NATIONAL DAN SAFETY PROGRAM. BIRDVOOD DAM … · NATIONAL DAN SAFETY PROGRAM. BIRDVOOD DAM...

NATIONAL DAN SAFETY PROGRAM. BIRDVOOD DAM CVA-0034'A). .JAMES R!V-ETC(U)MAR 80 M BAKER 0ACW65-78-O-0016

WICLASSIFIED NL

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,, spdmme-nt has been a,3proved_hl". d sale; 1',sase anis unlimited.

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SECURITY CLASSIFICATION OF THIS PAGE (When Date Entered) 5

REPORT DOCUMENTATION PAGE READ INSTRUCTIONSBEFORE COMPLETING FORM

I. REPORT NUMBER T ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER

VA 00344 _* 4. TITLE (end Subtitle) Phase I Inspection Report S. TYPE OF REPORT & PERIOD COVERED

National Dam Safety Program Final. BIRDWOOD DAM -ABE AM OUNT A6. PERFORMING ORG. REPORT NUMBER

ALBERMARLE COUNTY, VA

i 7.M9c fl)~Baker, Jr. S. CONTRACT OR GRANT NUMBER(&)

Michael Baker, Jr., Inc.4301 Dutch Ridge Road, Box 280 -D

Beaver, Pennsylvania 15009 DACW6578D00169. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASK

AREA & WORK UNIT NUMBERS

II. CONTROLLING OFFICE NAME AND ADDRESS '2. REPORT DATE

U.S. Army Engineering District, Norfolk March 1980803 Front Street 13. NUMBER OF PAGES

Norfolk, VA 2351014. MONITORING AGENCY NAME & ADDRESS(I different from Controlling Office) 1S. SECURITY CLASS. (of thie report)

UnclassifiedISa. DECLASSI FICATION/DOWNGRADING

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Approved for public release; distribution unlimited.

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IS. SUPPLEMENTARY NOTES

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

IS. KEY WORDS (Continue on revers* side if necesaury end identify by block number)

Dams - VANational Dam Safety Program Phase IDam SafetyDam Inspection

20. ABSTRACT (Continue on reverse aide It necessary and identify by block number)

(See reverse side)

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20. Abstract

Pursuant to Public L4 92-367, Phase I Inspection Reports are preparedunder guidance containd in the recommended guidelines for safetyinspection of dams, pub4 hed by the Office of Chief of Engineers,Washington, D. C. 23014.- 6 The purpose of a Phase I investigation isto identify expeditiously those dams which may pose hazards to humanlife or property. The assessment of the general conditions of the damis based upon available data and visual inspections. Detailedinvestigations and analyses involving topographic mapping, subsurfaceinvestigations, testing, and detailed computational evaluations arebeyond the scope of a Phase I investigation; however, theinvestigation is intended to identify any need for such studies.

3Based upon the field conditions at the time of the field inspectionand all available engineering data, the Phase I report addresses thehydraulic, hydrologic, geologic, geotechnic, and structural aspects ofthe dam. The engineering techniques employed give a reasonablyaccurate assessment of the conditions of the dam. It should berealized that certain engineering aspects cannot be fully analyzedduring a Phase I inspection. Assessment and remedial measures in thereport include the requireme ts of additional indepth study whennecessary. . -

2'Phase I reports include project information of the dam andappurtenances, all existing engineering data, operational procedures,hydraulic/hydrologic data of the watershed, dam stability, visualinspection report and an assessment including required remedialmeasures.

SECURITY CLASSIFICATION OF THIS PAGE(Whon Date Entered)

PREFACE

This report is prepared under guidance contained in theRecommended Guidelines for Safety Inspection of Dams, forPhase I Investigations. Copies of these guide-ines may beobtained from the office of the Chief of Engineers, Washington,

D.C. 20314. The purpose of a Phase I investigation is toidentify expeditiously those dams which may pose hazards tohuman life or property. The assessment of the generalcondition of the dam is based upon available data and visualinspections. Detailed investigation and analyses involvingtopographic mapping, subsurface investigations testing, anddetailed computational evaluations are beyond the scope of aPhase I investigation; however, the investigation is intendedto identify any need for such studies.

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 andinspection 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 conditionsthat are reasonably possible), or fractions thereof. Becauseof the magnitude and rarity of such a storm event, a findingthat a spillway will not pass the design flood should not beinterpreted as necessarily posing a highly inadequate condi-I. tion. The design flood provides a measure of relativespillway capacity and serves as an aid in determiningthe need for more detailed hydrologic and hydraulic studies,considering the size of the dam, its general condition, T .and the downstream damage potential. : .,

hsbeen a)T"$d2 1981 -Ifor puhiicrey.r and sa!-; j-distribution is unlimited.j

PHASE I INSPECTION REPORTNATIONAL DAM SAFETY PROGRAM

CONTENTS

Page

Preface ...... ........................ iBrief Assessment of Dam ....... ............... 1Overall View of Dam ........ ................. 5Section 1: Project Information ..... ........... 7Section 2: Engineering Data .... ............. ... 11Section 3: Visual Inspection .... ............ .. 13Section 4: Operational Procedures ... .......... . 15Section 5: Hydraulic/Hydrologic Data .. ........ .17Section 6: Dam Stability ..... .............. .. 19Section 7: Assessment/Remedial Measures ........ ... 21

Appendices

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

NAME OF DAM: BIRDWOOD DAMii

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Name of Dam: Birdwood DamState: VirginiaCounty: AlbemarleUSGS 7.5 Minute Quadrangle: Charlottesville West, VAStream: Morey CreekDate of Inspection: 13 November 1979

BRIEF ASSESSMENT OF DAM

Birdwood Dam is an earthfill dam approximately 270 feet longand 26 feet high, with a 70 foot wide, irregularly shaped,earthen emergency spillway. The dam is owned by the Universityof Virginia. The dam, located approximately 1.1 miles westof Charlottesville, Virginia, is used for agricultural watersupply. Birdwood Dam is a "small" size - "high" hazardstructure as defined by the Recommended Guidelines forSafety Inspection of Dams. Visual inspection and ofTfceanalyses indicate defclncies requiring immediate attention.

Using the Corps of Engineers' screening criteria for initialreview of spillway adequacy, the 1/2 Probable Maximum Flood(1/2 PMF) was selected as the spillway design flood (SDF).The SDF was routed through the reservoir and found to overtopthe dam by a maximum depth of 1.6 feet with an averagecritical velocity of 5.9 f.p.s. Total duration of damovertopping would be approximately 1.1 hours. The spillwayis capable of passing only 50 percent of the SDF or 25 percentof the Probable Maximum Flood (PMF).

The dam and appurtenant structures were found to be ingenerally poor overall condition. According to Bureau ofReclamation standards, the embankment width and downstreamslope are considered inadequate. The embankment is heavilyovergrown with trees and brush, major erosion has occurredin the emergency spillway, there are several areas of seepagealong the toe of the embankment, and there are no facilitiesfor drawdown of the reservoir. There is no trash rack onthe principal spillway intake, the principal spillway conduitis leaking near the outlet, and there is an animal burrow inthe crest of the dam.

Due to the poor condition of the spillway and the probabilityof dam failure in the event of overtopping, the spillway isadjudged as seriously inadequate and the dam is classifiedas unsafe, non-emergency.

NAME OF DAM: BIRDWOOD DAM

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The following remedial measures should be undertaken immedi-ately: the reservoir should be at least partially drained,professional consultant should be engaged to determine~~spillway adequacy and dam stability, excess vegetation

should be removed to the degree recommended by the professionalconsultant, the seeps should be checked regularly for turbidityor increase in flow, and a warning system and emergencyaction plan should be developed and implemented.

The following should be accomplished as part of the generalmaintenance of the dam: repair the animal burrow on the damcrest, install a trash rack on the principal spillway intake,install a staff gage, and cut the vegetation on the damregularly.

Since the inspection was conducted, the owner has drainedthe reservoir. The principal spillway was broken off at thebottom of the riser and the embankment has been breached.

Original signed tyMICHAEL BAKER, JR., INC. SUBMITTED: JAMES A. WALSH

James A. Walsh, P.E.Chief, Design Branch

Original Signed by:~Ronald G. Vann

Michael Baker, III, P.E. RECOMMENDED:Chairman of the Board and a Jack G. Starr, P.E.Chief Executive Officer Chief, Engineering

original signed by:

APPROVED: Douglas L. Hailer

Douglas L. HallerColonel, Corps of Engineers

SMICHAEL District EngineerSBAKER III

NO. 3176 ~ Date: MAR_1_4______


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NAME OF DAM: BIRDWOOD DAM ID# VA 00344

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. The main responsibility is toexpeditiously identify those dams which maybe a potential hazard to human life or property.

1.2 Description of Project

1.2.1 Description of Dam and Appurtenances: BirdwoodDam is an earthfill embankment approximately26 feet high' and 270 feet long. The up-stream and downstream embankment slopes areapproximately 3H:lV (Horizontal to Vertical)and 2H:lV respectively. The crest of the damis approximately 10 feet wide and has aminimum elevation of 501.5 feet Mean SeaLevel (M.S.L.)2 at a point adjacent to theemergency spillway.

The principal spillway, located approximatelyat the dam centerline, is a 6 inch verticalcast-iron pipe at elevation 496.7 feet M.S.L.with no trash rack. The principal spillwayexits at elevation 479.7 feet M.S.L. into thedownstream channel at the toe.

'Measured from the bottom of the cut-off trench to the embank-ment crest.

2All elevations are approximately Mean Sea Level as approximatedby interpolation from USGS Quandrangle.

NAME OF DAM: BIRDWOOD DAM7

The emergency spillway, located in the left3

abutment, is an earth spillway approximately70 feet wide. The spillway has eroded tobedrock in places and migrated from itsoriginal channel. The invert elevation ofthe control section is 497.3 feet M.S.L.There are no facilities for dewatering thereservoir.

1.2.2 Location: Birdwood Dam is located on MoreyCreek approximately 2.2 miles upstream fromMoores Creek, a tributary to the RivannaRiver, in Albemarle County, Virginia. Thedam is situated on the University of Virginiaproperty approximately 1.1 miles west of theCharlottesville, Virginia, city limits.Access to the dam is obtained via a privateroad located on U.S. Route 250 0.3 mile westof the junction of U.S. Route 29 Bypass andU.S. Route 250. A Location Plan is includedwith this report.

1.2.3 Size Classification: The maximum height ofthe dam is 22 feet; the reservoir storagecapacity to the crest of the dam, elevation501.5 feet M.S.L., is 46 acre-feet. Therefore,the dam is in the "small" size category asdefined by the Recommended Guidelines forSafety Inspection of Dams.

1.2.4 Hazard Classification: Within 700 feetdownstream of Birdwood Dam along the outletchannel are two residential structures. Lossof human life is highly probable in the eventof dam failure by overtopping. For thisreason, Birdwood Dam is classified in the"high" hazard category according to theRecommended Guidelines for Safety Inspectionof Dams. The hazard classification used tocategorize dams is a function of locationonly and has nothing to do with its stabilityor probability of failure.

1.2.5 Ownership: The dam is owned by the University

of Virginia, located in Charlottesville,Virginia.

1.2.6 Purpose of Dam: The reservoir was originallyconstructed for agricultural water supply;however, it is no longer used extensively forthat or any other specific purpose.

3Facing downstream.NAME OF DAM: B IRDWOOD DAM

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1.2.7 Design and Construction History: Designrecords do not exist for the dam; however,the dam was constructed under the supervisionof Mr. R.O. Anderson who was the farm managerat the time. According to Mr. Anderson, Moore,Kelly and Reddish, of Orange, Virginia,conducted the earth moving activities in theearly 1930's. This company is still in opera-tion in a descendent firm, Moore Golf, Inc.,Culpepper, Virginia.

1.2.8 Normal Operational Procedures: This reservoiris normally operated at the level of theprincipal spillway, elevation 496.7 feetM.S.L. No formal operating procedures arefollowed for this structure. See Paragraph4.1 for detailed operating procedures.

1.3 Pertinent Data

1.3.1 Drainage Area: The drainage area tributaryto the dam is 0.47 square mile.

1.3.2 Discharge of Dam Site: The maximum dischargefrom the reservoir is unknown.

Principal Spillway:Pool level at top of dam . . . 2 c.f.s.

Emergency Spillway:Pool level at top of dam . . . . 980 c.f.s.

1.3.3 Dam and Reservoir Data: Pertinent data onthe dam and reservoir are shown in the followingtable:

TABLE 1.1 DAM AND RESERVOIR DATA

ReservoirCap acity

Elevation Area Acre- Watershed LengthItem feet M.S.L. acres feet inches feet

Top of dam 501.5 6.6 46 1.8 1400Emergency spillway invert 497.3 5.0 22 0.9 1270Principal spillway crest

(normal pool) 496.7 4.8 19 0.8 1260Streambed at downstream toe

of dam 478.8 - - -

NAME OF DAM: BIRDWOOD DAM I9

Rog. A&M

SECTION 2 - ENGINEERING DATA

2.1 Design: There were no design reports available for

preparation of this report; however, phone contact wasmade with R.O. Anderson of Charlottesville, Virginia,the Birdwood Farm Manager who overviewed the constructionof the dam in the early 1930's. According to Mr. Anderson,there is no core wall within the dam; however, there isa cut-off trench 3 to 4 feet below the normal groundelevation. The design did not include any toe drains.

2.2 Construction: There were no pre-construction or as-built plans available for review. R.O. Andersonstated that the dam was constructed by Moore, Kelly andReddish, of Orange, Virginia. He recalled that the damwas built in the early 1930's.

2.3 Evaluation: No design drawings or construction recordswere available for review. Evaluations contained inthis report are based primarily on field observations,measurements taken during the inspection, and interviewswith University of Virginia personnel. No assessmentof the engineering was possible due to lack of designdata.

NDNAMEOF DM: iROD A

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SECTION 3 - VISUAL INSPECTION

3.1 Findings

3.1.1 General: The field inspection was conductedon 13 November 1979. Skies were overcast andrain persisted throughout the day. Therecorded temperature was 450F and groundconditions were damp due to the rain. At thetime of the inspection, the pool elevationwas 496.9 feet M.S.L. and the tailwaterelevation was 478.8 feet M.S.L. No recordwas found of any previous inspections. Theembankment and appurtenant structures werefound to be in poor condition at the time ofinspection. The following are brief summariesof deficiencies found during the inspection.A Field Sketch of conditions is shown asPlate 1. The complete visual inspectioncheck list may be found in Appendix III.

3.1.2 Dam: The upstream and downstream embankments,crest, and abutments were extremely overgrownwith trees and brush (see Overall View ofDam). Surface cracks were not observed;however, some sloughing was apparent midwayup and on the left side of the downstreamembankment. The entire embankment was damp,particularly on the left side junction ofembankment and abutment, where a small marshexists. Inspection team members were able tosink a rod 1 to 1.5 feet deep into this area.The right junction was also damp. The down-stream embankment surface seemed somewhatirregular; however, vegetation prevented abetter assessment. Noticeable seepage wasfound along the toe of the dam resulting inmarshy areas (see Photos 5 and 6). Flowswere less than one gallon per minute each.The junction between the spillway and damshowed signs of erosion. The upstreamembankment had riprap lower than the waterlevel. There is an animal burrow on thecrest of the dam.

3.1.3 Appurtenant Structures: The approach anddischarge channel of the emergency spillwayare severely eroded to the underlying bedrock.The discharge channel has migrated to theleft of the intended channel and has allowederosion to depths of ten feet and more tooccur.


The principal spillway is a 6 inch cast-ironpipe. The inlet was submerged at the time ofinspection; however, it is apparently verticaland has no trash rack. The outlet protrudesfrom the downstream face of the dam and hasseveral small holes in the bottom of the pipenear the downstream end. The outlet channelitself is clear; however, heavy brush andtrees vegetate the overbanks, extending up tothe channel banks. There is no emergencydrawdown facility.

3.1.4 Reservoir Area: The surrounding hillsidesare gradually sloped and well vegetated. Theupstream embankment has riprap below thepresent water level. There was no sedimentationobserved. Three small reservoirs are locatedupstream.

3.1.5 Downstream Channels: The channel itself isclear; however, the vegetation of the overbanksis very heavy and consists of trees and heavybrush. There are two residences 700 feetdownstream.

3.2 Evaluation: Due to the location of the two residencesdownstream, there is concern for the stability of thedam. The seepage areas and marshy grounds should befurther investigated and continually monitored forturbidity and/or increase in flow which would indicatethe potential for piping of embankment material. Thereservoir level should be drawn down and a trash rackplaced on the principal spillway. The leak in theprincipal spillway conduit should be repaired.

The emergency spillway should be regraded and seeded.Excess vegetation located on the dam, around the principalspillway outlet, and within the downstream channelshould be removed and the embankment and toe areasshould be reinspected after removal of the excessvegetation. A staff gage should be installed to monitorreservoir levels above normal pool.


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SECTION 4 - OPERATIONAL PROCEDURES

4.1 Procedures: Operation of the dam is an automaticfunction maintained by the principal spillway and theemergency spillway. Water entering the reservoir flowsinto the principal spillway at elevation 496.7 feet

M.S.L. When the inflow is sufficient the reservoir jlevel rises above elevation 497.3 feet M.S.L. anddischarges through the emergency spillway.

4.2 Maintenance of Dam: Maintenance of the dam is theresponsibility of the owner. An inspection or maintenanceschedule has not been instituted.

4.3 Maintenance of Operating Facilities: There are nofacilities requiring operation at the dam.

4.4 Warning Systems: At the present time, there is nowarning system or evacuation plan in operation.

4.5 Evaluation: Maintenance of the dam in the past hasbeen inadequate and must be improved. An annual inspec-tion and maintenance program should be implemented.

Since there are two homes in the downstream damagearea, a warning system and emergency action plan shouldbe developed and implemented.


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SECTION 5 - HYDRAULIC/HYDROLOGIC DATA

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

5.2 Hydrologic Records: No rainfall or stream flow recordswere available at the dam site.

5.3 Flood Experience: There were no high water marks orote-rinformation about past floods available at thedam site.

5.4 Flood Potential: The Probable Maximum Flood (PMF),1/2 Probable Maximum Flood (1/2 PMF), and the 100-yearflood were developed and routed through the reservoirby use of the HEC-l DB computer program (Reference 9,Appendix V) and appropriate unit hydrographs, precipita-tion, and storage-outflow data. Clark's T and Rcoefficients for the local drainage areas ere 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, Appendix V).Rainfall losses for the 100-year flood were estimatedat an initial loss of 1.5 inches and a constant lossthereafter of 0.15 inch per hour. An initial loss of1.0 inch and a loss rate of 0.05 inch per hour wereused for the PMF and 1/2 PMF.

5.5 Reservoir Regulation: Pertinent dam and reservoir dataare shown in Table 1.1, Paragraph 1.3.3.

Regulation of flow from the reservoir is automatic.Normal flows are maintained by the crest of the riserwith an elevation of 496.7 feet M.S.L. Water alsoflows past the dam through the ungated, vegetatedemergency spillway in the event water in the reservoirrises above an elevation of 497.3 feet M.S.L.

Outlet discharge capacity was computed by hand; reservoirarea was planimetered from the Charlottesville West,Virginia, 7.5 minute USGS quadrangle; and storagecapacity was computed directly by the HEC-l program.All flood routings were begun with the reservoir atnormal pool.

5.6 Overtopping Potential: The probable rise of the reservoirand other pertinent information on reservoir performanceare shown in the following table:


TABLE 5.1 RESERVOIR PERFORMANCE

Hydrographs100-year

Item Normal(a) flood 1/2 PMF PMF(b)

Peak flow, c.f.s.Inflow 1 700 2508 5597Outflow 1 633 2508 5543

Peak elev., ft. M.S.L. 496.9 500.7 503.2 504.2Emergency spillway (c)(elev. 497.3 ft. M.S.L.)

* Depth of flow, ft. - 3.4 5.9 6.9Average velocity, f.p.s. - 8.5 12.2 13.7Duration of flow, hrs. - 16.9 24.3 26.2

Non-overflow section (c)(elev. 501.5 ft. M.S.L.)Depth of flow, ft. - - 1.6 2.7Average velocity, f.p.s. - 5.9 7.6Total duration of over-

topping hrs. - 1.1 2.7Tailwater elev., ft.M.S.L. 478.8

(a) Conditions at time of inspection.(b) The PMF is an estimate of flood discharges that may be

expected from the most severe combination of criticalmeteorologic and hydrologic conditions that are reasonablypossible in the region.

(c) Depth and velocity estimates were based on critical depthat control section.

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

5.8 Evaluation: Birdwood Dam is a "small" size - "high"hazard dam requiring evaluation for a spillway designflood (SDF) of a magnitude between that of the 1/2 PMFand PMF, inclusive. Since there are only two homes inthe downstream damage reach, the 1/2 PMF was selectedas the SDF. The 1/2 PMF was routed through the reservoirand found to overtop the dam by a maximum depth ofapproximately 1.6 feet, with an average critical velocityof 5.9 f.p.s. Total duration of dam overtopping wouldbe approximately 1.1 hours. The spillway is capable ofpassing only 25 percent of the PMF.

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


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SECTION 6 - DAM STABILITY

6.1 Foundation and Abutments: There is no informationavailable on the foundation conditions. The dam is inthe Piedmont physiographic province of Virginia.According to Mr. R. 0. Anderson, who overviewed theconstruction, there is a cut-off trench 3 to 4 feetbelow the normal ground elevation, but there is nofoundation drain. As noted in the visual inspection:some sloughing was apparent on the downstream embankment;there was a very wet, marshy area at the junction of".he downstream embankment and the left abutment; thedownstream embankment surface seemed somewhat irregular;and noticeable seepage was found along the toe of thedam.

6.2 Embankment

6.2.1 Materials: There is no information availableon the nature of the embankment materials.The area soils are generally low-plasticclays and silts.

6.2.2 Stabiliy: There are no available stabilitycalculations. The dam is 26 feet high and 10feet wide. It has an estimated upstreamslope of 3H:lV and a measured downstreamslope of 2H:lV. The dam exists at normalstorage pool. It is not known whether thedam was ever subjected to a maximum storagepool. The dam has a freeboard of approxi-mately 0.6 foot from maximum control storage.There are no facilities for dewatering thereservoir, so the embankment is not subjectedto a drawdown.

According to guidelines presented in Designof Small Dams by the U.S. Department of theInterior, Bureau of Reclamation, for smallhomogeneous dams, with a stable foundation,not subject to a drawdown, and composed oflow-plastic clays and silts (CL, ML); therecommended slopes are 3H:lV upstream and2.5H:lV downstream. The recommended width is15 feet. Based on these guidelines, theupstream slope is considered to be adequate;however, the downstream slope and width areconsidered to be inadequate.


6.2.3 Seismic Stability: The dam is located inSeismic Zone 2. Therefore, according to theRecommended Guidelines for Safety Inspectionof Dams, the dam is cons-ered to have nohaizar-from earthquakes provided staticstability conditions are satisfactory andconventional safety margins exist.

6.3 Evaluation: There is insufficient information toadequately assess the stability of the dam. However,the visual inspection revealed severe seepage problems.Also, based on the Bureau of Reclamation guidelines, thewidth and downstream slope are inadequate. Also, thespillway is incapable of passing the design flood andovertopping flows are considered detrimental to theembankment. Overtopping flows are shallow and onlylast 1.1 hours, but the velocity approaches 6 f.p.s.,the effective eroding velocity for a vegetated earthembankment. Based on these conditions, the embankmentis considered not sound and the services of a qualifiedgeotechnical engineering firm should be retained toperform a stability check of the dam. It is recommendedthat the reservoir be at least partially drained toalleviate the seepage pressure.

NAME OF DAM: BIRDWOOD DAM20 £

SECTION 7 - ASSESSMENT/REMEDIAL MEASURES

7.1 Dam Assessment: The dam and appurtenant structures aregenerally in poor overall condition. Based on theBureau of Reclamation guidelines, the width and downstreamslope of the embankment are considered inadequate.

There are several areas of seepage along the toe of thedam. The worst area is located along the contactbetween the left abutment and the downstream embankment;the entire left abutment contact area was wet and soft.

Members of the inspection team were able to push asurvey leveling rod into the soil to a depth of 1 to1.5 feet in this area. The emergency spillway haseroded to bedrock and has migrated out of its originalchannel. There is an animal burrow on the crest of thedam. There is no trash rack on the principal spillwayintake and the principal spillway conduit is leakingnear its outlet. There are no facilities for dewateringthe reservoir. The entire embankment is heavily overgrownwith trees and brush.

Using the Corps of Engineers' screening criteria forinitial review of spillway adequacy, the 1/2 PMF wasselected as the SDF for the "small" size - "high"hazard classification of Birdwood Dam. It has beendetermined that the dam would be overtopped by the SDFby a maximum depth of 1.6 feet with an average criticalvelocity of 5.9 f.p.s. and that total duration of damovertopping would be 1.1 hours. The spillway is capableof passing only 50 percent of the SDF or 25 percent ofthe PMF.

Due to the poor condition of the embankment and theprobability of dam failure in the event of overtopping,the spillway is adjudged as seriously inadequate andthe dam is classified as unsafe, non-emergency.

The recommended remedial measures are considered urgentand, therefore, should be accomplished immediately.

7.2 Recommended Remedial Measures: It is recommended thatthe following repair items be undertaken immediately:

The reservoir should be at least partially drained toalleviate the seepage pressure. The owner shouldengage the services of a professional consultant todetermine by more sophisticated methods and proceduresthe adequacy of the spillway and the stability of theembankment. The owner should periodically check andrecord the amount of flow from the seeps along the toe.Also, seepage should be checked for turbidity. Increased


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flow and/or turbidity may indicate the potential forpiping of embankment material.

The recommendations of the consultant should includemeasures required to improve the stability of theembankment, to increase the spillway capacity and toprovide erosion protection in the spillway, and torepair the leak in the principal spillway conduit. Theconsultant should also make recommendations as to theextent of tree and brush removal from the dam.

The owner should develop and implement a warning systemand emergency action plan. Until corrective measuresare completed, the dam should be checked during periodsof heavy run-off. If evidence of piping of embankmentmaterial is detected or if dam overtopping is imminent,warning should be issued to the downstream inhabitants.

The following items should be accomplished as part ofthe general maintenance of the dam:

1) Excavate, fill, compact, and seed the animalburrow on the crest of the dam.

2) Install a trash rack on the principal spillwayintake.

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

4) After the trees and brush have been removedfrom the dam, cut the vegetation on the damregularly.

7.3 Remedial Measures Taken: Since the inspection, thereservoir has been drained; the principal spillway wasbroken off at the bottom of the riser and the dam hasbeen breached. A copy of the letter advising theVirginia State Water Control Board that the reservoirwas being drained is included in Appendix IV.


r APPENDIX I[ PLATES

CONTENTS

Location Plan

Plate 1: Field Sketch

Plate 2: Typical Cross Section

Plate 3: Top of Dam Profile

t

~NAME OF DAM: B IRDWOOD DAM

t BIRD WOOD-- DAM

VA.

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BIRDWOD Hows

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SCALE 1: 24000

0 tooo 1" 10 4000 ow0 600 Tom0 Fig?

BIRDWOOD DAMLOCATION PLAN

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ROAD

2 HOMES IN _ I\\ ' FIELD SKETCHDOWNSTREAMAREA BIRDWOOD DAM

• "MICHAEL BAKER,JR., INC.13 NOVEMBER 1979

X-INDICATES VISIBLE WATER PLATE I(SEEPAGE <I GAL./MIN.)

NO SCALE

ATER'

//LRIGINAL EMERGENCY GAS/SPILLWAY CHANNEL

(GRASSY)

/XTMEL VEGETATION COVERED

LEFT RIGHTA-BUTM ENT AUMN

ABUTENT .~.. ~ 'MARSHY A VEGETATION CHANGE

L: LITTLE VEGETATION TO BROWN STALKLIKEw PLANT- DYING

z w EMBANKMENT

4X3 URO HILLSIDEU0 CREST

LJX =) ROCK RIPRAP 1

VIDENCE 0OF HIGHER WATER

LEVEL (NOT VISIBLE)

WOODED

RESERVOIR SLOPES

/

NOTE:

UPSTREAM AND DOWNSTREAM EMBANKMENT ABUTMENTSCRESTAND DOWNSTREAMCHANNEL ARE VERY OVERGROWN.DOWNSTREAM EMBANKMENT SURFACE SEEMED IRREGULAR -HOWEVER VEGETATIONPREVENTED BETTER OBSERVATION.NO KNOWN TOE DRAINS.

__________________________ I

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APPENDIX II

PHOTOGRAPHS

IL

.77

CONTENTS

Photo 1: Looking Upstream at Erosion in Emergency Spillway

Photo 2: Upper End of Emergency Spillway

Photo 3: Six Inch Cast Iron Outlet Pipe; Water Seepingfrom Below Pipe

Photo 4: Damage Area - Home on Left has Basement Garage

Photo 5: Marshy Area at Toe of Dam, Fifty Feet Left ofOutlet Pipe

Photo 6: Seepage Area at Toe of Dam, Twenty Feet Left ofOutlet Pipe

Note: Photographs were taken on 13 November 1979.


ii~

BIRDWOOD DAM

PHOTO 1. Looking Upstream at Erosion In Emergency Spillway

PHOTO 2. Upper End of Emergency Spillway

BIRDWOOD DAM

A

PHOTO 3. Six Inch Cast Iron Outlet Pipe; Water Seeping from Below Pipe

PHOTO 4. Damage Area - Home on Loft Has Basement Garage

BIRDWOOD DAM

PHOTO 5. Marshy Area at Toe of Dam, Fifty Feet Left of Outlet Pipe

PHOTO 6. Seepage Area at Toe of Dam, Twenty Feet Left of Outlet Pipe

4 1IIIi

APPENDIX III

VISUAL INSPECTION CHECK LIST

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APPENDIX IV

CORRESPONDENCE

UNi VERSITY OF VIRJINIA-1 OFFICE OF UNIVERSITY PLANNING

MWRANDtMK

To: Mr. William Middleton

From: Waller S. Hunt, Jr. i

Re: Inspection of Birdwxood Dams

In your memrandum of 6 Noveber 1979, you asked if I had any recordsrelative to the dams at Birdwlod.

I am acquainted with the gentler who apparently designed those damsand who overviewed their construction. Fortunately, he is living inCharlottesville, and while retired from the Federal Soil ConservationOffice, can be reached for discussion. His name is R. 0. Anderson,and lives on Oxford Road.

Mr. Anderson, upon graduating from Virginia Tech, took a job as farmmanager at Birdiood in early 1930's. It was during his term on thefarm that the dams were built. He took into account, according tomy discussion with him, the then established water shed and designedthe size of the flow pipes and the type of water retainaged facilitydesired. He has indicated that if we were to design those dams today,they would not have as steep an incline on the exposed side ofthe dam, w)uld probably have a much larger overflow pipe and a large,grassed emergency spillway.

Probably the local Office of Soil Conservation will give you the sameinformation. Mr. Cofier, of that office, is very aware of thedesign provisions for new dams and can certainly furnish anyinformation you may need for- repairs to the dam. I beliea herecently looked at those dams and furnished somea information toBil Tharpe.

W5Hjr: cvc

cc: Mr. H. I. Tayior

IV- 1

WASHINGTON HALL, CHARLOTTESVILLE, VIRGINIA 22903 (804) 924-3718

Pic

UNIVE=RSITY OF VIRGINIADEPARTMENT OF BUILDINGS AND GROUNDS

OFFICE OF THE DIRECTOR UNIVERSITY OF VIRGINIA

CHARLOTTESVILLE. VIRGINIA 22903

January 10, 1980

Mr. R. V. Davis OExecutive SecretaryCommonwealth of VirginiaState Water Control Board2111 Hamilton Street ,Richmond, Virginia 23230

Dear Mr. Davis:

This will acknowledge your letter of December 28, 1979,concerning the unsafe condition of the Birdwood Dam, as determinedby the firm of Michael Baker, Jr. Inc. in an inspection conductedon November 13, 1979, under contract to the Norfolk District, U.S.Army Corps of Engineers under the National Dam Safety Program.

Please be advised that we have taken action to drain thislake, with a contractor starting work this date and expected tocomplete the work within A to 5 days. Pending receipt of thePhase I Inspection Report and completion of recommended correctivemeasures, the lake will remain drained.

William D. MiddletonDirector

cc: George L. Jones, State Office of Emergency and Energy ServicesLinda Peacock, Office of Emergency and Energy ServicesJ. G. Starr, Norfolk District Cores of Engineers

IV-2

APPENDIX V)I

GENERAL REFERENCES

GENERAL REFERENCES

1. Bureau of Reclamation, U.S. Department of the Interior,Design of Small Dams, A Water Resources TechnicalPublFicati-on, 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 - Hill

Book 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-I), 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, Wasg-ngton, D.C., May 1975.


V-1

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).

14. 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, UnitedStates East of the 105th Meridian," Washington, D.C.,June 1978.


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NATIONAL DAN SAFETY PROGRAM. BIRDVOOD DAM … · NATIONAL DAN SAFETY PROGRAM. BIRDVOOD DAM...

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