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RD-R144 158 NATIONAL PROGRAMI FOR INSPECTION OF NON-FEDERAL-vn /LAKE-DAWISON DAM (CT @..(U) CORPS OF ENGINEERS WALTHAMMA NEW ENGLAND DIV AUG 79

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SECURITY CLASSIFICATION OF T041S PAGE em...n Date Entered)

REPORT CUETTOPAEREAD INSTRUCTIONSDOCUENTAION AGEBEFORE COMPLETING FORM

1. REPORT 44116111111 2. GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG .auaMIER

CT 0031914. TITLE (and Sub*5ilej S. TYPE OF REPORT a PERIOD COVERED

Lake Dawson Dam INSPECTION REPORT

NATIONAL PROGRAM FOR INSPECTION OF NON-FEDERAL S. PERFORMING ONG. REPORT NUMIDER

Das _ _ _ _

7. AuTmN(s) S. CONTRACT ORt GRANT NUMNER(e)

U.S. ARMY CORPS OF ENGINEERSNEW ENGLAND DIVISION

S. PERFORMING ORGANIZATION NAMIE AND ADDRESS 10. PROGRAM [LaMENT. PROJECT, TASK

ARIA & WORK UNIT NUNSE9RS

11. CONTROLLING OFFICE NAME ANO ADDRESS IL. RSPORT OATS

DEPT. OF THE ARMY, CORPS OF ENGINEERS August 1979NEW ENGLAND DIVISION, NEDED 12. NUMBER OF PAGES424 TRAPELO ROAD, WALTHAM, MA. 02254 90

14. MONITORING AGENCY NAME I AOORESS(01 different Ono CORAWIMu *glide) IS. SECURITY CL.ASS. (09 1116 ipo)

UNCLASSIFIEDI~.DC SSI PIC ATION/ DOWN GRADING

IS. DISTRISUTION STATEME.NT (*f usi Aware)

APPROVAL FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED

17. DISTRIBUTION STATEMENTo (ad the abeiv..t enteredon, pJio10. son"n hras m epee

It. SUPPLEMENTARY NOTES

Cover program reads: Phase I Inspection Report, National Dam Inspection Program;however, the official title of the program is: National Program for Inspection ofNon-Federal Dams; use cover date for date of report.

III. KEY WORDS (ftslun an, r,"O ego"d of .OSMY m8d Id6a"if'y s wee A)

DAMS, INSPECTION, DAM SAFETY,

Connecticut Coastal BasinWoodbridge, Connecticut

20. ABSTRACT (Caftiftnt On reverse old* it 00066004Y 401d 1d,16811010 63P 6dea mmml.,The earth embankment dam is approximately 9604- feet long and rises approximately48 feet above the downstream bed of the West River. Based upon the visual inspectiorat the site and past performance, the dam appears to be in good condition. Basedupon the size (Intermediate) and hazard classification (High) of the dam in accord-ance with Corps of Engineers Guidelines, the test flood will be equivalent to theProbable Haximu Flood (PMF).

DD I jO '7I 14 73 LOITION OF I "OV ISIS OBSOLETE

* DEPARTMENT OF THE ARMYNEW ENGLAND DIVISION. CORPS OF ENGINEERS0 424 TRAPELO ROAD

REPLY TOWALTHAM, MASSACHUSETTS 02154

'EEDATTENTION~ OF: NOV 28 1979

Honorable Ella T. GrassoGovernor of the State of Connecticutstate CapitolHartford, Connecticut 06115 -

* Dear Governor Grasso:

fl Inclosed is a copy of the Lake Dawson Dam Phase I Inspection Report,which was prepared under the National Program for Inspection ofNon-Federal Dams. This report is presented for your use and is basedupon a visual inspection, a review of the past performance and a briefhydrological study of the dam. A brief assessment is included at the

* beginning of the report. I have approved the report and support thefindings and recommendations described in Section 7 and ask that you -

keep me informed of the actions taken to implement them. This follow-upaction is a vitally important part of this program.

A copy of this report has been forwarded to the Department of Environ-mental Protection, the cooperating agency for the State of Connecticut.In addition, a copy of the report has also been furnished the owner,New Haven Water Company, New Haven, Connecticut 06511.

* Copifs of this report will be made available to the public, uponrequest, by this office under the Freedom of Information Act. In thecase of this report the release date will be thirty days from the dateof this letter.

*I wish to take this opportunity to thank you and the Department ofEnvironmental Protection for your cooperation in carrying out thisprogram.

Sincerely,

Inc MAX B. SCHEIDER*As stated Colonel, Corps of Engineers

Division Engineer

0 j. . * *

Accession For • • .

TIS GRA&IDTIC TABUnannouned 0IJustit iat-on. . CONNECTICUT COASTAL BASIN

~ WOODBRIDGE, CONNECTICUT'Ditribution/ LAKE DAWSON DAMAvailability Code -

Avail and/oris special CT 00319. -iN Specilal

* 0

PHASE 1 INSPECTION REPORT

NATIONAL DAM INSPECTION PROGRAM

DEPARTMENT OF THE ARMYNEW ENGLAND DIVISION, CORPS OF ENGINEERS

WALTHAM, MASS. 02154 'DTICSEI-ECTEI I • .o.

AU6 1 3 1984AUGUST, 1979 AQ'D__IS _IBTION STATEMENT_ _ A

Approved for public releaselDiatribution Unlimited

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BRIEF ASSESSMENT

PHASE I INSPECTION REPORT

NATIONAL PROGRAM OF INSPECTION OF DAMS

Name of Dam LAKE DAWSON DAMInventory Number: CT-00319State Located: CONNECTICUTCounty Located: NEW HAVEN

UTown Located: WOODBRIDGEStream: WEST RIVEROwner: NEW HAVEN WATER COMPANYDate of Inspection: MAY 1, 1979Inspection Team: PETER M. HEYNEN, P.E.

CALVIN GOLDSMITHMIRON PETROVSKYGEORGE STEPHENS

M The earth embankment dam is approximately 960t feet longand rises approximately 48 feet above the downstream bed ofthe West River. A concrete corewall apparently runs the

* length of the dam. The concrete spillway at the left end ofthe dam is a 110 foot long broad crested weir with a vertical-sided concrete channel leading to a steep-sided channel cutinto natural ground. An upstream gatehouse near the right end

* of the dam houses the regulating outlets which consist of 2-36inch cast iron low level outlets, a 36 inch supply main to thetreatment plant immediately downstream of the dam, and an 8inch well drain.

Based upon the visual inspection at the site and pastperformance, the dam appears to be in good condition. No0evidence of instability was observed in the embankment,spillway, spillway channel, or other appurtenances.

Based upon the size (Intermediate) and hazard classifica-tion (High) of the dam in accordance with Corps of EngineersGuidelines, the test flood will be equivalent to the ProbableMaximum Flood (PMF). Peak inflow to the reservoir is 20,100cfs; peak outflow is 19,000 cfs with the dam overtopped 1.7feet. Based upon our hydraulic computations, the spillwaycapacity is 9900 cfs, which is equivalent to 52 percent of therouted test flood outflow.

r0

It is recommended that the owner initiate further studiesto perform a more refined hydraulic/hydrologic study by aqualified engineer to determine more accurately the spillwaycapacity and overtopping potential. Recommendations should be 0 Omade by the engineer and implemented by the owner to increasethe project discharge capacity if called for by the refinedhydraulic/hydrologic study.

It is further recommended that the owner initiate an in-K vestigation by a registered engineer qualified in dam design, S S

hydraulics, and inspection to 1) evaluate and make recommend-ations to monitor, control, and/or eliminate the seepage em-anating from the downstream area of the dam, 2) assess theamount and seriousness of uplift pressure exerted on the con-crete spillway channel slab, and 3) develop a program ofrepairs for leaking expansion joints and cracks in the con-crete spillway and spillway slab.

The above recommendations, and any needed remedialmeasures are further discussed in Section 7, and should be

u instituted by the owners within two years of their receipt ofthis report. •

Peter M. Heynen PE..Project Manager 0. 'Cahn Engineers, Inc. I " "

Senior Vice PresidentCahn Engineers, Inc...

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This Phase I Inspection Report on Lake Dawson Dam

has been reviewed by the undersigned Review Board members. In ouropinion, the reported findings, conclusions, and recommendations are S •

consistent with the Recommended Guidelines for Safety inspection of

Dams, and with good engineering judgment and practice, and is hereby

submitted for approval.

H. ~PW. NEGiAAI4JR.,EM tW(W'er Con ol Branch

nIKeer ing Division

JOSEPH A. MCI.LROY, MLMBER - -

1 1Foutdation & Materials BranchEngineering Division

CARNEY tU TERZIAN, CHAIRMANChief, Structural SectionDesign BranchEngineering Division.

APPROVAL RECOMMENDED:

JOE B. FRYARChief, Engineering Division

.. . .. . . .. _ 66 0 . . . . . . 5_ _ . . . .. . ..,- il i iI

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PREFACE

This report is prepared under guidance contained in theRecommended Guidelines for Safety Inspection of Dams, forIiPhase I Investigations. Copies of these guidelines may beobtained f rom the Of fice of Chief of Engineers, Washington,D.C. 20314. The purpose of a Phase I Investigation is toidentify expeditiously those dams which may pose hazards tohuman life or property. The assessment of the generalcondition of the dam is based upon available data and visualI Linspection. Detailed investigation, and analyses involvingtopographic mapping, subsurface investigations, testing, anddetailed computational evaluations are beyond the scope of aPhase I Investigation; however, the investigation is intendedto identify any need for such studies.

in reviewing this report, it should be realized that thereported condition of the dam is based on observations offield conditions at the time of inspection along with dataavailable to the inspection team. in cases where thereservoir was lowered or drained prior to inspection, suchaction, while improving the stability and safety of the dam,

V removes the normal load on the structure and may obscurecertain conditions which might otherwise be detectable ifinspected under the normal operating environment of thestructure.

It is i. -tant to note that the condition of a damdepends on n, .rous and constantly changing internal andexternal conditions, and is evolutionary in nature. it wouldbe incorrect to assume that the present condition of the damwould necessarily represent the condition of the dam at somepoint in the future. Only through continued care andinspection can there be any chance that unsafe conditions will

1i be detected.

Phase I inspections are not intended to provide detailedhydrologic and hydraulic analyses. In accordance with theestablished Guidelines, the Spillway Test Flood is based onthe estimated "Probable Maximum Flood" for the region

P (greatest reasonably possible storm runoff), or fractions Sthereof. Because of the magnitude and rarity of such a stormevent, a finding that a spillway will not pass the test floodshould not be interpreted as neccessarily posing a highlyinadequate condition. The test flood provides a measure ofrelative spillway capacity and serves as an aid in determiningthe need for more detailed hydrologic and hydraulic studies,considering the size of the dam, its general condition and thedownstream damage potential.

.8 ivS

OLS S ~ S5 5 5

TABLE OF CONTENTS 0

Page

U m Letter of TransmittalBrief Assessment 1,ii

Review Board Signature Page iiiPreface ivTable of Contents v,vi,viiOverview Photo viiiSite Location Plan ix

SECTION 1: PROJECT INFORMATION

1.1 General .............................. 1a. Authorityb. Purpose of Inspection Programc. Scope of Inspection Program

1.2 Description of Project .............. 2

a. Locationb. Description of Dam and Appurtenancesc. Size Classificationd. Hazard Classificatione. Ownershipf. Operatorg. Purpose of Damh. Design and Construction Historyi. Normal Operational Procedures

1.3 Pertinent Data ...................... 4a. Drainage Areab. Discharge at Damsitec. Elevationsd. Reservoire. Storagef. Reservoir Surface

L g. Damh. Diversion and Regulatory Tunneli. Spillwayj. Regulating Outlets

v

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~~ SECTION 2: ENGINEERING DATA

2.1 Design ..... ~...............*** 8

a. Available Datab. Design Features

* ~ c. Design Data

2.*2 Construction. .. .. .. .. .. ............. 8

a. Available Datab. Construction Considerations

2.3 Operations ....... ................ 8

2.4 Evaluation . .. ................... 8

a Availabilityb . Adequacy

-c Validity

SECT'ION 3: VISUAL INSPECTION

- 3.*1 F ind i~n .............................. 9

a. GeneralLb . Dam0

c. Appurtenant Structuresd . Reservoir Areae. Downstream Channel

3.2 Evaluation ......o............ ......... 11

SECTION 4: OPERATIONAL PROCEDURES

4.1 Regulating Procedures .................. 12

4.2 Maintenance of Dam............ 12

4.3 Maintenance of Operatn Faiiis. 2

4.4 Description of An" Warning Systemin Effect.......................... 12

(24.5 Evaluation ................... .......... 12 -

SECTION 5: HYDRAULIC/HYDROLOGIC

5.1 Evaluation of Features.......... .. 13

a. General* .bo Design Data

c. Experience Datad. Visual Observationse. Test Flood Analysisf. Dam Failure Analysis

vi

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SECTION 6: STRUCTURAL STABILITY 0

6.1 Evaluation of Structural Stability... 15

a. Visual Observationsb. Design and Construction Datac. Operating Recordsd. Post Construction Changese. Seismic Stability

SECTION 7: ASSESSMENT, RECOMMENDATIONS & REMEDIAL MEASURES

7.1.DamAssessment...................... 17

a. Conditionb. Adequacy of Informationc. Urgency*d. Need for Additional Information

- 7.2 Recommendations ...................... 17

7.3 Remedial Measures .................... 18

a. Operation and Maintenance Procedures

7.4 Alternatives ......................... 19

APPENDICES

U Page No.

Appendix A: Inspection Checklist A-1 to A-6

Appendix B: Engineering Data and Correspondence

Dam Plan, Profile and Sections Sheet B-i1List of Existing Plans B-1Summary of Data and Correspon-dence B-2Data and Correspondence B-4 to B-53

;£ Appendix C: Detail PhotographsLocation Plan of Photographs Sheet C-iPhotographs C-1 to C-5

Appendix D: Hydraulic/Hydrologic Computations

Drainage Area Map Sheet D-1 1 _Computations D-1 to D-16Preliminary Guidance For i - viiiEstimating

Appendix E: Information As Contained In TheNational Inventory of Dams E-1 S

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PHASE r INSPECTION REPORT

LAKE DAWSON DAM

SECTION I - PROJECT INFORMATION

1.1 GENERAL

a. Authority - Public Law 92-367, August 8, 1972,authorized the Secretary of the Army, through the Corps ofEngineers, to initiate a National Program of Dam Inspectionthroughout the United States. The New England Division of theCorps of Engineers has been assigned the responsibility ofsupervising the inspection of dams within the New EnglandRegion. Cahn Engineers, Inc. has been retained by the NewEngland Division to inspect and report on selected dams in theState of Connecticut. Authorization and notice to proceedwere issued to Cahn Engineers, Inc. under a letter of March30, 1979 from John P. Chandler, Colonel, Corps of Engineers.Contract No. DACW 33-79-3-0059 has been assigned by the Corps- -

of Engineers for this work.

b. Purpose of Inspection Program - The purposes of theprogram are to:

1. Perform technical inspection and evaluation of non-federal dams to identify conditions requiring0correction in a timely manner by non-federalinterests.

2. Encourage and prepare the States to quickly initiateeffective dam inspection programs for non-federaldams.

3. To update, verify and complete the National Inventoryof Dams.

c. Scope of Inseection Program - The scope of this PhaseIinspection report includes:

1. Gathering, reviewing and presenting all available dataas can be obtained from the owners, previous owners,the state and other associated parties.

2. A field inspection of the facility detailing thevisual condition of the dam, embankments andappurtenant structures.

'A0

3. Computations concerning the hydraulics and hydrology

of the facility and its relationship to the calculatedflood through the existing spillway. I

4. An assessment of the condition of the facility andcorrective measures required.

It should be noted that this report does not passjudgement on the safety or stability of the dam other than on avisual basis. The inspection is to identify those features of

WI the dam which need corrective action and/or further study. S

1.2 DESCRIPTION OF PROJECT

a. Location - The dam is located on the West River in arural section of the Town of Woodbridge, County of New Haven,

- State of Connecticut. The dam is shown on the New Have8 0U.S.G.S. Quandrangle Mapoas having coordinates latitude N 4020.0' and longitude W 72 58.7'.

b. Description of Dam and Appurtenances - The dam is 960+

feet long and its top width is 18 feet. The top of the dam is48 feet above the bed of the West River. Construction is ofearth fill with a concrete core wall. Both upstream and down-stream faces are at a slope of 2 horizontal to 1 vertical. Theupstream face of the dam is covered with hand placed roundedriprap to within 3 feet of the crest of the dam. There is anupstream gate house near the right end of the dam which con-tains all regulating outlets. At the downstream toe, directly 0opposite the gate house, is the original gate house, no longerused as such, which now houses an emergency power generatingsystem. Also downstream from the toe are 2 buildings housingwater treatment facilities and a fisl filter system. A 6 inchtile drain runs along the toe for 185- feet, to the left of theoutlet works.

The spillway is a broad-crested compound weir which spillsinto a concrete channel, the configuration of which is shownon Sheet B-1. The upstream approach channel is on a shallow

* inclination and is covered with trap-rock riprap. The spill-way discharge channel is a concrete lined sloping channel as S .shown on Sheet B-l, and is keyed into bedrock. There are holesin the crest to install flashboards, but the operatorindicated they had failed during this past winter and therewere no plans to replace them. The outlets, all gated at theupstream gate house, consist of two 36 inch cast iron lowlevel outlets, a 36 inch supply main to the treatment plant __J_facilities fed from a wet well in the gate house, and a 6 inch

2

well drain. The wet well is fed by 4 intake windows, gated at--the upstream face of the gate house. All gates are manuallyoperated and all are in operable condition. Also in the gatehouse is a new electric pump which will be used to pump waterto a treatment plant, now under construction, at the upstreamend of the lake.

c. Size Classification - INTrERMEDIATE - The dam impounds1080 acre-feet of water with the lake level at the top of theearth embankment dam, which at elevation 166.8 is 48 feetabove the old stream bed. According to the RecommendedGuidelines, this dam is classified as intermediate in size.

d. Hazard Classification - HIGH - Immediately downstreamof Lake Dawson Dam is the water filtration plant and onehouse. Approximately one mile downstream from the dam isKonolds Pond, along the shoreline of which are at least 10 lowlying residential structures which would be in the path ofrapidly rising flood waters due to a breach of Lake DawsonDam. The flood waters would overtop Konolds Pond Dam byapproximately 8 feet, subsequently discharging in thedownstream channel which runs through the heavily urbanizedWestville area of New Haven, which has many low lyingresidences.

e. Ownership - New Haven Water Company90 Sargent DriveNew Haven, CT 06511Mr. Jack Reynolds (203) 624-6671

iif. Operator -Mr. Ken SeatonNew Haven Water Company(203) 393-1619

g. Purpose of Dam - Public Water Supply.

h. Design and Construction History - The following- 0information is bellieved to be accurate based on the plans andcorrespondence available. The dam was constructed in 1889-1890 by the New Haven Water Company, as engineered by LucianA. Taylor. in 1919-1920 an upstream gate house was built bythe New Haven Water Company to replace the original downstreamgate house. The engineer was Albert B. Hill. In 1968-1969,the spillway was widened and lowered, and a new drain systemwas installed along the downstream toe. This was engineeredby Malcolm Pirnie, Engineers and constructed by the BrunalliConstruction Company.

a 3

i. Normal Operational Procedures - The main supply outletis opened as needed for water supply purposes. The var'ouslevel inlet gates are opened as needed to maintain waterquality, based on samples taken from different levels of thelake. One low level outlet is partially opened during the dryseason to provide water for the river. The low level outlets *are opened for flushing for several hours once a year. Duringthe inspection, one low level outlet was fully opened to emptythe lake in order to facilitate the construction of the newtreatment plant at the head of the lake. The operatorreported the lake will be drained for an indeterminate lengthof time, most likely about 2 years.

1.3 PERTINENT DATA

a. Drainage Area - 13.4 square miles of rolling, woodedterrain, of which 0.8 square miles drains directly to Lake .....Dawson, and 12.6 square miles drains to upstream lakes whichfeed Lake Dawson. Dams whose drainage areas contribute tothat of Lake Dawson include Lake Chamberlain and Glen LakeDams on the Sargent River, and Lake Bethany, Saw Mill PondDam, and Lake Watrous Dam on the West River.

b. Discharge at Damsite Discharge from the lake isthrough a 36 inch supply main, two 36 inch low level outletsand an 60 inch well drain.

1. Outlets Works (Conduits): 7-36 inch low leveloutlet pipes at8-

S invert el. 118.8± t

1-36 inch main supplypipe at invert el.126.31-6 inch well drain

2. Maximum known flood ?100 to 7300 cfs@ damsite: during Oct. 16, 19SS

flood. 'Existing infor-mation)

3. Ungated spillway capacity@ top of dam el. 166.8: 900 cfs

4. Ungated splllway capacity@ test flood el.: N/A

5. Gated spillway capacity@ normal pool el: N/A

6. Gated spillway capacity* test flood el.: N/A

4

94 S 5 0 0 *___9~~9~~~~S ...

7. Total spillway capacity @test flood el.: N/A

8. Total project discharge@ test flood el. 168.5: 19,000 cfs

c. Elevations (Feet Above Mean Sea Level)

1. Streambed at center-

line of dam: 119.3-

2. Maximum tailwater: N/A •

3. Upstream portal invertdiversion tunnel: N/A

4. Recreation pool: N/A

5. Full flood control pool: N/A

6. Spillway crest: 158.3

7. Design surcharge(original design): N/A 0 0

8. Top of dam: 166.8

9. Test flood design surcharge: 168.5

d. Reservoir - .

1. Length of maximum pool: 3500+ ft.

2. Length of recreation pool: N/A

3. Length of flood control pool: N/A - * .

e. Storage


2. Flood control pool: N/A S

3. Spillway crest pool: 1080 acre-ft.

4. Top of dam: 1540 acre-ft.

5. Test flood pool: 1670+ acre-ft. - 9

f. Reservoir Surface


2. Flood control pool: N/A S 05

So S __• • 0 ... 0€ . • • S S 0 • e_ 0_

3. Spillway crest: 61.1 acres 0

4. Test flood pool: 76 + acres

5. Top of dam: 76 acres (estimated)

g. Dam

1. Type: Earth fill withconcrete corewall

2. Length: 960- ft. j7-

3. Height: 48 ft.

4. Top width: 18 ft.

5. Side slopes: ?H to IV (Upstream)2H to IV (Downstream) 0

6. Zoning: N/A

7. Impervious Core: Concrete Corewall

8. Cutoff: N/A 1 0

9. Grout curtain: N/A

10. Other: N/A

h. Diversion and Regulating Tunnel - N/A

i. Spillways

1. Type: Broad-crested compoundconcrete weir 0

2. Length of weir: 110 ft.

3. Crest elevation: 158.3

4. Gates: N/A

5. Upstream Channel: Shallow slope. Traprock riprap.

6. Downstream Channel: Concrete near-horizontalwith one vertical 4' step.

7. General: Vertical-sided concretechannel curves rightand narrows to 50ft. in width

6

~ . 0 0 0 0 _ 00 0 *

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j.Regulating Outlets

1.Invert: 118.8t

2. Size: 2-36 inch

3. Description: 2 cast iron low leveloutlets.

4. Control Mechanism: Hand operated sluice

gates at upstream gatehouse

5. Other: N/A

7

SECTION 2: ENGINEERING DATA

2.1 DESIGN

a. Available Data - The available data consists of -

I tk drawings, correspondence, records, and specifications by theNew Haven Water Company, the Connecticut D.E.P., Joseph W.Cone, and Malcolm Pirnie Engineers.

b. Design Features - The drawings, correspondence,records and specifications indicate the design features statedI i. previously herein.

c. Design Data - There were no engineering values,assumptions, test results, or calculations available for theoriginal construction. Design data for the 1968-1969 lowering

* of the spillway is included in Appendix R~.

* 2.2 CONSTRUCTION

a. Available Data - The available construction drawingsconsist of a set of plans entitled "Lake Dawson Dam-SpillwayModifications", by Malcolm Pirnie Engineers, dated June, 1968.

b. Construction Considerations - Record drawings areavailable for the 1969 reconstruction of the spillway.

2.3 OPERATIONS

b. Lake level readings are taken daily. To our knowledge,the dam spillway capacity has never been exceeded. No otherformal operating procedures are known to exist.

2. 4 EVALUATION

I- a. Availabilty - Existing data was provided by the Stateof Connec-ticut and by the owner. The owner made the facilityavailable for visual inspection.

b. Adequacy - Due in part to the uncertainty as to the* actual location, composition, and depth of the concrete

corewall, there was not sufficient detailed engineeringinformation to perform an in-depth evaluation of the dam.Therefore, the Phase I assessment of this dam must be basedprimarily on visual inspection, performance history, hydrauliccomputations, and approximate hydrologic judgements.

c. Validity - A comparison of record data and visual-observations revealed no observable significant discrepanciesin the record data.

SECTION 3: VISUAL INSPECTION

3.1 Findings

a. General -The general condition of the dam is good,however, ispection did reveal some areas requiring attention.The reservoir water level was at elevation 156, 10.8 feetbelow the top of the dam, at the time of our inspection.

b. Dam:

Crest - The crest of the dam is a grassed earthembankment which showed no signs of cracking, settlement orsubsidence.

Upsrea Slpe- The upstream slope is covered withhand placed r prap and is generally in good condition as shownin Photo 1. Riprap is rounded, and 12 inches or less indiameter.

Downstream Slope - A view of the downstream slope in*Photo 2 sh-ows it to be covered with sparse vegetation. in

general, its condition is good and it appears to be stable. Novisible signs of seepage were discovered on the downstream

*slope. in an area approximately 75 feet from the inletstructure, there were observed two mounds of soil with verysparse grasscover at 1/3 and 2/3 of the way up from toe of thedam, respectively. It is possible these mounds were formedafter the installation of new drain pipes during 1969; they do

5 not appear to present a problem to the dam.

The toe of the dam is covered with grass (Photo 2).One wet spot was observed at a central part of the toe of thedam and a second one was noted along the bank of the low leveloutlet discharge channel. The operator reported that thecentral area was dried up two or three years ago by

* installation of a 4 inch PVC drain pipe from near the toe ofthe dam, and a 12 inch cast iron pipe from the drain pipe tothe low level outlet discharge channel. At the intersectionof both pipes the water level was 4 to 6 inches below theground elevation (See Photo 2), and the discharge from the 12

1..- inch cast iron pipe was approximately 60 to 100 gallons perminute at the time of our initial inspection. There is aseepage exit point near the left bank of the low leveldischarge channel, approximately 30 to 40 feet upstream of thesteel drain outlet, with a flow rate of 0.2 to 0.5+ gallons perminute at the time of our initial inspection (Photo 6). Asubsequent inspection 2 to 3 weeks later when the reservoirwas drained, indicated only a soft wet area with no flowevident from the seep, nor from the 12 inch cast iron drainpipe further downstream.

*-AI

9

Spillway -The concrete spillway and concrete spillwaychannel are generally in good condition. In the inspectionperiod the spillway was dry and the reservoir water level was27 inches below the spillway crest. The flashboards failedand were taken out in January of 1979 and never replaced, as

I ~ reported by the operator. The concrete training walls havesome cracking with leaking expansion joints in the left wall.The spillway channel slab has a central longitudinal crackwith seepage, from the bottom of the slab (See Photo 9).Concrete deterioration is located along the crack, causedperhaps by freeze-thaw cycles.

Discharge of approximately 4 to 6 gal./min. from both6 inch drain pipes from beneath the channel slab was observed.A slight seepage flow was noticed also from under the rightside of the slab. There is a substantial 1+ foot deep wash-outunder the left side of the end of the slaTb (Photo 10). Thiswas most likely caused by heavy flows passing over thespillway during past years. However, there was no cracking inthe concrete observed at that location on the spillwaychannel.

- Several leaks with efflorescence are located at thelef t stone masonry retaining wall adjacent to the concretespillway channel along mortar joints and in drain openings(Photo 8). These could be caused by both seepage f rom thereservoir and by natural groundwater.

c. Appurtenant Structures - The concrete intake chamber[i of the upper gate house, the new concrete service bridge and

* the low level outlet concrete headwall (Photo 5) are in goodcondition, with no evidences of significant cracks or

* spalling.

d . Reservoir Area -The reservoir area is bordered on the11 west by Conn. Route 69. The area surrounding the reservoir is

* wooded and largely undeveloped. Recently the New Haven waterCompany started construction of a new treatment plant at theextreme upstream end of the reservoir, which required partialdraining of the reservoir. The operator reported that thiswork would be completed over a two year period.

e. Downstream Channel - The downstream spillway dischargechannel runs into a channel cut into natural soil and rockformations. The natural channel bottom is covered withvarious sizes of boulders and cobbles (Photo 3). The channelbanks are steep and have been eroded in some places. Threeseepage springs with discharges from 0.5+ gal./min. to 5+gal./min were discovered on the rock -exposures of thidownstream spillway channel right bank at a distance of 150 to200 feet from the end of the concrete spillway (Photo 4).

10

3.2 Evaluations

Based upon the visual inspection, the dam appears to be ingenerally good condition. The following features which couldinfluence the future condition and/or stability of the dam

I L were identified:

1. Wet areas at the downstream toe of the dam, the waterflowing from the 1? inch cast iron drain pipe from oneof the wet areas, and the water level at theintersection of the perforated concrete and cast ironpipes could be indications of seepage through the damwhich could worsen, especially under a full reservoircondition.

2. The new drainage system of the dam installed in 1968and 1969 should be inspected at the manhole, and itscondition should be evaluated by maintenancepersonnel. The seepage rate at the outlet of thedrain pipe should be monitored, as excessive flowcould indicate an unsafe condition in the dam.

3. Leaking cracks in the concrete training walls and thespillway slab and channel should be sealed and theconcrete deterioration (cracks, potholes) should berepaired to prevent a further, more serious deterio-ration of concrete.

4. The wash-out under the end of the concrete spillwayslab could lead to serious deterioration of the -concrete slab.

5. Uplift water pressure in the foundation of theconcrete slab of the spillway channel could alsodamage the slab if not properly relieved.

LI

?'- e • • • • • • • • • • • • 0

SECTION 4: OPERATIONAL PROCEDURES

4.1 REGULATING PROCEDURES

Regulating procedures consist of operating the main supplygate and inlet windows as needed for water supply purposes.One low level outlet is partially opened during dry periods toprovide water downstream. Lake level readings are takendaily.

4.2 MAINTENANCE OF DAM

The downstream face of the dam has a cover of vegetationwhich is somewhat sparse in some areas. Grass is cutregularly and brush is cut twice per year. In addition, thedownstream area is sometimes grazed by sheep. Three years 0ago, the New Haven Water Company instituted a yearly programof inspection of all their dams, including Lake Dawson Dam, bya consultant experienced in the field of dam inspections.

4.3 MAINTENANCE OF OPERATING FACILITIES

Maintenance of operating facilities is on an as-neededbasis. Gate operating mechanisms are greased several timesper year. The low level outlets are opened once a year forseveral hours for flushing.

b 4.4 DESCRIPTION OF ANY FORMAL WARNING SYSTEM IN EFFECT

No formal warning system is in effect. Emergencies arereported to the New Haven Water Company office.

4.5 EVALUATION

The operations and maintenance procedures are generallygood, however, there are some areas requiring improvement. Aformal program of operations and maintenance procedures shouldbe impleumented, including documentation to provide completerecords for future reference. A formal warning system shouldbe developed and implemented within the time frame indicated 9in Section 7.1c. Remedial operations and maintenancerecommendations are presented in Section 7.

-9- _0

. SECTION 5: HYDRAULIC/HYDROLOGIC

i 5.1 EVALUATION OF FEATURES

a. General - Lake Dawson is used as a storage reservoir*for water supply, however the dam is a high spillage - low

storage project, as the reservoir storage effect on the PMF - .inflow/outflow is minimal. Although the majority of inflow toLake Dawson is from the outflow of Glen Lake and Lake Watrous,

L two upstream water company reservoirs, the regulation of thePMF by these two reservoirs is minimal and their effect on theP4F peak inflow to Lake Dawson has been neglected in ourcomputations.

The broad-crested concrete spillway has provisions for theinstallation of flashboards. The flashboards, designed tofail under two feet of head above them, were in place until thestorms of January 1979, at which time they collapsed.Although the owner has no plans to reinstall the flashboards,some attention was given in our computations to the hydraulic

- conditions during the PMF event, both with, and without theflashboards. It was concluded that operation with flashboardsin place would reduce the surcharge storage capacity of the

* reservoir, however the spillway capacity will not actually bereduced due to the design of the flashboards for failure undertwo feet of head, ie. a water level 4.5 feet above the spillwaycrest. This flashboard design failure would result in adischarge of approximately 1000 cfs.

b. Design Data - No computations could be found for theoriginal design of the dam. Results of hydraulic designs wereavailable for the 1969 spillway redesign and construction,L however no actual computations were obtained (See Appendix B).

c. Experience Data - No information on serious problemsituations arising at the dam were found, nor has it ever beenreported that the dam has been overtopped. The maximum heightof water over the spillway crest was approximately 2.5 feetduring the October 16, 1955 flood. It should be noted this

t_ height was prior to the redesign of the spillway to itspresent elevation and configuration.

d. Visual Observations - Visual inspection does notindicate that any blockage of the channel would be likely.The spillway discharge channel immediately downstream of theend of the concrete channel is a nearly vertical sided channelcut into natural soil and bedrock exposures. The channel

• "curves to the right and, under heavy flows, will be subject toerosion along the channel bank, however serious blockage ofthe channel due to this erosion is not anticipated.

13

e. Test Flood Analysis - The test flood for this highhazard, intermediate size dam is equivalent to the ProbableMaximum Flood (PMF). Based upon "Preliminary Guidance forEstimating Maximum Probable Discharge", dated March, 1978,peak inflow to the reservoir is 20,100 cfs (Appendix D-2);peak outflow is 19,000 cfs with the dam overtopped 1.7 feet(Appendix D-10). Based upon our hydraulics computations, thespillway capacity is 9,900 cfs, which is equivalent toapproximately 52% of the routed Test Flood outflow.

f. Dam Failure Analysis - Utilizing the April, 1978,"Rule of Thumb Guidance for Estimating Downstream Dam FailureHydrographs", the peak failure outflow from the dam breachingwould be 133,100 cfs. A breach of the dam would result in a 20foot high wave immediately downstream of the dam at the houseand filtration plant. The breach outflow will enter KonoldsPond approximately one mile downstream rapidly raising thewater level and causing Konolds Pond Dam to be overtopped byapproximately 8 feet. The high water level in Konolds Pondwill affect at least 10 residences along the shorelineupstream of the dam, while the outflow of about 30,000 cfsfrom Konolds Pond would be discharged into the heavilyurbanized area of Westville immediately downstream.

U! 1

- 14

0. . . . 0 0 ..... • .- . . . . . .9 0.. . . ..

SECTION 6: STRUCTURAL STABILITY

6.1 Evaluation of Structural Stability

a. Visual Observations - The visual inspection did notSdisclose any indication of stability problems. The

inspection revealed:

1. Seepage flows probably through the lower zones andfoundation of the dam which caused the wet areasdownstream of the toe.

2. Seepage flows under the concrete spillway and,possibly, through the left abutment adjacent to thes p illway.

The seepage could lead to a decrease of the damreliability in the future and at present it could cause a

* lessening of the stability of the spillway structure (upliftpressure) and accelerated deterioration of the spillway byfreezing - thawing cycles of the concrete.

*b. Design and Construction Data - The design andconstruction data is not sufficient to permit an in-depthanalysis of the stability of the dam. Data available does notinclude information concerning the dam cross-sections such aslocations or configurations of the concrete or masonrycorewall, nor does it contain information on the properties ofthe foundation.

c. Operating Records - The operating records do notinclude any indications of dam instability since itsconstruction in 1890.

d. Post Construction Changes - The post constructionIt changes consist of:

1. Construction of the intake gate house in 1920.

2. Construction of the new wider and larger concretespillway and spillway channel in 1969 to providecapacity to pass a storm in excess of the Westfield,Massachusetts storm of 1955.

3. The material excavated during the lowering of thespillway was placed adjacent to the left downstreamtoe of the dam and to the right of the spillwaydischarge channel.

4. Construction of the fill berm placed at the downstreamslope adjacent to the lower gate house andinstallation into the berm of the drain pipe systemwith a manhole in 1969.

The new gate house and spillway construction yieldincreases in the dam stability normally associated withincreased discharge capacity. Placing excavated material fromthe spillway along the downstream toe will increase the cross-.section and hence the stability of the structure, provided itdoes not cause a build-up of hydrostatic head within the dam,L which will depend upon the permeability of the natural on-sitematerial placed. The effect of the berm at the right end issimilar; in this case, the toe drain effectively provides anoutlet for seepage, thus reducing hydrostatic pressures withinthe dam.

e. Seismic Stability - The dam is in Seismic zone 1 andaccording to the Recommended Guidelines, need not be evaluatedfor seismic stability.

16

SECTION 7: ASSESSMENT, RECOMMENDATIONS AND REMEDIAL MEASURES

7.1 Dam Assessment

a. Condition - Based upon the visual inspection of thesite and past performance, the dam appears to be in goodcondition. No evidence of structural instability was observedin the dam or its appurtenant structures. There are some

* areas requiring attention including the seepage problems underthe embankment and the concrete spillway. Recommendations andremedial measures are presented in Sections 7.2 and 7.3,respectively.

Based upon the "Preliminary Guidance for EstimatingMaximum Probable Discharges" dated March, 1978, peak inflow tothe reservoir is 20,100 cubic feet per second; peak outflow is19,000 cubic feet per second with the dam overtopped 1.7 feet.Based upon our hydraulics computations, the spillway capacityis 9,900 cubic feet per second, which is equivalent toapproximately 52 percent of the routed test flood outflow.

b. Adequacy of Information - The information available issuch that an assessment of the condition and stability of thedam must be based solely on visual inspection, the pastperformance of the dam, and sound engineering judgement.

c. Urgency - It is recommended that the measurespresented in Section 7.2 and 7.3 be implemented within twoyears of the owner's receipt of this report.

h d. Need for Additional information -There is a need formore information as recommended in Section 7.2.

7. 2 Recommendations

LA registered professional engineer qualified in damdesign, hydraulics and inspection should undertake furtherstudies in four areas pertaining to the hydraulics of the dam.

a. Based upon the computations in Appendix D, the dam*spillway capacity will be exceeded by the Test Flood. The

owner should consider initiating more sophisticated floodrouting by hydrologists/hydraulics engineers to refine the

*spillway design flood figures. A study should be undertakento determine more accurately the spillway capacity andovertopping potential. Recommendations should be made by theengineer, and implemented by the owner, to increase the

- project discharge capacity based upon the more sopisticatedhydraulic/hydrologic study.

b. Seepage emanating from near the toe of the dam, bothat the wet spots near the right toe of the dam, and the seepsfrom along the sides of the spillway channel embankments at

17

_~ ~~~ - - - -0 -~ 0 - - -

the left end of the dam, should be monitored during dryperiods with high and low water conditions in the reservoir.An assessment should be made of the origin and significance of

* all the seeps with respect to fluctuations in the reservoir* water level, and if deemed necessary, recommendations should

be made for the control or elimination of some or all of theseepage. The assessment of the seepage should attempt toevaluate the permeability of the dam, its foundation, thespillway base, and the left abutment by determining relativeamounts of seepage through each.

c. An assessment should be made of the uplift pressureperiodically being exerted on the concrete spillway channelslab. The adequacy of present measures designed to relievethe uplift pressure should be examined, and if needed,recommendations should be made to further reduce upliftpressures and to prevent seepage from surfacing through theconcrete slab.

d. A program should be developed to repair leakingexpansion joints and cracks in the concrete spillway andspillway slab.

7.3 Remedial Measures

ai. Operation and Maintenance Procedures - The followingmeasures should be undertaken within time frame indicated inSection 7.1c, and continued on a regular basis whereapplicable.

11. Round-the-clock surveillance should be providedby the owner during periods of unusually heavy precipitation.The owner should develop a formal warning system with localofficials for alerting downstream residents in case of anemergency.

2. A formal program of operation and maintenance -- -

procedures should be instituted and fully documented to* provide accurate records for future reference.

3. The New Haven Water Company has instituted a*yearly program for inspection of all their dams, including

Lake Dawson Dam, by a consultant competent in the field of daminspection. This program, which has been in effect for thepast three years, should be continued in the future on atechnical basis and should include the operation of the lowlevel outlets.

4. The wash-out under the spillway channel slab end-should be filled with suitable material and compacted to

*increase the stability of this zone. Areas of settlement orerosion behind the spillway training walls should also befilled in.

18

7.4 Alternatives

This study has identified no practical alternatives to theabove recommendations.

19@

APPENDIX A

- INSPECTION CHECKLIST

.

jr VISUAL INSPECTION CHECK LIST •

PARTY ORGANIZATION

PROJECT___ 2_2" DATE: /lt '~/7

PRJET eaeIa-L2dJ4L TIME:

WEATHER: . 70 '

W.S. ELEV. U.S. DN.S

L PARTY: INITIALS: DISCIPLINE:

1. A c&A'A 4 , P// 6' CZV* 6 ,pAe ,$ ..7,

2. CO Vot,6ew% ~ ________ 2 # 6 -7,Ag 7S.Tc

46 P &.A ________ (s,,C ges, Ts;c

5s. A'BaOV ABg 44_______ /flv,sReo

6.

PROJECT FEATURE INSPECTED BY REMARKS

1. 'eren pA1m 6C/YP A 6A A

2. &IS5 F,47-E #QaJ6w~~e~i ~6 "~

*3. ~{w 4-&re~ i.c~lrL Rr4 l. SPI 41 WA Y * | #

5.~ 0 oW.57TKEAM CffAA1A,eI.

6.

7.

9.

10. i9

12.

4I

* _ --- . .. 0 _ * I!.... O 0" O

0 -

0 ... O . 0 ... O 0 -- 01 0- O O 0 ._

PERIODIC INSPECTION CHECK LISTPage 4 42 1 S

PROJECT .D044&_ DATE AlA /

PROJECT FEATURE A,_iQN -. _AA,f A1,6,4A ,/A2.'T i ,,'. ,' ,5

£ p.

AREA EVALUATED CONDITION

DAM EMBANKMENT

!crest Elevation - --

ICurrent Pool Elevation

Maximum Impoundment to Date .N1'

Surface Cracks ... c . &. ' '2.

Pavement Condition frk.A

,Movement or Settlement of Crest J%'OWE OS.E R V'..

lateral Movement NO).'0 8SE ?

Vertical Alignment AEA '0Cf.

Horizontal Alignment; O0. D-~~C NO A E P R.N " 7-

I A ... ..

;Condition at Abutment and at Concrete NStructures

'Indications of Movement of Structural Nor oSSERVEDItems on Slopes

L Trespassing on Slopes NC'

Sloughing or Erosion of Slopes or Nc ' b S E k\"EDAbutments

Rock Slope Protection-Riprap Failures &c" CCA.P1/V AlT

Unusual Movement or Cracking at or /Vo A f OS•

Near Toes

Unusual Embankment or Downstream I Er A A e;. AA 7, A. .u85 7.4A '-

Seepage -iA .t -E.'F - I?' 6 .,TF! :qA.,'

Piping or Boils

Foundation Drainage Features , ?'E A ACA &

, Toe Drains

Instrumentation System ,

5 _ __ •* .... • .. • •.... . 0 0 S 0 0 0 0 0 •

PERIODIC INSPECTION CHECK LISTPage ,--i3 ..

PROJECT ZAA-E _DAWV6PA' ,,f DATE I/A y /. /, /791

PROJECT FEATURE BY , C,6 f '.,


OUTLET WORKS-INTAKE CHANNEL AND.INTAKE STRUCTURE 0

:a) Approach Channel

Slope Conditions

Bottom Conditions

Rock Slides or Falls

Log Boom

Debris "

Condition of Concrete Lining

Drains or Weep Holes r .. ,4

b) Intake Structure

Condition of Concrete

Stop Logs and Slots -' ' "

IL:

L .0_ • . . . _ _.o _ _ . . . . .O . .• . .. .. 0 0.....O0 ... e 0 • 0 0

PERIODIC INSPECTION CHECK LIST Page 4-.

PROJECT Y A.- . , Z,,' -4 .P €! DATE ."

PROJECT FEATURE O T //'7 (f i- c / .7.' o ', ,-.2 ,I0


IOUTLET WORKS-CONTROL TOWER

-a) Concrete and Structural /'- ' A ,4 . 6 , ./-2 . C Ai " F

General Condition

Cond ition o f J oint s A 'A - ., ,Spalling

0

Visible Reinforcing

Rusting or Staining of Concrete

Any Seepage or Efflorescence 4 ? . :.'- "Joint Alignment

Aer C ,"; ' ' :

Unusual Seepage or Leaks in Gate A e- vChamber

Cracks i4.

Rusting or Corrosion of Steel C , A -

I b) Mechanical and Electrical

Air Vents

Float Wells

Crane Hoist

Elevator

Hydraulic System

Service Gates

LEmerec Gate Ac N

Lightning Protection System

Emergency Power System

Wiring and Lighting System

.. . .• ... _ .. . _ •0.. •. .o _ o 0 .o 5 .* . . . S 5 0 0 0 o.

PERIODIC INSPECTION CHECK LIST

PROJECT --. -! .T.,r __'" '

PROJECT FEATURE___ BY L ' e "" "' c-'"


'OUTLET WORKS-OUTLET STRUCTURE AND, OUTLET CHANNEL

:General Condition of Concrete A'&. #£A.)f,./. -, Gc')

)Rust or Staining A,. ''r

'Spalling SCA/E

:Erosion or Cavitation

Visible Reinforcing '. E

,Any Seepage or Efflorescence A ",

!Condition at Joints V c , £

IDrain Holes A"

Channel

Loose Rock or Trees Overhanging A'C' LChannel

Condition of Discharge Channel icC, & 6 A.. 'tY. ;''-.

IL ~CA.)TC4

_ --- 0 0 0 0 0 0 0 0.

PERIODIC INSPECTION CHECK LISTPage A-

PROJECT ZAAt DAJTK .,, -tjp ~

j PROJECT FEATURE S44./ 4 4 A.,.$'_ BY b" , '. ,

ARIEI. EVALUArED CONDITION

CUTLET WORKS-SPILLWAY WEIR, APPRO)ACHAND DISCHARGE CHANNELS

a) Approach Channel

General Condition

Loose Rock overhanging Channel

S Trees Overhanging Channel

Floor of Approach Channel r

ib) Weir and Training Walls

General Condition of Concrete: "r

* I Rust or Staining

. i .. ,Spalling ' "

Any Visible Reinforcing

= * i Any Seepage of Efflorescence | .z-- , . 'w &CACA '

Drain Holes

C) Discharge Channel oy10

General Condition (c.-*.'.~*.'.*

Loose Rock Overhanging Channel - ' /' C 'A : I

Trees Overhanging Channel I"'

Floor of Channel I., I

Other Obstructions ,

PERIODIC INSPECTION CHECK LISTPage 4- 7 S 0

PROJECT ~4,& PXWSO.0A I 0A,4_

PROJECT FEATURE_ , 7_Y

AREA EVALUATED CONI) ITION

OUTLET WORKS-SERVICE BRIDGE ReF 7 9 / ft /'Z' 3 PP-A* ',fr( /losg

I a) Super Structure @ OI

Bearings o

Anchor Bolts

Bridge Seat O

Longitudinal Members

Under Side of Deck 0In

Secondary Bracing

Deck

Drainage System V/A

I Railings

Expansion Joints

Paint AlIA

. b) Abutment & Piers.

General Condition of Concrete Goe,

Alignment of Abutment Nor O8 85 D vi.

Approach to Bridge oz

Condition of Seat & Backwall

, 0

S

_ ... * . _. _ .oe • .0... 0 . 0 O_ 0 0 0 0 S 0

I

I.

I S

S

APPENDIX B

ENGINEERING DATA AND CORRESPONDENCE S

S

0

S IS

-- 9--

0 0 0 0 0 ~ *0 *0 0 0 0 0 0 0 0 0

-LAKE -AJM-

tm A

ILmm NNW 1~- @w~ m

60 U U

me %

~~now

SECTION A-A

0TO OF OW6

ELEL105

UPLLW Lmu. o

1. flM 7M 08 COWM CAW0 EVORM MD "W~Y ANDMW_ A UT OF PLUS SifhiL *L DW4O L

* i~in WM M A MM ON AM S. OMS

Poimlo. 'sn TOPOWC PEAVLS CWU5

t.EITOO pow AK "m aW Tm - USER omcoMM~u mgU mIEN) M1MO 4 SOPEET M9 I* M*A LbS MTIA it JA. MW CW4Vin mm ow in 1

mLucc6ucLI UEW ua.

S.', N~ATMOAL PROAM Of ISIMC? OF NWNFt DAM

MLOAPLAN, IEUEASIND S4 ECTIOIS

*ATM CWWiW L*XE DO" DAM

M ms m sy T! - CL AV00mQmy

M. M_00 IfM -I" ame -left S-1

LIST OF EXISTING PLANS

"New Haven Water Co.West River SystemI Plan of Lake Dawson GatehouseTown of Woodbridge, Ct."Office of Albert B. Hill, Consulting EngineerJune, 1919

*New Haven Water Co., New Haven, Conn.Dawson Dam Spillway Modification"6 sheetsMalcolm Pirnie EngineersJune, 1968

Li

LI - 0

1 U) >)

to W.Q Z~- 0 C W

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E- - N 4) 0 iv ' C C) 04 1 to 0- -0W4 - '54.,- M40 -4 -. L0 -- - W 4414( 0j 'laV5 O-4 -44 4~. ifv r-4' S- w $ - .)0CQ 0 V -ij '5 '.a-- JLa '53 r-4 to 0mt) A

0 U U4 u~C 40La to) toa 00044 C 4 44) o ( a0 U '50to 00 OV 05 4-a CM-4 w a-foto% 4

coU 4id m~-. AC to.-- 1% 4-1W 3t 004 U4

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ONzON 0% m 0/ -4 4

inventoried ".SUPERVISION OF DAMS L oInventoried INVENTORY DATA L -

By i

Date tc9 MAY1 tRLo4-

Name of Da n or Pond L.4 KC: bA j S OrV/

Code No. W -S '7.9 " "

Nearest Street Location (?ouT- C

Town _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

U.S.G.S. Quad. .eW - IAVE/ - S

Name of Stream vJC.St |AV.VV.. At

Ourner ?'JCI. H-AVJC'I W.,ATL4 C0joMV'A'j)_

Address 1 too , . .o ) .

NcvJ "AVf

Pond Used For 'vJATi.Z. Su9PLY

Dimensions of Pond: Width ,04o1 Fc'e' Leng-'i Woo TM T A.c 5 gtL

Total Length of Dam o> FtZT" Length of Spillwa n*- F T . ..

Location of Spillway CAST CAb op OAM

Height oZ Pond Above Stream Bed F Q:

Height of Embankment Above Spillway ,,6 r

Type of Spillway Construction C Otc a E T..

Type of Dike Construction LAi2.b4 . £.tP- a.AP tjSt9mT.

Downstream Conditions JCl.:J ,,Av J

Summary of File Data _

Remarks

B-4

Would Fniiinw Cauine lMDlng'? .. . . .Class

NEW HAVEN WATER COMPANY * S

STATISTICS ON DAMS*

NAME DawsonSUPPLY SYSTEM West River 0

LOCATION Woodbridge

DATES: ORIGINAL CONSTRUCTION 1889-1890

ADDITIONS, ALTERATIONS 1919-1920; 1968-1969 - 0

MEAN HIGH WATERELEVATION LENGTH

CREST** 164.0 1000- Ft.

TOP OF CORE WALL

SPILLWAY 157.50 110 Ft.

B. 0. AXIS 117.0 2@ 240 Ft. each

BED OF RIVER 116k

DEEPEST FOUNDATION 109f

bFREEBOARD: CREST TO SPILLWAY 6.50 Ft.

CREST TO TOP OF CORE WALL

HEIGHT: CREST TO BED OF BROOK 48± Ft.

" CREST TO DEEPEST FOUNDATION 55k Ft.

TYPE Earth and Concrete Corewall

TOP WIDTH--MAX. BOTTOM WIDTH (Ft.) 18± -- 200k

UPSTREAM SLOPE H/V 2/1

DOWNSTREAM SLOPE H/V 2/1

TRIBUTARY WATERSHED (Square Miles) 13.0

RESERVOIR AREA (Acres) 69.5

RESERVOIR TOTAL STORAGE (MG) 352

RESERVOIR USABLE STORAGE (MG) 237

*See individual sheets for more details**Crest Length includes spillway Date 8112/74

B-5

... 0__O __ o . .• .. .. ..O__ . .. *• _0 . _ 0 0 9 9• 9 S _0

jE OF DAM DN O

0 Le

woot. cte~ir en..J pfjcj~ 1111-noI - ?It fPrl-a i WAhen &Le~idn Sc\8V- ®rv LZgn,2J16orilk?,

,t~~~~, 3,, ?'.- .A 4 A' !.? ~ jv~.

CTO COSRUTOCt I I WA 1- 0 tez cv. A re~mS4Yhl b~~1 - 7rspj~je

f42cIL C- q/) tie~.i n 4h Oc ?~dr . 7 r (~c~-. ~~~~~~~~ e k.e7Tt), _,A /--~

leg,,dkei n, , ?rrA a~~ hlse ezt o -- on ,4

lr--161ol 'Am,4Y'~i. TkLO C ~o42JAf

ELEVATION LEKT (Yree)MIC

5- ILLWAf 1S7,50 1iM-wW. J10 Ton of~ i/ash 6neA4(5 or- B.o _J/. Aii-1u . 2'OCciZ3A .Ie/)i

Z PJ OF R"JER -t 1/4e MU.W)_ _ _ _ _ _ __ _ _ _ _ _ _ _

1) F.P C T FN~fJ-Atb2 J4*-Aj*-%V__ _ __ B-6

t jj~r~laTc. FROM BED F 0 r- BOOK - 1'4 8 ree14. NE I IAT F IZOI D E P-ST F 00 NtbO-r (0 55 Fee

I Trop. Vw1 1-I4 & 18 Fo-e efI. MA)(IMUM WIDTI4 AT BOTTOM zo Z e- e e+17. UPSTREAM -SLOPE 2 40oy o&.. lw

Ilk DOWNSTIRt-hM SLOPQ It"

I FPEC- BOARD3 SPILLWAY TO C~e' P F

-SPILLwAY TO TOP OF coe~l-. ~ I ee

z. MIS C. DArA.

tn iCl Scz IY en ot

71 WATLE15"E TRIBOTAR>' TO:

OPTREA DM VANS_

To-TAL TRA~I-~D IBUTAU( To rivs DAM /3.0 Sq.1i.

2' R'-5ETRVo0r AREA AT- FLOW& LItJG 9. Av2., IL-sC-PZvp- cAPACITY A'T FLOW Lb'e Z ?57- W. 6q

Z RESER~VOiZ USA13LG CAPkCITY(rolewe-i autle)TopW y' 2 37 ma *iz

Z 5. VUPSTP-C-A& DAMS(

1~bm, DAN.S H- ,) ro54 13c !2&7 VPentLLIk,± x~e... P-/4 el, c/Lts., A? 100

B-7

0 0 _ 20 _0 0 0 0 00_0 0 0 0 S S 0

A/ ~

MoiN A. L. Cobln.Ji., PresidentT con: Joseph A. lkvario, Chief traginsee

Re: West River Watershead.

Flood c...dlttons to) 19V, at anid jpstveao from the Whal.ey Avenue1r.-O,.. Ln W**ttl., gsetstiy £rua2.uted ti t). West lti.... actuL~Y wort,the itrso'lL it hay storm tu £dlh from sevatat w.Atorsheds:

Went live *yti.X west arid s;,tf West Rock. Cvv.it.a y ,~g'..nder

Lt1e Wh i y Ave..at !)rtdje.0

2. An area stat L 14 at Lte Ytale Go~[ Course ponds arid extending -iurth tothe FounICti ,street - Walley Avenue aea, Jistiiii,& to West RLvet.

J. Wilt*rgretn Biook Lying east of West lock. It enters West liver aboutbrJL) test nort1 Oi1 the WhalLety Avenue bridge.0

4. Farm Brook. east of West 'tock. starting about. osirn miLe north of ParadiseaU- ~ IHamdov *:id daining south into Wintergreen brook stp.*ut 1900 feat

ouottioast of ttre Springslide Nowai.

A,, ciiadLr) lying between 3 and 4 above, which starts aliout oiie*half 0w. -P asi of Patadise Park. Let Hotedeti and dcaitte so'uth tnLO VL'ntergteen Siuk'at A plii. Li tte brookatlde IkiusInS &ses of mew Havea.

t. 3..qvut P..- watetshod which stietches Opbirtvatiy (con Arch Street I,,turn:. . south toi Citfe Street it% Mew Have'.. 'Che brook from %ever Pond runs0,a :AtthWoo. O'Atrt~I1 'v@&11ergjreen gruok abOUt '106 feat 11orth of the WhalLeyAV* . tiride.

The watersheds tributary to the Whalley Avenjue bridge total 29.3aquAt it iles which I have broken dowii, for atiaiysts. ito three main are"s:

IL Noth of said tributary to Dawson Dow L3.9 sq. mi.Winterareei Dam 1.5 sq. mi.

asotaing watershed !3.9 sq. mi.To~gi29.3 sq. aL.

The Me"j Havenr Water Comipany owns ppiazimately onei square mild of the S1.5 sqtare oil** of watershed LitbuLary to Lake Wi"tergreen and about ' squaremaies of Che 13.9 equate milis of watershed tributary to Lake hUson. Thebalance is @wis~d by itrurto. The Company pvue! -and, used for water supplypu paes ooiy. arid we& I foested. has not cott, Luted to any increase Inflood aunoff. In fact the Company's forestry program bas attacked somedecrease in the rate of atom water runotf from the laid.- 0

The balance of the Lead owned bay othesrs a .d draing LO the WhlteyAveniue bride has been and wili continuas to :is devoioped fur housing, schools,iid- stay aid col Logo&. Mheia rcuf a, driveways, streets and padrking areasL'n:e~Ase the Owousit avid rate of stru water ruwuoffs avid at as water sewers, where-Iasal d, accelerate tie* runoff. -

B-8

-2o

Our reservoirs generally start to so down early in Juno and 0 0

conitLnoe to go down until Late in the year. Abou.t halt the year'!sreftIlLngstarts about the middle of November and about Lis* middle of December therest of the years. Occasionally. as recently experienced, our reservoirsstart to refill In January and very occasLonally in February. Our reservoirsthus are in a positios during the hurricane Season to receive end retaL alarge portion, and sometimes all. of the storm runoff fsoe the 15.4 square 0 0

miles tributary i timm.

In August L955 hurricane Connie, followed by Diann*. brought heavyrains to this area. Dianne caused considerable damage Ln NiLford and thelower Naugatuck VaLley. In the period August 6 to 14 inclusive raLnfalL atLake Devon totalled 4.L4". On August 18 and L9 hurrLcane Dianne brought anadditional 6.67 . In one 24 hour period 4.87" fell at Daeson.

In thLs eutended storm period our reservoirs received and retained477 million gaiLons of vater. Glen, Vatrous, Chamberlain. Istaer end Wieter-green retained all the ranoff reaching them, allowing nothing to So downstream. 0Davon, on auguet 19th, with its eml tributary watershed of 0.6 sq~are maloe,finally filled byt the depth of flow over the spillvay was only one half anInch. The data is Listed herewith:

efore the Ltorms After the ItorueReservoir level Killioni gals. Reservoir Level Killion gals. *

to fill to filllLv;on dov0 0' 1/2" 1 full 0Glen 2L' 3" 140 down 10' 3" 1Wroue " b' 40" 209 " 2' 71 86Chamier I k gp ty 164 4 ' 10" 49Se'dan:" dawn 4 6" 138 FUSL 0 0 •idnterreen " ' 6' 66 vu 2 ' 5" 25

Tv, t 10 I LI 241

Amount retained 716 - 241 - 4)7 miLlion gallons.In addition-about 9 million gellons per day throughout the entire storm periodwas alSo uttiated for water supply purposes. •

Th heavy storm on October l to 17 inclusive In 1955 produced floodsand considerable damage in the Westville area. Our raia gauge at Dawsonregistered 8.84" of rainfall in this period. Of this 5.85" fell t one 24 hourpert-d alone. Our reservoirs were all full after this storm but prior to

7 filLing they stored anid retained 251ILLion gallons of water as shown In theAsta below:

Rorvoir level M jLLon Ale. to flitDes(-. over 0' 1/2' 0Glen down 5' i" 45Vatrous " 2' 6" 63 - SCbaterlen " 9' 4" aslathany " 0' l/Z" 2Wintergreen of 3' 3"6 33

251

ts addition, at the height of the storm water runoff our reservoirstm",jrarily stored 215 million gallons additional above tli&Li spillway, -9prevouting eves higher flood Levels down stream by rolaaigat this over a

__ " _ _ _.o .... 0. . .. _ .o. • . . 0

) -3-

7 . greater period of time. The data La herewith:

Deth, above SsiiLwav Surface Acres Acre-feet PU.,lLLon le .Dameon 2' 59' 7 L 172 55.5Glen 2' 7 27 70 22.6Vatroue Is L11 110 211 (d..

3 ChamberLets 29 0" 37 74 23.9Bethany of li" tO6 91 31.3Wintergreean t 0" 44 44 14.V

215.5

The effect of reservoir sturag above the spillway level on downmtrea -

flood conditione can be checked by comparing the flood runoff from the renervoLr 0controlled WLerebeds with that of the other watersheds as toLlovae

1. Fro. Ia% level records (depths on spillvay) I have computed that at peakrunoff approaimtely 1425 cubic feet per second were pasaing our Dawson endVintergreen dams. For the 15.4 eq. siLLes of tributary watershed this La anaverage runoff rate of 92 cubic feet per second per square mile of wetershed.(Septenber 1938 hurricane runoffs were in the 40 to 60 range).

2. The peak flow under the Whalley Avenue bridge, computed by Consultants forthe State. wea 3.525 cuLc feet per second. Subtracting above 1425 cusec. loaves2,10) ousec. contributed by the remining, uicontrolted 13.9 square mtLes or atan average ru'f rate of [5i cubic feet per eec. per square idle.

Peak runoff rate fram the uncontrolled portio, s of the watershede

tberefore was about 50 per cent higber thee from the controlled watersheds forthis parLicul&r storm. This is pot surprisien vthen you consider the absence

of large reservoLre and the Large amount ot Lapervloue surfaces in the built up,'residentlal, cometeis., school and industrial re..s.

Consultants for the State reported that a 41 inch diameter sewersuspended under the floor of the bridge restricted the flow ares of the bridge.accentuating flood tonditlo.is upstream. in order to pase the cemputed possibleflood flow at this point -larger than the 3,525 cusec. - the Consulteat .reca=a nded that the sewer be replaced with a siphan "nder West River and that.additLoeaL watetway capacity be provided by widening the bridge.

Since ILs flood Now Haven Water Company has raised Ch.mberlain Dam35 ,iL increasing its storage from 164 mlLIosi gallons to 89. million gallori.1huo ii the fugure additional space has been jrovlded to store and retain flood -

'hile Company owned land will remltol well forested, retaining norsal)Lield and runoff, the areas owned by others will continue to be developed forother uses - uses which will inevitably increase the mouti of storm rua Ofa n d t h e.... . . . . ... .. ... . - I k

/

5 '

• " B-IO

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NEW HAVEN WATER COMPANY" . NEW MAV1. CONNRCTICUT 00800

7e/. IVA 4 3 April 12, 1965

5 l:r. Joseph W. Cone,Civil Engineer.

12'. !Ivemeyer Place,Greenvich. Conn.

Dear Mr. Cone:

fifterring to your letter of Apr!1 2, 1965, we encloasjpci.

1. Data forus for Chamberlain, Glen, Bethany, Watroug aid Davscu Does.

2. Plans for above dams. -

3. Sanitation map showing limits of watersh-d tributary to abcve dome.

In the period from 1937 to the present, depths over the spIllvays

oi the above dams in most ca es .have been less than one foot. -... ..

Our rain gauge at Lake Dawson recorded a total of 4.;4" :n tteAugust 8 - 14, 1955 storm. It recorded 6.b" on August 18-19, 1955. inone 24-hour period rainfall totalled 4.8;". None of the runoff went

downstream but Lake Dawson was full at the end of the storm.

The Lake Dawson rain gauge recorded 8.84" of rain in :.e

October 14-17, 1955 storm, or which 5.85" fell in one 24-hcxir period.

This storm filled the four upstream reservolrs. azimum depths onspillways occurred on October 16, 195 5 and are recorded on the data forse,

hAmberlain Dam van raised in 1958-1959 and a new largerspillvay vs provided. Storage was increased from the original 164 .If1ion.gallons to the present 894 million gallons.

If you will let me know when you wish to make a field Iuepctioi,I will be $led to make the necessary arrangements.

Yous very truly,

NEW RAVEN WATER COMP71N

oseph A. Fovawo

Chi*ef legine

• " "B-11

0 _ ... 0 ... 0 0 0 0 • ! • 9 9. ! _J__

1965

REPORT

CONCERNING DAM

Owned by

NEW HAVEN WATER CO.

BETHANY

WATROUS

CHAMPERLAIN

GLEN

DAWSOIi

on the

WEST & SAROEN-T FI.I"ViG

Jo W. Cone PogoJune 1965

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*I ND EX

Part I Page

Letter of Tranamital 1-4Watershed 5-6 0

Precipitation 6-8

Flood Flow 1955 8-9

il Q a 9 A26 vs Conn Formula 9-10

Spillway Capacity 11

MAP, Comparison Check 11-12

Betbany 12-13

Watrous 13

Ch,ribe rla in 14

Glen145

Dawson 15-17

Ge ne ral 17

Part II

NOTE: Maps# graphs, etc., mro in separate

folder.

B -

B-13

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..C£T|CUT ftuOiesmArsON * 4gm~L IgwumQNI isumnsm sI.

124 HAVgEurrT PLACS

GOMuuWmCN. C@#4iiCTICUv

June 26, 1965

mr,, William P, SanderWater Resouroes Commission

I State Office Building -Hartford 15, Conn. Re: Dams #35 - 1 to 5

Now Haven Water Coo

Dear Mr. Sander:

L First# I apologize for not completing this assign- 4

ment more promptly; reasons being that a low quality

virus for over a month left me with no pep mentally or

physically, and delays in obtaining certain plans and e

information.

The assignment was- 'we would like to know the

present condition of these dams - Bethany - Watrous - •

Dawson on West River and Cbamberlp.ln - Glen on Sargent

River, a tributory to West River above Dawson Dame

In my opinions the "condition" of these dams Is

good as regards masonry of the throe masonry gravity

L, damns and the upkeop of two earth embankment dams*

But as reeard to whether or not the dams are safe,

partionlarly as regard spillwsAN capacity, ry opinion is

as follows:

35-1 Bethany Spillway is inadequate. However a thin

sheet over a length of 990' will do comparatively

little damage except to highway. The gravity

9otion is safe.

* 0-

B-14

• ........o .. . .• . .e e

Mr. William P. Sander -2- June 26, '65

35-2 Watrous Generally same remarks as for Bethany.

35-3 Chamberlain Spillway in adequate in every respect

* as is the dam. It is reasstrlng to find a spillway S

that will carry 1525 cfs per sq. ml. on 4.I sq. mi.

Note Items #26 & 28 on Data Shoct.

35-4 aen Spillway is nowhere naar aloquate. In fact,

Oct. 155 flood nearly overtopped earth section at

left or east abutment. Section of dam is safe.

Right abutmoit should be raised to protect ,

highway.

Left abutment should be investigated:-

(a) To determine whether or not there is a core 0

wall.

(b) Possibility of emergency spillwar or fuse

plus*

(c) Note Items #26 & 28 on Data Shoot.

35-5 Dawson Present spillway is entirely inadequate

t,, carry probable flocda of the present and future.

In fact, th3 dam would have beer overtopped if

certain saving factors had !-it b .,, , -rent in

oct. 1955.

(a) Not an excesaivo rainfa!l, only about R of

50 yr. (Compare with precipitation graphs)

(b) Several ot reservoirs were below FL (See data

0 notes by ?avaro whicb you have)

B-15

S S 0 S * . *_ _A ... * .. *..s.... @0 0 e 0 0

1, 0(c) Flood Q '5 at Dawson of about 2100 ofs has

an R value 3.8 (2100 " 5601 equivalent to

120 yr on old Conn. curve and 55 yr on re-

vised 1965 curves (See graph PL 13)

Items #26 & 28 on Data Sheet are particularly

illuminating*

It doos not need a lively it.lnation to visualize

what would happen to Westville and Now Haven if Dawson

should be overtopped; Norwich failure would be peanuts

comparatively.

A brief discussion of pertinont data and situations

follows. Also there are prints of sections of dams,

0 precipitation graphs and various other graphs that I

usod or are pertinent to this Invostigation for general

* Information or checking purposes.

Please excuse the informality ani crudness of the

matter submitted, the objective betng to reduce oosts to

th3 mIhnmum.

I would observe that Mr. Navqro, 14r. Ferris and Mr.

Eeynolds of the New Havon Water Co. were most cooperative

as was Mr. Thomas of tih) U..'. (ieuo:,ical Survey.

My recommaondation Is that th. Now Haven Water Co*

be advi3od that their consultuig v,'itieers should inves-

tis;ate the entire syste*, with particular emphasis on

B-16

. .0 0._ * S

,~ Mr, William Pe Sander 4~-June 26, 165

conditions at Glen and Dawson,, And submit corrective

measures*

Yours very truly,

JWC/4r J. 'd. Cone

Enc: Part IIPhotos (11)

A

B-17

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NEW HAVEN WATER COMPANYNoW HAVEN, CONNECTICUT 0650 0

J 'Il-. 1 T, W.E -Esou

CON-,,JSSIUNMr. William Wise, Director, 1 REC E Fi r/--- ---Water Resources Comission, J IState Office building,Hartford 15, Conn. SW R.D.....

Dear Mr. Wise: .... ..........

ILAs promised we are writing to report pro.ress to date on thestudies of our West River System.

Oyr consultants, Malcolm Pirnie Eng neers, have lathered allavailable data concerning the 1955 hurricane storms and the characteristics .of the West River and Sargent River watersheds, reservoirs, and dams. This Iinformation has been supplemented by a field investigation by them.

They are usinj the unit hydrograph method of analysis. Theirfirst step is to reconstruct one of the 1955 storms and route it thronghthe watersheds. If, by this procedure, they can produce, within reason,the conditioni which were observed at the various dams during the 1955 . 0storms, the characteristics of the unit hyIrolraph and the procedure canbe considered verified.

Vith the procedure verified, th^,. plan to route a 100-year stormand a 1000-year storm thwu~h the reservoir .,stemas. The results of theseruns ,'*11 be used to determine what inproveme-nts to recommend. Stability I _I anal"ses will be made after the desi-n hydratl-tc conditions have beendetern ned.

To date our consultants have completed their -eneral hydrologicinvestigations; have constructed unit-hydro:raphs to be used with thedraina:'t areas tributary to each dam and reservoir; have selected andarrancd rain'all data to be used for the 1955 storm and for the 100-yearand llgO-year storms and have computed in-flow hydrographs into each of theres, ivoi rs for the 1915'storms. Ratin curves are being computed for eachspillway. When these computations are completed the 1955 storm will berout-d through the system in order to verif,; the procer ._ir.

Our conrult-,nts advise that their fiwl report should be readyby !,t, end of September.

Y ,r- vr tru,"NF!4 ILAVEIT WATER COMPANY.

0 ~selI A.NevaroCIS, WW ngli neer

-Ij 1.55 0B-18

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. ... 0 .0 0. 0_.0. ._ .0 .. . . . . .. . . . " . . . . .. ..

NEW HAVEN WATER COMPANYNEW HAVEN, CONNECTICUT

REPORT ONFLOOD FLOWS AND SPILLWAY CAPACITIES -

WEST RIVER SYSTEM DAMS

- JANUARY 1967

-W

MALCOLM PIRNIE ENGINEERSOffice Park

226 Westchester AvenueWhite Plains, New York 10604J

B-19

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0

I. PURPOSE AND SCOPE

On June 26, 1965, Mr. Joseph W. Cone, Dam Consultant to .

Ithe Water Resources Commission, reported to the Commission

the results of an assignment by the Commission to study the

present condition of the dams owned by the New Haven Water

I Company on the West River and its tributaries. Mr. Cone's

report, which will be sUmmarized later, was not intended to

be a comprehensive study of the dams in question. It indi-

cated that spillway capacities on four of the five dams

concerned were less than considered desirable, and recommended

that a more detailed engineering study be made by the Company

to determine deficiencies, if any, and the necessary cor-

rective measures.

Subsequently, Malcolm Pirnie Engineers was authorized to -

study the adequacy of all spillways in the West River system

and make recommendations as to changes and additions.

B-20

_ ,0 .... 0 • . •... . .. 0 0

2

II. DAMS INVESTIGATED

The dams under investigation store water for the West

pRiver or Woodbridge system and are located on the West andSargent Rivers of Connecticut. The dams impound runoff

from a total drainage area of 13.6 square miles, the southern

extremity of which lies approximately one and four-tenths

miles north of the New Haven city line. The system has a

yield of about 10 million gallons per day. - •

The following tabulation contains pertinent data con-

cerning the dams and reservoirs studied.

6 Bethany Watrous Chamberlain Glen Dawson

Date Built 1892- 1914 1899- 1907 18891931 1959

Drainage Area S.M.

Direct* 3.8 3.3 4.0 1.7 0.8

Total 3.8 7.1 4.0 5.7 13.6

Res. Cap. MG 650 725 894 197 325 7

Res. Area, Acres 105 109 102 26 69.5

Spillway Data

Elev., MSL 432 22- 398 220 -5.5 . . ..

Freeboard, Ft. 4.25 5.0 12.0 4.0, 6.0

Length, Ft. 80 70 50 40 80

*Does not include drainage area above upstream dam.

Additional data are as follows:

Bethany - Gravity masonry section built in 1892, faced with -__

concrete in 1931. Downstream embankment. Bpl21way on dam

_. .... _ 0 . . .0 o 0o _ _ _ _

J

crossed by bridge of limited headroom. Downstream channel

not limiting.

Watrous - Lies two miles downstream from Bethany Dam ....

on West River. Watrous is a gravity concrete section with

an earth embankment on the downstream side. Its spillway is

not obstructed and the channel leading from the spillway is - -

not limiting. Watrous Dam is about 0.6 miles upstream from

Lake Dawson.

Chamberlain - Chamberlain was built of earth on the

Sargent River branch of the West River, with a masonry core

wall, in 1891. It was raised 35 feet and a new spillway was

constructed in 1958-59. It has a side channel spillway with s

ample downstream channel capacity.

Glen - Glen Dam is a gravity concrete structure on the

Sargent River one and one-half miles below Chamberlain Dam. .

Dawson - Dawson Dam was built in 1889. It is an earth

structure with a concrete core wall. The spillway channel

was damaged in the 1955 hurricane flood and rebuilt shortly S

thereafter.

The West River continues to flow in a southerly direction

below Lake Dawson, passing through Konolds Pond and between

New Haven and West Haven to Long Island Scund, about six-miles

away.

B-22

-... . ..

sk. iIII. REPORT OF STATE WATER RESOURCES COMMISSION

Mr. Joseph Cone's report considered flood experiences

I at each of the West River damns and estimated the flows that

spillways of these dams could carry safely. The report did

not include a detailed study and was in effect a reconnais-

L sance study of the structures in question. A detailed study

was left up to the Company, and this present report concerns

more detailed studies of each dam and spillway.

Mr. Cone's conclusions are summarized as follows:

(1) A storm with a recurrence Interval of 1,000 years

probably should be used in studying dam safety.

(2) The most severe storm of record in the West River

area, that of October 1955, was probably one with

a recurrence interval,-of less than 100 years.

(3) The West River drainage area is approximately at

the lower size limit of the Connecticut Formula.

Flood flow from its smaller parts can probably be

better estimated using the formula below:

Q RF xLF xFF x9A 2/3

L Q = Flow, cfs0_RF = Rainfall FactorLF = Ground Cover FactorFF = Frequency FactorA = Area in Acres

(1Spillway capacities of the five reservoirs of the

West River system are estimated as follows:

B-23

5

Dam cfs csm

Bethany 1,980 540

* Watrous 2,660 380 0

Chamberlain 6,300 1,525

Glen 1,120 195

Dawson 2,870 215

(5) The report concludes as follows:

(a) Bethany should be able to carry a flow of over

4,000 cfs and with a 1,000-year storm would be

overtopped by one foot.

- (b) Watrous spillway will barely carry flood from 9 0

its direct watershed and hence is deficient in

capacity by the flow from Bethany or 4,000 cfs.

* (c) Chamberlain has an adequate spillway. ' 0

(d) Glen was nearly overtopped in 1955 and will be

overtopped by a greater storm.

1 (e) Dawson was nearly overtopped in 1955 and can

be expected to be overtopped with any greater

storm.

(6) It recommends a comprehensive study with corrective -

measures to be applied as soon as possible.

B-24

FROM SECTION V: FLOOD FLOWS) 13

These estimates indicate that at peak flow the Bethany

Heservoir is about 1.3 feet below the top of the dam;

Chamberlain Reservoir is about 7.7 feet below the top of the

dam; and Watrous Reservoir is about 0.3 feet below. Both

Watrous and Bethany are masonry sections and little or no

freeboard is essential, although some is usually allowed to -

prevent waves from splashing over the dam.

The spillway at Glen Dam will presently carry about

1,200 cfs before the dam is overtopped. It is estimated I S

that this storm is of the magnitude that has a recurrence

interval of about 300 years. The 1,000-year storm, as used

-" in this report, would produce a reservoir elevation about 0

1.0 foot above the top of the dam. The dam is of masonry and

could withstand overtopping. The overflow would be volumin-

* ous and would result in considerable erosion below the dam.

In our opinion the risk is too great to continue operation

of this reservoir with tbe present spillway capacity even

though overtopping of this reservoir is not likely to cause

danger to life and the property.of others below the West

River system. Methods of increasing spillway capacity are.. . . . --- - 0

dt.;cussed in ' lction VI.

Dawson spillway will carry a flood of 3,620 cfs with no

f'reeboard. With 2 feet of freeboard, the minimum we consider

fea-ible fo:' this dam, the 3pillway will carry about 1,900 cfs.

ihe estimatc2. outflow for the 1,000-year st,;rm is 5,300 cfs.

In our opin.lo, the Dawson spill-,iy can safely carry a storm

with a frequncrnc of about 150 years. Dawson is the lowest

B-25

0 6. • _ . . • . .... 0 0 0 0 0 0 0 0 _0

14

dam in the series on the West River systcm and is located

above a populated and developed area that probably would

suffer severe damage and possible danger to life in case

of failure. As it is an earth dam that must not be over-

topped, even by wave runup, its spillway capaciLy must be

*increased materially. Methods of doing so are discussed in

Section VI.

Westfield, Massachusetts, Storm of 1955

To investigate the effect of a storm similar to the

Westfield, Massachusetts, storm of August 1955, the Norfolk,

Connecticut, recording rain gage record of the storm was

adjusted to equal the 24-hour readings taken at the Westfield

gage and the resulting storm was transposed to the West River

watershed. Hydrographs were constructed for runoff from the

storm,which flows were routed through the reservoir system.

This storm produced much more water than the 1,000-year

storm, and the peak flows are of the magnitude of 50 per cent

L greater. The following tabulation compares the two storms.

Outflow from Reservoir, cfsReservoir 1,000-Year Storm Westfield Storm

. Bethany 1,500 2,200 /190 ""Chamberlain e'C,' 1,800 2,700 "

Watrous 2,800 4 300. .2 &

Glen 2,300 A3,800 Po'Dawson 1,M5,300 4 8,700 34:o

Figure 2 shows a visual comparison of the two storms in

terms of outflow from Dawson Reservoir. -

"B-26

S S S .e S 0 0 0 S

h 000

(5~00O lves/field, moss /I

-6000 -/000 yea/--

14000

2000

0 /0 4 oJ0oLI ?7we (h'ou.--.r)

AWA4SON'

COMPAIsoIv 0,,c Oor7-.zO,Y/-/D/0G/RAPH5 -/000 Ye-AfRJTQRM VS /4'FF/l=1LD,MA4SS. s5 To,9 A4

B-27

15

The Westfield storm produces outflows within the spill-

way capacities of Bethany Ind Chamberlain. Watrous is

overtopped by about 0.2 feet. In view of the uncertainty of S 0

the estimates and the construction of the dam, this slight

overtopping does not appear of great concern.

I?. Both Glen and Dawson would be overtopped to a greater B

extent than in the 1,000-year storm, and this factor has

been kept in mind in considering methods of increasing spill-

way capacity discussed in Section VI. S

* J

i 0 O

B-28

0 0 0 0~0 0 0 0 0 _0 0 0 0 0 0 0

- - - -

16

Vl. METHODS OF INCREASING SPILLWAY CAPACITY

In our opinion there is.no need to consider modifica-

5 tion of the Bethany, Chamberlain or Watrous spillways to 0 0

provide additional capacity to carry flood flows. Serious

consideration must be given to the effect of probable future

flood flows at Glen and Dawson spillways.

Glen Dam

For Glen spillwa.to carry the 1,0.00-year flood without * .0

overtopping the present dam and ,wthout, use of theblowoff

will require in i A~ np the S illway length to 78 feet or,

withrsentenjath, -increasing the freeboard to 6.0 feet.(/er/5.P 6

To carry the Westfield storm requires increasing the spillway. .. ..... . . . .. -. -. . . . . . *... . .. . .. . . ... .. . ,

length toj -et or-the. freeboard to 9.2 feet using the a,,; (present length. The factor of safety against overturning for ".

Glen Dam, as determined in Section VIII, is as small as can

be tolerated when the water level is 4 feet above the spillwayj~~crest, so raising the dam does not appear feasible. ... ...

It appears possible.to add the required length by build-Ing an extension to the existing spillway at a 90 degree

L angle or by installing an auxiliary spillway at the north end

of the dam. Either is feasible, although there are advantages

to confining such work to the present spillway location so a

common discharge channel may be used. The existing spillway

may also be replaced by a side channel spillway 95 feet long.

Glen Reservoir has a small storage capacity and is

principally used to provide workable head conditions for

B-29

the Sargent River portion of the West River system. Lower-

ing the normal reservoir level 5 feet would decrease storage

*by about 40 million gallons and would reduce the yield of

the West River system a very small amount. At full reservoir,

pressures would be reduced about 2 psi.

Although the urgency of providing more outflow capacity

for Glen is not as great as for Dawson, it is advisable to

modify the Glen spillway at an early date. The least expen-

sive method of doing so appears to be by lowering the

spillway crest as shown in Figure 3 to permit passing future

extreme floods without overtopping the non-overflow section

of the dam. For the 1,000-year storm used in our sty.._the...-.-...-

spillway should be lowered at least 2 feet. For the

* Westfield storm it should be lowered 5 feet. In view of the

uncertainty of all methods of eztimating future flood conditions

and the minor effect on system operation if this plan is

followed we recommend lowering the Glen sp!!Jwa

Tiie cost of cutting down and reshaping the spillway crest is

estimated to be of the magnitude of $5,000. The work does not

require extenslvc preparation and can be started at any time. S

Crest gates could be installed on the spillway after

lowering to maintain present storage. They wold add approxi-/ •

mately $100,000 to the cost.

An alternate method of obtaining the necessary spillway

capacity while maintaining present water levels would be to

rebuild the spillwoy. This alternate will cost about $100,000,

approximately the same as the crest gate alternate. Given the

B-30

.... * . . . . .. 0 _ O . .• .. .. O _.• 5 5 0 0

-- ~ ~ ~ D 226~ ~ WZv

&o,?TrE/ 204, (o'

-- c r~~ LI. ZI& SPILWASC L :14#=I- p

- K,-,' - iop. j/. 2/

18

two choices, we prefer extending the fixed spillway rather

than utilizing crest gates with their attendant maintenance

and operation problems.

Dawson Dam

The spillway at Dawson Dam now is 80 feet long. To

IL carry a flood of 5,300 cfs, without freeboard, the spillway

must be lengthened by about 40o feet. With 2 feet of free-

board, the length must be increased 140 feet. To carry the

Westfield storm of 8,700 cfs without freeboard would require

extending the spillway 115 feet. Extensions beyond about

30 feet by projection of the spillway line are difficult -

because of topographical conditions. Extending a side channel-

spillway northward alongside of the reservoir would neces-

sitate channel construction through the existing spillway ---channel. Detailed studies have not been made, but preliminary

examination indicates that it will be less costly to lower the

existing spillway: If the spillway is lowered 5 feet and [~ -

2 feet of freeboard are allowed, it will carry a flow of about

7,200 _cfs. This is more than the 1,000-year flood of 5,300

c-fs and less~ than the Westfield storm of 8,700. The Westfield

storm would reduce freeboard to about 1 foot. The cost'' of

lowering the spillway 5 feet would be somewhat greater than

lowering it 3 feet, which would allow no freeboard for the__

1,000-year storm, but the major difference would be in rock

excavation, and the added safety would be worth the difference

in cost. We recommend lowering the spillway 5 feet as shown

in Figure 14, at an estimated cost of $125,000. B-32

S0 S 0 0 0 0 0 0 00 0 5 0 0 0

I SIV' A t

Step

J /

Co.'[c .± .,•/

iI - +

I 1 u p

L ... Co'i_ -_- _

t/

L )/ 0

EZ15 0 Ea0 O

P -Oposed Ale AS/0 b

S~C/t<NA A

-160

1060 6/ /00 40~~W

/ C,~f ~.'r2C

ZCWE IN 1.AW5-., SPIL60Y B-3

19

Dawson Reservoir is at too low an elevation for direct

service, and its yield is now pumped into The system when

needed. Lowering the spillway 5 feet would reduce storage I o

by about 110 million gallons and wou].d reduce slightly the

yield of the West River system. Other considerations may

indicate the need of maintaining water levels at present -0-

flow line elevation. If so, crest gates may be installed

at a cost of approximately $150,000, making the total cost

of the work approximately $275,000. •

B0

--

20

VII. EFFECT ON YJRLD OF LOWERING SILTWAY ORESTS

If Glen spillway is lowered 5 feet, storage is reduced 0

about 40 mg. If Dawson is lowered 5 feet, the loss in

storage is 102 mg. Total storage loss if both spillways are

lowered is 142 mg. 0

During the 1964-66 dry period, water produced from

May 20, 1964, to November 1, 1966, averaged about 8.1 mgd.

The minimum amount left in storage in February 1966 was about S

626 mg. With no reserve allowance, and assuming that the

reservoirs refill by next June, the supply could have been

F. increased about 0.6 mgd and the system yield would be 8.7 mgd. L

If 20 per cent storage was allowed for emergency reserve, the

*yield would be approximately 8.2 mgd.

The loss in storage by lowering the spillway would have

decreased yield over this dry period by 0.13 mgd. During wet

periods when the system refills each year, loss of yield

would be greater and, in a year when Dawson is below flow line

level for a 6-month period,-the reduction would be about 0.8 mgd.

B-36

00

u 21

VIII. STABILITY OF DAMS

* Stability of each dam in the West River system has been

investigated. Chamberlain and Dawson are earth dams with

satisfactory sections. Bethany and Watrous are masonry dams

£ with massive earth backup on the downstream side. There is

no question as to their stability.

Mlen is an exposed masonry dam and its stability has

been investigated against over turning. *Because of the con-

struction, it is safe against sliding. When full to the crest

of the non-overflow section, presently 4I feet above the

spillway elevation, the factor of safety against overturning

is 1.18. If the darn Is raised one (1) foot, which could be

easily done, the factor of safety decreases to 1.11, as shown

* in Figure 5. Since uplift is probably less than assumed, we

estimate that the darn is safe against overturning as long as

the maximum water level does not exceed the top elevation of

the existing non-overflow section. We do not recommend an.,

increase in height.

B-37

.j >•... /.-.

"- // 1'.0o

'LI -." *.•L i I I1 ' '

-- memo..

* It"

/ I--* > I '. ..

II / I

I

-'CAiLE I" -20'

B-38I J L .li i __ I• .. . .. .. J.. . . . . . .. -.. .m - -... .. . . . -_ -- t . ."

__ • S 0 _ 0 0 0 • 0 0 _ S S 5 0 0 0

,.- .,"

Ir

F270OO 75'YrR.-lv 26x3.

-9

3B-3

VNWPW4mm W.S/O5~ O0A

22

IX. RECOMMENDATIONS

We recommend that the Water Company increase the capa--

city of' the spillways at Glen and Dawson Dams by lowering

each of these spillways approximately five (5) feet. Since

a major storm may occur at any- time, the work should be done

as soon as possible.

B-40

00

,, .... .... .. .... .. .. ...... CO MilISSIUN

NEW HAVEN, CONNECTICUT COIVEI,, RECEIVED •

NOV 1 67[z ~ANSWE It ....

MEMORANDUM REPORT TO WATER COMPANON FILED. ........

INVESTIGATION OF THE EFFECTS OF A FLOODPRODUCED BY THE MAXIMUM POSSIBLE STORM

ON SPILLWAYS OF WEST RIVER SYSTEM

AUGUST 2, 1967

* 0

The effect of the "maximum possible storm" on the West

R.iver. System Is reported in this merao'':mdum.

The "naximu:' possible storm" eri, s 1.','.Ined and

qu;,it.3 tatively estimated in U. S. Wor-h. r Fur-.!au :iydro-

,,..-",,,Iogical R..h.port No. 33 e!nt toc1 "0?: onr1. Variation

oV ' Probable ".1'hxirum Pr'cipitat ioL >.;t .)if t,e 105th

.j.crld an for Areas from 10 to 1,000 -pilco rI," and Dura-

tions of 6, 12, 211 and 18 Hours." The report defines the

"i.axtmum possible precipitation" as "the critical depth-

d:.-itlon-aroa ra'nfall relation for a oarticular area during

V:. . ..... ith, i thu year that ,would re.m lt It ' ;ondittons

u , i- a tual storm in tle vcgton ,.re .n :,',..Sed to

...;ent th 1,t critic.il, moteorol -',Ji.al. ,il t.ons that

• .. , ldrI.-d ,tobable fC oC, ,uTn(,.''

A:" ho;n o)r !'xhlb.t 1, t.c rae i' ". 2 iu ..d for the

'.'.,:: 1", vev' Syst.,,r analy..es foe f'or ,hv'", ': ) ! ant) 1.2 hours

or. :Ili "1r0i or 11') ."dlq ;lI''t i, (''i' ', , ' 1olt. ll!Q~t eV . 'e

t o' tho v : In ty .r : ltvn, "',, ..: ,:u;. The hourly I - .

B-41

... • _* _! _.o 0 • 0• _... 0 .0 0 • .0 * 0 0 0 0!

o st I A - ji vj. L 1 .c LL%.

Figure 4, page 32 of U. S. Department of 1.he Tinterior

publication "Design of Small Dams." 'Ihr. ~It.,'ibution is a

comparatively severe one with 50 per cent of the 6 hour total

3 falling within 1 hour.

The sequence in which the hourly totals were arranged

Is in accordance with the rcqcommendat ton made on page 50 in

"Design pf Small Dams." The arrangement of the 12 hourly

izncre-:,ents is 11, 9, 7b, 5, 3, 1, 29 )4, 6, 8, 10, 12, where

the number represents the order of magnitude with the lowest

number representing the largest magnitude. This, arrangement

CX',vs a flood greater than one based on the ( ris ;ijmntiof that

the Freatest hourly increment of raln ocur; 'luring the

-O it hour11 or a storm

:,II 2 eftcc t iv 0, runo ff-uroducinr i ~~ a estimated

1),-. A iractuing 1 inch initial intlt'r!A a 0.1 inch per

ho-ir t.hcreaf'tur fromn the total rainfall .

In order to pass the unusually highi flows for the "maximum

no,7Fble sitormn," several modifications of both the length and

c~s;height of spillways were tried. "tp1llw.a.y rating curves

::i1 ;(tige aelc ty curvoo for eactihi tho Nvi 1 vozuervol rZ are

:;Qnon Eh1 L2 and Exhibit 3, rcpc. y y

T'he ttril.t --hyd z'cgz'aphs and routhn;t '.uu: employed are

--no outl meol In cuir ronei't of .Iaiii ri It t',)6( . rir:tailed

~ at cu -%re shim rn on LExhittit 11 , p:t -os I tlh ough8

Yho 1iza'1c1--oiit f'low ecurvez3 for ea;,rh of thie v'OJ;'voI rs are

, o-n on Exhi i t 53, pages 1 thuh . A;, tit i-.Imii tcant

S ~ C r'ct 11- 11 )ht aln ('rlom 1,-i) w~Kw~~t, , the 1i

B-42

-9 ~O *= @.

fAiU .&i. I 42 b,' UW& us& &4Aa,.- .L . ) jU't: al L I I.L UV rne same

with a spillway 250 feet long.

The'hnaximtum possible" flood outflows at epch of the West

River reservoirs and the condittonisi ', t,pe I I Iways are

summarized below:

Dam Peak Spillway Free- Maximum ttr:ad (ft.)Discharge Board Over Over Dames ft. Spillway Crest

r Chamberlain 7200 12.0 10.8 -1.2

Glen 9665 9.0* 11.3 +2.3

Bethany 7350 4.25 5.2 +1.0

Watrous 15400 5.0 7.1 +2.1"

DawsonE0' Spillway 26,260 11.5' 13.8 +2.3

M 250' Spillway 26,260 11.0' 9.0 -2.0 •

O *Froeb :trd above proposed nIoW :ill clevot I!) n

B-4I L ,+~ ... _+. ,

0.. +

•B-43

* _ _ _9~~ 0 0 _ 0 6_ 0 0 S 0 0

' NEW HAVEN WATER COMPANYNEW'HAVEN, CONNECTICUT

DESIGN REPORT -

DAWSON SPILLWAY

Our report of January 1967 recommended lowering thespillway of Dawson Dam five feet to increase its capacity 0 o

* to approximately 7,200 cfs. This report was reviewed bythe Water Resources Commission of Connecticut whichrequested that an investigation be made of the effect ofrouting a maximum possible flood through the West RiverSystem. This study was made. -.

The following tabulation shows the estimated floodsthat would occur under varying conditions.

Estimate of Record - 2,300 cfs1000 year storm - 5,300 cfsTransposed Westfield Storm - 8-700 cfs 0Maximum Possible - 27,000 cfs

C Conditions at the dam and downstream from the dam-were considered and it was concluded that any storm mater-ially exceeding the 1000 year'storm would cause great5 damage downstream and that the damage would not be materially .greater if Dawson Dam were breached during the storm. Afterreviews with the Water Company it was decided to submit plansto the Water Resources Commission that would pass the 1000year storm and such.additional flow as could be carried bywidening the spillway a reasonable amount. o 0

!" We have made studies of alternate designs of thechannel downstream from the spillway. Our January 1967 re-.port showed a-chute type spillway with a slope of about 4 percent. The chute must be curved in plan to suit the topography.At the higher flows investigated unstable flow conditionsaround the curve result in very high water elevations at theouter edge of the curve with transitory waves which create inour opinion a dangerous hydraulic condition. To be sure of'containing the waves would require very high chute wallsand a very elaborate energy dissipation device at the end ofthe-chute would be required. * O

Our studies indicate that a very much safer design willresult with less than criticalslopes in the outlet channeland that-the cost will be less.

I' ,..,,g ' I ,, 1 I , ,. I B-44_

' , I , ... .1.1

I, *. * i i ,., *-I

• .I .*." --.

0 0 S 00 0 0 0 0 0 0 0 0 0 0

*-The stepped channel design which results from the useof flatter slopes can be built in various widths. Thenarrowest feasible width is found to be 50 feet. At thiswidth the critical depth which'will occur at each drop inthe channel floor is approximately 7 feet for the 1000 year - -

storm of 5300 cfs. 0

The present spillway is 80 feet wide. We find itfeasible to increase this width to 110 feet. Therequired head on an ogee spillway for the 1000 year stormis 5.5 feet. Using this as a desip storm and a freeboard of3.5 feet the spillway crest should be 9. feet below the top of

U *. the dam or at Elevation 155.0.

At the above crest elevation and no freeboard the spill-way will carry 10,400 cfs which is:more than the 1000 year orWestfield transposed storms. At thls flow critical depthin the 50 foot wide channel is about 11 feet.

If the spillway is lowered to increase flow the down-stream channel must be widened, otherwise the flow over thespillway is reduced because of submersion.

r In our opinion the most reasonable design is for astepped spillway channel 50 feet wide with a capacity of10,400 cfs flowing full and an ogee spillway 110 feet long.The spillway will cArry the 1000 year storm with a freeboard

'.* :of 3.5 feet and with no freeboard will carry a storm of 10,400cfs. p t

To completely contain a flow of 10,400 cfs would requireextending the 50 foot wide spillway channel about 340 feet.The proposed new channel intersects the existing paved channelabout 204 feet from the overflow crest. If the new channelis terminated at this point, and the old channel used for

3thebalance of the distance, flood flows up to approximatelyhistoric floods could be carried. Larger floods including the1000 year storm would not be contained in the old portion of

* the channel. However no damage to the dam could occur and theconvex side of the curved channel is on the uphill side withbed rock apparent at shallow depth. All erosion that could 9occur is on Water Company land and the Water Company prefers totake the risk of damage. Therefore the spillway channel willbe built to discharge into the existing channel as shown on theplans.

Fig. I shows hydraulic details of the design. D -

MALCOLM PIRNIE ENGINEERS

S 0

B-45

•7_ 0 _.O

......... ...

aU . 0 ~ , -

a. >

aa.at'. :III0 Iu A-,

Ilal ~ i a aij Ia a

I a aill. ~ 'aB-46

IV . i a ~,fl, _Now"a

I'O14 D-4 STATZ OF CONNECTICUTWATER RESOURCES COMMISSION '_"

State Office Building S SHartford, Connecticut

APPLICATION FOR CONSTRUCTION PERMIT FOiK DAN

New Haven Water Company :.C.CI4 . / I __

,.',I,.: Box 1470

New Haven, Connecticut ', 203-772-2550

Loc. Li,; Ot Structure: New Haven and

._ Woodbridge __ _ __ _ _ _ Shown on USGS Quadrangle Vicinity, Con.

;Xr. of Stream West River at 1 inches south of Lat. 4 1 0-22'-3-

and 3 inches east of Long. 73°-00'- - .

.~:.:,-(ills for reaching site from nearest village or route intersection:(.skttch on reverse side)

See Attached Plans -_._......_.._

a application for: (New Construction) (Alte~tion) (Repair) (Removal)(check one or more of above)

.- nd is to be used for: Stora7e

. of Pond: width- 1,000 f t . length 3,500 ft. area 69.5 acres5.0' without temporary flashboard.'C

' h of water inmediately above dam: 7.5' with temporary_ flashboard '

S th of dm: 900 ft,

f s1!ilway: a0 ft.

* .f abutments above spillway: 9 ft,. ____.--_.----

F tpillway construction: Concrete

,'ike construction: Existing earth structure with a concrete core wall

* .,, section will be set on: (Bedrock) (Gravel) (Clay) (Till)(check one of above)

*u. r,: Spillway section will be set on bedrock or compacted dam

material including old core wall.

," Signed: ., A9 r(owner)

Name of Engineer, if any MALCOLM PIRNIE ENGINEERS

L: how details of B47:.ction on reverse side

___ __ 0 0 0 0 0 0

0. 0 -- do"

Show only features of samnple wi~ich areaplicable and diinenajions which roiflect your 1I -

SSKETCH N. LOCATION SKETCs-

See Attached Plans S

IL

LAN SITE PLAN ..

1 1= 900'

?ROPOED POD -rp = 3,500'PROOSE PN TW= 110' ,

VSECTION SPILLWAY SE~CTION

a = 18'b ovaries 10' to 13'

f c -1c - 60'0 e =12'

fh = 3.5t

b h = 5.5' (1,000 year storm)Concrete Conc I r = varies 0 to 10'

.. /Zt~a/ lede ~NOTE...774 1e d 9If there are two methods of dischurgo _Show

* .(;TION DIKE SECTION (Eitng)

m m = 10'

p = 6.5' with temporary flashboard-.

LI v P = 9.0' without temporary flashbo

u ~ u = 5' min. (varies)v 50' max. (varies) B-48

_~~~~~f. 0 .

August 20, 1968

MEMO TOO File

FROMs William He O'Brien III

SUBJECT a Lake Dawson Dam - Woodbridge0

In reviewing the design for the modifications of the subject dam,

the following additional information was obtained from a Mr. Raymond Dugandzic,

of Malcolm Pirnie Engineers.

The flashboards are designed to fail with water elevation at 159.5

* (two feet above the top of the Flashboards). This is based on a yield stress S

of 35,000 PSI and ultimate strength of 60,000 PSI for the pipe steel.

The proposed spillway will pass the Westfield storm with a freeboard '.=1.58 feet.

B-4

0 0 O

PNTRDEPARTMENT MESSAGE SAVE TIME: 1IdudWvilite meSS&gSC die acceptIable.STO-ICIta-se Is carbon if yon really wteed d copy. it iy~eu'rftew, ismoie lari lioNe. __

TO FieAGENCY DATEMrh 2, 197,--. Water Resources Coimmission.

FROM WliMH 'resII AGENCY TELEPHONE

WiliamH. 'Bre~ II ~ ej~ e. CnzmnissiorL--Civil Engineer

SUBJECT Dawson Lake DamWobjg - --

On Feb. 24, 1971 the undersigned inspected the subject

dame The work appears to have been well done and in conform-ance with the approved plansg however, there were several leaks,one of which was quite substantial thru the construction jointsof the bottom of the exit channel at the base of the ogee spill-way. The water level was approximately 6 inches below the con- -

crete crest of the dam and about 3 feet below the top of theflashboards. These leaks may become substantially greater witha full pond. These leaks however do not appear to effect thesafety of the structure.

There was just a slight flow in the new 6 inch outletsthrough the concrete headwall into the existing stream at thewest end of the dam.

Civil Engineer

WHOsljg

B-50

41 9 * *

Much 31, 1971

Mft Joseph A. NovatoChief EngineerNew Hewn Water CaQany 0 eNew Haven, Connecticut 06506

Res Dawson DomWoodbridp

Doea W. NvesO

On February 24, 1971 the undersigned inspected the subjectdom. There were several leaks, one of which was quite substantial,through the construction joints of the bottom of the exit channelat the base of the , Ogea spillway. The water level was approxi- -.

ately six inches below the concrete crest of the dam.

It is assumed that the presence of these leaks indiateeithera malfunction of the six inch perforated concrete drain pipes underthe spillway channel slab or else there is a water barrier preven-ting water from reaching this perforated pipe. It appears that thepossibility exists of a piping condition under the spillway section. * *We therefore do request information on the as built conditions ofthe epillway as defined in Section b-b on sheet four of five of theapprowd plans. The notations indicate that the spillway sectionmay be set on rock in same areas and on compacted dam material inothers. We would like a definition of these areas. Thank you for *this information. .

Very truly yourst

William H. O'rien, IIICivil Engineer

B-51

*- 0 0 • _9.. • .• • 0 0 0 _ 0 0 S

r g .. : *A - I S

NEW HAVEN Wate r COMPANY100 Crown Street I New Haven, Connecticut / 06506 (203) 772-2550

April T, 1971

State Water Resources Ccm.,ssionState Office BuIldingHartford, Connecticut 06115

Attention: Mr. William H. O'Brien, III

Civil Engineer •

Dear Mr. O'Brien:

This is to acknovledge your letter of March 31, 1971and to confirm my call to you in regard to Dawson Dam.

We inspected the spilway several weeks ago and willmake another inspection in warmer wather, at which time,we -ill vrite you further.

I have requested AS-built prints from our Consultantsand will forward one set to you when I receive them. The

* entire length of the spillwy section was carried down torock. There were five (5) keyed expansion Joints, eachbeing sealed by a rubber expansion seal with the usualcircular sections or bulbs on both sides.

Very truly yours, ..NEW HrAVEN WATER COKPAZIY

eph A. Novaroce President-Engineering 3 9..

JAJt:Jc,.p

,. STATE WATER RE,;OURCES

"' E C F.. I. V z

.. ' APR 121971,. ,ANSWERED

/, " ",)" ',REFERRED LI •

FILED

B-52

S .. . 0 " 0 ... 0 0 0 _ 0 o.0 0 0 * • 0_

7Project_ Lolkt J-o..'inn -7P nF- Dkol A1y2 Sheet.B~O ______ of

Computed By / iAChocked By 6*JDate 7

Field Book Ref. Other Refs. ________________ Revision* __________

StCL~Ce jrorn ..~is+c~n ffC ow 0i 0

*side of vi Wt EhvtV-I, 0'" ow&Asice o$ t1%*I l~e- VcdI O'-t'- 0")

-ckI%01 es OS W ~ ~ tII o0f 42 of OCLIVII

W CA

0'164000 002oo2-

1' 63.20 S 163.9

163-56 300, 163.9

,41 13.56 12

4o3.o' 164.1

1,6 14.5 Scoo

20 434 550' 16:5.8 7

25 1644.1 600161

30 ~164.56.'

'4o164.7 IS~O

LeJ4 wintoJI I6B- 53

RD-A144 158 NATIONAL PROGRAM FOR INSPECTION OF NON-FEDERAL DAMS 2/'2

LAKE DAWSON DAM (CT 8 .(U) CORPS OF ENGINEERS WALTHAMp IMR NEW ENGLAND DIV AUG 79

UNCLASSIFIED F/G 13/0 3EIIwuumhIIIIIIIIIIIIIIIIIlfflfflf'IIIIIIIIIIlfflffl

"11.0 lial 8 jWnil- M Q2

II I1.25 111111.4 11.6

MICROCOPY RESOLUTION TEST CHARTNATION4AL BUREAU Of STANDARES-1963-A

%L

* S

I SO

a 0 0

* 0APPENDIX C

DE'T'A IL PHOTOGRAPHS

* 0

* p.

* p. I* ~

p -

m~-~-~ ~

- ~ 0 9.

- 0 0z4

0 0 0U

viii .0 0

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US AMY NGIEERDIV.NEWENGANDLake Dawson DamCOARPSNGEE OfV NEW ENGLAND NATIONAL PROGRAM OF West River

CALTHNGNEES NC INSPECTION OF Woodbridge, Connecticut L ... q

WALLINSPORD, CONN. NON- FED. DAS CE* 2? 660 xA.__________DAMS__ IXTE May ' 79 PAGE

-_ IQ

PHOTO 3- View of natural spillway channel from downstream. 9 0

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PHOTO 4 -Seepage on right slope of spillway discharge channel. 0

O RPS O ENGINEERS NEENGLAND NATIONAL PROGRAM OF Lake Dawson Dam

WALTAM, ASSINSPCTIO OF Woodbridge, ConnecticutCAN ENGINEERS INC. INPETONO 27 660 KAI WALLINGFORDCON. NON- FED. DAMS ~ My79PGC-

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PHOTO 6 -Low level outlet discharge channel downstream of dam.Note minor seepage on the left slope of the channel. 0

CORPS OF ENGINEERS NATIONAL PRGAMO West RiverDa

WLHMMASINSPECTION OF WobigConnecticut 0CAHN ENGINEERS INC. 127 660 K

WALLINGFORD, COWNM N ON- FED. DAM S ~ My'9PG -

L ENINE EiT Ma '7 0AG C-3SS S 0 0 S

£PHOTO 7 -General view of spillway channel and weir from I 0downstream.

PHOTO 8 -Seepage through left stone masonry wall adjacent 0to concrete spillway channel.

US ARMY ENGINEER Div. NEW ENGLAND ILake Dawson DamCORPS OF ENGQINEERS INATIONAL PROGRAM OF West RiverI

WALTMAM , MASS.I ISECINO Woodbridge, Connecticut S

CAHN ENGINEERS INC. INSPEC7I660OFWALLINOR CONN.____

____27_660__

WALINGORO COU.NON- FED. DAMS DATEMay '79 PAGE C-_4

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NON FE.AM

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PRELIMARY GUIDANCE

FOR ESTIMATING

MAXIUM PROBABLE DISCHARGES

PHASE I DAM SAFETY

INVESTICATIONS

New England bivision* Corps of Engineers

Match 1978

r XIM. PROBABLE FLOOD FFLOWSNED RESERVOIRS

Prjct_ .A. HPF(:fs) (sq. ml.) cfsfsq. mi.H 1. tall Meadow Brook 26.600 17.2 1,5462. East Branch I5,00 9.25 1,6753. Thomaston 158,000 97.2 1,6254. Northfleld Brook 9,000 5.7 1.580S. Black Rock 35,000 20.4 1,715

69 Hancock Brook 20,700 12.0 1,725 0* 7. Hop Brook 26,400 16.4 1,6108. Tully 47,000 50.0 94n9. Barre Falls 61,000 55.0 1,10910. Conant Brook 11,900 7.8 1.525

11. Knightvll.e 160,000 162.0 987 S12. LIttleville 98,000 52.3 1,87013. Colebrook River 165,000 118.0 1,40014. Had River 30,000 18.2 1,65015. Sucker Brook 6.500 3.43 1,89516. Union Village 110.000 126.0 87317. North Hartland 199,000 220.0 90418. North Springfield 157,000 158.0 99419. Bell Moumtein 190,000 172.0 1,10520. Towshend 228,000 106.0(278 total) 820

* 21. Surry Hountain 63,000 100.0 63022. Otter Brook '5,000 47.0 95723. Birch Hill 0,00 47.0 50524. Zest Brimfield 73,900 67.5

725.0 We7.5ll 1109525. Veatylleo 38.400 99.5(32 net) 1,200L 26. West Thompson 85,000 173.5(74 net) 1,15027. Hodges Village 35,600 31.1 1,14528. BuffumvIlle 36,500 26.5 t,37729. Mansfield Hollow 125,000 159.0 78630. West Hill 26,000 28.0 928

31. Franklin Falls 210,000 1000.0 21032. Blackwater 66,500 128.0 52033. Hopklnton 135,000 426.0 31634. Everett 68,000 64.0 1,06235. MacDowell 36,300 44.0 825

3" ii

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MAXTHMU1 PROBABLE FT.W SBASED) ON TWICE THE

STANDARD PROJECT FLO(,D(Flat aud Coastal Areas)

River SPF D.A. 1PF(C ) (sq. mi.) (des/sq. mti.)

1. Pawtuxet River 19,000 200 190

L 2. M111 River (R.I.) 8.500 34 500 S

3. Peters River (R.I.) 3,200 13 490

4. Kettle Brook 8,000 30 510

5. Sudbury River. 11,700 86 270 0

6. Indian Brook (Hopk.) 1,000 5.9, 340

7. Charles River. 6,000 184 65

8. Blackatone River. 43,000 416 200

9. Quinebaug River 55,000 331 330

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ESTIMATING EFFECT OF SURCHARGE STORAGEON MAXIMUM PROBABLE DISCHARGES

P 2QP

IL -

STEP 1% Determine Peak Inflow (Opi) from GuideCurves.

*STEP 2% a. Determine Surcharge Height To Pass6i

b. Determine Volume of Surcharge(STORi) In Inches of Runoff.L c. Maximum Probable Flood Runoff In NowEngland equals Approx. 19"', Therefore

Qpz = p, X 11 STOR) I-19

*STEP 3: a. Determine Surcharge Height and"STOR2' To Pass' Qp 2"

b. Average "STORi" and 'STOR?. andDetermine Average Surcharge andResulting Peak Outflow 'QQp3*.

.- A

SURCHARGE STORAGE ROUTING SUPPLEMENTk

STEP 3: a. Determine Surcharge Height and

"STOR2" To Pass "Qp2"

b. Avg "STORi" and "STOR2" and

Compute "Qp3".

c. If Surcharge Height for Qp3 and

"STORAVO" agree O.K. If Not:

STEP 4: a. Determine Surcharge Height and"STOR3" To Pass "Qp3 t

b. Avg. "Old STORAVG" and "STOR3" S

and Compute "Qp4"

c. Surcharge Height for Qp4 and --

"New STOR Avg" should Agree

closely

vi

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SURCHARGE STORAGE ROUTING ALERNATE

QSTOR)

FOR KNOWN Qpi AND 19" R.O.

Qp2 STOR E L.

EL.

vii

"RULE OF THUMB" GUIDANCE FOR ESTIMATINGDOWNSTREAM DAM FAILURE HYDROGRAPHS

opt

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STEP I: DETERMINE OR ESTIMATE RESERVOIR STORAGE (S) IN AC-FT AT TIME OF FAILURE.

STEP 2: DETERMINE PEAK FAILURE OUTFLOW (Qpl). .

Wb= BREACH WIDTH -SUGGEST VALUE NOT GREATER THAN 40% OF DAMLENGTH ACROSS RIVER AT MID HEIGHT.

Yo TOTAL HEIGHT FROM RIVER BED TO POOL LEVEL AT FAILURE.

LSTEP 3: USING USGS TOPO OR OTHER DATA, DEVELOP REPRESENTATIVE STAGE-DISCHARGERATING FOR SELECTED DOWrNSTREAM RIVER REACH.

STEP 4:- ESTIMATE REACH OUTFLOW (Qp2) USING FOLLOWING ITERATION.A. APPLY Qp1 TO STAGE RATING, DETERMINE STAGE AND ACCOPMANYING

VOLUME (VI) IN REACH IN AC-FT. (NOTE: IF V, EXCEEDS 1/2 OF 5,

SELECT SHORTER REACH.)B. DETERMINE TRIAL Q p2'

Qp2 (TRI AL) QP, VSC. COMPUTE V2 USING Q12(TRIAL).

D. AVERAGE VI AND V 2 AND COMPUTE 0p2*

STEP 5: FOR SUCCEEDING REACHES REPEAT STEPS 3 AND 4.

APRIL 1978

*' "

viii

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APPENDIX E

INFORMATPION AS CONTAINED INTHE NATIONAL INVENTORY OF DAMS

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