AD-A106 316 SCINABEL ENGINEERING ASSOCIATES RICHMOND VA F/B 13/13NATIONAL DAM SAFETY PROGRAM. LEATHERWOOD CREK NUMBER 3 DAM (IN--ETC(U)JUN 81 R E MARTIN, C S ANDERSON, .J STARR OAC65-1--0020

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ADA106316

PHASE I INSPECTION REPORTNATIONAL DAM SAFETY PROGRAM

OCT -

PrEPAKO FUR

-~ P4OPOLK, V04IA *8610

el 1027 296

FGANOE RIVER BASIN

?V4E C' DAM: IEAMOOOM CM NO. 3LOCATM.N MM4I CLOMY, VIPMNIAINVENOI&' NMBM1: VA. NO. 08904

PIAS I IU5PBIOt JIUFNkTIO~hL DAM SAF~rY PFOGAM

NDM"J DISTRICI' WIRPS OF EN4GINHIM803 FI STr

NMRMVU, VIICINIA 23510

By

SCHNABE L4G~D ASSOCIMES, P.C.,

J. K. TII4tO AM ASSCIAE, IM.

tCURITY CLASSIFICATIO Of Tti-tS 9@ ~. e eed _____________

REPWI O MENTT ACEREAD DG5TRUCiIIS

I.RPTNMEPRTDC ETTONPG DEPOSE COMPLETIG VOWN GOVT ACCEfSWO NO , I I N S ATALO NUNS S

VA 08904 W -m14. TITLE (and S, oa) S. 9rp OfP M A s9mOD COVVAS

Phase I Inspection Report Final

National Dam Safety Program _

Leathervood Creek No. 3 Henry County, VA s. PEwFORMING 0o4. 9*0?Nu SER

7. AU TmORna) -11. CONTRACT Ae GRANT NUMD81I-0 )

Schnabel Engineering Associates, P. C.J. K. Timmons and Associates, Inc. I DACW..65-81-D-002G

-9. PER0FORMING ORGANIZAT1ON NAME AND ADDRISSA OR UNT. NURST,

Schnabel Engineering Associates, P. C. -J. K. Timmons and Associates, Inc. I. ) -j1 -

I. CONTROLLING OFFICS NAME AND ADDRESS . N.PORT DAT!

U. S. Army Engineer District, Norfolk I I MUwW§OVAGES803 Front St., Norfolk, VA 23510

NI ORINF AS9NCY NAM & A RS5(11ief0lawt ft.. CantIollhn O) IS. SECURITY CLASS. (ef OUdS 1.9.1)

National Dam Safety Progrm. Leatherwood Unclassified

'- Creek Number 3i(Inventory Number VA 08904) IS& ef C A TIFGA

Roanoke River*#-asin, Henry County, - LE IATION OWNGRAOING,Virginia. Ph aseI Inspection Report. -

Approved for public release; distribution unlimited

17. DjIStIUTIOM STATOMT foe o abei rmosod i. 95.4 I it 9gbtoret Aim AWpu)

,S. Suft -mL~, m4 ICopies are obtainable from National Technical Information Service,

Springfield, Virginia 22151

IS. KEY WORDS (CamnMte an reeo aide It neoee'y and 1l~0l1 bY blyeek m Iwne)

Dams - VANational Dam Safety Program Phase IDam SafetyDam Inspection

2. ASITRACT (Cmteb ORSevwe side Ii fto.e a mmd 1dt011Y bY Mloak smhIe)

(See Reverse Side)

DD :nM°, 1473 EDITION OF I NOV S IS OSSOLETE

SKCURIT Y OL.AM ICATONM O, TI PAmE (I'uIJP WO a rwM.

I !av

.MMTV CLAIFICATION OV T041S PAeGU(Ua.DA)

20. Abstract

Pursuant to Public Law 92-367, Phase I Inspection Reports are preparedunder guidance contained in the recomended guidelines for safetyinspection of dams, publis~ed 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 orproperty. The assessment of the general conditions of the dam is basedupon available data and visual inspection. Detailed investigation andanalyses involving topographic mapping, subsurface investigations,testing, and detailed computational evaluations are beyond the scope of aPhase I investigation; however, the investigation is intended to identifyany reed 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.0

CT

4 , ISU~iTY CL.ASIPiICATiON O ~SPS hmDn bm

PREFACE

This report is prepared under guidance contained in theReccmmended Guidelines for Safety Inspection of Dams, for Phase IInvestigations. Copies of these guidelines may be obtained frcnthe Office of Chief of Engineers, Washington, D. C. 20314. Thepurpose of a Phase I Investigation is to identify expeditiouslythose dans which may pose hazards to human life or property. Theassessment of the general condition of the dam is based uponavailable data and visual inspections. Detailed investigation, andanalyses involving topographic mapping, subsurface investigations,testing, and detailed omputational evaluations are beyond the scopeof a Phase I Investigation; however, the investigation is intended toidentify 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 atthe time of inspection along with data available to the inspectionteam. In cases where the reservoir was lowered or drained prior toinspection, such action, while improving the stability and safety ofthe dam, removes the normal load on the structure and may obscurecertain conditions which might otherwise be detectable if inspectedunder the normal operating environrment of the structure.

It is important to note that the condition of a dam depends onnumerous and constantly changing internal and external conditions,and is evolutionary in nature. It would be incorrect to assume thatthe present condition of the dam will continue to represent thecondition of the dam at sane point in the future. Only throughfrequent inspections can unsafe conditions be detected and onlythrough continued care and maintenance can these conditions beprevented or corrected.

Phase I inspections are not intended to provide detailed hydrologicand hydraulic analyses. In accordance with the established Guidelines,the Spillway Test flood is based on the estimated "Probable MaximunFlood" for the region (greatest reasonably possible storm runoff), orfractions thereof. Because of the magnitude and rarity of such astorm event, a finding that a spillway will not pass the test floodshould not be interpreted as necessarily posing a highly inadequatecondition. The test flood provides a measure of relative spillwaycapacity and serves as an aid in detemining the need for more detailedhydrologic and hydraulic studies, considering the size of the dar, itsgeneral condition and the downstream damage potential.

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TABLE OF CXNI'S

Page

Preface ......... ........................ ....

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

Overview Photos ......... .................... 4

Section 1: PRJEXr INFORMATIN ..... .......... 5

Section 2: ENGflERING DATA ..... ........... 9

Section 3: VISUAL INSPErION ... ........... .12

Section 4: OPERATIcNAL PCEIXJRES .......... . 15

Section 5: HYDRAULIC/HYDROUOGIC DAfTA ......... .. 17

Section 6: DAM STABILITY. .................. .. 21

Section 7: ASSESSM r/Ru-EDIAL MEASURES ...... .. 26

Appendices:

I - Maps and Drawings

II - Photographs

III - Field Observations

IV - Design Report

V - Stability Data

VI - References

PHASE I REPORTNATIONAL DAM SAFETY PROGRAM

BRIEF ASSIS OF DAM

Name of Dam: Leatherwood Creek No. 3 DamState: VirginiaLocation: Henry CountyUSGS Quad Sheet: Martinsville EastCoordinates: Lat 360 44.41 Long 790 46.3'Stream: West Fork, Leatherwood CreekDate of Inspection: June 30, 1981

Leatherwood Dam No. 3 is a zoned earthfill structure about 407

ft long and 41.2 ft high. The principal spillway consists of a

reinforced concrete riser and a 42 inch diameter concrete outlet pipe

which extends through the structure. An earth emergency spillway is

located at the left abutment with a 200 ft wide bottom and 3H:1V side

slopes. The structure is classified intermediate in size and is

assigned a significant hnazard classification. The dam is located on

the West Fork of Leatherwood Creek approximately 1.5 miles west of

leatherwood, Virginia. The dam is used for irrigation, flood control

and recreational purposes, and is owned and maintained by Mr. Charley M. Finney.

Based on criteria established by the Department of the Army,

Office of the Chief of Engineers (OCE), the appropriate Spillway

Design Flood (SDF) is the PMF. The spillways will pass 30 percent

of the Probable Maxim= Flood (PMF) or 60 percent of the SDF without

overtopping the dam. During the SDF, the dam will be overtopped for three

hours up to a maximn of 1. 7 feet and reach a maximum velocity of

5.7 fps. Flows overtopping the dam during the SDF are not considered

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( .

detrimental to the embankment with respect to erosion. The spillway

is judged inadequate, but not seriously inadequate.

The visual inspection did not reveal any problems which would

require immediate attention. A summary of the design stability analyses

for the upstream slope under drawdown conditions were reviewed and found

to be acceptable. The downstream slope meets requirements reomned by

the U. S. Bureau of Reclamation, however, the embankment crest is 6 ft

narrower than recommended.

It is recommened that the owner implement an emergency action plan

to warn the downstream dwellings of any dangers which may be

imminent.

The following routine maintenance and observation functions should

be initiated within the next twelve months:

The grass and weeds on the dam eubankxrent and in the emergency

spillway should be cut at least once a year and preferably twice a year.

Maintenance is recommended in the early summer and fall. Existing trees

on the dam should be cut to the ground and removed. Logs laying on the

embankment should also be removed.

The eroded area along the left side of the emergency spillway approach

channel should be backfilled, ccupacted and reseeded. Debris should be

removed from the trash rack and the top of the riser. A staff gage

should be installed to monitor water levels.

-2-

SCHNABEL ENGINEERING ASSOCIATES, P.C. /J. K. TIMONS & ASSOCIATES, INC.

Ray E. 4ftn, Ph.D.. .. \

Comonwealth of Virginia

Submitted by: Approved:

Original signed byfl Original signed byiiCarl S. Anderson, Jr. Ronald E. Hudson

Carl S. Anderson, Jr., P.E. Ronald E. HudsonActing Chief, Design Branch Colonel, Corps of Engineers

Conmnder and District Engineer

Reconnended by:

Original signed b,

.ACK G. STARR

Jack G. Starr, P.E.Chief, Engineering Division

L

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(Mau

Leathenqood Dam No. 3 -Lake

Damn

Overview Photographs

-4-1

SECTION 1 - PR3JECT INFORMATION

1.1 General:

1.1.1 Authority: Public Law 92-367, 8 August 1972, authorized

the Secretary of the Army, through the Corps of Engineers, to initiate

a national program of safety inspection of dams throughout the United

States. The Norfolk District has been assigned the responsibility of

supervising the inspection of dams in the Comonwealth of Virginia.

1.1.2 Purpose of Inspection: The purpose is to conduct a

Phase I inspection according to the Recanrended Guidelines for Safety

Inspection of Dams (see Reference 1, Appendix VI). The main

responsibility is to expeditiously identify those dams which may be a

potential hazard to human life or property.

1.2 Project Description:

1.2.1 Dam and Appurtenances: Leatherwood Creek No. 3 Dam is a zoned

earthfill structure approximately 407 ft long and 41.2 ft high.* The

crest of the dam is 12 ft wide, and side slopes are approximately 2.5

horizontal to 1 vertical (2.5H:IV) on the upstream and downstream

slopes of the dam. A 10 ft wide berm occurs between elevation 745.3

and 746.3 msl on the upstream slope. The upstream slope is 3H:lV

below the berm. The crest of the dam is at elevation 772.2 msl. "As built"

drawings show the presence of a core trench which extends to "firm bedrock"

and a seepage drain beneath the downstream slope. There is no slope

protection on the upstream face of the dam.

*Height is measured from the top of the dam to the downstream toe atthe centerline of the stream.

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(' . __-

The principal spillway consists of a reinforced concrete riser

inlet. The riser has an internal opening of 9 ft by 3.5 ft, and is

approximately 27 ft high. The riser has a low level orifice

(3.5 ft by 1.25 ft) at an invert elevation of 744.8 msl and two overflow

weirs at elevation 755.3 msl. A 36 inch diameter slide gate in the

riser at an invert elevation of 733.3 msl is available to drain

the lake. The outlet pipe is a 42 inch diameter concrete pipe which

outlets at an elevation of 731 msl into a Bradley Perterka impact basin.

(See Plate 5, Appendix I.)

The emergency spillway (EMS) consists of a vegetated earthen

channel spillway located at the left abutment, having a crest

elevation of 766.6 msl. The EMS has a bottom width of 200 ft at the

control section and 3H- IV side slopes, and is in a cut section. (See

Plate 2, Appendix I.)

1.2.2 1ccation: Leatherwood Dam No. 3 is located on the west

fork of Leatherwood Creek, 1.5 wiles west of Leatherwood, Virginia.

(See Plate 1, Appendix I.)

1.2.3 Size Classification: The dam is ciassified as an

intermediate size structure based on its height and maxim= lake

storage potential as defined in Reference 1, Appendix VI.

1.2.4 Hazard Classification: The dam is located in a rural

area; however, based upon the proximity of inhabited dwellings located

1.5 miles downstream, and several dwellings 5 miles downstream, the

dam is assigned a "significant" hazard classification. The hazard

-6-

classification used to categorize a dan is a function of location only

and has nothing to do with its stability or probability of failure.

1.2.5 ownership: The darn is owned and maintained by Mr. C-%arley M.

Finney of Martinsville, Virginia.

1.2.6 Purpose: Recreation and flood control.

1.2.7 Design and Construction History: The dam was designed and

constructed under the supervision of the United States Deparment of

Agriculture (USDA), Soil Conservation Service (Sc.S). The structure was

constructed by LarranDre Construction Coupany and completed in 1964.

1.2.8 Normal Operational Procedures: The principal spillway is un-

gated, therefore, water rising above the low level orifice and overflow

weirs of the riser outlet is automatically discharged downstream. Normal

pool is maintained at elevation 745 nsl just above the invert of the low level

orifice in the riser. Flood discharges which cannot be absorbed by storage

and the riser, flow through the emergency spillway at pool elevations above

766.6 msl. The 36 inch diameter gate at elevation 732.3 msl is manually

operated, and is available to lower the lake elevation below normal pool

for maintenance purposes.

1.3 Pertinent Data:

1.3.1 Drainage Area: The drainage area is 9.84 square miles.

1.3.2 Discharge at Dam Site: According to the owner, the

maximum known flood at the dam site occurred in April 1977 when an

estimated pool elevation of 760 msl was observed. This corresponds to

an approximate discharge of 226 CFS.

-7-

.........

Principal Spillway Discharge:

Pool Elevation at Crest of Dam (elev 772.2) 272 CFS

Emergency Spillway Discharge:

Pool Elevation at Crest of Dam (elev 772.2) 7500 CFS

1.3.3 Dam and Reservoir Data: See Table 1.1, below:

Table 1.1 - DAM AND RESERVOKIR DATA

Reservoir

Storage

Elevation Volumefeet Area Acre Watershed Lengthmsl Acres Feet Inches Miles

Crest of Dam 772.2 135 2400 4.6 2.0

Emergency SpillwayCrest 766.6 110.5 1695 3.2 1.8

Ic Level OrificeCrest 744.8 34 160 .3 .9

Streambed at Down-stream Toe of Dam 731.0 - - - -

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( ,

SILION 2 - EMINEEING DATA

2. 1 D : The dam was designed and constructed under the

direction of the USMA, Soil Oonnsarvaton Service (SCS). "As built"

drawings and design data are available in the office of the State

(oservationist, U. S. Soil Conservation Service, Federal Building,

k= 9201, 5th and Marshall Streets, RichInd, Virginia 23240.

A subsurface Lnvestgation was caxxicted at the site by the SCS

during the intial design stages. The investigation cosisted of

excavating 47 test pits. Subsurface profiles and a report of the

investigation with foundation rex nxiatilons were prepared k:Aed upon

geologic field reconnaissance, test pit data and laboratory testing. A

copy of the design report is included as Appendix IV. Test vii: locations,

subsurface profiles and test pit logs are pr e ted on Plates 2, 3 and 6

of Appendix 1, respectively.

The dam is a zoned, conpactad earthfill embankmet. The earthfil]

requ.irements shc*..i on Plate No. 4, Appendix I, specify that MH materials

be placed in Section No.1, i.e. tne ccc"t Df theclam. Soil classification

is vy the Unified Soil Classification System, ASTM D-2487. The upstream

slope, crest and downstream slope (Section No. 2) were to be constructed

with SM materials. Select borrow areas for each section of the enbankmnt

were specified. "As built" durankment slopes for the structure are

illustrated on Plate 4 of Appendix I.

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I.v

Plate No. 3, Appendix I indicates the dam is founded on overburden

and includes a cutoff trench which extends through alluvial and residual

soils to "firm rock." The cutoff also extends to the same materials

in both abutments. No field permeability tests were taken during the

subsurface investigation, however permeability rates of 0.1 ft/day to

10 ft/day were assumed for the foundation soil materials based on

similarities with Leatherwood Creek No. 2-A dam site. According to the

geotechnical nmswrandum, Appendix V, "The alluvial sands below 3 to 4

feet were described as 'unstable' with a 'fairly stable' residual sand

noted between these and rock. This foundation may be weaker and

wore ccmpressible than that tested from Site 5."

Although a cutoff or core was specified, a seepage drain was

included beneath. the downstream slope. The design report stated that the

trench drain at "c/b = 0.6" be constructed to control the phreatic line

and relieve pressures from seepage through the partially weathered rock.

The drain consists of a 4 ft wide trench which includes 6 inch diameter

bituunous coated, perforated corrugated metal pipe enclosed in a

granular envelope. Design details are included in the back of Appendix V,

while "as built" details are shown on Plate 4 of Appendix I.

The principal spillway was designed as a drop inlet structure

consisting of a reinforced concrete riser, a 42 inch conduit and

Perterka Impact at the outlet end of the conduit. The ergmgcy spillway

(EM) is designed to acaxmvdate a 50 year flood without the pool

elevation exceeding the EMS.

-10-

The emergency spillway (EMS) consists of a vegetated earthen

channel spillway located at the left abutment, having a crest elevation

of 766.6 msl. The EMS has a bottom width of 200 ft at the control

section and 3H:lV side slopes, and is in a cut section. (See Plates

2 and 3, Appendix I.)

The design report and supplementary data provided by the SCS

includes detailed laboratory test data describing the physical

properties of the materials used to construct the ertankment. Shear

parameters used in design of the embankment were determined by

consolidated undrained triaxial compression tests as follows:

SECTICN SOIL SHEAR STRENC1 PARAMETERSAngle of

Internal Friction Cohesion

Embankment MH Pcu = 190 c = 800 psf

SM Ocu = 30.50 c = 300 psf

Embankment stability was checked by the Swedish Circle Method Analysis and

a factor of safety of 1.95 was calculated for full drawdown on the upstream

slope (2.5H:IV with berm). A method of "slices" analysis was also performed

for a draon condition on the upstream slope. The minnmum factor of

safety calculated was 1.56.

2.2 Construction: The construction records were not furnished

by the SCS office in Richmrnd, but they are available from the SCS

office in Washington, D.C.

2.3 Evaluation: "As built" drawings are generally representative

of the structure. Field neasuremnts indicate that the embankment crest

is 3 ft narrr than shown on the "as built" drawings. Hydrologic and

hydraulic calculations were available for evaluation. There is sufficient

information to evaluate foundation conditions and efbankment stability.

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( '

SErION 3 - VISUAL INSPBCTICN

3.1 Findings: At the time of inspection, the dam appeared to be

in good condition. Field observations are outlined in Appendix III.

3.1.1 General: An inspection was made on June 30, 1981 and the

weather was cloudy with a temperature of 80 0F. The pool and tailwater

levels at the time of inspection were 745 and 731 nsl, respectively,

which corresponds to normal pool and tailwater elevations. Ground

bonditions were dry at the time of the inspection. Maintenance inspections

are performed jointly by SCS and the Blue Ridge Soil and Water Conservation

District on an annual basis. Inspection reports are available in the

Soil and Water Conservation District office in Collinsville, Virginia.

3.1.2 Dam and Spillway: The enbankment slopes and crest were heavily

vegetated with tall grass and briers making observation difficult. Scattered

small trees less than 1/4 inch in diameter were also present. A few

scattered logs exist on the upstream slope as a result of previous high

water, extending to a level equal to the top of the intake structure.

No sloughing or erosion was noted on the embankent, however, very

dense vegetation restricted visual observation. The only observed erosion

was in the approach channel of the emergency spillway. Along the left

upstream edge of the left abutment-energency spillway contact is a

deeply eroded area 7 ft - deep, 15 ft + long and 5 ft - wide. It is filled

with weeds and residual soils are exposed.

The downstream toe of the enbankmant was dry and no seepage was en-

countered. 1W 6-inch CmP toe drains were encountered, one on the left and

one on the right side of the plunge pool. No flow was observed, as the

plunge pool level was slightly above the toe drain inverts.

The riser structure and cutlet pipe showed no signs of deterioration

and were functioning properly at the time of inspection. Debris was

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present in the low level intake trash rack and logs were present

on top of the riser. According to the owner, the slide gate has not been

operated since it was installed. The iipact basin and outlet channel

indicated no signs of deterioration. The emergency spillway was well

vegetated except for the previously described minor erosion in the approach

channel.

3.1.3 Reservoir Area: The reservoir area was free of debris and

the perimeter was wooded. The reservoir is located in a valley with

gentle side slopes. Water was clear and sedimentation was not

observed.

3.1.4 Downstream Area: The downstream channel is 15 ft wide

and is located in a valley with steep side slopes. This valley

is heavily wooded except for an area 50 ft either side of the channel

which is a neadow. Approximately 1.5 miles downstream, there is a

dwelling about 15 ft above the stream channel. Approximately 5 miles

downstream, there are several dwellings about 10 ft above the stream

channel and several coxaurcial facilities 15 ft above the channel.

3.1.5 Instrumentaticn: No instrumentation (nonuments, observation

wells, piezameters, etc.) was encountered for the structure. There is

no staff gage.

3.2 Evaluation:

3.2.1 Dam and Spillway: Overall, the dam was in good condition

at the tine of the inspection. There is an annual inspection and maintenance

program for this structure. Maintenance of the dam at the tine of the in-

spection appeared to be inadequate. The ebankment, including its crest

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and slopes should be mowed at least once a year, but more preferably

twice a year. The presence of trees on the embankment, particularly

those at pool level on the upstream slope, may prcmote the development

of deep rooted vegetation and this type growth can encourage piping

within an embankment. All trees growing on the embankment should be

cut to the ground and removed fram the embanment. Logs laying on the

embankment should also be removed.

The erosion observed in the emergency spillway should be corrected.

It is recommended that the eroded area be properly backfilled, compacted,

and the surface reseeded to prevent further erosion.

The outlet pipe and intake structures are in good structural

condition. The condition of the operating appurtenances could not be

deterdned. Debris should be reroved from the trash rack and the top

of the riser. A staff gage should be installed to monitor water levels.

3.2.2 Downstream Area: A breach in the Leatherwood Creek No. 3

Dam during extreme flooding would possibly create a hazard to the

downstream dwellings.

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SECTION 4 - OPERATIONAL PROCEDURES

4.1 Procedures: The nornal storage pool is elevation 745 msl or

0.2 ft above the crest of the principal spillway low flow inlet. The

lake provides an irrigation supply, flood control and recreation.

Water automatically passes through the principal spillway as the water

level in the reservoir rises above the low level crest. Water will

also pass automatically through the overflow crest when the water

level in the reservoir exceeds elevation 755.3 zisl and autmatically

through the emergency spillway when the pool level exceeds elevation

766.6 nsl. A 36 inch slide gate valve at the low point in the riser

structure is provided to drawdown the reservoir below normal pool.

4.2 Maintenance of Dan and Appurtenances: Maintenance is the responsi-

bility of the owner and the Blue Ridge Soil and Water Conservation District.

Maintenance is acconplished by a joint annual inspection by SCS and Soil and

Water Conservation District personnel. Maintenance deficiencies are noted

and recomended remedial measures are made to the owner. If the owner fails

to comply with these reoman*dations, maintenance is then performed by the

Blue Ridge Soil and Water Conservation District.

4.3 Warning System: At the present time, there is no warning system

or evacuation plan for the dam. The dam is monitored by SCS personnel

during periods of heavy precipitation and runoff.

-15-s o

p.

4.4 Evaluation: The dam and appurtenances are in good operating

condition, but maintenance of the dam appeared to be inadequate. An

emergency operation and warning plan should be developed. It is recorended

that a formal emergency procedure be prepared and furnished to all

operating personnel. This should include:

a. How to operate the dam during an energency.

b. kho to notify, including public officials, in case

evacuation from the downstream area is necessary.

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(. .'. S

S=CION 5 - HYDRAULICS/HYDROu)GIC DATA

5.1 Design: Leatherwood Dam No. 3 was designed by the Soil

Conservation Service (SCS) as a multi-purpose dam, and hydrologic and

hydraulic data is available, and stage-storage and stage-discharge

data were used in the evaluation. This structure is a Class "A" dam

according to the SCS classification method.

5.2 Hydrologic Records: There are no records available.

5.3 Flood Experience: According to Mr. Charley M. Finney, an

estimated maximnum pool elevation of 760 msl occurred in April 1977.

This corresponds to a peak flow of approximately 276 CFS.

5.4 Flood Potentials: In accordance with the established guide-

lines, the Spillway Design Flood (SDF) is based on the estimated

"Probable Maximum Flood" for the region (flood discharges that may be

expected fra the most severe ccbination of critical meteorologic and

hydrologic conditions that are reasonably possible in the region), or

fractions thereof. T1he Probable Maximum Flood (PMF) and PMF hydro-

graphs were developed by the HEC-I DB Computer Program(Reference 4,Appendix VI).

Precipitation amounts for the flood hydrograph of the PMF were taken

from the U.S. Weather Bureau Information (References E and 6, Apendix VI).

Appropriate adjustments for basin size and shape were accounted for.

These hydrographs were routed through the reservoir to determine

maximum pool elevations.

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5.5 Reservoir Regulations: For routing purposes, the pool at

the beginning of flood was assumed to be at elevation 745 msl.

Reservoir stage-storage data and stage-discharge data were utilized

from the existing design report. Floods were routed through the

reservoir using the principal spillway discharge up to a pool storage

elevation of 766.6 msl and a combined principal and emergency

discharges for pool elevations above 766.6 msl. Pool elevations above

772.2 msl were routed over the non-overflow section of the dam.

5.6 Overtcpping Potential: The predicted rise of the reservoir

pool and other pertinent data were determined by routing the flood

hydrographs through the reservoir as previously described. The

results for the flood conditions ( PMF and PMF) are shown in the

following Table 5.1:

1

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%£

TABLE 5.1 - RESF__MJ1 R PER F INAE

Hydrograph

NormalFlaw PMF PMF

Peak Flow, CFSInflow 10 19,408 38,817Outflow 10 18,578 37,132

Maximum Pool ElevationFt, msl 745 773.9 776.4

Non-Overflow Section(Elev 772.2 msl)Depth of Flow, Ft - 1.7 4.2

Duration, Hours 3.0 5.0

Velocity, fps* - 5.7 8.9

Tailwater ElevationFt, ins1 731 747.8 753

*Critical velocity

5.7 Reservoir Lptying Putential: A 36 inch diameter gate at a,

elevatior. 732.3 mrsi is capable ol drainina thc reservoir tnrough the

outlet pipe. Assuming that the lake is at normal pool elevation (745

rnsl) and there is 10 cfs inflow, it would take approximately 1.5 days

to lower the reservoir to elevation 733.8 msl. Tnis is equivalent to

an approximate drawdown rate of 7.5 ft/day based on the hydraulic

height measured from normal pool to the invert of the drawdown pipe

divided by the time to dewater the reservoir.

-19-

. ... ... J. ,,. _K .-

I

5.8 Evaluation: The U. S. Army, Corps of Engineers' guidelines

indicate the appropriate Spillway Design Flood (SDF) for an

intermediate size, significant hazard dam is the PMF to PMF.

Because of the risk involved, the PMF has been selected as the SDF.

The spillway will pass 30 percent of the PMF without overtopping the

crest of the dam (60 percent of the SDF). During the SDF, the dam

will be overtopped for three hours up to maximum of 1.7 feet and reach

a maximum velocity of 5.7 fps.

Hydrologic data used in the evaluation pertains to present day

conditions with no consideration given to future development.

-20-

SECTION 6 - DAM STABILITY

6.1 Foundation and Abutments: The dam is located along the

western edge of the Piedmont Physiographic Province of Virginia. The

site is underlain by the Leatherwood Granite, which is typically a coarse

grained to porphyritic granite and is approximately 1020 million years

old. Detailed geologic maps of the area do not indicate the presence of

any faults in the site vicinity. Site geology is presented in more detail

in the Design Geologic Report, which is included as Appendix IV.

The subsurface investigation indicated that along the centerline of

the dam, the site was underlain by shallow alluvial and residual soils

over weathered bedrock. The bedrock surface was sarewhat irregular along

the principal spillway. Bedrock was enoountered fran 3 to 5 ft on the

right abutment and 1 to 5 ft on the left abutment. Test pits showed the

emergency spillway cut to be free of rock except at Station 4+20 on the

centerline.

The alluvial sands below 3 to 4 ft were described as "unstable with

a fairly stable residual sand noted between these and rock." It was

recommended in design that areas of low density silt or sand under the

fill with density less than 77.0 pcf should be removed and replaced with

compacted fill. It was stated in the design report (Appendix V) that

"this foundation may be weaker and more coapressible than that tested fram

Site 5."

-21-

The potential for seepage through the foundation was recognized,

and a cutoff or core was included in the design. Moderate permeabilities

ware anticipated for the overburden soils and the designer expected some

seepage through all weathered bedrock. The "as built" drawings show

the presence of a drainage trench under the downstream portion of the

embankment to collect any seepage which may occur.

6.2 Embankment:

6.2.1 Materials: "As built" drawings indicate the dam is a zoned

structure. Section No. 1 of the dam, consisting of the cutoff and

interior core, was constructed with soils classifying as M. Section No.

2 (the upstream slope, the downstream slope and crest) was constructed

with SM materials. All specified materials were excavated from select

borrow areas. Fill materials in both sections were to be compacted to

95% of maxinum dry density in accordance with ASTM Standard D-698 (Standard

Proctor). Clrnpacted densities and shear strength values for the

embankment materials are sumarized on page 2 of Appendix V. Specifications

for maximnum lift thickness and maxium rock sizes were not observed in the

design data provided.

No one-dinensional consolidation test was performed, however,

the SCS soil mechanics laboratory estimated fram the consolidation phase

of the shear tests that approximately 5% settlement might be expected in

the base of the' fi. It was recommended that a 1.25 ft overfill be

provided to compensate for residual settlement in the fill and foundation.

-22-

d .-

6.2.2 Subdrains and Seepage: In attempt to control seepage, a

cutoff was constructed to bedrock below the more permeable alluvial soils

in the floodplain and extending into the abutments. Details are shown on

Plate 3 of Appendix I. An internal drainage systen was also constructed,

consisting of a drainage trench beneath the downstream portion of the

embankment to collect any seepage which may occur. Drainage pipes were

provided for transmitting the collected water to the plunge pool. During

the field inspection it could not be determined if the drains were

functioning properly because their inverts were below the discharge pool

level. In attempt to prevent piping around the principal spillway pipe,

7 anti-seep collars were included as shown on Plate 5 of Appendix I.

6.2.3 Stability: A stability analysis was performed for the upstream

slope at this structure and the report describing the engineering design

data used is included in Appendix V. These data were reviewed along with

the stability analysis and were found to be acceptable. The minimum factor

of safety calculated for the upstream slope for the drawn down condition

is 1.56 as given in Appendix V. Reference 1, Appendix VI, recommends a

factor of safety of 1.2. A stability analysis was not performed for

the downstream slope.

The dam is 41.2 fthighand has a crest width of 12 ft. The upstream

slope is 2.5H:lV with a 10 ft wide berm at pool level between elevations

780.5 and 781.5 msl. The upstream slope then continues at a 3H:lV slope

below normal pool. The downstream slope is 2. SH: Iv. The dam can be subjected

to a sudden drawdown since the lake level can be drawn down at a rate of

7.5 ft/day. This exceeds the critical rate of 0.5 ft per day for earth

dams. According to the guidelines presented in Design of Small Dams,

-23-

U. S. Department of the Interior, Bureau of Reclamation for small

homogeneous dams, with stable foundation, subjected to a drawdown and

with an embanaent of SM to M materials, the recoivended downstream slopes

range from 2H:lV to 2.5H:IV. (A homogeneous dam was considered for this

evaluation because Section No. 2 materials are not as coarse as those

described as shell material in the Design of Small Dams .) The recommeded

crest width is 18 ft. Based upon these general guidelines, the downstream

slope is adequate, although, the ebankment crest is 6 ft narrower than

recmended.

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

Therefore, according to the Recommended Guidelines 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: Based upon the visual inspection and the design

report, the foundation is considered sound. The factor of safety for the

upstream slope during the drawdown condition meets the U. S. Army, Corps

of Engineers guidelines. Although a stability analysis was not performed

for the downstream slope, the "as built" slope meets the requirements

recommended by the U. S. Bureau of Reclamation. Overtopping is not

considered detrimental to the dam with respect to erosion because of the

shallow depth and short duration of flood. Also the critical velocity

is slightly less than 6 fps, the assumed effective eroding velocity for a

vegetated earth embankment. The embankment crest is 6 ft narrower than

recommended by the U. S. Bureau of Reclamation, however, based upon the

-24-

performance history of the structure and the short overtopping duration,

the narrow width is not considered a problem.

Since no undue settlement, cracking or sloughing was noted at the

time of inspection, it appears that the embankment is adequate for uximin

control storage with water at elevation 745 nol.

-25-

I&

S.

SECTION 7 - ASSESSMET/REEDIAL EASURES

7.1 Dam Assessment: Sufficient engineering data is available for

assessing the dam. The visual inspection revealed no findings that proved

the dam to be unsound. There is an annual inspection and maintenance

program for this structure, but there is no emergency operation and warning

plan. Overall, the dam was in good condition at the tine of inspection.

U. S. Army, Corps of Engineers guidelines indicate the appropriate Spill-

way Design Flood (SDF) for this dam is the PMF. The spillway will pass

30 percent of the PMF (60 percent of the SDF) without overtopping the

crest of the dam. During the SDF, the dam will be overtopped for three

hours up to a maximum of 1.7 feet and reach a maxinum velocity of 5.7 fps.

Flows overtopping the dam at a maxixum velocity of 5.7 fps during the

SDF are not considered detrimental to the embankment with respect to

erosion. The spillway is judged inadequate, but not seriously inadequate.

Field measurements indicate the embankment crest is 3 ft narrower than

shown on the "as built" drawings. Review of available stability data

indicates the structure is stable as designed.

7.2 Recomrended Remedial Measures:

7.2.1 Emergency Operation and Warning Plan: It is recomTended

that a formal emergency procedure be prepared, prominently displayed,

and furnished to all operating personnel. This should include:

1) How to operate the dam during an emergency.

2) Who to notify, including public officials, in case

evacuation from the downstream area is necessary.

-26-

( a..

7.3 Required Maintenance: The inspection revealed the following

maintenance items that should be scheduled by the owner during a regular

.maintenance period within the next 12 months.

a) The grass and weeds on the dam embankment and in the emergency

spillway should be cut at least once a year and preferably

twice a year. Maintenance is recomended in the early summer

and fall.

b) Existing trees on the dam should be cut to the ground and

removed fran the embankment. Logs laying on the embankment

should also be removed.

c) The eroded area along the left side of the emergency spillway

approach channel should be backfilled, compacted and reseeded.

d) Debris should be removed from the trash rack and the top of

the riser.

e) A staff gage should be installed to monitor water levels.

-27-

4 *

APPENDIX I

NAPS AND DRAWINGS

Egglseston, Cern IV ~ ji,

P~ /

* Q' ~.4eseroir1

* ~J~eseervorroN

BM

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-A.--- - .' --*C.j

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N ~~~ ~ ~ ~ 1 .A- 1.F IA '* AX i4fO N

'SPLATE 2

-44()/U -J000 -?40 .4 r ~ O 'c' ~O .^ 4SCC C

790AOLGADAa 740

770 SX/6V 16k *4769 AZZY AC9. 0 ,'770

r~Jr7ffR(NCYS/ItWW.4frb' 76.

740 74.0

750 API MO0

7740

720 fXCRAFE ,AO r'RMf *DC AND*4C~/U 4"/t J' 7wm 3 , SIA 7f ' Q/A

PIQf/lLt ALONG CLATFLIA'6 ODAIi

21

l fa Skac 's

tIA jrWA rf~ * doriD

le"- - -

I. __ V- -

'/ 7j~~st~e~ ~r~ fti's~f- VCA*Aw

I.'.~l 0 -. A

766. I I

ITI

710

N S, TO 67AG MO

LIAT

MlL

AM0 .5f

~iO7~6ALOIC ENTRLIE F~tER6WCYSPIl Wqj TAPICAl EACA VA/ SEC/O1N i9V~rfWi CMEN i,

fI150 20,00 . 2,5o S3'0e 3,i5D, 4vWO 4fg'O

"So 755 -. C e.-e

2A TEO 7J. .5ES8R NA

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1A1f O PT4ASMACALrAIRWO lf'/ )rIE

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0 VA SEEPAGE DRAIN DETA1L_-

A A

P-L AT Ef _______________________________________________ _________________VA___

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PLAN-VIEW

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- .. ~ e". EEL SCHEDU..E 1

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LEu* ~ r ic a 5013-- .I4 5 23 -22 ' 7 '2.3' 50-8 I

*1 20 6 41 -2.

LE~~~~ 4,7~. Fac 2 3 ~ ?~24 3 2

7 2 7 25 .s--

20 6 3 2 9 .402

7-0 25'0 3 63 2 'C R01II 5 7l40 2 30- 5 I Ai_;

316 39 39 026G.2 5 29 - S.-

A -6 24 34L 7 0 2 0 3 t t '

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349 46 6 z0 __5__7F

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42 _ .4 C-43-

514F IS _ P 122 - &u. 5 '2 *-. ,Iw FACES 4 20 1-t4b 2 4 44T5!

-46 .6 . - 649 2 .7-5 '

SECTION fA-A 26430FA~r25 -6A

4, f 5 WFV. -L 46

FIELD 8E(N*D P81WF BARS 54 2___ t___AROUND 6 OIA BCCMP --

325N 50 __ 5

CINSTRUCTION~ ! ~S_ _____

JOINT 61 -- ! .a62. __ __ 5 _ _

-.- f 6504!fHAN6 6 c

__T TL 9-

2 3.2~@'. L ~ ,PAR TYPES

4,

SE-CTION A -A ovsor FAcr QUANTITIES

N0 6 BARS 466 ?%AhoM FT 731 LBLSNo8 7 G8*5 252 06acWB1 3152 9 LBS

CLASS "a TYPE I .IIfL_ Cu To0l

94 DAM NO.3 PET7ERS BRANCH -

L06- LEA THRODCEKWA7 TSHEDR____~p IMPACT BASIN DETAILS

r mar N-. V~AIIW -'*'

LE I j:i~~'~ **-

uS@6 DOi VI f-~ jE TION LONG oft PLAU 8ma or IVI au Ap VA-485-P

- , - I -. aid

APPENDIX II

PHOT~OGRAPHS

Photgrap No 1 Ustram Sopx

Photograph No. 1 - Dowstream Sope

Photcxgraph No. 3 -Intaiku Structurc!(Note Debris in Lkw Flow (Orifice)

Photograph No. 4 - Outlet Structure

11-2

i -I . -11 1

..... ....

Photograph No. 5 -Emrergency Spillway

Photograph No. 6 - Downstream Channel

11-3

APPENDIX III

FIEL OBSERVATIX'Z

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APPENDIX IV

DESIG Ic ETOR

DESIGN REPORTC,

LEATHERWOOD CREEK WATIMSHEDDAM NO. 3

HEIM Y COUNIT, VIRG INIA

This floodwater retarding dam is located on Peters Branch ofLeathervood Creek approximately 1-1/4 miles northwest of Leatherwood,Virginia. Sheet 4 of this report, together with the Martinsville,Virginia-North Carolina 15 minute quadrangle published by the U.S.Geological Survey, may be used to locate the structure.

The design of this dam is in accordance with criteria establishedby the Soil Conservation Service, U.S. Department of Agriculture. It isa class (a) structure as defined in Washington Engineering MemorandumSCS-27.

This is one of five flood retention structures designed to reduceflooding in the Leathervood valley. It will retard a 50-year frequencystorm without discharge occurring in the emergency spillway. Thisretention capacity Is equivalent to 2.86 Inches of runoff from a 1,250acre watershed area.

The structure consists of a compacted earth fill with cutoff tobee-rock under the centerline of the dam. A drainage trench is includedunder the downstream portion of the embankment to collect any seepagewhich may occur.

The drop inlet principal spillway consists of a reinforced concreteriser, tngether with a 42-inch diameter conduit of reinforced concretewater pipe and a Bradley Perterka impact basin to dissipate energy atthe outlet end of the conduit.

The emergency spillway is designed as an earth cut into siltysands in the left abutment.

A typical cross section of the earth fill and a sunmary ofpertinent design information is given on sheet 5 of this report.

The results of hydraulic and hydrologic determinations are givenin the following table:

RE E EN E DR'AWING NO.REFERENCE: U.S.DEPARTMENT OF AGRICULTURE VA-483-R

SOIL CONSERVATION SERVICE

UPPER DAISY. PENNSYLVANIA "-bSHEET 1 OF5ENOIV4 92RING A W TERSHED PLANNING UNIT DATE 1 2 1 6 6 3

-, -, -

+ + l '--

4£

DESIGN REPORT

Factor Surface Runoff Peak Peak Elev. of Storage Element ofWhich De- Area in Inflow Outflow Maxizum in Structuretenriiners Acres Inches c.f.s. c.f.s. Stage Ac.-Ft. DeterminedStage by Maximum

Stage

50-year 34 0.54 744.8 186j, Crest ofsediment orificeaccumulation

t

50- .ear 110.5 3.22 252 766.6 1695/ Crest offrequency emergencystorm spill-waymoisturecondition II

0.6 x6-hour 122.5 3.37 5480 2170 769.0 1770 Design high

poin. rain- water

fall moisturecondition 11

di. x6-hour 135 4.17 10,060 8120 772.2 2190 Top of dam

point rain-fall moisturecondition II

'/Does not include 13 acre-feet of sediment allocated to flood pool.

-/Emergency spillway crest determined by utilizing TR-10

The time to empty 100 percent of the flood storage is 9.1days.

Copies of the geology and soil mechanics laboratory reports used inthe design of this structure are attached.

The following publications were used in the design of this dam:

National Engineering Handbook No. 5, HydraulicsNational Engineering Handbook No. 4, HydrologyNational Engineering Handbook No. 6, Structural DesignEngineering Division Technical Releases Nos. 2, 5 and 10

RE ER N E:DAW ING NO.REFERENCE: U.S.DEPARIt4ENT OF AGRICULTURE VA-483

SOIL CONSERVATION SERVICEO!CFING & WATERI"ED PLANNING UNIt SHEET 2 or .

rAP'., PENNSYLVANIA DATE 12-16-63

L64

DESIGN REPORT

. _, Copies of these publications may be obtained from Mr. Tom F. McGourin,

State Conservationist, USDA, Soil Conservation Service, Richmond

Virginia

Concurred:

Gerald E. Oman R. C. Barnes, Jr.

Design Engineer State Conservation Engineer

Vincent MceeverHydrologist

Robert F. FonnerGeologist

C

REFERENCE: DRAWING NO.

U.S,DEPARTMENT OF AGRICULTURE VAWINGNO.

SOIL COMSERVATION SERVICE V

ENGINEERI!'- & WATERSHED PLANNING UNIT SHEET.. 3PF ANUPPER DARBY, PENNSYLVANIA DATE " 12-16-63

" ! .7.. _ T , . ., . .. ... ... ....hi , ,,.. .. .... i Jwf

L

DESIGN REPORT*

LEATHERWOOD CREEK WATERSHED PROTECTION PROJECTSITE NO. 3, PETERS BRANCH

VA-483-RHENRY COUNTY, VIRGINIA

36045 '

0

C. o

36040'

- REFERENCE: U.S.DEPARTMENT OF AGRICULTURE DRAWING NO.

MARTINSVILLE, VA-NC SOIL CONSERVATION SERVICE VA-483-1R15' QUAD SHEET 4 OF 51947• t DATE .5-23-63

~~i

DESIGN REPORT

; Sunnry Sheet

JECT VS CT/OAJSE9 P/LT (,----A77?2 sE TMe SILTY SAND (SM)

R-PR!SMI TED oy TvE LOGS OF MA;TER1/4 A#PReSEATEP BY TH40,6S iF FwS'Pwy e BOeeow 4E4EA4LM2GfNCy 5PLLWAY "/'P-ZOI 7 rp. Co FO, ' 7V /F P ?4 Tow

/F 6 FAOo " 7"0 14" TP- /0/ FIF1 TF~/ O ( P$' F° P2 / e0/'/ O/ 7016 P20,

TO v, T.P 102 A*OAol 'T0

7:.5.3 - 746,3

S SfCT/OV 2 Z07 0/1 I SFCTI0/ 2

-- I

64uTOI- T'A/c- / JF[PAG" DPe IA

Typical X-Section

I. Watershed dataA. Structure class -(a)B. Drainage area 6,)O0 Ac.C. Time of concentration - T 5.4 "Hrs.D. liydrologlc curve number -'C

1. Moisture condition IIn "722. Moisture condition III

II. Principal spillwayA. Conduit

1. Size (I.D.) 42 In.2. Length 202Ft.

B. Riser

1. Size 3.5x9.0 Ft2. Height 2 Ft.

C. Weir length Id.0 Ft.D. Orifice size 1. 235 in.E. Pond drain size _ 6 in.

III. Emergency spillw ,"A. Width 200 Ft.B. Side slopes 3:1 IVC. Length of level section 20 Ft.D. Egit lotr secio (E. Maximm velocity atcontrol section (D.H.W.) 6.75FtecF. i)ration of flow (D.H.W.) thrcogh emergency spi ii.69 Hr,0. Frequency of use

REFERENCE: DRAWING NO.U.S.DEPARTMENT OF AGRICULTURE VA-.3SOIL CONSERVATION SERVICE

IENGINEERING & WATERSHED PLANNING UWJT SEET 0F....UPPER DARBY. PENNSYLVANIA

DATE 12-16-63

AI . . -- =' ll l<-= - . .. = . . . [llil... .. l l ll.. . rllrI /

:*i : UNI~tL, ,AJ% DIP-41WN11 U &Af- U~LU

C DETAILED GEOLOGIC INVESTIGATION OF DAM SITES

GENERAL

teVIRGINIA HENRY - .rLee ~.~.hdatherwood CreekStat nl3- -- e I _ _Wterhe

SI4PWWIIISO~Fun clasrs Branc nube - __. _ _~ _..... Site group Structure Clas 853_______

tne Kae ACK, T., Geologis FP 2 Pti Case backhue± 5/63 -

-'-f-rure &no i t. Joep size. make moe et

SITE DATA

9.6. 298 Earth Fill Flood ?eetoDrainage acea vie o'T. acres Type oft st'u~tuj _ _____.... PuPose . - -- ___________

Direction of valley tier! .~e " - ~ a Mu re~sh of fill feetjet e~gno ~t 1 .

Estimated uglurre nf cur 3 71,~ ?2,50 cubic - hi

* . STORAGE ALLOCATION

ir -am. a, ! Scuface Atom sk~res, Depth at Dam Ifeet)

sed men:133i.000

2l100 126.0 34.5

SURFACE GEOLOGY AND PHt4SiOGRAPHY

ftysioliaptrc clsrituFiedm 'nt - Prc_.vincct - Topograuby' ___II! Attifrdt o' beas (lip -nonle Strike none

St~piresS 'of abutmen's ,26 - przen R'~ :D!2, _prcen? t i cf lloOtodia, a! centerion of ism -125

-General geoilogy a'i.e siei neli y the Le athe rwoodgr an it e f ortntiolt 5 whhijs of

probable Paleozc~ic _age. At this loCCaltv, he formation ranges from a grite to a

) syenite. Quartz, whicht is an Tsecain granite, ranges from 3 to 16 percent.,

In the syenite,plagioclase feldspar bectines an important mineral. It occurs up to

25 percent of the volume of rocks. This high plagioclase syenite is on the higher

elevations of the left abutment. The Lloyd SOil that is on the left side of the emergency

spillway is furmed from this more basic byenite. ___________

The content of black biotite mica ranges. frvut 1_ rqO _,e Ab±&. A high

biotite content for a eranite syen ite. _In milny _pjacesi~~e black color to the*rock#. Muscovite mica is present in minor amounts. -- _________

Peter's Branch flows through a narrow valley at the dam site. Recent stream

.alluvium fills the narrow flood plain. The stream flows in a stream channel that

ranges from 2 to 3k feet below the flood plain. The stream is slowly degrading.

aces of former meanders are at the dams us t a_ps1rcmtrearToa am aidi IraI

tributaries flow in a strongly entrenched dendritic pattern. Traces of former pmene-

Vk*/- I/

%L

Pge #2

plairation ar, s-ill observable') iH that th, tops of all hill Lri-t s aregenerally at t! - zar elevat ion. The topou;raph) has reached carly , maturitv.

Centerline ,! tit Dam

Both abutm,,,nts are underlain by syenite that has a h.gh content of bIackbiotite mice. The depth of the rockline ranges from 3 to 5 feet on the rightabutment. On the left abutment it ranges from I to 5 feet. The syenite ap.-ars

unjointed fri' surface observation.

The floo'd plain is underlain by recent stream alluvium. The- upper 3 to 4

fet of this is moist silty to sandy Congaree soil. Below this is a wet reduced

gray layer of silt and sand which ranges from 4 to 8 feet in thickness.

Below this reduced alluvial layer is a light yellowish red silty materialthat is a buried residual soil. It is not wet. Rock fragments and mica flakes

are present. In comparison to the sandy wet alluvial material, this lattermaterial appears fairly stable. It was observed from several test pits thatthis dryer layer is underlain by weathered rock.

Emergencv Spil wav

The emerAencv spillway is located-in the left abutment. Test pits showedthe spillway cut to be free of rock, except at station 4+20 on the centerline.

Here the rockl i,. - C. 'urs tw'. feet above ,-adc.

Two siil t'.-es are Dresert Ln the erier-ency spillway. The four test pits

on the left siJ, snowed Lloyd soil to ht present. This soil has a tight clayeyB horizon and a loose micaceous C horizun. The centerline and the right sidehave Cecil s, £l *hat also has a clavev R horizon and a loose micaceous C horizon.For constru,-t ion purp, ses, the B horizlns of these two soils are similar. Alsothe two C ht-rizcns are extremely simila . Th, B horizons of these are consideredto be betttr cvnstruction material than th: C rorlzon,%. If there is need foradditional borrow, the left slope 01 the vmer;_eicy spillway can be benched.

Borrow Artea

Tw, burro.w areas were. n'V'stLiateJ. Cne is below the waterl;ne on theleft side cf th,, stream. 1he other is above the waterline on the aame side c.ftht stream. The borrow area below -h)e waterline is narrow, averag2ing only 5L,feet in width, it consists uf residual Cecil soil and colluvial Thurmont

soil. The averag useable depth of these soils is approximately 5 feet. Thepart of this borrow area mort than 800 feet from the centerline of the dam isinaccessible to the extent that it is almost unuseable. It is bordered on the

stream side by a swamp and on the hill side by a fairly steep slope.

The second borrow area is above the waterline. It is largely composed

::. of shallow Cecil soil that averages 4 feet in depth. This area is accessibleto the dain site.

..

Page *3

I- Principal Spillway

/ Three possible conduit trenches were i. estigated. Pipe trench A intersects

t the ceatecline of the dam at station 24&50.. Under the riser, weathered rockwas found at 12 feet. It was not encountered under the outlet. A large

spin offir graitewasin this trench. It lies within I to 5 feet ofteground surface for 50 feet on both sides of the damn centerline. To cut thisspine down to a depth of 2 feet below the cradle would require the rem~oval ofat least 520 cubic yards of granite. In this pipe trench the area under the

.riser and outlet will have to be excavated and backfilled to a depth of 7 feet.

Pipe tre nch B intersects the centerline of the dam at station 2+92. -It* parallels pipe trench A at a distance of 40 feet. No rock was encountered

In this trench. +From the rise~r to 40 feet left of the dam centerline, no*firm soil was encourltered even to a depth of 11 feet below ground.level. A

fairly firm buried residual soil occurs for approximately 25 feet along thispipe trench in this area left. if the centerline of the dam. The riser and

".'"'he outlet of this pipe trench will be on unstable alluvial material.t'11 4

4 _,A~ third pipe trench was investigated. It is 25 feet liia of pipe trench A.'In this pipe trench the granite spine was encountered at 7 feet below ground-.level. The buried soil was encountered in test pits at a depth of 6 to 7feet for 50 feet on either side of the centerline of the dam.

-7 3 ~ P.

~i. A

Sca le

Leahero. grnt an -niewt

Scagle s fedsa

GELahOGI d rAnit Fi THEit ARASROUDN ITpegATitesWO CRnd migmatENR ONYVRII

Leatherwood ~ ~ ~ ~ ~ 4F 4rntLihotogesodVT?

structure~~~ (budrFdfue

UNIILD bIAILb UL)PAR IM 4'I Ul- AGHICULIUNE

SOIL CONSERVATION SERVICE

SOIL SAMPLE LISTSOIL AND FOUNDATION INVESTIGATIONS

Location Henry County, Virginia Owner

Leatherwood Creek Peters Branch 3Wotershed Sub-watershed Site No._

Submitted by Mack, T Date June 19 63

Sent by Truck Government B/L No.(carrier)

Field IType ofLob. Sample i Somple Description Depth Sample

No. Nc. Location Grid or Slation From To Undist. Disi.

LARC E-

101-1 Borrow Area 90' Rt. 4+74 A 1 6 x

102-1 Ditto 70' Rt. 7+00 1 13 x

201-1 Emergency Spillway 100'Lt. 2+00 1 6 x21 "- K -7 3 llway21 Ditto 6 16 x

__206-1 "-2+00 -V E.Spillway 1 6 x

20t-2 Ditto 6 14 x

SMALI

50-1 F Toe Drain -3+68 £ Pipe A I 6 x

501-2 " Ditto 6 11 x

502-1 " 65'LL.3+75 j Dam 1 5 x

- -- -

- -- ~1[- ,_______

Originol to Soils LO0ootory bStt-oevtoiCnpy to Eand WP Uni Sheit "o eesDistribute other copies as directed by State Conservationist Sh~. o heats

J .

APPENDIX V

STABILITY DATA

- -- F- " ---

UNITED STATES GOVERNMENT

* MemorandumTO R. C. Barnes, State Conservation DATz: August 28, 1963

Engineer, SCS, Richmond, Virginia

FR OM Rey S. Decker, Eead, Soil Mechanics laboratory,SCS, Lincoln, Nebraska

SUBJECT: Virginia WP-08, Leatherwood Creek, Site No. 3

ATTACMIEITS

1. Form SCS-354, Soil Mechanics laboratory Data, 2 sheets.2. Form SCS-355, Triaxial Shear Test Data, 2 sheets.3. Form SCS-352, Compaction and Penetration Resistance Report, 6 sheets.4. Form SCS-357, Summary - Slope Stability Analysis, 1 sheet.5. Form SCS-372, Recommended Use of Excavated Material, 1 sheet.6. Geologic Plans and Profiles.

INTERPRETATION AND DISCUSSION OF DATA

FOUNDATION MATERIALS

A. Classification and - The site is on slightly weatheredgranite. It was invesLzig ed by backhoe test pits only, and thedepth to rock is not defined if over 10 feet to 12 feet.

logs indicate the materials may class about the same as on Site 2-A,ranging from Z,, to CL and MK.

B. Consistency, Strength and Compressibility: The alluvial sandsbelow 3 feet to 4 feet were described as "unstable" with a "fairlystable" residual sand noted betWeen these and rock.

This foundation may be weaker and more compressible than thattested from Site 5.

C. Permeability: Permeability of both soils and bedrock is assumed

to be low as on Site 2-A.

14BANKCvENT MATERIALS

A. Classification: Soil classes of these samples are S.1 and MH. TheMH on this site is finer and the SM is intermediate in clay sizeand compacted density to those previously shear tested. Thesurface 3 feet to 4 feet may be more plastic than the compositesindicated on this site also.

, ., I

L.

S .- 2 -- R. C. Barnes -- 8/28/63Rey S. DeckerSub j: Virginia VIP-08, Leatherwood Creek, Site No. 3

. B. Compacted Dry Densities: Standard compaction tests yielded maxim=._ dry densities of 90.0 p.c.f. to 93.5 p.c.f. for iM and 98.0 p.c.f.

to 105.0 p.c.f. for SM.

C. Permeability: Rates for compacted MI should be very low. Thosefor compacted SM will largely vary inversely to density.

D. Shear Strength: The fine M and the most well graded SM were testedat 95 of Standard density. The specimens were saturated, and con-solidated, undrained triaxial tests were performed. Shear para-meters were interpreted as = 19, c = 800 p.s.f. for the M, and

= 30.50, c = 300 p.s.f. for the SM. These values are recommendedfor design.

E. Consolidation: The consolidation phase of the shear tests indicateabout 5% settlement may be expected in the base of the fill.

STABILITY ANALYSIS

A 41.4-foot dam with 10 feet of foundation no weaker than the embank-ment was assumed. Pilure arcs werc tried in the 2 1/2:1 over 3:1upstream slope with a 10-foot berm. They showed such high safetyfactors under full drawdown that no other trials were made. See thesummary on Form SCS-357.

REC O.'._2,_.DA wrbOi S

A. Site Preparations: Areas of low-density silt or sand under thefill with less density than 77.0 p.c.f. should be removed andreplaced with compacted fill.

B. Cutoff: A cutoff or core is indicated. Unless it can bottom onfirm rock at leLst up to the sediment pool elevation, a foundatioAdrain will be required. Backfill with the most plastic materialavailable.

C. Principal Spillway: All three locations investigated have objection-able features. A slightly skewed location near t Station 3+75appears to offer better foundation conditions even though thealignment may not be so desirable. It is suggested this beconsidered.

D. 'Drainage: No measures are needed if the cutoff is bottomed onfirm rock. Otherwise a foundLtion trench drain at c/b o.6 isneeded.

3 -" R. C. Barnes -- 8/28/63Rey S. DeckerSubj: Virginia wP-08, Leatherwood Creek, Site No. 3

E. Eba-Lment Design: The following are recommended:

1. Selectively place the 1.1 in the backfill and center sectionand the S:.! in both shells. The low-density SM. should gointo the downstream base.

2. Place all materials at 951p of Standard (B-2) density. SeeForm SCS-372 for minim, densities and allowable moistureranges.

3. Make embamn:-ent slopes 2 1/2:1 over 3:1 upstream with theslope change and a 10-foot berm at elevation 745.3; and2 1/2:1 downstream.

4. Provide overfill of 1.25 foot to ccmpensate for residualsettlement in the fill and foundaticn.

C. Prepared by:

B . Phi__, Lo~s

Attac cments

cc: R. C. Earnes (3)E. 1-1. Kautz, U:er ... (2)G. W. Grubb, ULper Darby, Pa.

C

- - / U. S. Z-?A,1::r:.T CF Z L I L ErO, C5m SDI .11' :''fl: S , C L-5 $'CS

,IL CC;

10., L : -':; I CS L .::TO 7.7• ....... ~ ~ " SLCE ST:!LIT7 "...:- , ,IS

State Pro) ectCJ F ,'___________"Cieikd y -

__, t __ _ _e ___-_ " Analysis Mede By

Checked by.

Method of Analysis -

C3Location 47______0 o

1, ! , .-p Ie No.

-__ __ __ i I__ _ _ _ .- ,c~ < ' __ _ _ __ _ _ __ _ _ _

_>_____ II __ _ _ I___ -____ ___ __ ...!Codto(np. ~ Opt. Sat. Opt. j Sat. Opt. Sat IOpt . si.

______ I I ______L2 I ' I ___

44. Tan3 __ _ 2K _____ ! I i s _

- :P.~r, :YSLOPE-

,01. !) Tric" Slozse i ciir, s I K

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(1 • ,, - _ - -

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C, - K --7- .- , '... . -. ...

.. -: . [ .... _ _ _ _ _ _ _ _ _ _ _ _ _ _

0-

D fDC.,.%S T E 4 S LOPE

0 Tra _______ Conditions

0 I

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Co , I __ __ _ _ _ _ _ _ __ _ _ _ _ _ _

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-- ' i lnf ,,I ..... ... , ,--'-

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COMPULA TION !>HEL.

SCS-522 REV 5-58 SOIL CONSERVATION SERVICE

STATE iPROJECT

B HECKUE"BY JDATEO

SUBJECT . \'SB" . . .3_i_." .... SHEET ......OF .

;:.- ,.--.7 .--..... ...

* - -a 1'"O z : .

; .,: i .! , x . -n r ! I -

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-- - . . .. I* o : . ...,. .e .

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APPENDIX VI- REFERENCES

1. Reoomended Guidelines for Safety Inspection of Dams, Department

of Army, Office of the Chief of Engineers, 46 pp.

2. Design of Small Dams, U. S. Department of Interior, Bureau of

Reclamation, 1974, 816 pp.

3. Geology of the Snow Creek, Martinsville East, Price and Spray

Quadrangles, Virginia by J. F. Conley and W. S. Henika, Virginia

Division of Mineral Resources Reports of Investigations 33, 71 pp.

4. HEC-1 Dam Break Version, Flood Hydrograph Package, Users Manual

for Dam Safety Investigations, the Hydrologic Engineering Center,

U. S. Anry Corps of Engineers, September, 1978.

5. Hydrcneterological Report No. 33, U. S. Department of Ccarerce,

Weather Bureau, U. S. Department of Army, Corps of Engineers,

Washington, D. C., April, 1956.

6. Technical Paper No. 40, U. S. Department of Ccmmerce, Weather

Bureau, Washington, D. C., May, 1961.

L ,

DATE

FILMED'