F/ 13/13 NATIONAL DAM SAFETY PROGRAM. …AD-A103 720 BAKER (MI CHA IEL) JR INC BEAVER PA F/ 13/13 NATIONAL DAM SAFETY PROGRAM. BEATTIES MILLPOND DAM (INVENTORY N -ETC(UI APR 81 J A

AD-A103 720 BAKER (MI CHA IEL) JR INC BEAVER PA F/ 13/13NATIONAL DAM SAFETY PROGRAM. BEATTIES MILLPOND DAM (INVENTORY N -ETC(UIAPR 81 J A WALSH DACW65-R0-D-R3Z

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Name of Dam: Beatties Millpond DamLocation: Hanover County, State of Virginia LEVE(:Inventory Number: VA 08535 L

PHASE I INSPECTION REPORTNATIONAL DAM SAFETY PROGRAM

0 0

CDTIC

SEP 3 19810A A

PREPARED FOR

NORFOLK DISTRICT CORPS OF ENGINEERS

803 FRONT STREETNORFOLK, VIRGINIA 23510

Th1dm documnent has been apprOm

" PREPARED BY for pulc reletse aod sale, itsL dis1butio'i is tunliited.

M ICHAEL BAKER, JR., INC. ....BEAVER, PENNSYLVANIA 15009

81 9 03.045

SECURITY CLASSIFICATION OF THIS PAGE (W1man DateaEntereoD

REPORT DOCUMENTATION PAGE BRE FORM

I- fIEPOR'TPNUMBER ji OVT ACCESSION NO. 3. RECIPIENT'S CATA4LOG NUMBER

VA 08535 C'.KJ~/ (4. TITLE (and Subtttl*) TYPIE OF REPDLAJP40 COVERED

80 Frn Street

* 1~. MOIfTRING AGNC NAME & emtIon ot0lngOfc) . SECRORY CLASSN. ROJET hareoTS

I11. CONLTROLLING OF/DmootRAOIN

SCHEDULE

* IS. .ODSTRI.UT15'TMN of t~eReot)

Approved for public releade; distribution unlimited

' J /4111e I-- -A17. DISTRIBUTION STAT111f~ abstract eitred in &lock 20, It difeent from Resport)

IS. SUPPLEMENTARY NOTES

Copies are obtainable from National Technical Information Service,Springfield, Virginia 22151

19. KEY WORDS (Continue on reveres side It necesary7 and Identify by block number)

a Dams -VANationri. Dam Safety Program Phase IDam SafetyDamn Inspection

ft Aa~TRAC? T ' f~ton sosess eb fneeesa d~entIly by block numbr)

DD Mn 103 0 m of, I~ Nov 6B is OBSOLETE 2 ja775SECUITy CLASSIF1tCATtOrt OF THIS PAGE jaDl Entered)

4 OF THIS PAGEL(Wm Data [email protected]

20. Abstract

Pursuant to Public Law 92-367, Phase I Inspection Reports are preparedunder guidance contained in the recommended guidelines for safetyinspection of dams, published by the Office of Chief of Engineers,

Washington, D. C. 20314. The purpose of a Phase I Inspection is toidentify expeditiously those dams which may pose hazards to human life

or property. The assessment of the gereral conditions of the dam is

based upon available data and visual inspection. Detailed investigationand analyses involving topographic mapping, subsurface investigations,testing, and detailed computational evaluations are beyond the scope of aPhase I investigation; however, the investigation is intended to idenifyany need for such studies.

Based upon the field conditions at the time of the field inspection andall available engineering data, the Phase I report addresses thehydraulic, hydrologic, geologic, geotechnic, and structural aspects ofthe dam. The engineering techniques employed give a reasonably accurateassessment of the conditions of the dam. It should be realized thatcertain engineering aspects cannot be fully analyzed during a Phase Iinspection. Assessment and remedial measures in the report include therequirements of additional indepth study when necessary.

Phase I reports include project information of the dam appurtenances, allexisting engineering data, operational procedures, hydraulic/hydrologicdata of the watershed, dam stability, visual inspection report and anassessment including required remedial measures.

MCuAITY CLASSIPICATION OP THIS PAGOECtm, Date lt.teo

PREFACE

This report is prepared under guidance contained in theRecommended Guidelines for Safety Inspection of Dams, forPhase I Investigations. Copies of these guidelines may beobtained from the Office of the Chief of Engineers,Washington, D.C. 20314. The purpose of a Phase I investi-gation is to identify expeditiously those dams which maypose hazards to human life or property. The assessment ofthe general condition of the dam is based upon available

, data and visual inspections. Detailed investigation andanalyses involving topographic mapping, subsurface investi-gations testing, and detailed computational evaluations arebeyond the scope of a Phase I investigation; however, theinvestigation is intended to identify any need for suchstudies.

In reviewing this report, it should be realized that thereported condition of the dam is based on observations offield conditions at the time of inspection along with dataavailable to the inspection team. In cases where the reser-voir was lowered or drained prior to inspection, such action,while improving the stability and safety of the dam, removesthe normal load on the structure and may obscure certainconditions which might otherwise be detectable if inspectedunder the normal operating environment of the structure.

It is important to note that the condition of a dam dependson numerous and constantly changing internal and externalconditions, and is evolutionary in nature. It would beincorrect to assume that the present condition of the damwill continue to represent the condition of the dam at somepoint in the future. Only through continued care and inspec-tion can there be any chance that unsafe conditions bedetected.

Phase I inspections are not intended to provide detailedhydrologic and hydraulic analyses. In accordance with theestablished guidelines, the spillway design flood is basedon the estimated "Probable Maximum Flood" for the region(flood discharges that may be expected from the most severecombination of critical meteorologic and hydrologic con-ditions that are reasonably possible), or fractions thereof.Because of the magnitude and rarity of such a storm event, afinding that a spillway will not pass the design floodshould not be interpreted as necessarily posing a highlyinadequate condition. The design flood provides a measureof relative spillway capacity and serves as an aid in deter-mining the need for more detailed hydrologic and hydraulicstudies, considering the size of the dam, its general con-dition, and the downstream damage potential.

UI I I I I III'' ' - + " :


CONTENTS

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

Brief Assessment of Dam ....... ............... 1Overall View of Dam ................... 7Section 1: Project Information ..... ........... 9Section 2: Engineering Data .... ............. . 13Section 3: Visual Inspection ... ............ . 15Section 4: Operational Procedures ... .......... . 19Section 5: Hydraulic/Hydrologic Data .. ........ . 21Section 6: Dam Stability .... .............. 23Section 7: Assessment/Remedial Measures ........ . 27

Appendices

I. PlatesII. PhotographsIII. Visual Inspection Check ListIV. General References

Accession For

Z-TIS GR.&II IDTIC TAB

U.-tannounced ElJustfication .

rN .Distri buti on/Availability Codes

lAvail and/or

Dl!t I Special

NAME OF DAM:' BEATTIES MILLPOND DAM

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17


Name of Dam: Beatties Millpond DamState: Commonwealth of Virginia

-* County: HanoverUSGS 7.5 Minute Quadrangles: Seven Pines, VA and Quinton, VAStream: Sandy Valley CreekDate of Inspection: 15 January 1981

BRIEF ASSESSMENT OF DAM

Beatties Millpond Dam is an earthfill embankment approximately413.9 feet highand 365 feet long with a 32 foot wide broad-

crested concrete weir spillway located at the left abut-ment.' The dam, located about 2.3 miles northeast of OldCold Harbor, Virginia, is used for recreation.- The dam isowned by Mrs. John Beattie, RT 4 Box 404, Mechanicsville,Virginia 23111.'-4Beatties Millpond Dam is a 'small4"size -

, ,2"significant" hazard structure as defined by the RecommendedGuidelines for Safety Inspection of Dams. The dam andappurtenant structures were in good overall condition at thetime of inspection. Maintenance of the dam is considered tobe inadequate. A stability check of the dam is not required.

Using the Corps of Engineers' screening criteria for initialreview of spillway adequacy, the 100-year flood was selectedas the spillway design flood (SDF). The spillway is capableof passing up to 40 percent of the SDF or 8 percent of thePMF without overtopping the dam. A dam failure from overtop-

*ping would not significantly increase the hazard to loss oflife downstream from the dam over that which would existjust before overtopping failure. However, overtopping flowsfrom the SDF are considered detrimental to the earth embank-ment. Therefore, the spillway is adjudged as inadequate butnot seriously inadequate.e

The visual inspection and office analyses indicate deficien-cies requiring remedial treatment.

'Measured from the streambed at the downstream toe to theembankment crest.

'Facing downstream.

NAME OF DAM: BEATTIES MILLPOND DAM

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A formal warning system and emergency action plan should bedeveloped and put into effect as soon as possible.

Regular inspections should be made of the dam and appurtenantstructures. A thorough check list should be compiled foruse by the owner's representative as a guide for the inspec-tions. Maintenance items should be completed annually.

If seeps develop and flows increase or if turbidity isnoted, a qualified geotechnical engineering firm should beretained to perform a stability check on the dam.

The following measures should be undertaken as part of aregularly scheduled inspection and maintenance program:

1) Cut off all trees and brush growing on the embank-ment at ground level. All trees with a trunkdiameter greater than 3 inches should have theirroot systems removed. The resultant holes shouldbe backfilled, compacted, and seeded.

-1 2) Establish a good grass cover over the entireembankment.

3) Place riprap on the upstream embankment to minimizeerosion due to wave action.

4) Repair the eroded and undercut areas beneath thedownstream ends of the training and wing walls ofthe principal spillway. The eroded and slumpedareas should be backfilled, compacted and seeded.

5) After repairs are made to the principal spillway,examine the area at regular intervals for renewedsigns of seepage.

6) Rebuild the concrete step in the principal spillway.

7) Place riprap at the pool of the spillway to preventscouring of the pool and erosion of the areasbeneath the concrete step and the wing and trainingwalls.

8) Divert the flow from the natural spring in thehillside downstream from the right abutment awayfrom the toe of the dam.

9) Remove the tree obstructing the approach area ofthe principal spillway.


j3 IinAIR PAM U.*IKAMW UU

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10) Remove the trees obstructing the lower end of thedischarge channel.

1) Install a staff gage to monitor reservoir levelsabove normal pool.

Original signed oy

" MICHAEL BAKER, JR., INC. SUBMITTED: JAM A. WALSHJames A. Walsh, P.E.Chief, Design Branch

Original signed by

Michael Baker, I, P.E. RECOMMENDED: JACK G. STARR

Chairman of the Board and Jack G. Starr, P.E.Chief Executive Officer Chief, Engineering

Original signed by:APPROVED: Douglas L. Haller

Douglas L. HallerColonel, Corps of EngineersDistrict Engineer

!~MICHAEL

BAKER III APR 2.1 L8NO.37 Date:

N O DAM. : M -AM


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NAME OF DAM: BEATTIES MILLPOND DAM ID# VA 08535

SECTION 1 - PROJECT INFORMATION

1.1 General

1.1.1 Authority: Public Law 92-367, 8 August 1972,authorized the Secretary of the Army, throughthe Corps of Engineers, to initiate a nationalprogram of safety inspections of dams through-out the United States. The Norfolk Districthas been assigned the responsibility ofsupervising the inspection of dams in theCommonwealth of Virginia.

1.1.2 Purpose of Inspection: The purpose is toconduct a Phase I inspection according to theRecommended Guidelines for Safety Inspectionof Dams (Reference 12, Appendix IV). Themain responsibility is to expeditiouslyidentify those dams which may be a potentialhazard to human life or property.

1.2 Description of Project

1.2.1 Description of Dam and Appurtenances: BeattiesMillpond Dam is an earthfill embankmentapproximately 13.9 feet high' and 365 feetlong. The crest of the dam is about 16 feetwide and the minimum elevation is at 1002.7feet Temporary Bench Mark (T.B.M.). 2 Theupstream embankment slope is approximately3.2H:lV (Horizontal to Vertical) and theslope of the downstream embankment ranges

Afrom 3.2H:lV to 4.5H:1V. There is no informa-tion available on any possible zoning of theembankment. No evidence of an internaldrainage system or slope protection for thedam was found.

'Measured from the streambed at the downstream toe of the damto the embankment crest.

2All elevations are referenced to a Temporary Bench Marklocated on the left side of the spillway crest. Theassumed elevation is 1000.0 feet.


9 M0119I PAMI 5.tagmail pIUM

The principal spillway is a cast-in-place,broad-crested concrete weir located at theleft abutment. 3 This spillway is 32 feetlong (measured perpendicular to the flow) andhas a minimum crest elevation of 999.8 feetT.B.M. Five equally spaced concrete piersare located across the upstream end of thespillway. The concrete weir is 18 incheswide (measured in the direction of flow).After passing over the weir, water flows downan 11.5 foot long concrete apron which has adownstream slope of 17 percent. The waterthen drops three feet to a concrete step thatruns the length of the spillway and is between2 and 4 feet wide. From this step, the waterdrops about 8 feet to a pool at the base ofthe dam.

On the right abutment, an old channel wasobserved which at one time reportedly containedthe raceway for the original mill at the dam.This channel has been filled from the upstreamcrest to the downstream toe of the dam.

The reservoir has a 3.93 square mile drainagearea south and west of the dam. Sandy ValleyCreek drains the watershed from the west anda small unnamed tributary drains from thesouth. The watershed area is moderatelysloping and is about 65 percent forested.The remaining 35 percent is primarily farmland.

There are no facilities for draining thereservoir.

1.2.2 Location: Beatties Millpond Dam is locatedin Hanover County, Virginia, approximately

2.3 miles northeast of Old Cold Harbor onSandy Valley Creek, a tributary to the Matade-quin Creek. A Location Plan is included withthis report in Appendix I.

1.2.3 Size Classification: Beatties Millpond Dam is13.9 feet high and the reservoir storage atthe crest of the dam (elevation 1002.7 feet)is 107 acre-feet. Therefore, the dam is in

'Facing downstream.


10

the "small" size category as defined by the

Recommended Guidelines for Safety Inspectionof Dams.

1.2.4 Hazard Classification: A feed mill, which isoperated on a part-time basis, is locatedabout 150 feet downstream of the dam belowthe right side of the embankment. VirginiaRoute 634 is located about 300 feet down-stream of the dam. The road embankment isabout one foot higher than the crest of thespillway. The access road to the feed millis located about halfway between the dam andVA Route 634. Loss of human life in theevent of dam failure is not considered highlyprobable. However, economic losses due todamage to the feed mill, the access road, andVA Route 634 are considered likely in theevent of dam failure. Beatties Millpond Damis therefore considered in the "significant"hazard category as defined by the RecommendedGuidelines for Safety Inspection of Dams.The hazard classification used to categorizedams is a function of location only and isnot reLated to stability or probability offailure.

1.2.5 Ownership: The dam is owned by Mrs. John(Frances) Beattie, RT 4 Box 404, Mechanicsville,Virginia 23111.

1.2.6 Purpose: The dam is used for recreationalpurposes.

1.2.7 Design and Construction History: The ownerindicated that a number of dams have existedat this site for 200 years. The present damis believed to have been built around 1921.According to the owner, the dam was breachedand partially rebuilt in 1959. No otherinformation on design and construction historywas available for use in this report.

1.2.8 Normal Operating Procedures: The reservoirlevel is maintained automatically by thecrest of the principal spillway (elevation999.8 feet T.B.M.). No formal operatingprocedures are followed for this structure.


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1.3 Pertinent Data

1.3.1 Drainage Area: The drainage area tributaryto the dam is 3.93 square miles.

1.3.2 Discharge at Dam Site: The maximum dischargefrom the reservoir is unknown. However, thedam is reported to have been overtopped in1939, 1959'and 1971. With the pool level atthe top of dam, the spillway is capable ofpassing 480 c.f.s.

1.3.3 Dam and Reservoir Data: Pertinent data onthe dam and reservoir are provided in thefollowing table:

TABLE 1.1 DAM AND RESERVOIR DATA

ReservoirCapacity

Elevation Area Acre- Watershed LengthItem (feet T.B.M.) (acres) feet (inches) (feet)

Top of dam 1002.7 32.6 107 0.5 5800Spillway crest 999.8 11.9 45 0.2 3700Streambed at

toe 988.8 - - -


12

SECTION 2 - ENGINEERING DATA

2.1 Design: Design plans, specifications, and boring logswere not available for use in preparing-this report.No stability analyses or hydrologic and hydraulic datawere available for review.

2.2 Construction: Construction records, as-built plans,and inspection logs were not available for review.

2.3 Evaluation: No design or construction records wereavailable for use in assessing the condition of thedam. All evaluations and assessments in this reportwere based upon field observations, conversations withthe owner and her representatives, and office analyses.


13

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SECTION 3 - VISUAL INSPECTION

3.1 Findings

3.1.1 General: The field inspection was conductedon 15 January 1981. At the time of inspec-tion, the pool elevation was at 1000.1 feetT.B.M., and the tailwater elevation was 989.3feet T.B.M. The weather was cloudy withoccasional snow flurries and a temperaturearound 30 degrees Fahrenheit. The groundsurface of the embankment and abutments wasgenerally frozen and a light dusting of snowwas present. The dam and appurtenant structureswere found to be in fair overall condition atthe time of inspection. Deficiencies foundduring the inspection will require remedialtreatment. The following are brief summariesof these deficiencies. A Field Sketch ofconditions observed during the inspection ispresented as Plate I in Appendix I. Thecomplete visual inspection check list isincluded as Appendix III. No record of anyprevious inspections was found.

3.1.2 Dam: The embankment was found to be in fairoverall condition. The upstream embankmenthas been moderately eroded due to wave action.There was no riprap observed on the upstreamembankment and the vegetative cover in thatarea consisted of weeds and small brush(Photo 2). A large part of the downstreamembankment was vegetated with a dense growthof small trees and brush (Photo 1). A smallslough was observed near the right center ofthe dam, but it is apparently stabilized byvegetation. A concrete wall and an oldchannel were rwserved at the right abutment(Photo 6). T1-s channel is backfilled down-stream from the crest of the dam. It appearsto have been the old raceway for the mill.

Above the junction of the embankment and theright abutment, the wooded hillside has beenslightly eroded in a few areas.

Seepage from a natural spring in the hillsidedownstream from the right abutment flowsalong the toe of the dam from right to left.


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No evidence of an internal drainage systemwas found during the inspection.

3.1.3 Appurtenant Structures: The principal spill-way (as described in Section 1.2.1) is acast-in-place, broad-crested concrete weir.The spillway is 32 feet wide with 3.5 foothigh concrete training walls. There was somesediment observed in the approach area to thespillway. A tree trunk partially obstructsthe right side of the spillway approach area.Five concrete piers are equally spaced acrossthe spillway near the crest. There is somespalling at the base of all the piers. Theconcrete is completely deteriorated at thebase of two of the piers. These two piershave fallen over and are being held in placeby steel rebars. There was some minor spall-ing and small cracks observed on the concretespillway. Water goes over the 18 inch longbroad-crested weir and flows down an 11.5foot long concrete apron which has a down-stream slope of 17 percent. The water thendrops 3 feet to a badly deteriorated concretestep that extends across the length of thespillway and is between 2 and 4 feet long.The area beneath the concrete step and thedownstream ends of the training walls andwing walls has been undercut and eroded(Photo 4). Steadily flowing seeps are comingfrom behind both walls. Seepage from theright side has apparently created a 3 foot

* deep slump hole behind the right trainingwall (Photo 5). After flowing over theconcrete step, the water takes a near vertical

41 drop of about 8 feet over a hard clay surfaceto a scoured pool at the base of the dam.From the pool, water flows into a 20 footwide discharge channel. The left bank of thechannel is an eroded and very steep 70 foothigh hillside. Trees have fallen off thisbank and are partially obstructing the lowerend of the discharge channel.

No emergency spillway or facilities fordraining the reservoir were observed duringthe inspection.

3.1.4 Reservoir Area: The slopes that surround thereservoir are moderately sloping and wooded.


16

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II

A few residences and cabins are located alongthe banks of the reservoir about 15 to 20feet above the normal pool elevation. Noindication of any significant erosion wasnoted. The extent of sedimentation was notdirectly observed, but it does not appear tobe significant. Soundings taken at the timeof inspection show the depth to be 11.4 feetat a spot approximately 50 feet offshore fromthe approximate center of the embankment.

3.1.5 Downstream Channel: The downstream channelbeyond the immediate discharge area is anatural channel with a generally flat gradientand moderately sloping sides. The channelflows through four 42 inch diameter corrugatedmetal culverts at the access road to the millabout 150 feet below the dam, and three 5foot diameter corrugated metal culverts underVA Route 634 about 300 feet below the dam.Below VA Route 634 the banks of the downstreamchannel contain thick brush and trees.

3.1.6 Instrumentation: There was no instrumentationat the dam site at the time of inspection.

3.2 Evaluation: In general, the dam and appurtenant struc-tures were in good condition. All trees on the down-stream embankment should be cut off at ground level.All trees with a trunk diameter greater than 3 inchesshould have their root systems removed. The resultantholes should be backfilled, compacted and seeded. Agood grass cover should be established over the entireembankment. Riprap should be placed on the upstreamembankment to minimize erosion from wave action. Thesmall slough near the center of the dam is apparentlystabilized by vegetation and is not considered serious.

Repairs should be made at the undercut and eroded areasbeneath the downstream ends of the training and wingwalls. The eroded and slumped areas behind the wallsshould be backfilled, compacted, and seeded. Theconcrete step in the principal spillway should berebuilt. Riprap should be placed at the base of thespillway to prevent scouring of the pool and under-cutting and erosion of areas beneath the spillway andspillway walls. After making these repairs, the areashould be monitored for renewed signs of seepage.


j17

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Seepage from a natural spring in the hillside downstreamfrom the.right abutment should be diverted away fromthe toe of the dam.

The tree partially obstructing the approach area to theprincipal spillway and the trees obstructing the lowerend of the discharge channel should be removed.

A staff gage should be installed to monitor reservoirlevels above normal pool.

NAME OF DAM: BEATTIES MILLPOND DAM18o

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SECTION 4 - OPERATIONAL PROCEDURES

4.1 Procedures: The operation of the dam is an automaticfunction controlled by the crest of the spillway atelevation 999.8 feet T.B.M.

4.2 Maintenance of Dam: Maintenance of the dam is theresponsibility of the owner. An inspection and mainte-nance schedule has not been instituted.

4.3 Maintenance of Operating Facilities: There are nooperating facilities on the dam.

4.4 Warning System: At the time of inspection, there wasno warning system or emergency action plan in operation.

4.5 Evaluation: Maintenance of the dam in the past hasbeen inadequate. Regular inspections of the dam andappurtenant structures should be made and documented.A thorough check list should be compiled for use by theowner's representative as a guide for the inspections.Maintenance items should be corrected annually. Inaddition, a formal warning system and emergency actionplan should be developed and put into operation as soonas possible.

All


- 19

- 4.

SECTION 5 - HYDRAULIC/HYDROLOGIC DATA

5.1 Design: No design data were available for use inpreparing this report.

5.2 Hydrologic Information: No rainfall, stream gage orreservoir stage records are maintained for this dam.

5.3 Flood Experience: According to the owner, the dam wasovertopped by flooding in 1929, 1959 and 1971.

5.4 Flood Potential: The Probable Maximum Flood (PMF),1/2 Probable Maximum Flood (1/2 PMF), and 100-yearflood were developed and routed through the reservoirby use of the HEC-l DB computer program (Reference 9,Appendix IV) and appropriate unit hydrograph, precipi-tation and storage-outflow data. Clark's Tc and R co-efficients for the local drainage areas were estimatedfrom basin characteristics. The rainfall applied tothe unit hydrograph was taken from publications by theU.S. Weather Bureau and the National Oceanic and Atmos-pheric Administration (References 16 and 17, Appen-dix IV). Rainfall losses for the PMF and 1/2 PMF wereestimated at an initial loss of 1.0 inch and a constantloss rate of 0.05 inch per hour thereafter. Rainfalllosses for the 100-year flood were estimated at aninitial loss of 1.5 inches and a constant loss rate of0.15 inch per hour thereafter.

5.5 Reservoir Regulation: Pertinent dam and reservoir dataare provided in Table 1.1, Paragraph 1.3.3. Regulationof flow from the reservoir is automatic. Normal flowsare maintained by the crest of the spillway, which isat elevation 999.8 feet T.B.M.

The outlet discharge capacity was computed by hand,reservoir area was planimetered from the Seven PinesVirginia and Quinton, Virginia, 7.5 minute USGS quad-rangles, and storage capacity curves were computed toelevations above the crest of the dam. All floodroutings were begun with the reservoir at normal pool.

5.6 Overtopping Potential: The probable rise of the reser-voir and other pertinent information on reservoirperformance are shown in the following table:


21

I I____________ _ PAM I0 I.KI I UM

TABLE 5.1 RESERVOIR PERFORMANCE

Hydrographs100-Year 1/2

Item Normal' flood PMF PMF2

Peak flow, c.f.s.Inflow 6.9 2,754 7,685 15,369Outflow 6.9 2,731 7,642 15,287

* Peak elev., ft. T.B.M. 1000.1 1004.9 1006.7 1008.6Non-overflow section'(elev. 1002.7 ft. T.B.M.)Depth of flow, ft. 2.2 4.0 5.9Average velocity, f.p.s. - 6.9 9.3 11.3Total duration of over-topping, hrs. - 6.8 20.8 28.0

Tailwater elev., ft. T.B.M. 989.3 - - -

'Conditions at time of inspection.2The PMF is an estimate of flood discharges that m-y beexpected from the most severe combination of criticalmeterologic and hydrologic conditions that are reasonablypossible in a region.3Velocity estimates were based on critical depth at controlsection.

5.7 Reservoir Emptying Potential: There are no facilitiesfor draining the reservoir.

5.8 Evaluation: Beatties Millpond Dam is a "small" size -"significant" hazard dam requiring evaluation for aspillway design flood (SDF) in the range between the100-year flood and the 1/2 PMF. Due to the risk in-volved, the 100-year flood was selected as the SDF.The SDF was routed through the reservoir and found toovertop the dam by a maximum depth of 2.2 feet and anaverage critical velocity of 6.9 feet per second(f.p.s.). Total duration of dam overtopping would be6.8 hours. The spillway is capable of passing up to8 percent of the Probable Maximum Flood (PMF) or 40 per-cent of the SDF without overtopping the crest of thedam.

Conclusions pertain to present day conditions and theeffect of future development on the hydrology has notbeen considered.


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7

SECTION 6 - DAM STABILITY

6.1 Foundation and Abutments: The dam is located in theAtlantic Coastal Plain geologic region in an areaunderlain by the St. Mary's formation of Tertiary age.The St. Mary's formation generally consists of uncon-solidated sands and clays. Soils exposed downstream ofthe left abutment were observed to consist of yellow,gray, and brown sandy clay or clayey sand of lowplasticity. Similar soils were observed in the dis-charge channel below the spillway of the dam. Noprevious information describing local subsurface con-ditions was available for the visual inspection orsubsequent analyses. It is not known how the dam waskeyed into the foundation and abutments.

6.2 Embankment

6.2.1 Materials: Information describing the natureof the embankment materials within the damwas not available for this inspection.According to the owner, who had breached thedam in 1959, the embankment materials arehomogeneous. During the visual inspection,theouter embankment materials were observedto consist of brown sandy clay of lowplasticity.

6.2.2 Stability: Design plans or the results of aprevious stability analysis were not availablefor use during this evaluation. Based on theowner's observations of the dam structure,the embankment is assumed to be a homogeneoustype. The dam is 13.9 feet high with a crestwidth of about 14 to 18 feet. The upstreamembankment was observed to slope at 3.2H:lV,while the downstream embankment was observedto slope from 3.2H:lV to 4.SH:lV. No facili-ties exist for draining the reservoir in theevent of an emergency, and the embankment isnot subject to rapid drawdown.

According to guidelines outlined in Design ofSmall Dams by the U.S. Department of Interior,Bureau of Reclamation, the upstream slope ofa small homogeneous dam constructed of slightlyplastic fine grained soils (CL,ML) with a


23

stable foundation should be 3.OH:IV, if-notjsubject to rapid drawdown. The corresponding

downstream slope should be 2.5H:lV. A crestwidth of 12.8 feet is recommended, consideringthe height of the dam. Based on these guide-lines, both the slopes and the crest widthare considered adequate.

No major signs of instability were observedduring the visual inspection. However,seepage was observed flowing from the abutmentand embankment behind the training walls andwing walls of the spillway. This seepage hascaused erosion of the embankment behind theright training wall with consequent settlementof the crest in a small area directly adjacentto the wall. In addition, the downstreamends of both training walls are exposed andundermined, due to the seepage. Elsewhere onthe embankment, minor erosion was observed onthe upstream face slightly above pool eleva-tion at the time of inspection. Other thanat the spillway, no seepage was noted at anypoint on or below the embankment. Brush andsmall trees were observed growing on parts ofthe embankment slopes.

6.2.3 Seismic Stability: The dam is located inSeismic Zone 1, which presents no hazard fromearthquakes, according to the Recommended

* Guidelines for Safety Inspection of Dams by* the Department of the Army, Office of the

Chief of Engineers. This determination iscontingent on the requirements that staticstability conditions are satisfactory andconventional safety margins exist.

6.3 Evaluation: The results of a previous stability analysiswere not available for review as part of this evaluation.Both the upstream and downstream slopes are adequatewhen compared to the Bureau of Reclamation guidelines.The crest width is about one to five feet wider thanrecommended. The embankment appears to be in fairoverall condition. The dam requires no further checkof stability at this time. However, the problemsdiscussed above, including the seepage at the spillwayand vegetation on the embankment, require furtherattention in order to prevent serious problems in thefuture. Remedial measures are discussed in Section 7.


24

As described in Section 5 of this report, the dam wouldbe overtopped by the SDF. The maximum depth of flowover the crest would be 2.2 feet with an average criticalvelocity of 6.9 f.p.s. The total duration of overtoppingwould be 6.8 hours. Because the critical velocity

-, would exceed the effective eroding velocity for avegetated earth embankment of 6.0 feet per second, andthe duration and depth of overtopping would be substan-tial, the potential overtopping flows are considered tobe detrimental to the stability of the embankment.


1 __ ____ ___ ____ ____ ___25

SECTION 7 - ASSESSMENT/REMEDIAL MEASURES.4

7.1 Dam Assessment: There was no engineering data availablefor use in preparing this report. Deficiencies dis-covered during the field inspection and the officeanalyses require remedial treatment. The dam andappurtenant structures are generally in fair condition.Maintenance is considered inadequate. A stabilitycheck of the dam is not required.

Using the Corps of Engineers' screening criteria forinitial review of spillway adequacy, the 100-year floodwas selected as the SDF for the "small" size - "signifi-cant" hazard classification of Beatties Millpond Dam.The spillway is capable of passing up to 8 percent ofthe PMF or 40 percent of the SDF without overtoppingthe non-overflow section of the dam. A dam failurefrom overtopping would not significantly increase thehazard to loss of life downstream from the dam overthat which would exist just before overtopping failure.However, overtopping flows from the SDF are considereddetrimental to the earth embankment. Therefore, thespillway is adjudged as inadequate but not seriouslyinadequate.

There is no flood warning system or emergency actionplan currently in operation.

7.2 Recommended Remedial Measures: A formal warning systemand emergency action plan should be developed and putinto effect as soon as possible. Regular inspectionsshould be made of the dam and appurtenant structures.A thorough check list should be compiled for use by theowner's representative as a guide for the inspections.Maintenance items should be completed annually. Ifseeps develop and flows increase or turbidity is noted,a qualified geotechnical engineering firm should beretained to perform a stability check on the dam.

The following measures should be undertaken as part ofa regularly scheduled inspection and maintenance program:

1) Cut off all trees and brush growing on theembankment at ground level. All trees with atdnk diameter greater than 3 inches shouldhave their root systems removed. The resul-tant holes should be backfilled, compactedand seeded.


27 "I'iGI PAM MLONOf 7MUJ

2) Establish a good grass cover over the entireembankment.

3) Place riprap on the upstream embankment tominimize erosion due to wave action.

4) Repair the eroded and undercut areas beneaththe downstream ends of the training and wingwalls of the principal spillway. The erodedand slumped areas should be backfilled,compacted and seeded.

5) After repairs are made to the principalspillway, examine the area at regular intervalsfor renewed signs of seepage.

6) Rebuild the concrete step in the principalspillway.

7) Place riprap at the pool of the spillway toprevent scouring of the pool and erosion ofthe areas beneath the concrete step and thewing and training walls.

8) Divert the flow from the natural spring inthe hillside downstream from the right abut-ment away from the toe of the dam.

9) Remove the tree obstructing the approach areaof the principal spillway.

10) Remove the trees obstructing the lower end ofthe discharge channel.

11) Install a staff gage to monitor reservoirlevels above normal pool.


28

n n'nN I p m !nm ! w nl , i n . ~ F ul

APPENDIXI

PLATES

I

N

S *4

CONTENTS

Location Plan

Plate 1: Field Sketch

Plate 2: Top of Dam Profile

Plate 3: Cross Sections of Dam

NM O

J7

-4

NAEO-A: BATISMLPN A

MILLPOND MILLPOND DAM

-N4

19 0

2.~~~~~ IN...75OINO,

QUADRANGLSCAL 1:26700ISD 97

o .

It~ CL zLJow -q wgcc

0 -JLL (4) WZ

W~ Sj

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LU)

8ii

00

MICHAE CAER JR( Nw.o 15 JAUR W9

NO~~~ SCLEPAT

MICHAEL BAKER, JR., INC. Subject A________________ S.O. No.______

THE BAKER ENGINEERS PectlIaes Mau.o~ '. Shoot No.- o........f

Box280 Top of D-~ Pr'rAle- Drawing No. _____

BaeP.IMComputed by HK Checkedi by Date

TOP OF 0#9M 'PROFILE LOoI"&~v DOWNSrJTREAM1

'a 'PILWAYMINIMUM TOP Of- 0"~

E LeATWO 14001 FT T

0400 1+00 2400 3.00 44100

owv- --...

'44

I.L

MICHAEL BAKER, JRF., INC. Subject -V'tR-f-IAA D 4M's S.O. No._______THE BAKER ENGINEERS 8 eaties MiLL PCAo Obm Shoot No.-....of.......

Box 80 -e C'vs.%. s-ef-tevAs Drawing No._____

*Beaver, Pa. 1IS0 Computed by Chocked by Date

DAMv C A OS -5 ECrIOA A T STA.I/+60

CREST WI07re is8 FEET

.0 40 (0 otoo ~(r0 . 0)0DISTANCE (r

DA~M CR~O55-SECTIONP AT STA. -2+2-0

CREST WIDTH z If FE I *

I.-3, H' VILP

UJ-I

o 2-0 40 4,0 so too 12.0DISTAiNCE (F:pA~-~

.4

I

I

APPENDIX II

PHOTOGRAPHS

4-

AI

'A

CONTENTS

Photo 1: Downstream Embankment of Dam

Photo 2: Upstream Embankment of Dam

",Photo 3: View of Principal Spillway from VA Route 634

Photo 4: Left Side of Downstream Principal Spillway ShowingUndercutting of Training Wall

Photo 5: Hole Behind Right Training Wall

Photo 6: Right Abutment Area Showing Location of FormerRaceway for Mill

Note: Photographs were taken on 15 January 1981.

-i

-t


BEATTIES MILLPOND DAM

PHOTO 1. Downstream Embankmnt of Dam

PHO0TO 2. Upstream Embankment of Dam


~j~ti

PHOTO 3. View of Principal Spiliway from VA Route 634

.t

PHOTO 4. Left Side of Downstream Principal Spillway ShowingUndercutting of Training Wall


PHOTO 5. Hole Behind Right Training Wall

PHOTO&6 Right Abutment Area Showoing Locato of Former

Rcway for Witl

APPENDIX III

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APPENDIX IV

GENERAL REFERENCES

GENERAL REFERENCES

1. Bureau of Reclamation, U.S. Department of the Interior,Design of Small Dams, A Water Resources TechnicalPublication, Revised Reprint, 1977.

2. Chow, Ven Te, Handbook of Applied Hydrology, McGraw -Hill Book Company, New York, 1964.

3. Chow, Ven Te, Open Channel Hydraulics, McGraw - HillBook Company, New York, First Edition, 1959.

4. Commonwealth of Virginia, "Geologic Map of Virginia,"

Department of Conservation and Economic Development,and Division of Mineral Resources, 1963.

5. HR 33, "Seasonal Variations of Probable Maximum Precipita-tion, East of the 105th Meridian for Areas 10 to 1000Square Miles and Durations of 6 to 48 Hours," (1956).

6. King, Horace Williams and Brater, Ernest F., Handbookof Hydraulics, Fifth Edition, McGraw - Hill Book Company,New York, 1963.

7. Soil Conservation Service, "National Engineering Handbook -Section 4, Hydrology," U.S. Department of Agriculture,1964.

. 8. Soil Conservation Service, "National Engineering Handbook -Section 5, Hydraulics," U.S. Department of Agriculture.

9. U.S. Army, Hydrologic Engineering Center, "Flood HydrographPackage (HEC-1), Dam Safety Investigations, UsersManual," Corps of Engineers, Davis, California, September1978.

10. U.S. Army, Hydrologic Engineering Center, "HEC-2 WaterSurface Profiles, Users Manual," Corps of Engineers,Davis, California, October 1973.

11. U.S. Army, "Inventory of United States Dams," Corps ofEngineers, 9 September 1978.

12. U.S. Army, Office of the Chief of Engineers, "Appendix D,Recommended Guidelines for Safety Inspection of Dams,"National Program of Inspection of Dams, Volume 1, Corpsof Engineers, Washington, D.C., May 1975.


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13. U.S. Army, Office of the Chief of Engineers, EngineeringCircular EC-1110-2-163 (Draft Engineering Manual),"Spillway and Freeboard Requirements for Dams, Appendix C,Hydrometeorological Criteria and Hyetograph Estimates,"(August 1975).

i4. U.S. Army, Office of the Chief of Engineers, EngineeringCircular EC-1110-2-188, "Engineering and Design, NationalProgram of Inspection of Non-Federal Dams," Corps ofEngineers, Washington, D.C., 30 December 1977.

15. U.S. Army, Office of the Chief of Engineers, EngineerTechnical Letter No. ETL 1110-2-234, "Engineering andDesign, National Program of Inspection of Non-FederalDams, Review of Spillway Adequacy," Corps of Engineers,Washington, D.C., 10 May 1978.

16. U.S. Department of Commerce, "Technical Paper No. 40,Rainfall Frequency Atlas of the United States for Dura-tions from 30 Minutes to 24 Hours and Return Periodsfrom 1 to 100 Years," Weather Bureau, Washington, D.C.,May 1961.

17. U.S. Department of Commerce, National Oceanic andAtmospheric Administration, "Hydrometeorological ReportNo. 51, Probable Maximum Precipitation Estimates,United States East of the 105th Meridian," Washington,D.C., June 1978.

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