crest or downstream face. However, most of the upstreamface has experienced slope failure. The failure consists of areas of mino.rsloughing and areas of large failure surfaces with 4 feet of slip planeexposed. Several footpaths run down both the upstream and downstream facesfrom the crest. There is minor erosion around the principal spillway outletpipe. Several animal burrows are located on the downstream face. (See PlateIII, Appendix I and Photos No. 2, 3, 4 & 6, Appendix 11).

The portions of the upstream slope that have not failed are riprapped.The riprap extends from about 3 feet below pool elevation to about 12 feet upthe slope. Evidence of riprap is visible on the slope in the areas of minorsloughing, however, there is no evidence of riprap in the areas of largefailure surfaces. Apparently, the whole upstream slope was riprapped but theslope failure carried some of the riprap far enough down the slope, beneaththe water surface, to be unobservable (See Plate III, Appendix 1).

There is no noticeable sliding or settlement. There are no knownfounda! ion drains. The are no foundation drain outlets. There are no rockoutcrops in the area.

There is a pile of wet material along the downstream toe from a pointabout 75 feet left of the principal spillway outlet pipe to the outlet pipe.The area beyond the material up to the road approximately 300 feet downstreamof the dam is lower in elevation than the surrounding area and water isponded therein. The downstream area, to the right of the outlet pipe, isslightly higher in elevation, but is also wet from the toe to the road. Aditch runs down the right hillside about 30 feet downstream of the dam. Apatch of cattails is growing in the area where the ditch intersects the baseof the hillside. (See Plate II, Appendix 1).

The are no known embankment drains.

A material sample taken from the failure surface on the upstream slopewas classified as a high plastic, silty clay (CL) with some (34%) fine sand.

3-I

Ia

The crest is Wll vegetated with gross. The port ions of the upstreamolc" not involved in the Slope fai lure are well vegetated bath gross,Shrubs, and sapplings. T1he downstream slope is well vegetated bath grass.ground ivy, large shrubs. and scattered traps up to 6 inthes in diametr,.(See Photosa No. 1, 2. 11. 4ib' Appendix 11).

3.1.) Princtipal Spil Iiial A *."-in.ik CNP serves at, a jrop-inlrt Sri I.-tfir Coot r.'i sr.t 141 o f(ie pal ink pal apt I IbAY. trebars ace platod iiii r(Sb thetop Oif t 1.0 j (1 daIL I 1 4,V4,'It I tI~ It I r i * ,~ ;. ,, I . 0. -.

irbr~Oi .Te Ou le pip a I~a an I. ,M b.i .pas *.- tI b a L

emptites at t te tw Ant., a stilling basin. Ii.. 4out lot pipe is pa rt .allyISjbar rgle d tan t he 6 1t wi in j ba %a it. ( See- P#.,t ,% %,. I h 6, ApperaJ.* I I ?

). 1.4 Emergency Spiilba= The car rgent:v sp alway ia an open c .t htarlne,i n t he a aghItt atrrsr IV There are soame astal I pines lncat,'d in the tport ion of the cimt rol sect ion. Vegetat ion as Sparse.

3. 1. Inst rumerkatat iOn The re as n o ihat r,.ametat on o. t te I&* .

31.6 Re servir Area The reservoar slopes are gentle pastureland.The re Iaroe no s ig ns o i rervoi r s lope I ai l ure -)r short I in orIeros ion . Itieinspect iol tea. fab unable to evaliiate reservoir sedimeontat ion. An overal.

of.' 0 tie reervot r is provtded aIt lie beg-inning of the report

3.1.7 Dounstream Lhartnel The downstream channel as narrob andsall o%. tres a ne the channelI frm thle at iIalng basian to thei ro)ad. abo.,t300 feet downst ream. The area slopes are gentler and for the most parttreeless. There are two farm downstream of the dam that may sustain damasgeshould an embankment failure occur.

3.2 Evaluation: Overall the dam appeals ir a tir condition. The .iasua.linspection revealed certain preventative maintenance items which Should bescheduled as part of an annual maintenance programn. Those are

a. The footpaths on the face of the da should be reseeded.

b. The eroded area at the outlet pipe and the animal burrows should hefilled with compacted material and reseeded.

c. The wet areas along the tot should be monitored for any f lob. If anwflow develops, the services of a qualified grotechnical enginerier should beobtained to investigate the causes of the f loba.

8. The trees, sapplings and Shrubs on the dal should be cut off at theground surface. Any tree with a diameter larger than 3 inches should haveits root system removed and the subsequent hole filled with compactedmaterial and seeded.

C. The pine trees in the emergency spillway shotild be cut off at theground surface to prevent collection of debris, thereby restricting flow,during periods of flow throuigh the emergency spillway.

j

f. A staff&ae should be ittalled in the reservoir to extend above the

Crest of the dal.

S. Ih4, trees linang the dtwnstreaim channel frmo the dam to the roadshoul4 be Cut off at the round surface.

3-3),

SECTION 4

OPERATIONAL PROCEDURES

4.1 Procedures: The normal storage pool elevation is 500.0. which isthe crest of the drop-inlet (principal spillway). The reservoir providesrecreation and some flood control. Water passes automatically through theprincipal and emergency spillways as the reservoir rises above elevation50.0 and 504.0, respectively. A drawdown gate located in the reservoir isavailable to devater the reservoir.

4.2 Maintenance: There is no maintenance at Daley Dam.

4.3 Warninx System: At present time, there is no warning system orevacuation plan for Daley Dam.

4.4 Evaluation: The dam does not require an elaborate operational andmaintenance procedure. However, maintenance program should be developed,including documentation. An emergency operation and warning p in should bedeveloped. It is recommended that formal emergency procedures be pre aredand furnished to all operating personnel. This should include:

a. Now to operate the dam during an emergency.

b. Who to notify, including public officials, in case evacuation fromthe downstream area is necessary.

4-1

f4

SECTION 2

IIYDIAU LIC/YDEOLOGIC DATA

5.1 D s ej: The U. S. Department of Agriculture, SoilConservation Service, provided peak rate discharges from smallwatersheds for Daley Dow for a 2S-year reoccurrence interval.

5.2 tydroloji;€ Record: None ware available.

5.3 _ood-Exrience: The maximum flood at Daley Dom is unknown.

5.4 flood-Potnti4l: The 100-year flood, 1/2 Pm4 and P14? weredeveloped and routed through the reservoir by use of the NEC-IDAcomputer program (Reference 2, Appendix IV) and appropriate unithydrograph, precipitation and storage-outflow data. Clark's Tc and Icoefficients for the local drainage area were estimated from basincharacteristics. The rainfall applied to the developed unit

hydrograph was obtained from the U. S. Weather bureau Publications(Reference 3 and 4 of Appendix IV).

5.5 Reservoir Rejulation: Pertinent dam and reservoir data areshown in Table i.'

Water passes automatically through the principal and emergencyspillways as the reservoir rises above elevation 500.0 and 504.0,respec ti vely,

The storage curve was developed based on areas obtained from aU. S. Geological Survey Quadrangle Map. Survey data taken during theinspection was correlated to the Purcellville, Virginia Quadrangle Mapto help develop area-storage data. Rating curves for the non-overflowsection and the emergency and principal spillvays vere developed byhand calculations. In routing hydrographs through the reservoir, itwas assumed that the initial pool level was at the principal spillwaycrest (elevation 500.0). Flow through the principal spillway wasne glected.

5.6 OvertoyDinit Potential: The probable rise in the reservoirand other information on reservoir performance is shown in thefollowing table:

5-1

Table 5.1 RESERVOIR PZRyOR70 CE

Normal too I/Item Flow Year .. 1/2 PH? PH_ 2/

Peak flow c.f.s.

lnf low 1 1780 4860 9721

Outflow i 755 415 9018

Maximum elevat ionft. s1 500.0 506.32 508.85 509.9

Non-overflow section(elevation 508.0 ft. asi)

Depth of flow, ft. - - 0.85 1.9Duration, hrs. -- 2.5 4.25

Velocity, fps 3/ - 4.2 6.3Tailvater elevation

ft. mel 480.0. - -

j/ The 100-Year Flood has one chance in 100 of occurring in any given year.

2/ The PHF is an estimate of flood discharges that may be expected from the

most severe combination of critical meteorologic and hydrologic conditionsthat are reasonably possible in the region.

3/ Critical Velocity

5.7 Reservoir Emptyint Potential: A 12-inch slide gate, located at thebottom of the reservoir, is capable of devatering the reservoir. With thereservoir at normal pool (elevation 500.0), the pipe is capable of adischarge flow of about 16.2 cfs and essentially devater the reservoir inabout 9 days. This is an equivalent dravdovn rate of 2.2 feet per day.This is based on the hydraulic height of the dam divided by the time todewater the reservoir.

5.8 Evaluation: Based on the size (small) and hazard classification

(significant), the recommended Spillvay Design Flood (SDF) is the 100-YearFlood to the 1/2 PHY. Because of the risk involved, the 100-Year Flood has

been selected as the SDF. The emergency spillway will pass 25 percent ofthe PMF or 100 percent of the SDF without overtopping the crest of the dam.

Conclusions pertain to present day conditions. The effect of futuredevelopment on the hydrology has not been considered.

5-2

L -! ll -- "-

SECTION 6

DAN STABILITY

6.1 Foundation and Abutments: There is no detailed information

available on the local geology or the foundation conditions. The damis located within the Blue Ridge physingraphic Province of Virginia.

All drainage in the area flows in Goose Creek which drains eastwardinto the Potomac River. The area is underlain by the

Cambrian-Precambrian Catoctin Formation. Locally the Catoctin

consists of basic lava flows, schists and gneiss, arkose, conglomerate

and phyllite. As noted in the visual inspection, the downstream areais wet. According to the design drawings, the dam is keyed into the

foundation by a core trench and has a toe drain. It is unknown ifthere are any foundations drains. There are no foundation drain

outlets. The predominate foundation materials are relatively

pervious, stable, fine grained soils.

6.2 Embankment:

6.2.1 Materials: Embankment materials are high plastic silty

clays (CL) with some fine sand.

6.2.2 Stability: There are no available stability calculations.

The dam is 29.4 feet high and the crest measures 17 feet wide. Theupstream slope measures 3.OH:lV and the downstream slope measures

2.5H:lV. The design drawing shows a crest width of 14 feet and both

slopes to be 2.5H:lV. The dam is subject to sudden drawdown because

of the approximate reservoir drawdown rate of 2.2 feet per day which

exceeds the critical rate of 0.5 feet per day for earth dams. The

existing pool is at normal pool elevation. It is unknown if the dam

has experienced the maximum control storage pool which is at the

elevation of the emergency spillway (4.5 feet above normal pool).

According to the guidelines presented in Design of Small Dams.U.S. Department of the Interior, Bureau of Reclamation for small

homogenous dams, with a stable foundation, subjected to a sudden

drawdown and compoaed of low plastic fines (CL, ML), the recommendedslopes are 3.5H:lV upstream and 2.5H:IV downstream. The recommended

width is 16 feet. Based on these guidelines, the dam has an adequate

width and downstream slope, but an inadequate upstream slope. This

inadequacy is exemplified by the upstream slope failure discussed in

Section 3.1.2.

6.2.3 Seismic Stability: The dam is located in Seismic Zone 2.

Therefore, according to the RecommendedGuidelines for Safety

Inspection of Dams, the dam is considered to have no hazard from

earthquakes provided static stability conditions are satisfactory and

conventional safety margins exist.

6.3 Evaluation: There is insufficient information to adequately

evaluate the stability. The visual inspection revealed an upstreamslope failure. Also, based on Bureau of Reclamation guidelines, the

dam was designed with an inadequate upstream slope. It is recommended

that the services of a qualified geotechnical engineering firm be

engaged to perform a stability check of the dam.

6-1 I

SECTION 7

ASSESSMENT/REMEDIAL MEASURES

7.1 Dam Assessment: The available engineering data isinsufficient to evaluate the foundation conditions and the embankmentstability. There is no maintenance operations program or emergencyoperations and warning plan.

Based on criteria established by the Department of the Army,Office of the Chief of Engineers (OCE), the Spillway Design Flood(SDF) is the 100-Year Flood. The spillway will pass 25 percent of thePMF or 100 percent of the SDF without overtopping the crest of thedam. The spillways are adjudged as adequate.

The visual inspection revealed an upstream slope failure. Also,based on U. S. Department of the Interior, Bureau of Reclamationguidelines the upstream slope is inadequate. Therefore, the dam isassessed as unsafe, non-emergency.

The "unsafe, non-emergency" classification applied to a dam with astructural deficiency is not meant to connote that the dam is indanger of imminent failure. It does mean, however, that based on aninitial screening and preliminary calculations there appears to be aserious deficiency in the stability of the upstream slope. This couldlead to failure of the dam significantly increasing the hazard to lifedownstream from the dam.

7.2 Recommended Remedial Measure: It is recommended that within2 months from the date of notification to the Governor of theCommonwealth of Virginia, the owners engage the services of aqualified geotechnical engineering firm to perform a stabilityanalysis on the dam and recommend methods of eliminating the dangerimposed by the project.

Within 6 months of the notification of the Governor, thegeotechnical engineer's report should be completed and the ownersshould have an agreement with the Commonwealth of Virginia for a

reasonable time frame in which all recommendations should beimplemented. In the interim, a detailed emergency operations plan andwarning system should be promptly developed. The warning systemshould outline how to operate the dam in an emergency and who tonotify, including public officials, in case an evacuation from thedownstream area is necessary. Also, during periods of unusually heavy

precepitation, around-the-dock surveillance should be provided.

It is recwmmended that a regular maintenance operations program

and inspection program be instituted with provisions for accuraterecords of all maintenance and inspections performed. Also, theinspection revealed the following maintenance items that should beaccomplished as part of the regular maintenance program within thenext 12 months:

7-1

*I."' .... . . . J ll" ',m , ... ... .. . __- __ __ 1:* ,

a.' The footpaths on the face of the dam should be reseeded.

b. The eroded area at the outlet pipe and the animal burrowsshould be filled with compacted material and reseeded.

c. The wet areas along the toe should be monitored for any flow.If any flow develops, the services of a qualified geotechnicalengineer should be obtained to investigate the causes of the flow.

d. The trees, sapplings and shrubs on the dam should be cut offat the ground surface. Any tree with a diameter larger than 3 inchesshould have its root system removed and the subsequent hole filledwith compacted mat.rial and seeded.

e. The pine trees in the emergency spillway should be removed.

f. A staffgage should be installed in the reservoir to extendabove the crest of the dam.

g. The trees lining the downstream channel from the dam to theroad should be cut off at the ground surface to prevent collection ofdebris and restricting flow during periods of flooding.

7-2 _ 1I I-

'.

APPENDIX I

MAPS AND DRAWINGS

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PHOTOGRAPH S

PHOTO ICREST

PHOTO*2 UPSTREAM FACE

PHOTO 3SLOUGHING /EROSIONON UPSTREAM FACE

PHOTO*4 SLOUGHING/ EROSIONON UPSTREAM FACE

PHOTO*5 DOWNSTREAM FACE

PHOTO 6 ANIMAL BURROW ONDOWNSTREAM FACE

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PHOTO 48RESERVOIR DRAINOPERATOR

--. N

APPENDIX III

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APPENDIX IV

REFERENCE S

REFERENCES

1. Recommended Guidelines for SafetyInsjection of Dams, Office of

the Chief of Engineers, Department of the Army, Washington, D. C.

2. HEC-IDB Flood Hydrograph Package, (Hydrologic Engineering Center,

U. S. Army Corps of Engineers, September 1978.)

3. "Probable Maximum Precipitation Estimates, United States East of

the 105th Meridian," Hydrometeorololical Re ort N. 5.L (U. S.Weather Bureau, June 1978).

4. "Rainfall Frequency Atlas of the Unites States", Technical Paper

No. 40, (U.S. Weather Bureau, May 1961).

5. "Design of Small Dams", Technical Publication of United States

Department of the Interior, Bureau of Rpcisnation, Second Edition,Revised Reprint, 1977.

* S-

*. 4*V