AID-AO91 ROIMEL KELEPPER AND KAHL BALTIMORE MD F/6

AID-AO91 604 ROIMEL KELEPPER AND KAHL BALTIMORE MD F/6 13/13NATION4AL DAM INSPECTION PROGRAM. LAKE WHETSTONE (NDI ID NUMBER --ETC(U)JUL 80 E J ZE16LER DAC31-80-O050

UNCLASSIF IED NL

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MARYLAND L V

NDI ID NO. MD-53

MONTGOMERY * VILLAtbE FOUNDATION

PHASE I -INSPECTION REPORT

NATIONAL DAM INSPECTION PROGRAM

Prepared ForDEPARTMENT OF THE ARMY

Baltimore District, Corps of EngineersBaltimore, Maryland 21203

a-yNO RUNIMELKLEPPER & KAHL

C. Do 601 S~I oslig nlt

BaltmomMaryand 120

POTOMAC RIVER BASIN

WHETSTONE RIJN, MONTGOMERY COUNTY

MARYLAND

4VIKE VETSTONE

/ NDI ID .O. MD-53 ,c F"

MON'GOKERY- -V TL-,LA. FOUNDATIONGAIWRERSBURr, MARYLAND

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PHASE I INSPECTION SEPORT.


Prepared for: -

DEPARTnENT OF THE ARMYBaltimore District Corps of Engineers (75

Baltimore, Maryland 21203

By:RUMEL, KLEPPER & KAHLConsulting Engineers1035 N. Calvert Street

Baltimore, Maryland 21202

,Ju, , 8o.-

PREFACE

This report is prepared under guidance contained in the RecommendedGuidelines for Safety Inspection of Dams, for Phase I Investigations.Copies of these guidelines may be obtained from the Department of theArmy, Office of Chief of Engineers, Washington, D.C. 20314.

The purpose of a Phase I investigation is to identify expeditiouslythose dams which may pose hazards to human life or property. Theassessment of the general condition of the dan, is based upon visualobservations and review of available data. Detailed investigations andanalyses involving topographic mapping, subsurface investigations,material testing, and detailed computational evaluations are beyond thescope of a Phase I investigation; however, the inspection is intended toidentify any need for such studies which should be performed by theowner.

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

It is important to note that the condition of the dam depends on numer-ous and constantly changing internal and external factors which areevolutionary in nature. It would be incorrect to assume that thepresent condition of the dam will continue to represent the condition ofthe dam at some point in the future. Only through frequent inspectionscan unsafe conditions be detected and only through continued care andmaintenance can these conditions be prevented or corrected.

Phase I inspections are not intended to provide detailed hydrologic andhydraulic analyses. In accordance with the established Guidelines, thespillway design flood is based on the estimated "Probable MaximumFlood" for the region (greatest reasonably possible storm runoff), orfractions thereof. The spillway design flood provides a measure ofrelative spillway capacity and serves as an aid in determining the needfor more detailed hydrologic and hydraulic studies, considering thesize of the dam, its general condition and the downstream damage poten-tial.

The assessment of the conditions and recommendations was made by theconsulting engineer in accordance with generally and currently a~ceptedengineering principles and practices.

L.

I! II

POTOMAC RIVER BASIN

WHETSTONE RUN, MONTGOMERY COUNTYMARYLAND

LAKE WHETSTONENDI ID NO. MD-53

MONTGOMERY VILLAGE FOUNDATION

GAITHERSBURG, MARYLAND

PHASE I INSPECTION REPORT


July 1980

CONTENTS

Description Page

SECTION 1 - Project Information ISECTION 2 - Design Data 4SECTION 3 - Visual Inspection 6SECTION 4 Operational Procedures 8SECTION 5 - Hydrology and Hydraulics 9SECTION 6 - Structural Stability 12SECTION 7 - Assessment, Recommendations, and 13

Proposed Remedial Measures

APPENDICES -4 .,,-

Appendix Title

A Visual Inspection ChecklistB Engineering Data Checklist .C PhotographsD Hydrology and HydraulicsE Plates

F Geology



BRIEF ASSESSMENT OF GENERAL CONDITIONAND RECOMMENDED ACTION

Name of Dam: Lake WhetstoneNDI ID NO. MD-53

Size: Small (930 acre-feet, 33.8 feet high)Hazard Classification: High

Owner: Montgomery Village Foundation19231 Montgomery Village AvenueGaithersburg, Maryland 20760

State Located: MarylandCounty Located: Montgomery"Stream: Whetstone RunDates of Inspection: June 26, 1980 and July 15, 1980

Based on' the visual inspection, available records, past opera-

tional performance, and in accordance with the guideline criteria estab-lished for these studies, Lake Whetstone is judged to be in good condi-tion.

The water level in Lake Whetstone is normally maintained at eleva-tion 362 by way of a rectangular concrete drop inlet spillway. Sourcesof inflow to the lake include Whetstone Run inflow, storm drainage,surface water runoff, and rainfall on the lake surface.

No stability problems were evident for the embankment at the timeof the visual inspection.

Based on the hydrologic and hydraulic analyses, the Lake Whetstonespillway can pass approximately 59 percent of the Probable Maximum Flood(PMF) without overtopping. The spillway capacity is rated as inadequatebecause, even though the spillway can pass at least 50 percent of thePMF, analyses indicate that the spillway cannot pass the Spillway DesignFlood.

At the time of inspection, water was flowing from only the rightside of the twin box culvertwhich is the outlet works for the spillway.No blockage of the left side was observed from the outlet end of the twinculvert, but a blockage may exist in the bottom of the drop inletchamber, which is accessible by boat.

Although not apparent at the time of inspection, according to

conversations with the Owner, siltation of the lake is a continuingproblem. The dam was completed in 1966, and dredging was necessary in1972. It is estimated by the Owner that dredging will be required againin 1983. This problem of relatively rapid siltation has not been

resolved.

ii

Ia k e 1411 t - t oni4NIA ID No. MD-'-

The fo) I 'o 2 rn fil r~I-CS IT' r-1oMrnerdi'd to be accompli,'1''i tIc! Otw.n(r l~imely mannner:

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. vorrosivo 1''i -i~t ,0 -i part ial ly obF truci 2

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1 .r mA renrvc'ay0 ; -o tnmf which exist.

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LAKE WHETSTONENDI ID NO. MD-53

SECTION 1

PROJECT INFORMATION

1.1 General.

a. Authority. The Dam Inspection Act, Public Law 92-367,authorized the Secretary of the Army, through the Corps ofEngineers, to initiate a program of inspection of damsthroughout the United States.

b. Purpose. The purpose of the dam inspection program is to

determine if the dam constitutes a hazard to human life orproperty.

1.2 Description of Project.

a. Dam and Appurtenances. Lake Whetstone, completed in 1966, isretained by a zoned earthfill embankment. The embankment isapproximately 33.8 feet high at its maximum section andapproximately 1000 feet long. A drainage trench toe drain isindicated on available as-built drawings. Except for the1000-foot length of embankment, the shoreline of the lake wasconstructed by excavation into original ground.

Outflow from the reservoir can be accomplished by opening asluice gate at the base of the drop inlet structure. The gate

is manually operated and the gate stem is located on top ofthe drop inlet.

The various features of the dam and impoundment are shown onthe Photographs in Appendix C and on the Plates in Appendix E.A description of the geology is included in Appendix F.

b. Location. Lake Whetstone is located along to Whetstone Runin Montgomery County, Maryland. Lake Whetstone is shown onU.S.G.S. Quadrangle, Gaithersburg, Maryland, at latitude N390 10' 00" and longitude W 770 12' 20". A location map isincluded as Plate E-1.

c. Size Classification. Small (33.8 feet high, 930 acre-feet).

d. Hazard Classification. High. Downstream conditions plus thefact that a major roadway traverses the dam crest indicate

that a high hazard classification is warranted for Lake Whet-stone.

e. Ownership. Montgomery Village Foundation, 19231 Montgomery

Village Avenue, GQithersburg, Maryland 20760

f. Purpose of Dam. Aesthetics, Recreation and Flood Control.

g. Design and Construction History., Lake Whetstone was

designed, by Greenhorne, O'Mara, Dewberry, and Nealon, of

Fairfax, Virginia, and constructed in 1966. The generalcontractor for the dam was Northrup and Morrison, Inc. ofSilver Spring, Maryland. Detailed as-built drawings of the

embankment and appurtenances are available.

h. Normal Operating Procedure. The lake is maintained at thelevel of the drop inlet. If the water level in the lake mustbe lowered, a sluice gate located at the base of the dropinlet structure is opened.

1.3 Pertinent Data.

a. Drainage Area. 3.34 square miles

b. Discharge at Dam Site(cfs). 2715

c. Elevation (Feet).

Top of Dam 378.5 (design)377.8 (low point on crest)

Maximum Pool 374.3 (design flood level)

Normal Pool 362.0 (spillway crest)

Upstream Invert Outlet Works 344.74

Downstream Invert Outlet Works 341.92

Maximum Tailwater UnknownDownstream Toe 344

d. Reservoir Length (Feet).

Normal Pool Level 2400+

Maximum Pool Level 4600+

e. Storage (acre-feet).

Normal Pool Level 167Maximum Pool Level 692Top of Dam 930

f. Reservoir Surface (acres).

Normal Pool Level 26.6Maximum Pool Level 61.0Top of Dam 76.5

-2-

g. Dam.

Type EarthVolume of Fill 175,000+ cubic yardsLength 1000+ feetHeight 33.87 feetTop Width 92+ feetSide Slopes Downstream: 1V:3H

Upstream: 1V:3HZoning YesImpervious Core YesCutoff YesGrout Curtain None

h. Regulating Outlet.

Type 7.0' x 8.0' Twin Box CulvertsLength 282 feetClosure 48inch x 48inch sluice gateAccess Intake tower

Spillway.

Type Drop InletLength 60'Crest Elevation 362Gates NoneUpstream Channel LakeDownstream Channel Stilling Basin and

Whetstone Run

-3-

SECTION 2

DESIGN DATA

2.1 Design.

a. Data Available. Detailed as-built drawings of the embankmentand appurtenances, and the design report for the dam areavailable.

(1) Hydrology and Hydraulics. Hydrologic computations are

included in the design report.

(2) Embankment. A typical section of the embankment indicat-

ing a zoned core and cutoff is available and is included

as Plate E-2.

(3) Appurtenant Structures. Detailed drawings are availablefor the drop irl t and sluice gate structure, twin boxculvert, and stilling basin.

b. Design Features.

(1) Embankment. As-built drawings indicate that an earth

embankment approximately 1000 feet long and as much as 35feet high was constructed across the Whetstone Run streamvalley. The embankment now serves as the roadway founda-tion for Montgomery Village Avenue. The drawingsindicate the embankment was constructed with a crestwidth of approximately 92 feet, and has a zoned core anddrainage and cutoff trenches.

(2) Appurtenant Structures. The appurtenant structure forthe dam consists of the drop inlet, twin box culverts,and stilling basin. Detailed drawings of these struc-tures are available.

c. Design Data.

(1) Hydrology and Hydraulics. Pertinent computations and astorm hydrograph are included in the design report.

(2) Embankment. Cross-sections at several locations alongthe embankment are included in the design drawings, aswell as embankment centerline sections and drainage andcutoff trench profiles.

2.2 Construction. The dam was constructed by Northrup and Morrison,Inc. of Silver Spring, Maryland, however is is unknown what, ifany, construction supervision was provided. As-built drawings ofthe project are available.

-4-

2.3 Operation. No formal operating records have been kept for the dam.According the discussions with the Owner, the lake was lowered in1972 for maintenance dredging.

2.4 Other Investigations. None Reported.

2.5 Evaluation.

a. Availability. Detailed design information is available.

b. Adequacy. The available data is considered sufficient toevaluate the design and construction of the dam.

-5-

SECTION 3VISUAL INSPECTION

3.1 Findings.

a. General. The on-site inspection of Lake Whetstone consistedof:

(1) Visual inspection of the embankment, abutments, and em-

bankment toe.

(2) Visual examination of the appurtenant structures.

(3) Evaluation of the downstream area hazard potential.

The specific observations are shown on Plate A-i.

b. Embankment. The general inspection of the embankmentconsisted of searching for indications of structuraldistress, such as cracks, subsidence, bulging, wet areas,seeps and boils, and observing general maintenance condi-tiofis, vegetative cover, erosion, and other surficialfeatures. No evidence of structural distress was notedduring the inspection. A minor amount of erosion was notedjust above the upstream riprap slope protection at the right

end of the dam.

The crest of the dam was surveyed and the variance inelevation was 5 feet between the high and low point. Thisvariance is due to the vertical curve of the roadway acrossthe dam crest. The low point on the crest is approximately 8inches below the design crest elevation of 378.5, and islocated 50+ feet left of the intersection of the twin boxculverts of the spillway and the embankment. Freeboard atthe time of inspection was approximately 16 feet, and undermaximum pool (i.e. design flood) conditions would beapproximately 3.5 feet. The dam crest profile is included asPlate C-2.

c. Appurtenant Structures. The appurtenant structures weresatisfactory with the exception of the right headwall andleft wingwall located at the outlet of the twin box culvertand a potential blockage in the left side of the twin boxculvert. The right headwall is cracked, the toe drain outletthrough the right headwall is partially obstructed by acorrosion deposit, and erosion was noted behind the leftwingwall. The ability of the left side of the twin-boxculvert to function as designed may presently be impairedsince it was observed that most of the flow from the spillwayriser was being conveyed through the right side of theculvert.

-6-

d. Reservoir Area. It is apparent that much of the runoff from

the residential area which surrounds the lake flows into thelake. While no erosion was noted along the banks, overflow

from a sedimentation pond used to control runoff from anadjacent construction site empties into the reservoir.

e. Downstream Channel. The floodplain directly downstream ofthe dam is utilized primarily for recreation. Apartments are

located on either side of the floodplain recreational area.Failure of the dam could cause significant damage to several

of the apartment units located immediately downstream fromthe dam. Floodwaters from a dam failure could also damage

Watkins Mill Road, a secondary road crossing located approxi-mately 2800 feet downstream of the dam. A school is locatedupstream of the Watkins Mill Road bridge and above the flood-

plain. Based on these observations, a high hazard classifica-tion is warranted for Lake Whetstone dam.

3.2 Evaluation. The visual examination of Lake Whetstone indicates

that except for the few problems noted on the headwalls and wing-

wall at the outlet of the twin box culvert, and the potentialblockage of the left culvert, the embankment and appurtenantstructures are in good condition. An inspection of the twin box

culvert should be made to determine the reason for an apparent

blockage of flow in the left side of the twin box culvert.

-7-

SECTION 4OPERATIONAL FEATURES

4.1 Procedure. There are no formal operating procedures for the dam.

The reservoir level is normally maintained at elevation 362.0 bymeans of a drop inlet spillway.

4.2 Maintenance of The Dam. The maintenance of the dam is considered

good. The crest of the dam carries Montgomery Village Avenue,which is maintained by Montgomery County. The upstream face is

grassed, with a berm near the base and asphalt walkway. Riprap

slope protection is placed along the shoreline. The downstreamface is grassed. Both upstream and downstream slopes are mowed

regularly.

4.3 Maintenance and Operating Facilities. The maintenance of the

operating facilities is considered fair. The north headwall and

south wingwall of the outlet structure obviously need somerepairs. No scheduled formal inspection program for the

facilities exists.

4.4 Warning System. No formal warning system exists for the dam.

4.5 Evaluation. The maintenance of the dam is considered good, while

the maintenance of the operating facilities is considered fair.

-8-

SECTION 5HYDRAULICS AND HYDROLOGY

5.1 Evaluation of Features.

a. Design Data. The March 1966 Design Report for LakeWhetstone, Montgomery Village, Montgomery County, Narvand,indicates that the reservoir spillway design was based uponan inflow design flood of 9160 cubic feet per second (cfs)resulting from a 6-hour storm of 9.8 inches over the reser-voir's 3.34-square mile drainage area. A storm frequency wasnot indicated for the 9.8 inches of rainfall. Using the 9160cfs peak inflow rate, the maximum flood storage level wasestablished at an elevation of 374.3 feet above mean sealevel) and a freeboard of 4.2 feet was employed to establishthe design low point in Village Avenue, the thoroughfarecarried by the dam embankment, at an elevation of 378.5 feetabove mean sea level.

b. Experience Data. No records of maximum pool levels are

available.

c. Visual Observations. Several observations made during thevisual inspection of Lake Whetstone are particularly relevant

to the hydraulic and hydrological evaluation.

(1) Embankment. The survey of the dam crest profile per-formed during the visual inspection indicates that theexisting crest is slightly lower than its design eleva-tion of 378.5 feet above m.s.l., with its low point atelevation 377.8 feet above m.s.l. The elevation data forthe existing crest was employed in subsequent hydraulicanalyses.

(2) Appurtenant Structures. The drop inlet spillway and out-let works appear to have been constructed in accordancewith record as-built drawings. During the visual in-spection some debris was observed on the grating at thedrop inlet spillway. While the amount of debris presentwould not significantly affect the spillway capacity,continued accumulation of debris would eventuallyadversely affect the spillway's hydraulic capacity.

The ability of the left side of the twin outlet boxculvert to function as designed may presently be impairedsince it was observed that most of the flow from thespillway riser was being conveyed through the right sideonly. It is assumed, however, that this condition can becorrected, and therefore the design rating curvepresented in the design report for the outlet works hasbeen used in subsequent hydraulic analyses.

-9-

(3) Downstream Conditions. Failure of the dam impoundingLake Whetstone could cause significant damage to severalapartment units located immediately downstream from thedam and would sever the main traffic thoroughfare throughthe densely populated development, Montgomery VillageAvenue, which is carried by the dam embankment itself.In addition the failure may damage Watkins Mill Road. asecondary road crossing located approximately 2800 feetdownstream. In keeping with the potential hazard classi-fication established by the Office of the Chief ofEngineers (OCE), damage which may result to downstream

multi-family dwelling units, and which will result toM6ntgomery Village Avenue upon a dam failure, indicatesthat a high hazard classification be assigned to LakeWhetstone.

d. Overtopping Potential. According to the criteria promulgatedby the Office of the Chief of Engineers, the recommendedSpillway Design Flood (SDF) for a dam classified as "small"with a "high" hazard potential ranges between 50 and 100

percent of the Probable Maximum Flood (PMF). While classi-fied as a "small" dam, the capacity of Lake Whetstone puts itvery close to the "intermediate" classification which,

together with its "high" hazard classification, would requirethe use of 100 percent of PMF for its Spillway Design Flood.For this reason the 100 percent PMF has been selected as theSDF for Lake Whetstone.

The Probable Maximum Precipitation (PMP) index as adjustedfor the Lake Whetstone drainage area is 19.2 inches in 24hours. Employing criteria established by the Corps ofEngineers, Baltimore District, 100 percent and 50 percent PMFinflow hydrographs developed using the HEC-i computer programhave peaks of 8000 and 4000 cfs, respectively. It isimportant to note that these peak flows are significantly

less than the 9160 cfs design inflow previously determined inthe design report for a 9.8-inch storm of 6-hour duration.This disparity is understandable since it is recognized that

the Snyder method of synthetic unit hydrograph determinationemployed in the HEC-I model for dam safety investigationstudies may produce hydrograph peaks somewhat less than thosederived using other methods when applied to relatively small

drainage areas with comparatively short times of concentra-tion. However, in accordance with guidance provided by theCorps of Engineers, Baltimore District, no adjustments havebeen made to the PMF's determined for Lake Whetstone toaccount for this disparity.

-10-

PMF inflow hydrographs were routed through Lake Whetstone forpercentages ranging from 20 to 100 percent of the PMF with

each routing starting at the normal pool elevation of 362feet above m.s.l. For the 50 percent PMF routing, thereservoir water level reached an elevation of 374.8 feetabove m.s.l. or 3.0 feet below the low point in the dam crest.

For the 100 percent PMF routing, the reservoir water levelreached an elevation of 380.1 feet above m.s.1. overtoppingthe low point in the dam embankment by 2.3 feet. Results forintermediate routings are found in Appendix D.

It is interesting to note that while the percent of PFFrouting with a peak inflow rate of 8000 cfs overtopped the damembankment, the original design flood routing having a higherpeak inflow rate of 9160 cfs produced a flood pool level some

5.7 feet below that produced by routing the 100 percent PMFthrough Lake Whetstone. The reason for this difference is

that the total amount and duration of runoff produced by the100 percent PMF event is much greater than the total runoffamount and duration which would be produced by the originaldesign storm. Hence, passage of the 100 percent PMF event

through Lake Whetstone would require a greater amount offlood storage volume (accomplished by higher pool levels)

than that required by passage through the reservoir of theoriginal design flood event.

e. Spillway Adequacy. The analyses indicate that the LakeWhetstone spillway can pass approximately 59 percent of thePMF without overtopping of the dam. Since the analyses

indicate the spillway cannot pass the Spillway Design Floodbut can pass 50 percent of the PMF, the spillway capacity israted as inadequate, but not seriously inadequate, in

accordance with Office of the Chief of Engineers guidelines.

k-_1

SECTION 6STRUCTURAL STABILITY

6.1 Evaluation of Structural Stability.

a. Visual Observations.

(1) Embankment. Visual examination of the dam embankment

indicates that there are no wet spots, seepage, slumps or

other features that suggest embankment instability.

(2) Appurtenant Structures: A structural crack was noted

across the right headwall of the outlet structure.

Erosion was noted behind the left wingwall of the outlet

structure.

b. Design and Construction Data.

(1) Embankment. Based on the computations included in the

design report for the dam, a proper assessment of the

stability of the dam can be made.

(2) Appurtenant Structures. The available information

includes adequate data to assess the structural adequacy

of the appurtenant structures.

c. Operating Records. The structural stability of the dam isnot considered to be affected by the operational features ofthe dam.

d. Post-Construction Changes. The only apparent post-construc-

tion activity was the dredging of Lake Whetstone in 1972.

e. Seismic Stability. Lake Whetstone is located in Seismic Zone

1. Based on visual observations, the static stability of the

dam appears to be adequate. Consequently, the structure

should present no hazard from earthquakes.

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SECTION 7ASSESSMENT, RECOMMENDATIONS/REMEDIAL MEASURES

7.1 Dam Assessment.

a. Assessment. Lake Whetstone is a small storage, high hazardimpoundment. The dam embankment is in good condition and theappurtenant structures are in fair condition. A high hazardclassification is warranted because a dam failure couldresult in damage to apartments located immediately downstreamof the dam, damage to Montgomery Village Avenue across thedam crest, and damage to Watkins Mill Road located downstreamof the dam. Hydrologic and h~draulic analyses indicate thatthe Lake Whetstone spillway can pass approximately 59 percentof the PMF without overtopping the dam. Since the analysesindicate that the spillway cannot pass the spillway designflood but can pass 50 percent of the PMF, the spillwaycapacity is rated as inadequate, but not seriously inadequatein accordance with Office of the Chief Engineers guidelines.

b. Adequacy of Information. The availability of detailed infor-mation on the design and construction of Lake Whetstone isconsidered adequate for the Phase I report.

c. Urgency. The following recommendations should beaccomplished in a timely manner.

d. Need for Additional Data. At the present time, there is noneed to obtain additional data or conduct additional investi-gations at Lake Whetstone.

7.2 Recommendations/Remedial Measures.

The following remedial measures are recommended to be accomplishedby the Owner:

a. Repair the structural crack on the face of the north headwallof the outlet structure.

b. Remove the corrosive build-up which is partially obstructing

the northern toe drain outlet.

c. Repair the erosion behind the south wingwall of the outletstructure.

d. Inspect the chamber of the drop inlet spillway to determineif there is a blockage to the left side of the twin boxculvert, and remove any obstructions which exist.

e. Schedule formal periodic inspections of the dam embankment

and appurtenant structures.

f. Develop a formal warning system to alert downstream residents

in the event of emergencies.

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APPENDIX A

VISUAL INSPECTION CHECKLIST

PHASE I

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APPENDIX B

ENGINEERING DATA CHECKLIST

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APPENDIX C

PHOTOGRAPHS

LAKE WHETrSTONE

A. Upstream slope and walkway

B. Downstream slope of Dam

C-1

LAKE WHETSTONE

---

C. Drop inlet with trash grate

D. Riprap slope protection

C-2

LAKE WHETSTONE

E. Montgomery Village Avenue over crest of dam

F. Plunge basin with riprap protection (foreground)and sediment control pond and townhouses northof Whetstone Run.

c-3

LAKE WHETISTO)NE

G. Outlet conduits and toe drains

H. Erosion behind left wingwall of outlet structure

Mon tgome ry V illIage Ave'

Inlet

SCALE

010

tstone Run!W

G Plunge Basin

\H Oro*,\

tF w

3H\

A-W

Dro

-*-Camera Location And Direction/A Photograph Identification Letter

/ / PHASE I INSPECTION REPORT

I NATIONAL DAN INSPECTION PROGRAMLAKE WHETSTONE

'I MONTGOMERY VILLAGE FOUNDATION

GUIDE TO LOCATIONSCALE OF PHOTOGRAPHS

JULY 1980 PLATE C-1

IIC-)

I- L-m c=LAJ -j

>- -

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PHASE I NPETO RPR

NAIOA DA NPCIO RGANOIIVA313~c

-AEWETTN

DA0 RSTSRE

JULY 981)PLAT C-

APPENDIX D

HYDROLOGY AND HYDRAULICS

BASE DATA FOR DETERMINATION OF PROBABLEMAXIMUM FLOOD, UNIT HYDROGRAPH AND

INFLOW HYDROGRAPHS

Name of Dam: Lake Whetstone NDI-ID MD 53

Unit Hydrograph Parameters

Watershed Drainage Area 3.34 sq. miles

Main Channel Length L 2.7 milesMain Channel to Centroid Legih, Lca 1.3 miles

Lag Time tp = Ct (L x Lca) 3.64 hoursBasin Zone Location from Unit Hydrograph

Coefficient Map 33

Basiy CoefficientsCp 1.25

Ct 2.50

Inflow Hydrograph Parameters

Base Flow at Start of Storm 1.5 c.f.s./sq. mile

Initial Rainfall Loss 1 inch

Uniform Rainfall Loss 0.05 inches/hour

Ratio of Peak Discharge Used to ComputeBase Flow which Deviates from Hydrograph

Falling Limb 0.05

Ratio of Recession Flow occuring 10

Tabulation Intervals Later 2.0

Rainfall Data2

Probable Maximum Precipitation Index

for 24 hours and 200 square miles 24 inches

Percentage Adjustments of PMP for

Drainage Area6 hour storm 112%

12 hour storm 123%24 hour storm 132%

Basin Coefficients and Hydrograph Data established by Corps of

2 Engineers, Baltimore DistrictHydrometeorological Report 33, Corps of Engineers, 1956

D-1

R v A Tabulation of

Reservoir Area and Storage Vs. Elevation

Name of Dam: Lake Whetstone NDI-ID MD-53

Pool Surface I ReservoirElevation Area Storage

feet above acres acre-feetm.s.1.

348 0 0

350 3.2 3.2

352 5.1 11.5

354 8.3 24.9

356 12.0 45.2

358 15.7 72.9

360 20.7 114.6

362 26.6 166.6

364 31.4 224.6

366 36.0 292.0

368 41.5 369.5

370 47.4 458.4

372 53.6 559.4

374 60.0 673.0

374.3 (Maximum Flood 61 692

Pool)

376 66.6 799.6

377.8 (Top of Dam) 76.5 930

380 88.62 1092.62

400 178.02 34952

'Source: Design Report - Lake Whetstone Montgomery Village, Greenhorne,

O'Mara, Dewberry and Nealson, 10 March 19662Computed by Runnel, Klepper and Kahl

D-2

Spillway/Outlet Rating Curves1

Name of Dam: Lake Whetstone NDI-ID MD-53

Pool Weir Conduit SpillingElevation Control Control Dischargefeet above c.f.s. c.f.s. c.f.s.u.s * 1

362 0 0

363 186 186

364 526 526

366 1488 2200 1488

368 2734 2250 2250

370 4204 2400 2400-

372 2450 2450

374 2550 2550

374.8 2570 2570

376 2600 2600

378 2730 2730

380 2800 2 2800 2

380.1 2803 2 2803 2

382 2850 2 2850 2

385 2975 2 2

1Source: Design Report Lake Whetstone Montgomery Village, Greenhorne,

20'Mara, Dewberry and Nea1lon, 1.0 March 19662Computed by Rummel, Klepper & Kahl

D-3

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APPENDIX E

PLATES

C-3-

C2

iI

Slo°pe 3:1 / - 92' Wide Crest

i 2S e c t io n 1

Slope 1-

Filter Material j I " 'SIo

44- 40'

FILL MATERIAL

TYPE REQUIREMENTS

Section 1 ML* (Plasticity Index From 6 to 10)

Section 2 ML* (Plasticity Index Less Than 6)

* Silt And Clay Defined By Unified Soil Classification System

Scale 1" 20'

Seto I Sope2: Water Surface Elev. 362.0

Section 2

"-Existing Ground Line

C. St ripping Line

4' 401 Slope 1:1

10)6)

led Soil Classification Systemt

Sca Is 1" =201

TYPICAL SECTION

LAKE WHETSTONE

FROM AS hUILT GRAVINGBATED FEN. 7. 1961

SHEET NO. 4

___________________________________________________________PLATE E-2

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APPENDIX F

GEOLOGY

LAKE WHETSTONEAPPENDIX F

REGIONAL GEOLOGY

The Lake Whetstone Dam is located within the Piedmont Physio-

graphic Province and is situated on rock strata of the Wissahickon Forma-

tion, which is characterized by phyllites, schists, and sandstone and

conglomerate beds. Minor alluvial deposits have also been mapped along

Whetstone Run. The age of the Wissahickon and its stratigraphic rela-

tionship with adjacent rock formations are uncertain. It is estimated

that the thicknesses of the Wissahickon Formation exceeds many thousands

of feet. Strata in the vicinity of the dam dip very steeply to the east-

southeast.

F-i

e 'Il 1; /t' 20.(

454o

49N 7B7,~N

65 60~ .6

-720

/ LAKE WHETSTONE DAM 5

fi -. 20

lo. b?

Mill f. f

0

SCALEr

a iii. 21cREF EEN C: LAE WHTSTOE6DA

4E1LOr. MA OFt MONTrib MEACONYPEARE ITg TH TTEGOOG A

OF MRYLAD, ARYLND EOLOICASWEY DAED 153 LN44L, LEPPR &KAH

LEGEND

Wissahickon formi~on

I ~ ~ I (Bande ,in=e quartrrir vhti.[ j Wie, and acf6 wvt eonetie, quartzcomposed of msgoilte. eklorite, athile,quartz. Grading into roarsersehit to theeat. Inddes some Marburo ehit. Maybe Mhe eqiedlen? of Harper# to he tweit.Calcareous ayr are e :,non. 1ter-nuers witbh t.jamvwile pliess :

sandsone beds)

lJamsvllle phyllite

(Suft purpe or green phythte and diatein pLaces withJ.e amtdu1eA. Com.vosed of muscovite, chtore or ehlorilod.quarr, and Ane itm"ite or iron ozidedust. Interbedded with wreenstone andseriette sctst. In part equivalent toMarburg ,ethit in Frederi*k CountY.Underiatsn bv quaartzite bed)

AlluviumGol (Nom anot alon miar steamu)

Serpentine

REFERENCE: LAKE WHETSTONE DAMGEOLOGIC MAP OF MONTGOMERYCOUNTY, PREPARED BY THE STATEOF MARYLAND, MARYLAND GEOLOGICALSURVEY. RUIMEL, KLEPPER & KA-L

Documents

AID-AO91 ROIMEL KELEPPER AND KAHL BALTIMORE MD F/6