AD-AU91 447 WOODWARD-CLYDE CONSULTANTS PLYMOUTH MEETING PA FG 13/13NATIONAL DAM INSPECTION PROGRAM. PLACID LAKE DAMw NDS ID NUMB--ETC(UJ)

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PHASE I INSPECTION REPORT

NATIONAL DAM INSPECTION PROGRAM

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-_--NA I ZNSPECTION REPORT .NADTI ONTlD!P iN PROGAMA

Prepared by: '- . .

WOODWARD-CLYDE CONSULTANTS5120 Butler Pike

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Submitted to:

DEPARTMENT OF THE ARMYBaltimore District, Corps of Engineers

Baltimore, Maryland 21203

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! :. )PREFACE

This report is prepared under guidance contained in theRecommended Guidelines for Safety Inspection of Dams for Phase IInvestigations. Copies of these guidelines may be obtained from theOffice of the Chief of Engineers, Washington, D.C. 20314. The purpose ofa Phase I investigation is to expeditiously identify those dams which maypose hazards to human life or property. The assessment of the generalcondition of the dam is based upon available data and visual inspections.Detailed investigations, testing and detailed computational evaluationsare beyond the scope of a Phase I investigation; however, theinvestigation is intended to identify the need for more detailed studies.

In reviewing this report, it should be realized that thereported condition of the dam is based on observations of field conditionsat the 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 of thedam, removes the normal load on the structure and may obscure certainconditions which might otherwise be detectable if inspected under thenormal operating environment of the structure.

It is important to note that the condition of a dam depends onnumerous and constantly changing internal and external conditions, and isevolutionary in nature. It would be incorrect to assume that the presentcondition of the dam will continue to represent the condition of the dam atsome point in the future. Only through frequent inspections can unsafeconditions be detected, and only through continued care and maintenancecan these conditions be prevented or corrected.

Phase I inspections are not intended to provide detailedhydrologic and hydraulic analyses. In accordance with the establishedGuidelines, the spillway design flood is based on the estimated "ProbableMaximum Flood" for the region (greatest reasonably possible storm runoff),or fractions 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 the sizeof the dam, its general condition and the downstream damage potential.

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FPHASE I INSPECTION REPORT

NATIONAL DAM INSPECTION PROGRAM

Name of Dam: Placid Lake DamCounty Locatedt Carbon CountyState Located: PennsylvaniaStream: Laurel RunCoordinates: Latitude 410 2.0'

Longitude 750 37.0'Date of Inspection: June 12, 1980

Placid Lake Dam is owned by the Holiday Pocono CivicAssociation, Inc. The dam and reservoir are used forrecreational purposes. The dam was built as part of aresidential community and was completed in 1963.

Visual inspection indicates that the spillway sys-tem of Placid Lake Dam is in fair condition, the upstreamembankment face is in poor condition, the crest and downstreamembankment face are in good condition, and the vegetation isin very poor condition. The overall rating of the dam isfair.

In accordance with criteria established by Federal(OCE) Guidelines, the recommended spillway design flood forthis "Small" size dam and "High" hazard potential classifica-tion is one-half to the full Probable Maximum Flood (PMF).Based on the small total reservoir capacity and the limitednumber of downstream residences, the one-half PM? has beenselected as the spillway design flood.

Hydrologic and hydraulic computations presented inAppendix D indicate the spillway structure is capable ofdischarging the one-half PMF event without overtopping theembankment under design conditions. Existing conditions, withthe flashboard structure in place, reduce the spillwaycapacity to about 0.33 PM'. It is further assessed that theembankment is not likely to fail during the one-half PMF.Therefore, the structure is considered to have an winadequate"but not "Seriously Inadequate" spillway classification.

It is recommended that the following measures beundertaken immediately. tems 1, 3 and 4 should be performedunder the supervision of a registered professional engineerexperienced in the design and construction of dams.

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Placid Lake Dam, NDS ID PA 00616

(1) A detailed hydrologic/hydraulic investigationshould be performed to determine the best method ofincreasing the spillway capacity.

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(2) I"--e of rhe , the flashboard structureshould be permanently removed from the top of thespillway drop inlet.

(3) An investigation should be made into the actualcause of the apparent piping voids in the vicinityof the inlet conduit.

(4) The spillway conduit joints should be sealed and thetwo downstream pipe lengths should be monitored forpossible horizontal movement.

(5) Erosion of the upstream face should be halted andthe damaged embankment repaired.

(6) The inlet sluice gate and the reservoir drain gatevalve should be lubricated and exercised on aregular basis to insure their operational status.

(7) All trees and brush should be removed from the down-

stream embankment face, the embankment returned toits original condition, and measures taken toestablish a good stand of vegetation.

(8) The rock dam in the diversion channel should be re-moved.

Because of the potential for property damage andloss of life in the event of failure, a formal procedure ofobservation and warning during periods of high precipitationshould be developed and implemented for this facility. Thisprocedure should include specification of when the inletsluice gate should be closed to reduce reservoir inflow andwho shall perform this operation, and a method of warningdownstream residents if high flows are expected and provisionsfor evacuating these people in the event of an emergency. Itis recommended that an operation and maintenance manual bedeveloped, including a checklist of items to be inspectedregularly. It is further recommended that this manual includeprovisions for the maintenance of embankment vegetation in thebest possible condition.

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Placid Lake Dam, NDS ID PA 00616

Mary F, Beck, P.E. DatePennsylvania Registration 27447E S .0 .Woodward-Clyde Consultants

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JohnH Frederick, Jr., P.E.DateMary and Registration 7301 John w.".oodward-Clyde Consultants Fred Jr.

APPROVED BY: OES

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TABLE OF CONTENTS

PAGE

Preface iAssessment and Recommendations iiOverview Photograph v

SECTION 1 PROJECT INFORMATION1.1 General I1.2 Description of Project 11.3 Pertinent Data 4

SECTION 2 - ENGINEERING DATA2.1 Design 62.2 Construction 62.3 Operational Data 62.4 Evaluation 6

SECTION 3- VISUAL INSPECTION3.1 Findings 73.2 Evaluation 10

SECTION 4 - OPERATIONAL PROCEDURES4.1 Procedures 114.2 Maintenance of the Dam 114.3 Maintenance of Operating Facilities 114.4 Warning Systems In Effect 114.5 Evaluation 11

SECTION 5 - HYDROLOGY/HYDRAULICS5.1 Evaluation of Features 13

SECTION 6 - STRUCTURAL STABILITY6.1 Evaluation of Structural Stability 16

SECTION 7 - ASSESSMENT/REMEDIAL MEASURES7.1 Dam Assessment 187.2 Remedial Measures 18

APPENDIXA Visual InspectionB Engineering Data, Design, Construction

and OperationC PhotographsD Hyd rol ogy/Hyd raul icsE PlatesF Geology

vi

PHASE I INSPECTION REPORTNATIONAL DAM INSPECTION PROGRAM

PLACID LAKE DAMNATIONAL ID NO. PA 00616

DER NO. 13-97

SECTION 1PROJECT INFORMATION

1.1 General.

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

b. Purpose. The purpose of the inspection is todetermine if the dam constitutes a hazard to human life orproperty.

1.2 Description of Project.

a. Dam and Appurtenances. Placid Lake Dam is a homo-geneous earth embankment, approximately 22.5 feet high, acrossLaurel Run. The approximately 2,700 foot long dam impounds anestimated 240 acre-foot reservoir, with the reservoir level atthe top of the dam, within a 0.36 square mile drainage basin.The dam forms three sides of an approximately rectangularshaped lake. Laurel Run enters the reservoir through a 24inch sluice gate and 40 feet of 24 inch concrete pipe throughthe embankment near the right abutment. A diversion channelwas constructed to carry large flows in Laurel Run around thereservoir to the original stream bed downstream from the dam.A wooden weir was installed to direct the normal flow inLaurel Run into the reservoir rather than through thediversion channel.

Both the upstream and downstream side slopes of thedam have a design slope of 2H:IV. Existing downstream faceslopes range from 2.6H:IV to 3.5H:lV, and upstream slopesabove the waterline range from near vertical to 1.9H:lV. Adownstream berm with a lOH:1V slope was constructed over a onefoot thick filter blanket; Plate 2, Appendix E. The width ofthe berm is shown to be equal to one-third of the width of thedam embankment. The design embankment crest widths rangedfrom 10 to 13 feet, measured widths were 10 and 11 feet. Thedownstream face is protected by vegetation. The downstream

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face and crest of the dam were to have been covered with top-soil and seeded.

The spillway, approximately 800 feet from the rightabutment, consists of a concrete box drop inlet and 78 feet of48 inch reinforced concrete pipe with two anti-seep collars.Pipe joints are shown on the construction drawings as beingcaulked and mortared. The inlet is approximately six feet byeight feet and approximately eight feet deep. Water flowsover the spillway crest at elevation 1,667, dischargingthrough the concrete pipe beneath the embankment to a shallowplunge pool at the downstream toe. A six inch gate valve nearthe base of the inlet structure permits a partial drawdovn ofthe lake. (The spillway is not located at the maximumsection.) A wooden flashboard box structure is supported byfour bricks above the concrete inlet so that, at the time ofthe inspection, water flowed beneath the structure and intothe spillway inlet. During the summer recreation season, thebricks are removed and the reservoir level is raised by about22 inches.

The spillway outlet discharges into a shallow plungepool approximately 10 feet wide by 20 feet long. Dischargefrom the plunge pool flows through a 60 inch diameter concreteculvert beneath the access road to the diversion channel fromthe right abutment of the dam. The diversion channel ap-proximately parallels the dam for a distance of about 650 feetdownstream of the spillway to the original stream bed ofLaurel Run. Laurel Run then flows away from the dam in adirection approximately perpendicular to the dam.

The upstream face of the dam is protected by soil-cement. Approximately midway between the right abutment andthe spillway inlet is a sand bathing beach area on theupstream slope of the embankment.

b. Location. The dam is located on Laurel Run inKidder Township, Carbon County, Pennsylvania. The dam site islocated approximately 3.7 miles north of Laurel Run and StateRoute 534. The dam site and reservoir are shown on the USGSQuadrangle entitled "Blakeslee, Pennsylvania" at coordinatesN 410 2.0' W 750 37.0'. A regional location plan of PlacidLake Dam is enclosed as Plate 1, Appendix E.

c. Size Classification. The dam is classified as a"Small" size structure by virtue of its estimated 240 acre-foot total storage capacity and less than 40 foot height.

d. Hazard Classification. A "High" hazard classifica-tion is assigned to this structure consistent with the poten-tial for extensive property damage and possible loss of lifein the housing development downstream from the dam in theevent of failure of the dam.

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e. Ownership. The dam is owned by the Holiday PoconoCivic Association, Inc. All correspondence should be ad-dressed to Mr. Gerald R. Umbreit, Chairman, Holiday PoconoCivic Association, Post Office Box 57, Albrightsville,Pennsylvania 18210.

f. Purpose of Dam. The dam and reservoir are used forrecreational purposes.

g. Design and Construction History. Placid Lake Damwas designed by Richard N. Harrison, P.E., with consultationfrom Joseph S. Ward & Associates, Inc. The dam was originallydesigned as a zoned earth fill embankment, but the design wassubsequently changed to a homogeneous earth fill embankmentwith an upstream soil-cement face. The dam was constructed byCrandon Construction Company of Newton, New Jersey in 1962 and1963.

According to the construction drawings and a briefdescription of the dam construction, the initial constructioneffort was to strip the ground surface along the dam locationto a depth of about one foot. A one foot thick filter blanketwas then placed beneath the toe of the dam and beneath thedownstream berm. The embankment was constructed of availablesoil materials placed in a compacted lift construction. Docu-mentation of the quality of the embankment compaction is notavailable. When the embankment reached an elevation five feetbelow the design normal lake level, construction of the soil-

cement protection for the upstream face commenced. Cement wasspread over an area approximately seven feet wide at the up-stream face of the dam and then blended in with the lift ofembankment soils to a nominal depth of six inches. The mixedin place soil and cement were then moistened, mixed furtherand compacted. The soil-cement was then carried up insubsequent lifts with the fill to the crest elevation of thedam.

There are no inspection reports, letters or memo-randa available in the Department of Environmental Resourcesfiles relating to the post-construction history of Placid LakeDam.

h. Normal Operating Procedures. Under normal condi-tions, all flow is discharged through the drop inlet and the48 inch diameter pipe. This water is then discharged intoLaurel Run. During the recreation season, the flashboardstructure is placed on top of the drop inlet spillway to raisethe reservoir level 22 inches. The inlet gate at the rightabutment of the dam is left open to admit water to the reser-voir.

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1.3 Pertinent Data.

A summary of pertinent data for Placid Lake Dam ispresented as follows.

a. Drainage Area (square miles) 0.36

b. Discharge at Dam Site (cfs)Maximum Known Flood at Dam Site UnknownDischarge with Reservoir atTop of DamSpillway Crest at Elevation1,667 Feet 209

Spillway Crest at Elevation1,668.8 Feet 175

c. Elevations (feet above MSL) (1 )

Top of DamMinimum Existing CrestElevation 1,670.5

Design Crest Elevation 1,673.0 (withouttopsoil)

Spillway Weir Crest (normalpool without flashboards) (1) 1,667.0

Spillway Crest with Flashboards 1,668.848 Inch Pipe Outlet Invert 1,656.9Tailwater (2) (6/12/80) 1,657.0Upstream Side of Berm atMaximum Section 1,653.0Stream Bed Downstream ofMaximum Section 1,648.0

d. Reservoir (feet)Length at Normal Pool 87QLength at Maximum Pool 885

e. Storage (acre-feet)Normal Pool (1,667 ft) 155Top of Dam 240

f. Reservoir Surface (acres)Normal Pool 24

g. Dam DataType Rolled earth fillLength 2,700 feetHeight 22.5 feet

(1) Spillway crest elevation assumed to be 1,667 from USGSmap. All other elevations are relative to thiselevation.

(2) Downstream of spillway outlet

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Crest WidthDam 10 to ll feet

Volume 100,000± cubic yardsSide SlopesUpstreamDesign 2H:lVExisting, Above Waterline Near vertical to

l.gH:1VDownstreamDesign 2H:lVExisting 2.6H:lV to 3.5H:lV

Cutoff NoneGrout Curtain None

h. SpillwayType Concrete box drop

inlet & 48 inch RCPconduit

Size 6 feet by 8 feetLocation About 650 feet right

of original streambed

Energy Dissipator Plunge poolReservoir Drain 6 inch gate valve

located at base ofinlet

5

SECTION 2ENGINEERING DATA

2.1 Design.

a. Data Available. A summary of the engineering dataavailable for Placid Lake Dam is presented on the checklistattached as Appendix B. Principle documents containingpertinent data used in this report Include the permit forconstructing the dam issued on May 21, 1962, records of boringlogs and construction drawings, and a reprinted magazinearticle from "Constructioneer" dated August 12, 1963.

b. Design Features. Design drawings of the dam contain-ing plans, profiles and maximum sections are presented inAppendix E. A summary of the features of the dam is included inSection 1.3.

2.2 Construction.

The construction data are limited to the reprintedarticle from "Constructioneer" magazine that was obtainedthrough the courtesy of the Portland Cement Association.

2.3 Operational Data.

There are no operational records maintained for thisdam.

2.4 Evaluation.

a. Availability. All information presented herein wasobtained from reports and correspondence located in theDepartment of Environmental Resources files, supplemented withinformation supplied by the Portland Cement Association, andconversations with the Owner's representative.

b. Adequacy. The available data are not adequate toevaluate the engineering aspects of this dam.

c. Validity. There is no reason to question thevalidity of the available data.

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SECTION 3VISUAL INSPECTION

3.1 Findings.

a. General. Observations and comments of the fieldinspection team are contained in the checklist enclosed hereinas Appendix A, and are summarized and evaluated in thefollowing sections. In general, the appearance of theupstream embankment face is in poor condition, the crest anddownstream embankment face are in good condition, the vegeta-tion is in very poor condition, and the spillway is in faircondition.

b. Dam. The vertical alignment of the dam crest waschecked, an--the profile is shown on Sheet 5B, Appendix A.The crest elevation ranges from 1,670.5 to 1,674.0, ascompared with an original design elevation of 1,673 to 1,675.The dam crest is 10 to 13 feet wide, except in the bathingbeach and recreation area, and from that area towards theright abutment the crest width is 30 feet or more. Throughoutmost of its length, the crest of the dam is characterized by alight brown cemented sand and gravel. In general, there is noevidence of topsoil in either the crest or downstream face,and the dam crest is nearly barren of vegetation; Photograph7.

The upstream slope of the dam face ranges fromvertical to about 1.9H:lV above the water level. The slope ofthe dam face appears to be much flatter below the water leveland very much flatter in the bathing beach area. Throughoutthe length of the dam, the upstream face is benched at thepresent water level and has an almost stair step appearance ofthe horizontal layers of the soil-cement; Photograph 6. Thequality of the soil-cement was variable, ranging from hard tofriable. In some areas, erosion has undermined well cementedzones. Occasional discrete blocks of the soil-cement werefound lying loose at the water level. A slide from the filesof the Portland Cement Association was taken in March 1976,from the same point as Photograph 7 looking along the upstreamface. Comparing the two pictures disclosed essentially thesame condition of the upstream face although progressivedeterioration is occurring.

The downstream face of the dam generally appeared tobe sparsely vegetated, except in the vicinity of the recrea-tion area, where there is a well maintained grass cover.Occasional areas of the downstream face were eroded, perhapsas the result of foot traffic and rutted as the result ofrecreation vehicle traffic. In particular, an area in the

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vicinity of the existing stream bed is severely eroded as theresult of recreation and off-road vehicle traffic on the faceof the dam. A windrow of stumps was placed along the toe ofthe dam in this vicinity to discourage further trespass uponthe dam; Photograph 8. Downstream slopes were measured torange from 2.6H:lV to 3.5H:lV. The shallower slopes were inthe vicinity of the recreation area. Near the right abutment,a downstream slope of 9.5H:lV was measured where the embank-ment is of minimal height, and the downstream slope transi-tions into the original ground surface and from thence intothe diversion channel. Brush and trees up to four inches indiameter are growing on the downstream face of the dam. Theflat (10H:lV) downstream berm to the left of the access roadis very uneven with a stockpile of gravel. Depressions withinthe uneven area have standing water. At the downstream edgeof the slope, where the seepage intercepted by the blanketdrain would exist, the downstream woods begin. No seepage wasobserved, although the very heavy underbush made inspectiondifficult.

Normal flow in Laurel Run enters the reservoirthrough the sluice gate; Photograph 4. A weir, shown to theright in Photograph 4, has been placed at the entrance to thediversion channel. The top of the weir is about four feetbelow the dam crest. At a point 50 feet downstream of theweir, the diversion channel is about 15 feet wide with 3H:lVside slopes. A rock dam, Photograph 14, was constructedacross the diversion channel about 300 feet downstream of theweir. The right end of this dam washed out leaving a threefoot opening. Farther downstream, erosion has occurred on theleft channel bank, increasing the side slope to near vertical;Photograph 15. The diversion channel is dry to a pointimediately upstream of where the spillway discharge entersthe diversion channel. Standing water is in the channelupstream, and spillway discharge is flowing downstream of thepoint where the spillway channel joins the diversion channel.

c. Appurtenant Structures.

1. Inlet. The inlet structure at the rightabutment of thela-'mis shown in Photograph 4. This consistsof a sluice gate and 40 feet of 24 inch diameter reinforcedconcrete pipe through the embankment; Photograph 5. Stop logscan be installed on the upstream side of the sluice gate. Thesluice gate was opened at the time of the inspection. On thereservoir side of the inlet pipe, several large voidssurrounding the pipe were seen in the embankment. These voidsextend several feet back into the embankment, and the largestis approximately one foot high.

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2. Spillway. A concrete box drop inlet is shown onPhotograph 1. The interior of the drop spillway appears to bein good condition, with no evidence of cracking, staining ordeterioration of the concrete. As shown on Photograph 1, aflashboard structure is supported on bricks above the lip ofthe concrete structure. Four plastic pipes on the oppositeside of the flashboard structure were installed to dischargecool water from below the reservoir surface. A six inch gatevalve is on the drop inlet floor on the upstream side. Thevalve assembly is rusted and the handle is not affixed to thevalve.

A 48 inch reinforced concrete pipe extends from thedrop inlet through the dam embankment. The interior of thepipe joints showed frequent staining, leachate precipitationand missing mortar at the joints and occasionally staining orleachate precipitation through the conduit itself. There isalso occasional leakage at the pipe joints. The fourth jointfrom the downstream end had yellow-brown sandy silt clingingto the joint, apparently soil intrusion. The second and thirdjoints from the downstream end had cracks through the mortar0.5 and 1.0 inches wide, apparent lateral displacement. Nocaulking was noted at the first joint from the downstream end,and daylight could be seen through it.

The shallow plunge pool below the spillway is pondedwith a small amount of water and sustains a growth of cat-tails. Only a small amount of riprap stone is visible in thisbasin.

d. Reservoir. The reservoir side slopes are moderateand vegetated with grass or trees to the water's edge. Thereis no sediment accumulation observed around the intake struc-ture, and a small amount of sediment was observed near a smallstream flowing into the reservoir in the vicinity of the leftabutment. There was no debris observed around the reservoir'sedge.

e. Downstream Channel. From the stilling basin,discharge from the spillway flows through a 60 inch pipeculvert beneath an access road to the recreation area and intothe diversion channel. The pipe culvert appeared to be ingenerally good condition. However, there was some collapseevidenced at the roadway surface overhead. The downstreamside of the pipe culvert evidences severe erosion of theroadway embankment. The natural stream channel downstream ofthe dam is about four feet wide and about three feet high,with side bank slopes of about 1H:IV. Laurel Run flowsthrough a fairly wide floodplain that is characterized bymoderate tree growth and very heavy underbrush. There are atleast ten residential dwellings located near the naturalstream channel downstream of the dam.

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3.2 Evaluation.

In summary, the visual inspection of the damdisclosed no evidence of apparent past or present movementthat would indicate existing deep-seated instability of thedam. Damage to the embankment has resulted from erosion onthe upstream face and consists of voids in the vicinity of theinlet conduit. The cause of the voids should be investigated.

The vegetation protection of the dam is in poorcondition, with large bare patches and woody vegetation.Apparently, the topsoil application shown on the drawings wasnot made. The woody vegetation should be removed and grassesor Crownvetch should be established over the downstream face.The soil-cement appears to provide adequate protection to thedam crest.

The erosion of the upstream face of the dam abovethe water level is judged to be a characteristic weakness ofmixed in place soil-cement. Apparently, mixing of the cementwith the soil did not produce a homogeneous mixture throughoutthe full lift thickness. As a result, less cement was blendedwith the soil at the bottom of each lift. Althoughdeterioration appears not to have increased significantlysince 1976, it is continuing and should be halted. Erosionwas also noted around the inlet conduit at the right abutment.This could be a potentially detrimental condition and shouldbe investigated further. The downstream embankment face is ingood condition at the present time, except for the ruts andminor erosion around the inlet gate.

The spillway structure is in fair condition. Theconcrete drop inlet is in good condition. The reinforcedconcrete outlet pipe from the spillway is assessed to be inpoor condition, consistent with the cracked mortaring andleaking of the joints, and especially the apparent displace-ment of two downstream sections of pipe.

The reservoir drain and inlet sluice gate requireroutine maintenance. Both should be cleaned, oiled andexercised on a routine basis to assure their functioning.

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SECTION 4OPERATIONAL PROCEDURES

4.1 Procedures.

Lake Placid Dam is operated for recreational uses ofa private community. Normal procedures call for maintaining asummer water level in the reservoir 22 inches above thespillway crest elevation. During the non-recreation portionof the year, the flashboard structure is raised and thereservoir level is controlled by the concrete spillwaystructure. All flow is discharged through the spillway.

4.2 Maintenance of the Dam.

Maintenance of the dam is provided by the HolidayPocono Association. It appears that maintenance is primarilyoriented towards the recreational facilities rather than thedam.

4.3 Maintenance of Operating Facilities.

The Holiday Pocono Association also provides main-tenance for the operating facilities of the dam. Other thanthe seasonal changing of the flashboard structure at thespillway, there does not appear to be any regular maintenanceperformed.

4.4 Warning Systems In Effect.

There are no formal warning systems or proceduresestablished for implementation during periods of excessivelyheavy rainfalls.

4.5 Evaluation.

There are no written operational procedures, main-tenance procedures or any type of warning systems. Mainte-nance and operation procedures should be developed, includinga checklist of items to be observed, operated and inspected ona regular basis. Maintenance provisions should also providefor adequate maintenance of the embankment vegetation.

11

• I

Since a formal warning procedure does not exist, oneshould be developed and implemented for use during periods ofhigh rainfall. This procedure should contain a systematicmethod of warning downstream residents that potentially highflows are imminent or dangerous conditions are developing.

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SECTION 5HYDROLOGY/HYDRAULICS

5.1 Evaluation of Features.

a. Design/Evaluation Data. There are no original designor evaluation data available for review for this dam otherthan the notes shown on design drawings included in AppendixE. The watershed contributing runoff directly into thereservoir is long and narrow, approximately 6,000 feet longwith an average width of about 1,500 feet, having a total areaof 0.36 square miles. Elevations range from about 2,120 feetin the upper reaches of the watershed to a normal design poolelevation of 1,667. The watershed is completely wooded withsome residential development. The upper half of the watershedlies within state game lands and Hickory Run State Park. Thelower half of the watershed will be developed residentially.

Placid Lake Dam is an off-channel dam built over theoriginal stream bed. Laurel Run was re-routed around theembankment. The watershed contributing flow in the re-routedcreek is about 6,000 feet long and averages about 3,000 feetwide, having a total area of 0.55 square miles. Elevationsrange from a high of about 2,070 feet to an estimated channelinvert of about 1,648, where the re-routed channel joins theoriginal stream bed. The watershed is completely wooded, andabout two-thirds of it lies within Hickory Run State Park.Part of the watershed will be developed residentially.

In accordance with the criteria established byFederal (OCE) Guidelines, the recommended spillway designflood for this "Small" dam and "High" hazard potentialclassification is one-half to the full Probable Maximum Flood(PMF). Because the estimated total capacity of the reservoiris near the lower limit for a "Small" size classification andbecause of the relatively few inhabited structures downstream,the selected spillway design flood is one-half the PMF.

b. Experience Data. There are no records of reservoirlevels or rainfalls maintained for this dam. There are norecords or estimates of previous high water levels.

C. Visual Observations. At the time of the inspectionthe only condition observed that would indicate a reduction indesign spillway capacity is that a flashboard box structure isplaced on top of the permanent drop inlet, reducing theavailable freeboard. Observations regarding the condition ofthe downstream channel, spillway and reservoir are located inAppendix A and are discussed in greater detail in Section 3.

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d. Overtopping Potential. The overtopping potentialof this dam was estimated using the HEC-1, Dam Safety Version,computer program. A brief description of the program isincluded in Appendix D. Calculations for this investigationestimate a design spillway discharge of about 209 cfs with areservoir level at the minimum top of the embankment. Use ofthe flashboard structure reduces the maximum spillway dis-charge to about 175 cfs. The HEC-l program computed a 0.5 PMFpeak inflow to be about 363 cfs, assuming the inlet sluicegate is closed. It is estimated that the spillway will passabout 0.33 PMF without overtopping the embankment and that 0.5PMF will overtop the embankment at the left abutment by about0.6 foot for nearly six hours when the flashboards are inplace. Under design conditions, the spillway is capable ofdischarging the 0.5 PMF without overtopping the embankment atits minimum point.

An estimate of the effects of a 0.5 PMF storm overthe 0.55 square mile watershed, contributing to flow in LaurelRun, was also made. The peak 0.5 PMF value calculated by theprogram is 634 cfs. The hydrograph was routed through asection adjacent to the reservoir to check the possibilitythat flow in Laurel Run may overtop the embankment into thereservoir during the 0.5 PMF. Results indicated that duringthe 0.5 PMF, flow was not expected to enter the reservoir fromthe diversion channel. The outflow hydrograph from thereservoir and the channel hydrograph were added and routeddownstream to the hazard center.

e. Spillway Adequacy. A spillway that will not pass0.5 PMF without overtopping the embankment is rated as"Seriously Inadequate" provided two other conditions arepresent, one of which is failure of the dam by overtopping.As Placid Lake Dam is assessed not to fail as a result ofovertopping during the spillway design flood from its con-tributing watershed, the spillway classification for thisstructure and the existing conditions is considered to be"Inadequate" but not "Seriously Inadequate". If the flash-board structure were to be permanently removed or,alternately, the embankment crest raised, the spillway wouldbe considered to be "Adequate".

f. Downstream Conditions. Placid Lake Dam is con-structed within a residential community. About 700 feetdownstream of the dam are four houses, and another 100 feetdownstream are two more houses, that are subject to damage inthe event of a dam failure. The first floor of these houses isabout three feet above the channel bank. About 1,700 feetdownstream of the dam is the damage center, shown inPhotograph No. 16. Two houses are at approximately the top of

14

bank elevation, two others are about two feet higher. About200 feet farther downstream is Holiday Lake, essentially anoff-channel dam belonging to the community. Normal flows inLaurel Run bypass Holiday Lake, although high flows could beexpected to enter the upper end and flow over the dam itself.About 4,000 feet farther downstream, Laurel Run enters MudRun. At the confluence of the two streams is a mobile home,also subject to damage in the event of a dam failure.Therefore, a "High" hazard potential classification is jus-tified for Placid Lake Dam.

15

SECTION 6STRUCTURAL STABILITY

6.1 Evaluation of Structural Stability.

a. Visual Observations. Visual observations indicatedno evidence of existing or pending deep-seated embankmentinstability. The soil-cement at the upstream face is assessednot to provide adequate protection to the embankment againstwave action. Progressive deterioration and erosion of thesoil-cement on the upstream face indicates that repairs andreconstruction will be necessary. Similarly, erosion observedon the downstream face of the dam is assessed to not representa serious condition at this time. However, these eroded areasshould be repaired.

The 48 inch diameter discharge pipe from thespillway was observed to have cracked and leaking joints.Such leakage at the joints, if continued, could be apotentially detrimental condition. Apparent movement wasobserved of the two downstream sections of pipe. It isrecommended that these pipe joints be sealed to prevent anyfurther intrusion of soil from the embankment or leakage ofdischarge water out of the conduit.

b. Design and Construction Data. There are no designdata or calculations documenting the design analysis for thedam known to be available. Similarly, there are no calcula-tions or other documentation available regarding the spillwayor hydrologic/hydraulic design of this dam. All dataconcerning the physical features of the dam were obtained fromthe limited construction drawings available, a magazinearticle describing some of the dam construction, and visualobservations made for this inspection.

c. Operating Records. No operating records currentlyexist other than the noted seasonal change of the flashboardstructure at the spillway for recreational usage.

d. Post-Construction Changes. There is no documenta-tion concerning any post-construction changes. Based onvisual observation of the dam, there does not appear to havebeen any post-construction changes.

e. Embankment Stability. There were no embankmentstability evaluations located with the design drawings in theDER files. Based on the visual observation and geometricconfigurations, the dam appears to be stable at the presenttime, provided overtopping does not occur and erosion iscontrolled.

16

f. Seismic Stability. The dam is located in SeismicZone 1. Normally it can be considered that if a dam in thiszone is stable under static loading conditions, it can beassumed safe for any expected earthquake conditions. Sincethe dam is qualitatively assessed to be stable under staticloading conditions at the present time, it can also reasonablybe considered to be stable under seismic loading conditions.

17

SECTION 7ASSESSMENT/REMEDIAL MEASURES

7.1 Dam Assessment.

a. Evaluation. Visual inspection indicates that thespillway system of Placid Lake Dam is in fair condition, theupstream embankment face is in poor condition, the crest anddownstream embankment face are in good condition, and thevegetation is in very poor condition. Therefore, the overallrating of the dam is fair.

In accordance with criteria established by Federal(OCE) Guidelines, the recommended spillway design flood forthis "Small" size dam and "High" hazard classification is one-half to the full Probable Maximum Flood (PMF). Based on thesmall total reservoir capacity and the limited number ofdownstream residences, the one-half PMF has been selected asthe spillway design flood.

Hydrologic and hydraulic computations presented inAppendix D indicate that the spillway structure is capable ofdischarging a one-half PMF event without overtopping theembankment under design conditions. Existing conditions, withthe flashboard structure in place, reduce the spillway'scapacity to about 0.33 PMF. It is further assessed that theembankment is not likely to fail during one-half the PMF.Therefore, the structure is considered to have an "Inadeqate"but not "Seriously Inadequate" spillway classification.

b. Adequacy of Information. The combined visualinspection and simplified calculations presented in Appendix Dwere sufficient to indicate that further limited investiga-tions are required for this structure.

c. Urgency. It is recommended that the measurespresented in Section 7.2 be implemented as specified.

7.2 Remedial Measures.

a. Facilities. It is recommended that the followingmeasures be undertaken immediately. Items 1, 3 and 4 shouldbe performed under the supervision of a registered profession-al engineer experienced in the design and construction ofdams.

18

(1) A detailed hydrologic/hydraulic investigationshould be performed to determine the best method ofincreasing the spillway capacity.

(2) In lieu of the above, the flashboard structureshould be permanently removed from the top of thespillway drop inlet.

(3) An investigation should be made into the actualcause of the apparent piping voids in the vicinityof the inlet conduit.

(4) The spillway conduit joints should be sealed and thetwo downstream pipe lengths should be monitored forpossible horizontal movement.

(5) Erosion of the upstream face should be halted andthe damaged embankment repaired.

(6) The inlet sluice gate and the reservoir drain gatevalve should be lubricated and exercised on aregular basis to insure their operational status.

(7) All trees and brush should be removed from thedownstream embankment face, the embankment returnedto its original condition, and measures taken toestablish a good stand of vegetation.

(8) The rock dam in the diversion channel should beremoved.

b. Operation and Maintenance Procedures. Because ofthe potential for property -damage and loss of life in theevent of failure, a formal procedure of observation andwarning during periods of high precipitation should bedeveloped and implemented for this facility. This procedureshould include specification of when the inlet sluice gateshould be closed to reduce reservoir inflow and who shallperform this operation, and a method of warning downstreamresidents if high flows are expected and provisions forevacuating these people in the event of an emergency. It isrecommended that an operation and maintenance manual bedeveloped, including a checklist of items to be inspectedregularly. It is further recommended that this manual includeprovisions for the maintenance of embankment vegetation in thebest possible condition.

19

APPENDIX

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D

Sheet 1 of 12PLACID LAKE DAMCHECK LIST

HYDROLOGIC AND HYDRAULICENGINEERING DATA

DRAINAGE AREA CHARACTERISTICS: 100% wooded, approximately half will be developedresidentially.

ELEVATION TOP NORMAL POOL (STORAGE CAPACITY):1667.O feet (155 Acre-Feet).

ELEVATION TOP FLOOD CONTROL POOL (STORAGE CAPACITY): 1670.5 feet (240 Acre-Feet).

ELEVATION MAXIMUM DESIGN POOL:

ELEVATION TOP DAM: 1670.5 feet existing, 1673.0 feet,. design.

SPILLWAY

a. Elevation 1667.0 feet, normal, 1668.8 feet, swmer.

b. Type Concret drop inlet, 48" RCP conduit.

c. Width N/A

d. Length 78 feet

e. Location Spillover See Plates, Appendix E.

f. Number and Type of Gates None

OUTLET WORKS:

a. Type 6 inch gate valve.

b. Location Floor of drop inlet.

c. Entrance inverts Unknown.

d. Exit inverts 1656.9 feet.

e. Emergency draindown facilities The above.

HYDROMETEOROLOGICAL GAGES:

a. Type None within watershed.

b. Location N/A

c. Records N/A

MAXIMUM NON-DAMAGING DISCHARGE: Not determined.

PLACID LAKE DAM

HYDROLOGIC AND HYDRAULIC Sheet 2 of 12BASE DATA

DRAINAGE AREA:0(1) 0. 36 sua=re miles.

PROBABLE MAXIMUM PRECIPITATION (PMP)FOR 10 SQ. MILES IN 24 HOURS:(2i 22.5 inches.

ADJUSTMENT FACTORS FOR DRAINAGE AREA (%):(3)

Zone 1

6 Hours 111

12 Hours 124

24 Hours 134

48 Hours 142

SNYDER HYDROGRAPH PARAMETERS: (4)

Zone 2

Cp, Ct 0.45, 2.1RESERVOIR WATERSHED STREAM WATERSHED

L(5) 1. 37 miZe 1.89 mile

Lca (6) 0.66 mile 0.80 mile

tp=C (L.Lca)0-3 2.04 2.38

SPILLWAY CAPACITY AT MAXIMUM-WATER LEVEL(7 ) 209 cfs, design ,pillwaj crest elevation; 174 cfs, with

flashboarda

(1) Measured from USGS maps.(2) Hydrometerological Report No. 33, Figure 1.(3) Hydrometerological Report No. 33, Figure 2.(4) Information received from Corps of Engineers, Baltimore District.(5) Length of longest water course from outlet to basin divide, measured

fron USGS maps.(6) Length of water course from outlet to point opposite the centroid of

drainage area, (see Plate 1, Appendix E) measured from USGS maps.(7) See Sheet LJ.12of this Appendix.

SHEET 3 of 12

HEC-1, REVISEDFLOOD HYDROGRAPH PACKAGE

The original "Flood Hydrograph Package" (HEC-1),developed by the Hydrologic Engineering Center, Corps ofEngineers, has been modified for use under the National DamInspection Program. The "Flood Hydrograph Package (HEC-1),Dam Safety Version", hereinafter referred to as, HEC-1, Rev.,has been modified to require less detailed input and toinclude a dam breach analysis. The required input is obtainedfrom the field inspection of a dam, any available design/eval-uation data, relatively simple hydraulic calculations, orinformation from the USGS Quandrangle maps. The input formatis flexible in order to reflect any unique characteristics ofan individual dam.

HEC-I, Rev. computes a reservoir inflow hydrographbased on individual watershed characteristics such as: area,percentage of impervious surface area, watershed shape, andhydrograph characteristics determined from regional correla-tion studies by the Corps of Engineers, Baltimore District.The inflow is routed through the reservoir using spillwaydischarge data obtained from the field inspection or designdata. Flood storage capacity is determined from USGS maps ordesign information and verified by the field inspection. Inthe event a spillway cannot discharge 0.5 PMF withoutovertopping and failure of the dam, downstream channelcharacteristics obtained from the field inspection and USGSmaps are inputed and flows are routed downstream to the damagecenter and a dam breach analysis is performed.

Included in this Appendix are the HEC-l, Rev.pertinent input values and a summary print-out tables.

IT. M L DATI.ZL.2ILwaft SUBJECT_______________ SIfT OF...L........

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END BF NEARKm

FLfh : ~3SSAM P41111 4NEC-11sam ea SAFTY alm JULYv 1971

LADY IFICAT331 26 FB 7

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* PLACID LANE SMRNOST is aS. Pa 50616 Ka 10. 13-91

JUSnu SPIIIL CAale

AS an. oil 13? 10 INIi NETIC IPLT Iwar uuru

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IFLN AT hlnUA" SIICVLY to NEUROIR

let"0 3CINP ISCIN I1*11 JPIlT SOT INANE1 151411 3*01

in 0 0 5 5 0 0

11935 INS 431* N13IS3*PN DATAININ IBM TRIA S 1135S TRUPC RATIO IN I OA

I 1 .36 0, .71 #.@@ 000 0 1 0

SPFE PUS 36 PEECIP DATA17 9SPFE PRO 3 12 R24 141 in Il

0.00 22.36 111.0. 124.00 134.00 142.00 0.00 0.00tRhIPUE WII TIVE POKIAN 11 .100

5 0.00 5.4. 1.10 0.00 0.00 1.90 1.SO .01 900 0.00

331t Ih31SI*41 DATAT1. 2.64 002 .45 IT&- S

NICEV$I00 MAaITTs -4.50 OMI -. 01 RTIlE. 2.4

MIT NY3SMaaP 73 EU-U-#Et153 ORDINMSSS LII. 2.06 14501, CP* .45 ItS.. 1.02. 7. 1S. 23. 33. 4). 4a. 111. 3. 49.

46. 42. 39. 36. as. 3t. 29. 26. 24. 23.21. 19. it. 17. IS. 14. 13. 12. it. it.0t. f. 0. . 7. 6. 6. 6. S. S.4. 4. 4. 3 . 3. 3. 3. 1. 2.2. 2. 2. 2. 1 . ~ . *

M.14 3.11 P13103 RAIN [usI LogS cowP a 40.90 14.33 fal P13363 RATE two 3 CUSP 6

WS 25.56 23.11 2.33 19310.

f4 449.1( 59.)( 601 346.110)

NIIM1PN POSTING

WUin"h 10hYDOUN MaImR COUDITIONS

161*0 [COW 31100 ITAff .91.1 JPNT INK* 311*01 3*4910OU I S 0 0 0 0

11UN4TINS DATA31031 CLIII Ave 3 54100 33*w 09 1909 LIT*

0.0 6.060 0.30 I I 0 0 0

flIPS USTI LAS *803 x 163 $1014 1390*11 0 0 0.060 0.0410 0.000 -1"6?. -

STAS[ 1667.09 1660.00 1669.06 1670.0 1671.0 1672.40 1673..00 1604.01

F1.M 0.00 17.10 195.00 204.0 213.00 222.00 231.00 23010

SUEACE AREA. 2. 6. 12. 17. 24. 25.

CAPACITY@ 0 . 21. 65. 107. 109. 201.

ELEVATION~ 132. 1637. 1W2. 1665. 16. 113.

COIL 39491 CM0 EXPU ELI VI, COOL C*01* 1196.1640.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0

10OM CM~ EXPI 8*11131070.5 0.0 0.0 0.

CHIT LEIMU 0. 250. 1500. 2360. 2370.AT US 31100ELEVATION 1670.5 1671.1 1672.0 1672.5 1674.0

8990-A3EA ~F01 CINIP A1100.

137103 HIMOSAPH T0 S101*8 315101 REStRVOIO

11100 12069 IECON 11*91 JPLI "tR IMANE 131*01 3*610Ulf 0 0 0 0 0 1 0 0

3N1O$ IM1 ThEA IHOP 1335* TRIPC RATH1 IBM0 [SAN LOCAL1 .55 0.00 Vt3 3.00 0.000 0 1 0

PRECIP DATA1971 Fos 06 lit 024 .Rio 072 09A0.06 22.50 1ll110 124.00 134.00 142.00 0.00 0.00

LOIS DATA13091 113 31113 31101 [A 1 7* 1m30 31303 31011. CulTL ALSIX 31119

0 0.0o 0.00 1.0 0.0 0.00 1.00 3.00 05 0.06 0.0

19.' 2.10 CPO .45 1*4 0

311 -650 3033 -. 05 31130 2.00

WIT U13160A9 86 tIO-W-913113 OID1N*TI, LAS' 2.36 1011111 Cps .45 V0L. I.002. . . .16.u 44. 55. 62. 67. 69.66. 62. so: 4. 51. 40. 45. 42. 29. 37.24. 32. 20. 2N. 26. 25. 23. 21. 20. 19.

II 6I. is. 14. 14. 1$. 12. iI. 0t. IS.9.1 . P. 7. 7. . 6. 5. 1.5 0. 4. 4. 4. S. 3. 3. 3. 3.2 2. 2. 1. 2. 2. 2. 2. 1. I

so." 33.01 1169 "*in 3313 Lose coop 1 0110 33.3 P33206 141 1011 LIS COUP 6

SUN 31.13 19.55 2.40 31119.9 12.14 M5.84 61.)( 1016.29)

CDM L 4IO111, WiTION MKiIN M l5W

Him am INNIcI 1A1uC JPLI joI w IIA tlioEn losINg 1 0 0 0 6 4 0

ILI lm A" I111 lo l o LIT: o4.0 .09 €& I .O Il I 0I II~PLl

IM IN, LAG 611014l X TON I11 1'"Tl0 .000 0.000 0.0414 0. O

11441) "it) "is) ELNT EI"M ILITI IL..6330 .133 .O334 1670.3 160.3 10. J1117

€lM SECTION MIITI-TI IETpLV-T.0." 1680.30 11.00 f 1 M71.90 39.00 1671.3 I .3 1 I.00 1020.31

76.0 167I.30 l14.00 I601.0 106.10 16111.00

IINIK 0."0 .01 .01 .11 .16 .22 .29 v3 .43 .34.62 .71 .00 .10 .t7 1.06 1.16 I .23 1.36 ! .41

OHTFLN 0.00 33.6f 122.41 297.33 $20.4 625.21 l200.55 I60.3? 2262.2 2PIS.73343.lI 4417.39 $2i3.36 6169.23 7132.41 1111.41 pimm.7 miml llT.ni 13162.77

STAN l~~l 167 1.11 lue.43 I671.n 167t" .41 1672.1 I10.46 1673.11 1414.31 103.041675.36 1676.19 1676.62 1077.14 1477.67 1679.19 1679.72 1679.23 1679.7 1660.39

FLOW o.o0 33.69 122.60 217.33 $21.494 8I3.21' 12"M~ 161.37 2262.92 291|.731611.12 441?.$f $21.54 fdfd.n] 713.41 8131.41 9262.7I 10414.17 I1POW." 13162."

SECTION 0" FEET Nt M " DiON

12141 ICIIM /1CON |ITI JftT JlqT IlAi IllAK 11111

SLASl CLII A" Irmo TOOK lo~t IPP L.110.I 9.0" I .O0 1 0 O I

0 a 11O.000 1.00 0.000 O. 1

ONA PfN CDINWIL WHNING

21111 21042n l) M43) Et, T WARM~ AMu on.O700 .I140 .1000 161O.0 1611.1 12"I. An"D

303.09 I615.0M . 47,I111.01 6" ." IIII.20

I11040 1., ,oi .12 .. 9 .36 .46 .6 ,o ,.12 I.0J f.20 1.31 1."l .0 1.21 0.lf 11.11 IS.M

WTFLIS 9.00 1.11 6.14 11.11 It." 21P.l to .24 53.12 094 9.47103." I23.73 146.33 I71.3I 303.67 l2.26 462,19 ?44.1%1 1IS1.361 0311.39

ITl I614O00 1614.37 1#1#.?4 1611.II 1611.47 1611.14 I. 1611.21 1612.0 1."I 1613.311613.68 1114.15 1614.42 I614." 1613.16 1615.33 115.11 1616.16 111.63 1617.0

FLI 0."l 1.11 6.14 12.12 OP." 29.1s ".24 3.12 0P.84 14.47113.00 ffs.ps 146.33 I71.51 203.67 17.20 461.11 ?44.1% 113l.14 1131.39

SUtENY

0.0........ .6.l0 I il 0 .. .

PEA FLOW ANN SF004! (lND OF PFIS? hININ FOR NOFRmE PL461*120 EChISIC CONISTATIOU11FLOW 11 ChEW FEET PER 01130 ICIIC RETIE PER 51003

MIlA11N[ 111,12E 05031111 OILMUER)

RATIOS SPILlE9 10 FLOgWOPERATION STATION AREA PLAN* RATIO I RATTI0 2 MiTlo 3

.20 .40 .50

OIOOR*PN AT in .3 1 210. 291. 363.4 .3 4' 6;lfl( 3.123)4 10.333

ORITES TO UET .36 1 114. 196.. 204..131 4 4.251( 5.36)f 5.773f

BTN moP AT at .11 1 300. 507. 614.3 1.42) 4 10.7734 14.36)( 17.9614

OUTED TO US0 .55 1 300. 50. 634.1 3.42) IS.7")( 14.36)( 17.96)(

2 COBIKI1 CUN .11 1 10. 612. 031.( 2.363 ( 14.4114 11.3234 23.5414

1010119 To 14 .;I I SW. 6at. 034.4 2.36) 4 14.3914 19.30)4 23.13)4

50311101 D1 UFETT ANKYDIDWithout 11 ashboards

INITIAL VALK5 SPILUAT CNEI TOP OF SM3ELEVATION 3667.00 1667.00 1670.501103*01 455. 135. 240.OTFLON 0. 0. 209.

RATIO 163211" ian4 011111 0311fi IWAJm TIME OF IDE oFoF REEVIN 31313 Sf0100 ONTFLUN MVR TOV INIX UTFLOM FAILINIE

Pwl 0.3.14.1 0911 SN iC-FT CFO 30035 He03 m 001

.30 14660.62 0.00 III. 434. 0.01 44.00 0.00

.40 3663.14 0.00 207. 396. 0.00 44.25 0.00.50 1669.96 0.00 227. 204. 0.00 44.75 0.00

PLAN9 I STAION M3

16113 FLOICFS IMAS,IT W34*

330:" 1672.1 42.25 OFl MR 01

.50 634. 1672.6 42.21547.

PLAN I STAT1ON us

0033111 001111111 TINSRATIO FLN,CUO STAN",1 30000

.30 sm0. 3636.0 42.75 2 N00 AT 464?

.46 61. 1616.3 42.15 AT10

.110 n33. 3616.3 42.35AAT43

111l661*PU WUTINS

6IFL6 MN MM&IM - 1.,3T6I CIIlTION

[STAR ICUIP IECIE 11*1 JILT PItT INK 2lTAK* 161"

am CLUI Af 111 ISAU[ INT IP I. 1 6

0.0 #.to# 6.6 I 1 0 0 6

NEWS W6il LAG ~lSi(g I i from WlATI 1 O 6.00 #."1 6.O0 -1"9. -I

luT I6.10 169.13 1676.6 1671.60 1672.60 1673.0

FLO I."6 07.36 211.00 229.60 226.00 236.6

ItACE 1ll4. 2. 6. Ii. 17. 24. 25.

CAP6CITTl 6. 21. 6. 107. 169. 391.

ELEVATION 162. 1637. 1642. 465. 1665. 1673.

CnL WI1| COWI EIPI CLEV. WlL CMEA 0111668.1 1.6 O.6 6. 6.6 0. 6.6 4.

TOP.L CUP FlPD PANI4

1674.5 0.0 0.0 6.

CKIIIT LNT 6. 2M6. 6i . 2363. 2370.AT 0i9 KIMl

ILEWITII* 1676.5 1671,1 16s .6 1672.5 6674.0

PEAK FL0 ND SITORAG (EN V PERIOD) MONT*61 IN IIUlT.E PIAII-3TII ICNSHIC COI1U|A1IVI66FLOW Il CIIC FEET PE MSECOND MUIC K111 PER ICOII

hinCA 1! 166*61 ILi (MUS1 sIlOKINIi

N1TIO IPPII.I TO FLOWOPE1RTO 16 1 Ul6ill 1* A 3LAN IATO I RATIO 1 *11l 3

.36 .46 .30

I1INR3Pl AT IN .6 I 216. 291. 363..935 ( 6.17)1 0.23)6 10.21H

3061E TO "61 .36 I 156. 124. 0.1 .)31 1 4.414 6.34)1 6.49)1

3INOU*116 &I Val .55 1 30. 467. 6134.6 I.42) 1 10.77)( 14.36)( 171.6(

N6OT13 11 via .55 1 106. 2O7. 634.I 1.42) 1 1W.7714 14.36)H 17.96)

2 CONIIED CIA .Jl 1 514. 694. 697.6 2.36) 1 14.51)4 19.66)1 23.3114

101111 6 to 6l .JI I Si3. 694. 6M5.2.36) 6 14414 19.65) 2.34H4

- -

With flashboards1INITIAL WLUE SPILLAT CMIT TIP IF PAN

IL19"TIN 646.60 16110 1670.56IT=6* 1"9. 1"9. 240.SITFLIN0 0. 174.

RISI ou1111 NXI3O31 NIIN MSISU1 ISTIO TIME OF TIME IFIF KSEIfIl WN1 1100*61 IFLIS 661 TOP M* MMOSh FAIL II

PIP .I.ELEV MI61 M he-FT Us Own 11116 Hum1

.30 1676.37 0.of 237v5. 66 44.6 00.4 670.00 :30 246. 224. .0 43.7:00

.34 1671 .12 .&2 251. 30. 5.73 41.50 0.0

PLAM' I 6167506 lil

"KING11 N*34X61 TIMERNTIS FLIV,C~S GIAGE,FI "uas

.30 30 1672.1 42.23:40 SOL 1672.4 42.25 TOP OFRANAT.30 034. 1612.6 42.25 6l. 63

PLAN 1 61ATION NI

1*331.1 146111461 TIMERATIO FLA,C~lS IK T WAS17 166

013. 616.0 42.73 2 @1mmI AT 1617

.40 694. 1616.2 42.75 2 HOUSES AT 1616

.50 595. 1610.4 42.75

APPENDIX

E

li Big Boulder Lake

/G~/

14 19

~ _N'

0' Av lo

CABO COUTY~ DTA BTANE FRM US.GEOOGIALSUREYUA

SHET ENILDHCOYRNADBAELE6A

~'- ,~ri1.

.J.-if -- -l .0.0

at" Mt.C ' at- -ml- 1/

PC -LE EAPT ** f

o--- m - - -- --- -- - - - - - - --t -. a

* sYPtjILAL,~ CROSSZ EC T, BEUPW gRPog ELCT

4-LS. .0*-s1 0 10.

5-7-

-GO . 2

Hi 4M IO

ILI

!RLW L5PLAT 2

LS A

SECT0A~. ELLW AT A-A ,P

INLET STRUCTURE DETAIL 2 -i c-

I- o l TO -1 - - A

Pip1

I'-'fgTPPESoL*

3,

A- it

SECTIOk A-A i;!U -

C O- SECTOO Lf~ W. " ..- AA T C 51.jAw

CONJCRETE BLOCK ZROD' KJET

-4

CONCRETE COLLA

171

MIF1itI±TgLC

PLT4

APPENDIX

F

SITE GEOLOGYPLACID LAKE DAM

Placid Lake Dam is located in the PoconoPlateau section of the Applachian Plateau PhysiographicProvince. As shown in Plate F-i, the dam site area isunderlain by glacial drift of Pleistocene age which over-lies the sandstone and siltstone bedrock belonging to theDuncannon member of the Upper Devonian age Catskill Forma-tion. The unstratified glacial deposits in the dam sitearea consist of varying amounts of clay silt, sand andgravel with local accumulation of boulders especiallynorth of the dam area. No bedrock exposures were observedat the dam during the field inspection. Approximately1000 feet southeast of the dam a small area of sandstoneis exposed in a shallow quarry. Here bedding strikes north-northeast and dips approximately 10 degrees to the north-west. Jointing strikes predominately near east-west dippingmoderately to the south. The overall bedrock structure inthis region is characterized by a series of northeasttrending folds.

N .

a4 W

FBOULDER FIELD

pl K COLLUVhUv

- ~ (~'*N,

-~ . . - Lqki

I V11 Ad

liar ---------aroo

.dP, I/ GLACIAL DRIFT

F P AR K M COLUVI3

.r,. pi M ?llhtsiri *1 \-. 111,%% \~ NI

SPECgoY-OV

_~. ATLTE-

LI