HARRISBURG PA F/S FLEM CORORY AND CARPENTER LAKE DAM … · 2014. 9. 27. · ADAO B 588 GANNETT FLEM -INS CORORY AND CARPENTER ,INC HARRISBURG PA F/S 13/13 NATIONAL DAM INSPECTION

ADAO B 588 GANNETT FLEM -INS CORORY AND CARPENTER ,INC

HARRISBURG PA F/S 13/13

NATIONAL DAM INSPECTION REPORT. INDIAN MOUNTAIN LAKE DAM

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MUD RUN, MONROE COUNTYA

BAINLEYEV

PENNSYLVANIA

NDI ID NO. PA.0078DUl ID NO. 45-227

INDIAN MOUNTAIN LAKES CIVIC ASSOCIATION, INC.

PHASE I INSPECTION REPORT

NATIONAL DAM INSPECTION PROGRAM

ORICINAL CQNTAIN8 COLOR PLATES, ALL 000kREPRODUCriONS WILL BE IN BLACK AND 1" c

APrepared by

GANNETT FLEMING CX)RDDRY AND CARPENTER, INC.

NTHiS QUfa~i em lvank 17105 UJ 0i --T, 4t s TO DDC CQ

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1503 1 029

DISCLAIMER NOTICE

THIS DOCUMENT IS BEST QUALITYPRACTICABLE. THE COPY FURNISHEDTO DDC CONTAINED A SIGNIFICANTNUMBER OF PAGES WHICH DO NOT

REPRODUCE LEGIBLY.

4,

DELAWARE RIVER BASIN

MUD RUN, MONROE COUNTY

PENNSYLVANIA

INDIAN MOUNTAIN LAKE DAM

(,DI ID 1,A- 0783".!. DER ID Ift45-227" /

_NDIAN.UOUNTAIN LAKESgtVICPSS7OCIATION,' INC.

Co-n-4,Per-S vc ri 6.

PHASE I INSPECTION REPORT'35 - ;__ INATIONAL DAM INSPECTION PROGRAM

Prepared by

GANNETT FLE1IING CORDDRY AND CARPENTER, INC.Consulting Engineers

P.O. Box 1963Harrisburg, Pennsylvania 17105

For

DEPARTMENT OF THE ARMYBaltimore District, Corps of Engineers

Baltimore, Maryland 21203

ORIGINAL CONTAINS COLOR PLATES: ALL DO0REPRODUCTIONS WILL OF IN BLACK AND WHITE

". -- ---

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PREFACE

This report is prepared under guidance contained in theRecommended Guidelines for Safety Inspection of Dams,for Phase I Investigations. Copies of these guidelinesmay be obtained from the Office of Chief of Engineers,Washington, D.C. 20314. The purpose of a Phase I inves-tigation is to identify expeditiously those dams whichmay pose hazards to human life or property. The assess-ment of the general condition of the dam is based uponavailable data and visual inspections. Detailed inves-tigation, and anal.yses involving topographic mapping,subsurface investigations, testing, and detailed compu-tational evaluations are beyond the scope of a Phase Iinvestigation; however, the investigation is intended toidentify any need for such studies.

In reviewing this report, it should be realized that thereported condition of the dam is based on observationsof field conditions at the time of inspection along withdata available to the inspection team. In cases wherethe reservoir was lowered or drained prior to inspec-tion, such action, while improving the stability andsafety of the damn, removes the normal load on thestructure and may obscure certain conditions which mightotherwise be detectable if inspected under the normal

operating environment of the structure.

It is important to note that the condition of a damdepends on numerous and constantly changing internal andexternal conditions, and is evolutionary in nature. It

.Z.",;would be incorrect to assume that the present conditionof the dam will continue to represent the condition ofthe dam at some point in the future. Only throughfrequent inspections can unsafe conditions be detectedand only through continued care and maintenance canthese conditions be prevented or corrected.

Phase I inspections are not intended to provide detailedhydrologic and hydraulic analyses. In accordance withthe established Guidelines, the spillway design flood isbased on the estimated "Probable Maximum Flood" for theregion (greatest reasonably possible storm runoff), orfractions thereof. The spillway design flood provides ameasure of relative spillway capacity and serves as anaid in determining the need for more detailed hydrologicand hydraulic studies, considering the size of the dam,its general condition and the downstream damageA. potential.



PENNSYLVANIA


NDI ID No. PA-00783DER ID No. 45-227

4 ))D0 TA;3

INDIAN MOUNTAIN LAKES L7ICoauncedCIVIC ASSOCIATION, INC. ,Lifi~atiom

ByPHASE I INSPECTION REPORT D3'1t -tn

Avri1 itvC| Codes

NATIONAL DAM INSPECTION PROGRAM .Lva!lbLty codes

Dist pca

JANUARY 1980

CONTENTS

Description Page

t SECTION 1 - Project Information ........ .1SECTION 2 - Engineering Data ..... ......... 6SECTION 3 - Visual Inspection ...... .... 8SECTION 4 - Operational Procedures . . . ... 10SECTION 5 - Hydrology and Hydraulics . . ... 11SECTION 6 - Structural Stability . . . . . 14SECTION 7 - Assessment, Recommendations, and

Proposed Remedial Measures . 17

. "

- A-

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APPENDICES

Appendix Title

A Checklist - Engineering Data.B Checklist - Visual Inspection.C Photographs.D Hydrology and Hydraulics.E Plates.F Geology.

S -iii-

1*

PHASE I INSPECTION REPORTNATIONAL DAM INSPECTION PROGRAM

* BRIEF ASSESSMENT OF GENERAL CONDITION

- -. AND

RECOMMENDED ACTION

Name of Dam: Indian Mountain Lake DamNDI ID No. PA-00783DER ID No. 45-227

- Size: Small (13 feet high. 840 acre-feet)

Hazard Classification: High

Owner: Indian Mountain Lakes CivicAssociation, Inc.Albrightsville, Pa. 18210

State Located: Pennsylvania

County Located: Monroe

Stream: Mud Run

Date of Inspection: 16 November 1979

Based on visual inspection, available records,calculations, and past operational performance, IndianMountain Lake Dam is judged to be in fair condition. Theexisting spillway can pass the Probable Maximum Flood(PMF) with 0.6 foot of freeboard. The spillway capacityis rated as adequate. This analysis is predicated uponthe proper functioning (failure) of the flashboards on thespillway crest. If the low areas at the top of theembankment were raised, the freeboard would increaseto 1.2 feet. Needed repairs have not been made to somefeatures of the dam. There is no functional outlet worksat the dam.

A The following measures are recommended to beundertaken by the Owner, in approximate order of priority,immediately:

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(1) Install a gate operating mechanism for theoutlet works gate and construct a properly designed outletstructure at the outlet works.

(2) Repair the eroded areas on the upstream slopeand provide properly designed slope protection for theupstream slope.

(3) Perform an investigation and study to determinemeasures required to prevent further depressions fromoccurring behind the spillway walls, while at the same timeensuring the integrity of the spillway walls andembankment. Fill in the existing depressions and takeother appropriate action as required.

(4) Perform an investigation and study to determineif any foundation damage has occurred as a result of theexcessive seepage at the spillway. The study should alsodeterminie thle cause of the seepage and address measuresrequired to reduce the seepage to an acceptable amount.Take appropriate action as required.

(5) Repair the slough on the downstream slope of theemnbankment. After repairs are made, monitor the area.Should any change in the area occur, take appropriateat-tion as required.

(6) Remove trees and brush on or near theembankment.

(7) Fill in the low areas at the top of theembankment.

(8) Until investigations, studies, and remedial workare completed, the Owner should monitor the condition ofthe dam and appurtenant structures. Take appropriateaction as required should any changes in conditions occur.

* All investigations, studies, designs, and supervisionof repairs and construction should be performed by aprofessional engineer experienced in the design andconstruction of damis. M.oitoring programs should also beperformed or supervised by a professional engineer.

In addition, it is recommended that the Owner modifyhis operational procedures as follows:

I.v

(1)j Develop a detailed emnergencoprtn andwarning system for Indian Mlountain Lake Dam. This systemshould address the effects of a rise in the downstreamdepth of flow due to the proper functioning (failure) ofthe flashboards.

(2) Provide round-the-clock surveillance of IndianMountain Lake Darm during periods of unusually heavy rains.

(3) When warnings of a storm of major proportionsare given by the National Weather Service, the Owner shouldactivate his emergency operation and warning systemprocedures.

(4) Institute an inspection program such that thedam is inspected frequently. As presently required by the%Commonwealth, the program should include a formnal annualinspection by a professional engineer experienced in thedesign and construction of dams. Utilize the results todetermine if remnedial measuires are necessary.

(5) Institute a maintenance program to properlymaintain all features of the damn.

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77t. r. -


Submitted by:

GANNETT FLEMING CORDDRYA AND CARPENTER, INC.

"1 FREDERICK FUTCHKOProject Manager, Dam Section

Date: 11 February 1980

Approved by:

DEPARTMENT OF THE ARMYBALTIMORE DISTRICT, CORPS OFENGINEERS

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PENNSYLVANIA


NDI ID No. PA-00783DER ID No. 45-227

INDIAN MOUNTAIN LAKESCIVIC ASSOCIATION, INC.

PHASE I INSPECTION REPORT


SECTION 1

PROJECT INFORMATION

1.1 General.

a. Authority. The Dan Inspection Act, Public Law92-367, authorized the Secretary of the Army, through theCorps of Engineers, to initiate a program of inspection ofdams throughout 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. Indian Mountain Lake Damis a zoned, earthfill embankment. The design height ofthe dam is 13 feet at its maximum section. The dam is695 feet long, including the spillway. The spillway is aconcrete gravity weir located near the left abutment ofthe dam. It is 110 feet long and its crest is 5.7 feetbelow the design top elevation of the dam. Flashboardsthat are 1.7 feet high are provided along the spillwaycrest. The outlet works is located near the middle of the

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embankment to the right of the spillway. It consists of a24-inch diameter steel pipe with a concrete headwall andgate at the upstream end and a concrete outlet structureat the downstream end. The various features of the damare shown on the Photographs in Appendix C and on thePlates in Appendix E. A description of the geology ispresented in Appendix F.

b. Location. The dam is located on Mud Runapproximately 4.9 miles east of Albrightsville,Pennsylvania. Indian Mountain Lake Dam is shown on USGSQuadrangle, Blakeslee, Pennsylvania, with latitude N41 °00' 15" and longitude W75 ° 30' 25", in TunkhannockTownship, Monroe County, Pennsylvania. The upstream endof the reservoir is shown on USGS Quadrangle, PoconoPines, Pennsylania. The location map is shown onPlate E-1 in Appendix E.

c. Size Classification. Small (13 feet high, 840acre-feet).

d. Hazard Classification. High hazard. Downstreamconditions indicate that a high hazard classification iswarranted for Indian Mountain Lake Dam (Paragraphs 3.1fand 5.1c(4)).

e. Ownership. Indian Mountain Lakes Ciri~ckssociation, Inc., Albrightsville, PA 18210. Thepresident of the Association is Robert N. Mueller.Correspondence should be sent directly to the Association.

f. Purpose of Dam. Recreation.

g. Design and Construction History. The dam wasdesigned in 1959 by Leo A. Achterman, Jr., ConsultingEngineer of Stroudsburg, Pennsylvania. The design isshown on Plate E-2 in Appendix E. The permit to constructthe dam was issued in January 1960. Construction startedin the spring of 1960 under the supervision of Mr.Achterman. The Contractors were G. H. Litts and Son, andPaul L. Edinger. The dam was completed in August 1960.

In 1962, Mr. Achterman designed modifications tothe dam which are shown on Plate E-3 in Appendix E. Themodifications consisted of raising the embankment byapproximately 2 feet, raising the spillway approach andexit channel walls near the weir by about 2 feet, andproviding flashboards along the spillway crest. The

i.,

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permit to construct these modifications was issued in May1962. Mr. Achterman stated that, although he was notassociated with the construction of the work, he believedthat the Contractor was either Getz and Sons or LeonKeiper. Other data concerning these modifications are notavailable.

In 1964, Mr. Achterman designed deadmen tostrengthen the left spillway approach wall (Plate E-4).Construction of an adjacent structure and the associatedregrading required that the wall be strengthened.

The local residents refer to the impoundment asthe "Big Lake." There are other minor impoundmentsdownstream that are within the Indian Mountain LakesDevelopment.

h. Normal Operational Procedure. The reservoir isnormally maintained at the top of the flashboards withexcess inflow discharged over the spillway.

1.3 Pertinent Data.

a. Drainage Area. (square miles) 2.8

b. Discharge at Damsite. (cfs)Maximum known flood at damsite Unknown.Outlet works at maximum poolelevation 60Spillway capacity at maximum poolelevation 4,840

c. Elevation. (feet above msl)Top of dam (existing) 1799.1Top of dam (design) 1799.7Maximum pool 1799.1Normal pool (flashboard crest) 1795.7Spillway Crest 1794.0Upstream invert outlet works 1788.5Downstream invert outlet works 1787.1Streambed at toe of dam 1787.1

d. Reservoir Length. (miles)Normal pool 0.72Maximum pool 1.42

e. Storage. (acre-feet)Spillway crest 203Normal pool 313Maximum pool (design) 840

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f. Reservoir Surface. (acres)Spillway crest 49Normal pool 81Maximum pool (design) 190

g. Dam.

Type Zonedearthfill.

Length (feet) 585

Height (feet) (design) 13(existing) 12

Topwidth (feet) (design) 10(existing) 12

Side Slopes

Upstream (design) 1V on 3H(existing) 1V on 1.8H

Downstream 1V on 3H

Zoning Clay corewith hardpan.

Cutoff Clay corefounded on"impervious"foundation.

Grout Curtain None.

h. Diversion and Regulating Tunnel. None.

i. Spillway.Type Concrete

gravity weirwithnear-ogeecrest.Flashboardsare providedon the crest.

Length (feet) 110

1 I-4-

Spillway. (Cont'd.)

ElevationsWeir crest 1794.0Flashboard crest 1795.7

Upstream channel Reservoir.

Downstream Channel Concretepaved apronextending togrouted stoneexit channeland thence tonaturalstream.

j. Regulating OutletsType 24-inch

diametersteel pipe.

Length (feet) 69

Closure Gate atupstream end(see text).

Access None atpresent (seetext).

.

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SECTION 2

ENGINEERING DATA

2.1 Design.

a. Data Available. The available data aresummarized in Appendix A. The Pennsylvania Water andPower Resources Board reviewed the original design andordered minor revisions in the design. A report of theirreview is on file, as are some of the original designcomputations. The flashboard design is available for the1962 modification to the damn. No analysis by theCommonwealth for this modification is available.

b. Design Features. The dam and appurtenances aredescribed in Paragraph 1 .2a. The design features areshown on the Photographs in Appendix C and on the Platesin Appendix E. Plate E-2 shows the original dam prior toits modification in 1962. Plate E-3 shows themodifications made in 1962 to the dam. Plate E-4 showsthe 1964 modifications to the dam.

Although not indicated on the Plates, the designengineer believed that wire-mesh reinforcing was placed inthe spillway wall, spillway apron, and outlet worksconcrete.

C. Design Consideratiors. Specific designconsiderations are addressed in Section 5 and Section 6.

2.2 Construction.

a. Data Available. The only data available are therecollections, reported verbally, of the design engineer,who also supervised the original construction. No data

* are available for the 1962 or 1964 modifications to thedam.

b. Construction Considerations. The designengineer reported that no special problems wereencountered during the original construction except in thespillway area, where springs were encountered. Hereported that, as construction changes, drain material wasplaced beneath the spillway apron, drain holes were added

to the spillway apron and spillway walls, and drain

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material was added behind the spillway walls. He did notrecollect the details of the drain placement. Theavailable data raises no special concerns about theconstruction of the damn.

2.3 Operation. There are no formal records of operation.There is no evidence of any formal inspections of the damhaving been made after its construction.

2.4 Evaluation.

a. Availability. Engineering data were provided bythe Bureau of Dams and Waterway Management, Department ofEnvironmental Resources, Commonwealth of Pennsylvania.The engineer who designed the original dam and thesubsequent modifications provided additional dataverbally. The Owner made available the maintenancesupervisor for information during the visual inspection.

b. Adequacy. Design data and other engineeringdata are somewhat limited. The assessment is based on thecombination of available data, visual inspection,performance history, hydrologic assumptions, and hydraulic

* assumptions.

C. Validity. There is no reason to question thevalidity o the available data.

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material was added behind the spillway walls. He did notrecollect the details of the drain placement. Theavailable data raises no special concerns about theconstruction of the darm.

2.3 Operation. There are no formal records of operation.There is no evidence of any formal inspections of the damhaving been made after its construction.

2.4 Evaluation.

a. Availability. Engineering data were provided bythe Bureau of Dams and Waterway Management, Department ofEnvironmental Resources, Commonwealth of Pennsylvania.The engineer who designed the original dam and thesubsequent modifications provided additional dataverbally. The Owner made available the maintenancesupervisor for information during the visual inspection.

b. Adequacy. Design data and other engineeringdata are somewhat limited. The assessment is based on thecombination of available data, visual inspection,performance history, hydrologic assumptions, and hydraulicassumptions.

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

/12. .- 7-

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SECTION 3

VISUAL INSPECTION

3.1 Findings.

a. General. The overall appearance of the dam isfair, with deficiencies as noted herein. The locations ofdeficiencies are shown on Exhibit B-i in Appendix B.Survey data acquired during this inspection are presentedin Appendix B. On the day of the inspection, the pool was0.1 foot above the top of the flashboards.

b. Embankment. The embankment is in faircondition. The downstream slope has a shallow sloughwhich extends for about 10 feet along the top adjacent tothe spillway (Photograph A). Small trees are growingsporadically over the slope, especially near the rightabutment (Photograph B). The upstream slope is coveredwith brush growing sporadically except at areas whereerosion has occurred (Photograph C). The erosion issevere and especially bad at the junction of theembankment and the right spillway wall (Photograph E). Atthis area, the erosion has proceeded almost one-half wayacross the top of the dam. Except for the vegetation, noslope protection was observed on the upstream slope.

There was a flow of about 10 gpm along thedownstream toe between the outlet works and the rightabutment. This was determined to be surface runoff.Although this runoff could have obscured seepage throughthe dam, any such seepage would have been minor.

The survey performed for this inspection(Appendix B) revealed that the top of the embankment isabove its design elevation except adjacent to both sidesof the spillway, where it is a maximum of 0.6 foot belowdesign elevation. The survey also revealed that thedownstream embankment slope is in accordance with thedesign, that the topwidth is generally about 2 feet widerthan the design, and that the upstream slope is 1V on1.8H, which is considerably steeper than the 1V on 3Hdesign slope.

c. Appurtenant Structures. The spillway is in faircondition. Flashboards extend along the crest of theweir. There was a slight flow over the flashboards, whichhindered visual inspection. No deficiencies were observedat the concrete weir. Only a few flashboard pins could beinspected; they appeared to be in accordance with the

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21- -- =

design (Appendix A). The concrete spillway apronimmediately downstream of the weir is cracked at onelocation. Because the apron was submerged, the width andextent of the crack could not be determined. Drain holesare provided in the apron. Immediately adjacent to thecrack, one drain hole was discharging such that the waterflowing from it rises 2 to 3 inches above the flow in theapron (Photograph F). The two other drain holes that areimmediately adjacent to this drain hole also have asignificant amount of flow. There are many shrinkagecracks at the spillway walls both upstream and downstreamof the weir (Photographs F and H). No expansion orcontraction joints were observed in the walls. At a fewsmall areas on top of the spillway walls, minor peeling ofconcrete was observed. The spillway walls upstream anddownstream of the weirs have drain holes extending throughthem. The earthfill behind the walls is depressed atareas adjacent to the drain holes (Photograph H). Twoplastic pipes, which are believed to be drains fromadjacent buildings, extend underground to behind the leftspillway wall, where their ends are exposed because ofdepressions in the earthfill.

The outlet works is in poor condition. Althoughavailable drawings indicate that the outlet works has agate, no evidence of the gate operating mechanism wasobserved. The Owner's maintenance supervisor believed itwas submerged, but said that he had never seen it. Nodeficiencies were observed at the steel conduit. Theoutlet works structure has failed structurally. The leftsidewall has been removed and is lying about 30 feetdownstream on the overbank of Mud Run. The right sidewallis tilted and separated from the headwall (Photographs Iand J). There are structural cracks in the headwall(Photograph J).

e. Reservoir Area. The watershed area is swampyand covered mostly with-scrub brush. Development in thewatershed is minor. The most significant development isthe homes of Indian Mountain Lakes Development. Slopes in -the watershed are mild.

f. Downstream Channel. Mud Run extends downstreamfrom the dam through part of the Indian Mountain LakeDevelopment. The overbanks have very thick and tall brushgrowing on them. Eleven dwellings were observed near theI. stream downstream from the dam. One of the dwellings isabout 800 feet downstream from the dam. The others are

9 within a reach which extends from 1 to 2 miles downstreamfrom the dam. The downstream area is shown on Exhibit D-1in Appendix D.

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SECTION 4

OPERATIONAL PROCEDURES

4.1 Procedure. The reservoir is maintained at the top ofthe flashboards, Elevation 1795.7, with excess inflowdischarging over the flashboards. The gate at the outletworks is normally closed.

4.2 Maintenance of Dam. The Indian Mountain LakesMaintenance Supervisor is responsible for the maintenanceof the dam. Major repairs require approval by the Boardof the Civic Association. The dam is visited daily exceptin winter, when it is visited at least every two weeks.Brush is reportedly cut every three weeks. Formalinspections of the dam are not made.

4.3 Maintenance of Operating Facilities. There are nofunctional operating facilities at the outlet works.There are no formal maintenance procedures for theflashboards.

4.4 Warning Systems in Effect. The Owner's MaintenanceSupervisor stated that there was no emergency operationand warning plan. He stated that the dam is monitoredfrequently during periods of heavy rain.

4.5 Evaluation of Operational Adequacy. Judging by thedeficiencies observed during the visual inspection, themaintenance of the dam is inadequate. Inspections arenecessary to detect hazardous conditions at the dam.Functional operating facilities at the outlet works arenecessary so that the pool level can be drawn down forrepairs or during emergency conditions. Although thepresent condition of the flashboards is good, minorchanges could prevent them from functioning properly.Proper maintenance of the flashboards is necessary toensure that they function properly in event of a flood.The Owner should be aware that the correct functioning(failure) of the flashboards can result in significant andrapid rises in downstream depths of flow. An emergencyoperation and warning system is necessary to reduce therisk of dam failure should adverse conditions develop andto prevent loss of life downstream should the dam fail.

L.

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SECTION 5

HYDROLOGY AND HYDRAULICS

5.1 Evaluation of Features.

a. Design Data. The hydrologic and hydraulicdesign data available for review consist of thePennsylvania Water Power and Resources Board analysis ofthe original spillway capacity. The capacity wasdetermined to be 3,340 cfs, which was greater than theCurve "C" discharge of 3,110 cfs that was required by theCommonwealth. The original design for the exit channelhydraulics is available and is included in Appendix A.

The dam was modified in 1962. The flashboardstructural design computations are available and areincluded in Appendix A. No other hydraulic design dataare available for this modification.

The drainage area of 2.84 square miles used inthis report is based on recent USGS mapping; it isslightly greater than the drainage area of 2.66 squaremiles used for the original design.

b. Experience Data. The maintenance supervisorstated that in his recofTlection the largest flood occurredin 1976, when water in the spillway apron area was about1 .5 feet deep. It is beyond the scope of this report toestimate the discharge coincident with this depth.

C. Visual Observations.

(1) General. The visual inspection of IndianMountain Lake Dam, which is described in Section 3,resulted in a number of observations relevant to hydrologyand hydraulics. These observations are evaluated hereinfor the various features.

(2) Embankment. The low areas on the top ofthe dam reduce the spillway capacity.

(3) Appurtenant Structures. No hydraulicdeficiencies were observed at the spillway. The design ofthe flashboards (Appendix A) was checked and found to besatisfactory (Appendix D). The effects of the flashboardson the spillway discharge are included in the analysisdescribed hereafter. The location of the outlet worksgate provides upstream cutoff for the conduit. Because

V. ..

there is no gate operating mechanism, the gate ispresently inoperable, which is considered a seriousdeficiency because there is no means of drawing down thereservoir in case of an emergency. The design engineerstated verbally that it was his understanding that thegate operating mechanism had been damaged by ice and thatthe Owner was planning to repair it. He stated that hewas not involved with the repairs. The maintenancesupervisor did not mention any proposed repairs. He didnot recollect ever having seen the gate operatingmechanism.

(3) Reservoir Area. No conditions wereobserved in the watershed that might present a significanthazard to the dam.

(4) Downstream Conditions. No conditions wereobserved downstream from the dam that might present asignificant hazard to the dam. Although the designcapacity of the exit channel is less than the spillwaycapacity, the channel is sufficiently far from the damthat its overtopping would not be a hazard to theembankment. There are at least 11 dwellings that could beflooded by a failure of the damn. The thick growth on theoverbanks of Mud Run would retard flow, therefore creatinga higher depth of water than would normally be expected tooccur. Because of the possibility of flooding dwellings,a high hazard classification is warranted for IndianMountain Lake Damn.

d. Overtopping Potential.

(1) Spillway Design Flood. According to thecriteria etbihdbteOfice of the Chief ofEngineers (OCE) for the size (Small) and hazard potential(High) of Indian Mountain Lake Darn, the Spillway DesignFlood (SDF) is between one-half of the Probable MaximumFlood (PMF) and the PMF. Because of the downstreamconditions, the PMF is selected as the SDF for IndianMountain Lake Dam. The watershed was modeled with theHEC-1DB computer program. A description of the model isincluded in Appendix D. The assessment of the dam isbased on existing conditions and the effects of futuredevelopment are not considered.

(2) Summary of Results. Pertinent results areI. tabulated at th'e end of Appendix D. The analysis revealsthat Indian Mountain Lake Dam can pass the PMF with 0.6foot of f1reeboard. If the low areas at the top of the damwere filled in, the freeboard would increase to 1.2 feet.

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(3) Splla Adequacy. The criteria used torate the sil a aequacy of a dam are described inAppendix D. Because the dam can pass the PMF, thespillway capacity is rated as adequate.

21'

SECTION 6

STRUCTURAL STABILITY

6.1 Evaluation of Structural Stability.

a. Visual Observations.

(1) General. The visual inspection of IndianMountain Lake Dam, wFi-ch is described in Section 3,resulted in a number of observations relevant tostructural stability. These observations are evaluatedherein for the various features.

(2) Embankment. Brush and trees growing on theembankment are undesirable because their roots can damagethe embankment. The design drawings shown on Plates E-2and E-3 indicate that the embankment, except for the claycore, was to be constructed of "hardpan." The materialappeared to be a silty sand. These design drawings alsoindicate that riprap was to be extended on the raisedportion of the upstream slope. No evidence of the riprap -was observed. The soil used to construct the embankmentis apparently readily erodable. The combination of foottraffic and wave action has probably caused the erosion.The steeper-than-design upstream slope has probablycontributed to the erosion. This slope is probablysteeper than design because of the overbuild provided, asis evident from the existing profile of the top(Appendix B). During high pool conditions, the erosioncould increase rapidly and threaten the integrity of theembankment. The shallow slough on the downstream slopemay have been caused by the combination of poor compactionand the passage of mowing equipment on the slope. It is

46 not a significant hazard if no further movement occurs.

(3) Appurtenant Structures. The spillwaystructures are founded on overburden. As noted inParagraph 2.2b, drain material was placed beneath thespillway apron to relieve flow from springs. Details onPlate E-4 indicate that there are no cutoff facilities,such as a key, beneath the weir. Considering that the net

* head differential between the reservoir and the apron isabout 5 feet, the amount of localized seepage isI. excessive. The exit seepage gradient may be nearcritical. The excessive seepage could be caused by apervious stratum near the drain hole, by flow fromsprings, or by a subsurface channel that is eroded beneath

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the apron. The crack in the apron that was observed nearthe seepage could have been caused by settlement oruplift. If it was caused by settlement, it would not beof concern. However, if it was caused by uplift, therewould be concern for the integrity of the apron.

The shrinkage cracks in the spillway wallsprobably result from the lack of expansion or contractionjoints. They do not present a hazard to the damn atpresent, but they have the potential to start spalling.This would be a problem if neglected for a long period.The peeling of concrete at the tops of the walls is minorand not of immediate concern.

The depressions behind the spillway walls are ofconcern. Details are not available for the filter behindthe walls. It is believed that either the filter haswashed through the drain holes or fines in the soil havewashed through the filter. Flows from the plastic drainpipes have probably worsened the situation. Generally,drain holes are not placed in spillway walls upstream ofthe weirs. This negates the effect of the wall in actingas an impervious barrier and provides a short seepage pathbetween the reservoir and the area downstream from thespillway. The condition is potentially serious duringperiods of high flow. This condition may have exacerbatedthe erosion observed at the junction of the embankment andthe right spillway wall; some of the embankment may havewashed through the drain hole.

Conditions at the outlet works are of concern.The lack of a gate operating mechanism is evaluated inSection 5. The outlet structure has failed structurally.The sidewalls (Photograph J) dc not appear to have beenconstructed in accordance with the design drawings shownon Plate E-3. The increased load on the headwall, whichwas caused by the 1962 modification to the dami, is theprobable cause of cracking. The entire headwall andsidewalls are unable to support the loads placed againstthem.

b. Design and Construction Data. The designengineer reported that the only s tability analysisperformed during design was of an elementary andapproximate nature. The tops of the flashboards on thespillway weir are only 4.7 feet above the spillway apron.A review of the spillway section shown on Plate E-3indicates that the structures should be stable for theanticipated loads.

-15-

7-- - .-

C. Operating Records. There are no formal recordsof operation. There are no inspection records to aid inthe analysis of the observed deficiencies.

d. Postconstruction Changes. The 1962 and 1964modifications to the darm are assessed in Paragraph 6.1a.

e. Seismic Stability. Indian Mountain Lake Dam islocated in Seismic Zone 1. Earthquake loadings are notconsidered to be significant for small dams located inZone 1 when there are no readily apparent stabilityproblems at the dam. Since there were no readily apparentstability problems at the damn, its ability to resistearthquake loadings is assumed to be adequate.

-16-

SECTION 7

ASSESSMENT, RECOMMENDATIONS, AND

PROPOSED REMEDIAL ME~ASURES

7.1 Dam Assessment.

a. Saey

(1) Based on visual inspection, availablerecords, calculations, and past operational performance,Indian Mountain Lake Dam is judged to be in faircondition. The existing spillway will pass the PDIF with0.6 foot of freeboard. If the low areas at the top of thedan were filled, the freeboard would increase to 1 .2 feet.This analysis is predicated upon the proper functioning(failure) of the flashboards on the spillway crest. Thespillway capacity is rated as adequate.

(2) "leeded repairs have not b4:eri -,ade to somnefeatures of the darn.

(3) There is no functional outlet works for the

(4) A summary of the features and observeddeficiencies is listed below.

Feature and Location Observed Deficiencies

Embankment: Brush and trees;lack of slopeprotection onupstream slope;severe erosion onupstream slope; lowareas on top; sloughon downstream slope.

Spillway: Depressions behindwalls; shrinkagecracks and peelingalong walls;excessive flowthrough drain hole inapron; crack inapron.

-17-

Feature and Location Observed Deficiencies

Outlet Works: No operatingmechanism; headwalland sidewalls failedstructurally.

b. Adequacy of Information. The informationavailable is such that a preliminary assessment of thecondition of the dam can be inferred from the combinationof visual inspection, past performance, and computationsperformed as part of this study.

c. Urgency. The recommendations in Paragraph 7.2should he implemented immediately.

d. Necessity for Further Investigations. In orderto accomplish some of the remedial measures outlined inParagraph 7.2, further investigations by the Owner will berequired.

7.2 Recommendations and Remedial Measures.

a. The following measures are recommended to beundertakei by the Owner, in approximate order of priority,imediately:

(1) Install a gate operating mechanism for theoutlet works gate and construct a properly designed outletstructure at the outlet works.

(2) Repair the eroded areas on the upstreamslope and provide properly designed slope protection forthe upstream slope.

(3) Perform an investigation and study todeternine neasaires required to prevent further depressionsfrom occurring behind the spillway walls, while at thesame time ensuring the integrity of the spillway walls andembankment. Fill in the existing depressions and takeother appropriate action as required.

(4) Perform an investigation and study todetermine if any foundation damage has occurred as aresult of the excessive seepage at the spillway. Thestudy should also determine the cause of the seepageand address measures required to reduce the seepage to anacceptable amount. Take appropriate action as required.

1- (5) Repair the slough on the downstream slopeof the embankment. After repairs are made, monitor thearea. Should any change in the area occar, takeappropriate action as required.

-18-

(6) Remove trees and brush on or near theemibankmnent.

(7) Fill in the low areas at the top of theembankment.

(8) Until investigations, studies, and remedialwork are completed, the Owner should monitor the conditionof the dam and appurtenant structures. Take appropriateaction as required should any changes in conditionsoccur.

All investigations, studies, designs, andsupervision of repairs and construction should beperformed by a professional engineer experienced in thedesign and construction of dams. Monitoring programsshould also be performed or supervised by a professionalengineer.

b. In addition, it is recommended that the Ownermodify his operational procedures as follows:

(1) Develop a detailed emergency operation andwarning system for Indian Mountain lake Dam. This systemshould address the effects of a rise in the downstreamdepth of flow due to the proper functioning (failure) ofthe flashboards.

(2) Provide round-the-clock surveillance ofIndian Mountain lake Dam during periods of unusually heavyrains.

(3) When warnings of a storm of majorproportions are given by the National Weather Service, theOwner should activate his emergency operation and warningsystem procedures.

(4) Institute an inspection program such thatthe dam is inspected frequently. As presently required bythe Commonwealth, the program should include a formalannual inspection by a professional engineer experiencedin the design and construction of dams. Utilize theresults to determine if remedial measures are necessary.

(5) Institute a maintenance program to properlymaintain all features of the dam.

-19-

4 .

APPENDIX A

CHECKLIST ENGINEERING DATA

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APPENDIX E

CHECKLIST VISUAL INSPECTION

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EXCESSIVE FLOW FROM DRAIN HOLE,CRACK IN SLAB NEAR HOLE

DEPRESSIONS BEHINDFLOW-%, WALL NEAR DRAIN

HOLES.FLASHBOARDSALONG CREST\

~SHRINKAGESEVERE EROSION-- CRACKS

RESERVOIR- -MINOR PEELING ALONG TOP

10'MINOR SLOUGH

----IV ON 3H

HEADWALL CRACKED STRUCTURALLY,RIGHT WALL TILTED, LEFT WALL~MISSING

IV ON 1.8H - - ---,-

NO EVIDENCE OF ,,, MUD R UIN

GATE OPERATOR - " OUTLET WORKS

BRUSH -----SMALL TREES

PHASE I INSPECTION REPORTNATIONAL DAM INSPECTION PROGRAMSN TINDIAN MOUNTAIN LAKE DAM

INDIAN MOUNTAIN LAKES CIVIC ASSOC

RESULTS OFVISUAL INSPECTION

JANUARY 1980 EXHIBIT B-I

APPENDIX C

PHOTOGRAPHS


A. Downstream Slope

A

B. Top of' Damrn Reservoir at Right

C-1


C. Upstream Slope

D. Right Abutment

1. C -2

p I.. .'_


E. Upstream Slope Near Spillway

101

'. F. Spillway

C-3


G. Spillway Outlet Channel

Ii6H. Typical Depr'ession behind Spillway Wall

c-~4


I. Downstream Channel

J. Outlet Works Headwall

C-5

-LOCATION AND ORIENTATION OF CAMERA

H A PHOTOGRAPH IDENTIFICATION LETTER

FLASHBOARDSALONG CREST

RESERVOIR

PHAS ON 3NPCHORPR

I. NATIONAL DAM INSPECTION PROGRAMNOT TOSCALEINDIAN MOUNTAIN LAKE DAM

IINDIAN MOUNTAIN LAKES CIVIC ASSOCGUIDE TO LOCATION

OF PHOTOGRAPHS1 ______________________________________ JANUARY 1980 EXHIBIT C-I

APPENDIX D


A.

APPENDIXD


Spillway Capacity Rating:

In the recommended Guidelines for Safety Inspectionof Dams, the Department of the Army, Office of the Chiefof Engineers (OCE), established criteria for rating thecapacity of spillways. The recommended Spillway DesignFlood (SDF) for the size (small, intermediate, or large)and hazard potential (low, significant, or high) class-ification of a dam is selected in accordance with thecriteria. The SDF for those dams in the high hazardcategory varies between one-half of the Probable MaximumFlood (PMF) and the PMF. If the dam and spillway arenot capable of passing the SDF without overtoppingfailure, the spillway capacity is rated as inadequate.If the dam and spillway are capable of passing one-halfof the PMF without overtopping failure, or if the dam isnot in the high hazard category, the spillway capacityis not rated as seriously inadequate. A spillwaycapacity is rated as seriously inadequate if all of thefollowing conditions exist:

(a) There is a high hazard to loss of life fromlarge flows downstream of the dam.

(b) Dam failure resulting from overtopping wouldsignificantly increase the hazard to loss of life down-stream from the dam from that which would exist justbefore overtopping failure.

(c) The dam and spillway are not capable ofpassing one-half of the PMF without overtoppingfailure.

Description of Model:

If the Owner has not developed a PMF for the dam,the watershed is modeled with the HEC-1DB computerprogram, which was developed by the U.S. Army Corps ofEngineers. The HEC-1DB computer program calculates aPMF runoff hydrograph (and percentages thereof) androutes the flows through both reservoirs and streamsections. In addition, it has the capability tosimulate an overtopping dam failure. By modifying therainfall criteria, it is also possible to model the 100-year flood with the program.

APPENDIX ID

_________________ River BasinName of Stream: Mun RutjName of Dam: _ tniAg Mjotj1Axr,1 LAKENDI ID No.: 'PA- 00 793DER ID No.: Air_-_A_27

Latitude: N 41i oo' 1,5 Longitude: W 7VI 30' Z"Top of Dam Elevation: 17g4.7Streambed Elevation: I-17.1 Height of Dam: 13 ftReservoir Storage at Top of Dam Elevation: 40 acre-ftSize Category: MSM ....Hazard Category: _ __ _ _ (see Section 5)Spillway Design Flood: VARiE &FMPF ro aTF t,

-Qfi PMr- B;9LAAL

UPSTREAM DAMS

Distance Storagefrom at top ofDam Height Dam Elevation

Name (miles) (ft) (acre-ft) Remarks

DOWNSTREAM DAMS

f C " . ',- - * , -,D --,__ _ _ _/V 7 / / " / / '1 t / S , ' . " r v_ __.'_ _-

f

'V D-2

I 1 -

D£LAW e River BasinName of Stream: M iu0 ' k Q &Name of Dam: EDPA4 M # a

DETERMINATION OF PMF RAINFALL & UNIT HYDROGRAPHUNIT HYDROGRXPfl DATA

DrainageSub- Area Cp Ct L L a L' Tp Map Platearea (square miles miles miles hours Area

miles) (1) (2 (3) (4) (5) (6) (7) (8)

A :2.g 9 4 .. _5 -2L.l 9.03 .17 HTA 2 .oo 2 A-

Total (,Sq See Sketch on Sheet D-4(1) & (2): Snyder Unit Hydrograph cOefficients supplied by

Baltimore District, Corps of Engineers on maps andplates referenced in (7) & (8)

The following are measured from the outlet of the subarea:(3): Length of main watercourse extended to divide(4): Length of main watercourse to the centroidThe following is measured from the upstream end of thereservoir at normal pool:(5): Length of main watercourse extended to divide(6): Tp=Ct x (L x Lca) 0.3, except where the centroid ofthe subarea is located in the reservoir. ThenTp=Ct x (L') 0.6

Initial flow is assumed at 1.5 cfs/sq. mileComputer Data: QRCSN = -0.05 (5% of peak flow)

RTIOR = 2.0RAINFALL DATA

PMF Rainfall Index: .O in., 24 hr., 200 sq. mile.Hydromet. 40 Hydromet. 33

(Susquehanna Basin) (Other Basins)Zone: N/AGeographic Adjustment

Factor: 01A_____ 1.0Revised Index

Rainfall: ; 0RAINFALL DISTRIBUflON (percent)

Time Percent6 hoursI

12 hours24 hours48 hours72 h-urs

96 hours N/a

,D-3

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Name of Dam: V A,1 v0 TAM DT L-A 4e

STORAGE DATA:

Storage

Area millionElevation (acres) gals acre-ft Remarks

/781( =ELEVO* 0 0 017 9.0 :ELEV1 =A1 ,_ _2o_ :S1 i',6. a

______ _ 171 _ _"73;1719.7 _/90 _0 Ttp > Am/,Boo~ .. ac,,___ ____ ______

* ELEVO ELEV1 - (3SI/A I ) *P,,I IV** Planimetered contour at least 10 feet above top of dam

Reservoir Area at Normal Pool is- percent of subarea

watershed.

BREACH DATA: N OT U ED

See Appendix B for sections and existing profile of the dam.

Soil Type from Visual Inspection:

Maximum Permissible Velocity (Plate 28, EM 1110-2-1601) fps(from 0 = CLH 3 /2 = V.A and depth = (2/3) x H) & A = L-depth

HMAX = (1/9 V2/C2 ) _ _ ft., C = _ Top of Dam El.=

HMAX + Top of Dam El. = _ FAILEL(Above is elevation at which failure would start)

Dam Breach Data:

BRWID = ft (width of bottom of breach)* Z = (side slopes of breach)

ELBM = (bottom of breach elevation, minimum of• zero storage elevation)

WSEL = (normal pool elevation)T FAIL= mins _ _ hrs (time for breach to

develop)

I

Data for Dam at Outlet of Subarea - (see Sketch on Sheet D-4)

Name of Dam: Tv-IDxA(J M o Q r A- LAIF

SPILLWAY DATA: Existing DesignConditions Conditions

Top of Dam Elevation i-7qq. . 179.7Spillway Crest ElevationSpillway Head Available (ft)Type Spillway S99 FOLLo . G sH.s--'S"C" Value - SpillwayCrest Length - Spillway (ft)Spillway Peak Discharge (cfs)Auxiliary Spillway Crest Elev. _ _ _ r,4_C______j_-Auxiliary Spill. Head Avail. (ft) ".1,6 _ JI,Type Auxiliary Spillway N!IA NJ"C" Value - Auxiliary Spill. (ft) _ 4__ AI'llCrest Length - Auxil. Spill. (ft) .IA _ j_

Auxiliary SpillwayPeak Discharge (cfs) W_/__fA

Combined Spillway Discharge (cfs)

Spillway Rating Curve: 5 6 6 F 4 o4,- 0 P .HFELT,

Elevation Q Spillway (cfs) Q 'AwWiliy G' " bined) !(ea)/79f.7 0

/7qf.7 / 19? Y_0,17q'?, ___ __ ___ __ __ _ -___ __ ___ __ __

/79q. 7 57332

.___ _ /5' 370 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

OUTLET WORKS RATING: Outlet 1 Outlet 2 Outlet 3

Invert of Outlet )V 7.4 Invert of Inlet 1 _ SIR

Type EI ?', _"Diameter (ft) =D -___Length (ft) =LArea (sq. ft) =A ._ _N __ __ __ ___-_K Entrance -__._"K Exit I.__ _ __K Friction29.1N2 L/R 4 / 3 .73Sum of K . _ al

• (1/K) 0.5 = C 0.70Maximum Head (ft) HM _ __ __Q=CA v'2g(HM)(cfs) /_.0Q Combined (cfs) _ ___

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\ APPROXIMATE MINIMUM LIMITS OFDOWNSTREAM FLOODING SHOULDIDAM FAILURE OCCUR.I ! ,I ,

/NOTE:I / LIMITS OF DOWNSTREAM FLOODING ARE

,' / ESTIMATES BASED ON VISUAL OBSERVATIONS.THIS MAP SHOULD NOT BE USED INCONNECTION WITH EMERGENCY OPERATION

/1 AND WARNING PLAN.

////

/ I

I I/ I

*, PHASE I INSPECTION REPORT


INDIAN MOUNTAIN LAKE DAMINDIAN MOUNTAIN LAKES CIVIC AS

DOWNSTREAM2000 0 2000 DEVELOPMENT MAP

. SCALE: I IN.,2000 FT. JANUARY Iso EXHIBIT D-i'i ..f .• . .

¥/l ;\

APPENDIX E

PLATES

,

INDIAN MOUNTAIN

-INDIAN MOUNTAINLAKES DEVELOPMENT

PA. ROUTE 534

PHASE I INSPECTION REPORTNATIONAL DAM INSPECTION PROGRAM

INDIAN MOUNTAIN LAKE DAMINDIAN MOUNTAIN LAKES CIVIC ASSO

LOCATION MAP

4SCALE: I IN. r2000. FT. JANUARY 1980 PLATE E-1

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...r.,' DAM PRIOR MODIFICATION

----

JANU)ARY 1980 PLATE E-2

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NATONA DA INSP CTIO PHASEA

'I NATI~OU NCTIN LAKEGDAM

INDIA LAK S civic ASS

192MODIFICATION

-ANAR 180PLATE -

4~~~-s: ~OC'y ZAC4W4 4TIOAf8 C, 4'.4. srj*'

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~ ~ 0 ,0" INDIAN MOUNTAIN LAKE DAMA,., e -~core. t. epINDIAN MOUNTAIN LAKES CIVIC ASS

1964 MODIFICATION DETAILS

JANUARY 1980 PLATE E-4

APPENDIX F

GEOLOGY

I.


APPENDIX F

GEOLOGY

The Indian Mountain Lake Dam is located in MonroeCounty. The western half of the County lies within thePocono Plateaus section of the Appalachian PlateausProvince and is separated from the Glaciated Low Plateausection of the same province by the Pocono PlateauEscarpment. The most pronounced topographic feature inthe area is Camelback Mountain, which is a part of thePocono Escarpment. The greatest relief along theescarpment is 1 ,000 feet, which occurs at Ca:nelbackMountain. The escarpment has a aell-defined southwestwardtrend frori Camelback "Iountain blt is more irregularbetween Camelback and Mount Pocono, which lies to thenorth. Streams east of the escarpment drain directly intothe Delaware River, while those to the west drain to theLehigh River.

Inlian Mountain Lake Dam is located in the PoconoPlateau Section of the province. The Pocono Plateau isrelatively flat, with local relief seldom exceeding 100feet. The topography is characteristic of areas that wereglaciated during the Pleistocene Epoch; these charac-teristics include moraines, drml:nlins, eskers, kameterraces, glacial lakes and poor drainage, resulting innany swamps and peat bogs. The most striking glacialfeature is the mile-wide, end moraine that crosses thePlateau north of Interstate 80.

Indian Mountain Lake Dam is underlain by the PoplarGap Member of the Catskill Fonitiori. The Poplar GapMember is predo.inantly a gray sandstone and congloimeraticsandstone with interbedded silstones and shales. Sand-stones present are thick-bedded, fine-to coarse--grained,and exhibit very low, primary porosity due to a clay andsilica natrix. Effective porosity results fro, fracturesand parting planes. Conglomeratic sandstone occursprimarily as concentrates of sub-round to round quartzpebbles. The siltstones and shales at the site are thinbedded and also have low porosity.

The rocks are well-indurated and generally are notSusceptible to slope failure; however, the presence ofwell-developed bedding and joint planes will result insome rockfall from vertical and high-angle cut faces.

F-I

The bedrock is entirely overlain by glacial till ofLate Wisconsin Age. This till is basically an unsortedmixture of clay, silt, sand, and gravel. It is moderatelycohesive and is generally derived locally from thesandstones of the Catskill Formation. Thickness of thetill varies from 5 to 75 feet. The records of foundationexploration on Plate E-2 in Appendix E indicate the dam isfounded on this till.

F-

POPLARGA

CATSILLFORMATION

INDIAN MOUNTAIN LK A

20002000 INDIAN MOUNTAIN LAKES CIVIC ASSO

SCALE: I IN. -2000 FT. GEOLOGIC MAP

JANUARY 1980 EXHIBIT F-I

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HARRISBURG PA F/S FLEM CORORY AND CARPENTER LAKE DAM … · 2014. 9. 27. · ADAO B 588 GANNETT FLEM -INS CORORY AND CARPENTER ,INC HARRISBURG PA F/S 13/13 NATIONAL DAM INSPECTION