AD-A145 564 NATIONAL PROGRAM FOR INSPECTION OF NON-FEDERAL DAMS

COBALE MOUNTAIN RESER..(U) CORPS OF ENGINEERS WALTHAM

MA NEW ENGLAND DIV MAR 80

UNCLASSIFIED F/G 13/13 NL

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MICROCOPY RESOLUTION TEST CHART

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I CONNECTICUT RIVER BASINRUSSELL, MASSACHUSETTS

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J- COBBLE MOUNTAIN RESERVOIR DAM

M A 00068,

IPHASE I INSPECTION REPORT

NATIONAL DAM INSPECTION PROGRAM

8 ~SEP 1 7 1984

DEPARTMENT OF THE ARMY

NEW ENGLAND DIVISION, CORPS OF ENGINEERSWALTHAM, MASS. 02154

MARCH 1980TkW document h beft a provefC"4 pu!i11c reJfte wmd salemI5dW"butjon Is unftae,- 84' 09 05 098

I I

IINI ASSITFnSECURITY CLASSIFICATION OF THIS PAGE fWbhn Dole Entered)

READ INSTRUCTIONSREPORT DOCUMENTATION PAGE BEFORE COMPLETING FORMI. REPORT NUMBER Ia. GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER

4. TTLE and ubtiis) . TYPE OF REPORT A PERIOD COVERED

Cobble Mountain Reservoir Dam INSPECTION REPORT

NATIONAL PROGRAM FOR INSPECTION OF NON-FEDERAL 6. PERFORMING ONG. REPORT NUMBER

7. AUTHOR(&) S. CONTRACT OR GRANT HUMBER~.)

U.S. ARMY CORPS OF ENGINEERSNEW ENGLAND DIVISION

9. PERFORMING ORGANIZATION NAME ANO ADDRESS 10. PROGRAM ELEMENT PROJECT, TASKAREA 6 WORK UNIT NUMBERS

11. CONTROLLING OFFICE NAME AND AOOft9SS 12. REPORT DATE

DEPT. OF THE ARMY, CORPS OF ENGINEERS March 1980NEW ENGLAND DIVISION, NEDED 13. MUMSER OF PAGES424 TRAPELO ROAD, WALTHAM, MA. 02254 120

14. MONITORING AGENCY NAME 6 ADORESS(UI different frow Coalweilia Office) 1S. SECURITY CLASS. (at this eport0)

UNCLASSIFIED116a. DOECLASSIPICATION/OOWNGRADING

ICHROUL;

Ill. DISTRIBUTION STATEMENT (of ths Ropepa)

APPROVAL FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED

17. DISTRIBUTION STATEMENT (of the abstact enteeg in Block "O. it iteai Russ., Aheow)

III. 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.

19. KEY WORDS (Continue evi roewe. oldse if ROtcosoay enill identfy by IMO.b asmbee)

DAMS, INSPECTION, DAM SAFETY,Connecticut River BasinRussell, Massachusetts

20. A MST RACT (Can 10ue an revees side it neee4 inw d eny a" 041ech~ 111 609Aww ej

-'The dam is a sluiced earth fill between massive rock toe embankments. The top of thedam is about 730 feet long and about 250 feet above the valley botton at the toeThe dam is generally in GOOD condition, well maintained, with no excessive ordangerous leakage. The preliminary hydrologic and hydraulic analysis for thisLARGE size, HIGH hazard dam indicated that the spillway is adequate. The testfIld is the PMF and for a tributary drainage area of 45.8 square miles ofmountainous terrain which Is more than 80% forested, the unit discharge rate is 440

LDD FA00#1? 1473 1,-ITI1ONs oo/Nov se is OBSOLErt

DEPARTMENT OF THE ARMYNEW ENGLAND DIVISION. CORPS OF ENGINEERS

424 TRAPELO ROAD

WALTHAM. MASSACHUSETTS 02254

REPLY TOATTENT ION OF:

NEDEDD6198

Honorable Edward J. KingGovernor of the Commonwealth of

Massachuset tsState HouseBoston, Massachusetts 02133

Dear Governor King:

Inclosed is a copy of the Cobble Mountain Reservoir Dam (MA-00068) PhaseI Inspection Report, which was prepared under the National Program forInspection of Non-Federal Dams. This report is presented for your useand is based upon a visual Inspection, a review of the past performanceand a brief hydrological study of the dam. A brief assessment isincluded at the beginning of the report. I have approved the report andsupport the findings and recommendations described in Section 7 and askthat you keep me informed of the actions taken to implement them. Thisfollow-up action is a vitally important part of this program.

A copy of this report has been forwarded to the Department of Environ-mental Quality Engineering, the cooperating agency for the Commonwealthof Massachusetts. In addition, a copy of the report has also beenfurnished the owner, City of Springfield Water Department, Mass.

Copies 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 Quality Engineering for your cooperation in carrying outthis program.

Incl WILA .oDSNAs stated Colon. , Corps of Engineers

Actin Division Engineer

COBBLE MOUNTAIN RESERVOIR DAM

MA 00068

CONNECTICUT RIVER BASINRUSSELL, MASSACHUSETTS Accession For

NT 7 ' 71 A'

Codes1 . .. vai : , or

PHASE I INSPECTION REPORTNATIONAL DAM INSPECTION PROGRAM

NATIONAL DAM INSPECTION PROGRAMPHASE I INSPECTION REPORT

Identification No.: MA 00068Mass. DPW No.: 1-7-256-11Name of Dam: Cobble Mountain Reservoir DamTown: RussellCounty and State: Hampden County, MassachusettsStream: Little RiverDate of Inspection: November 15, 1979

BRIEF ASSESSMENT

The Cobble Mountain Reservoir Dam embankment is located in Russell,Massachusetts on the Little River about thirteen (13) miles above itspoint of discharge into the Westfield River at a point that is about ninemiles above its confluence with the Connecticut River. This facility islocated where the three Towns of Blandford, Granville and Russellabut, with the diversion tunnel inlet and the upstream toe dam lying inBlandford and the emergency spillway and intake control tower locatedin Granville. The dam is a sluiced earth fill between massive rock toeembankments. The top of the dam is about 730 feet long and about 250feet above the valley bottom at the toe. A spillway with a reinforcedconcrete overflow weir 135 feet long standing six (6) feet above thespillway floor has been cut through rock about 1500 feet south of thedam. An intake and power tunnel 10 feet by 11.5 feet has been driventhrough rock about 3000 feet south of the dam. A diversion tunnel10.5 feet by 10.5 feet is located through rock about 1000 feet northwestof the dam.

The dam is generally in GOOD condition, well maintained, with noexcessive or dangerous leakage. However, the stability of the embank-ment in modern engineering terms, particularly with respect to seismicloading and the potential for liquifaction of the hydraulic fill has notbeen analyzed, and for this reason, the dam has been rated as FAIR.

The preliminary hydrologic and hydraulic analysis for this LARGE size,HIGH hazard dam indicates that the spillway is adequate. The testflood is the Probable Maximum Flood and for a tributary drainage areaof 45.8 square miles of mountainous terrain which is more than 80%forested, the unit discharge rate is 1440 CFS/square mile. The inflowto the reservoir from the maximum probable flood would be about 66,000cfs. When routed through the reservoir by preliminary methods, themaximum outflow would be about 38,000 cfs which would flow over thespillway weir with about 15.3 feet of head. This leaves about 4.7 feetof freeboard to the top of the dam.

The spillway has a capacity of approximately 145% of the routed testflood outflow.

Failure of the dam could cause floodwater to race down the Little Rivervalley as much as 90 feet deep. The City of Westfield could be floodedup to about elevation 168 ft. MSL. This is about twenty (20) feetabove Main Street and Broad Street and would reach nearly to NobleHospital. About 5,000 acres of Westfield and Southwick might be flooded.Dikes along the Westfield River could be topped by several feet andmuch of the Merrick area of West Springfield and the Eastern StatesExposition grounds could be flooded as well as much low land in Agawamalong the Westfield and Connecticut Rivers.

The recommendation for seismic stability and liquifaction analysis shouldbe initiated within one (1) year of receipt of this report by the Owner.The remedial measures listed in Section 7 should be implemented withintwo (2) years of the receipt of this report by the Owner.

4%

1 042WtPOWERSMASSACHUSETTS REGISTRATION 23106

This Phase I Inspection Report on Cobble Mountain Reservoir Dam (MA-00068)

has been revieved by the tmndersigned Reviev Board members. In ouropinion. the reported findings, conclusions. and recommendations areconsistent with the Recomended Guidelines for Safety Inspection of1b_=., and with good engineering judgment and practice, and is herebyaubsitted for approval.

!'ARAIAST KATESU.N, IKDERGeotechnlcal Engineering BranchEngineering Division

CARNEY N. TERZI., DM]ERDesign BranchEngineering Division

RICHARD DIB(NO 0 HARM0Water Control Branch.ngineering Division

APP VAL EECOHO3NDs

Chief, Ragzeer 8 Biviseln

. "

PREFACE

This report is prepared under guidance contained in the RecommendedGuidelines for Safety Inspection of Dams for Phase I Investigations.Copies of these guidelines may be obtained from the Office of Chief ofEngineers, Washington, D.C. 20314. The purpose of a Phase I Investi-gation is to identify expeditiously those dams which may pose hazardsto human life or property. The assessment of the general condition ofthe dam is based upon available data and visual inspections. Detailedinvestigation, and analyses involving topographic mapping, subsurfaceinvestigations, testing, and detailed computational evaluations are be-yond the scope of a Phase I investigation: however, the investigation isintended to identify any need for such studies.

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

It is important to note that the condition of a dam depends on numerousand constantly changing internal and external conditions, and is evolution-ary in nature. It would be incorrect to assume that the present condi-tion of the dam will continue to represent the condition of the dam atsome point in the future. Only through continued care and inspectioncan there be any chance that unsafe conditions be detected.

Phase I inspections are not intended to provide detailed hydrologic andhydraulic analyses. In accordance with the established Guidelines, theSpillway Test flood is based on the estimated "Probable Maximum Flood"for the region (greatest reasonably possible storm runoff), or fractionsthereof. Because of the magnitude and rarity of such a storm event, afinding that a spillway will not pass the test flood should not be inter-preted as necessarily posing a highly inadequate condition. The testflood provides a measure of relative spillway capacity and serves as anaide in determining the need for more detailed hydrologic and hydraulicstudies, considering the size of the dam, its general condition, and thedownstream damage potential.

The Phase I Investigation does not include an assessment of the needfor fences, gates, no-trespassing signs, repairs to existing fences andrailings and other items which may be needed to minimize trespass andprovide greater security for the facility and safety to the public. Anevaluation of the project for compliance with OSHA rules and regulationsis also excluded.

TABLE OF CONTENTS

Section Page

LETTER OF TRANSMITTAL

BRIEF ASSESSMENT

REVIEW BOARD SIGNATURE SHEET

PREFACE

TABLE OF CONTENTS ii-iv

OVERVIEW PHOTO v

LOCUS PLAN 1 vi

LOCUS PLAN 2 vii

REPORT

1. PROJECT INFORMATION

1.1 General 1-1

a. Authority 1-1b. Purpose of Inspection 1-1C. Scope 1-1

1.2 Description of Project 1-1

a. Location 1-1b. Description of Dam and Appurtenances 1-2

1) Embankment 1-22) Spillway 1-33) Intake 1-34) Diversion 1-3

C. Size Classification 1-4d. Hazard Classification 1-4e. Ownership 1-4f. Operator 1-4g. Purpose of Dam 1-4h. Design and Construction History 1-5

i. Normal Operational Procedure 1-6

1.3 Pertinent Data 1-6

a. Drainage Area 1-6b. Discharge at Dam Site 1-6

ii

Section Page

2. ENGINEERING DATA

2.1 Design Data 2-1

2.2 Construction Data 2-1

2.3 Operation Data 2-1

2.4 Evaluation of Data 2-1

3. VISUAL INSPECTION

3.1 Findings 3-1

a. General 3-1b. Dam 3-1C. Appurtenant Structures 3-1d. Reservoir Area 3-2e. Downstream Channel 3-2

3.2 Evaluation 3-2

4. OPERATIONAL AND MAINTENANCE PROCEDURES

4.1 Operational Procedures 4-1

4.2 Maintenance Procedures 4-1

4.3 Evaluation 4-1

5. EVALUATION OF HYDRAULIC/HYDROLOGIC FEATURES

5.1 General 5-1

5.2 Design Data 5-1

5.3 Experience Data 5-2

5.4 Test Flood Analysis 5-2

5.5 Dam Failure Analysis 5-3

6. EVALUATION OF STRUCTURAL STABILITY

6.1 Visual Observation 6-1

6.2 Design and Construction Data 6-1

6.3 Post- Con st ruction Changes 6-1

6.4 Seismic Stability 6-1

iii

Section Page

7. ASSESSMENT, RECOMMENDATIONS AND REMEDIALMEASURES

7.1 Dam Assessment 7-1

a. Condition 7-1b. Adequacy of Information 7-1c. Urgency 7-1

7.2 Recommendations 7-1

7.3 Remedial Measures 7-1

7.4 Alternatives 7-2

APPENDICES

APPENDIX A - INSPECTION CHECKLIST

APPENDIX B - ENGINEERING DATA

APPENDIX C - PHOTOGRAPHS

APPENDIX D - HYDROLOGIC AND HYDRAULIC COM-PUTATIONS

APPENDIX E - INFORMATION AS CONTAINED IN THENATIONAL INVENTORY OF DAMS

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112 0 SNATIONAL PROGRAM OF INSPECTION OF NON-FED. DAMSMILES

-S." - '%o lp LOCUS PLAN 2FEET

FROM: GENERAL HIGHWAY MAP, CBL ONANRSRORDM(A008 USLHAMPDEN COUNTYCOBEMUTIREEVIDA MO68RSEL

HAMPDEN COUNTY MASSACHUSETTS

:SCALE: AS NOTED

4DATE : MARCH 1990

PHASE I INSPECTION REPORT

COBBLE MOUNTAIN RESERVOIR DAM

SECTION 1

PROJECT INFORMATION

1.1 General

(a) Authority

Public Law 92-367, August 8, 1972, authorized the Secretaryof the Army, through the Corps of Engineers, to initiate a NationalProgram of Dam inspection throughout the United States. TheNew England Division of the Corps of Engineers has been assignedthe responsibility of supervising the inspection of dams within theNew England Region. Tighe & Bond/SCI has been retained by theNew England Division to inspect and report on selected dams inMassachusetts. Authorization and notice to proceed were issued toTighe & Bond/SCI under a letter of October 24, 1979 from ColonelWilliam E. Hodgson, Jr., Corps of Engineers. Contract No. DACW33-80-C-0005 has been assigned by the Corps of Engineers for thiswork.

(b) Purpose

1) Perform technical inspection and evaluation of non-federaldams to identify conditions which threaten the public safeLyand thus permit correction in a timely manner by non-federalinterests.

2) Encourage and prepare the states to initiate quicklyeffective dam safety programs for non-federal dams.

3) Update, verify, and complete the National Inventory ofDams.

(c) scope

The program provides for the inspection of non-federal damsin the high hazard potential category based upon location of thedams, and those dams in the significant hazard potential categorybelieved to represent an immediate danger based on condition ofthe dams.

1 .2 Description of Project

(a) Location

Cobble Mountain Reservoir Dam is located on Little Riverabout thirteen (13) miles from its confluence with the WestfieldRiver which is at the east end of the City of Westfield. Cobble

1-1

Mountain Dam is west of the City of Westfield about 8.9 miles fromElm Street and Main Street via Granville Road and Wildcat Road inthe Town of Russell. The spillway and intake tunnel are in theTown of Granville. The dam is shown on U.S.G.S. topographicquadrangle "Blandford" and the spillway on U.S.G.S. topographicquadrangle West Granville. The dam is located at latitude N42'-07'-34JJ, longitude W 72'-53'-37ii. See Locus Plans 1 and 2.

(b) Description of Dam and Appurtenances

The dam consists of a hydraulic fill earth embankment about730 feet long and 250 feet high. A free overflow concrete spillwayweir and outflow channel is located about 1500 feet to the south,beyond Cobble Mountain. An intake tunnel control structure islocated south of the spillway about 3000 feet south of the dam. Adiversion tunnel intake control structure is located about 1000 feetnorthwest of the dam.

1) Embankment (B-1, B-2, 8-3, B-4, B-5, B-6, B-7, B-8,B-9, and B-i0)

The dam embankment, which has no appurtenant structureswithin its mass, is a sluiced hydraulic fill with a 1510 feetbase width along the stream and 50 feet wide at the top witha top length of about 730 feet. A rock diversion dam with animpervious zone seal at the upstream face forms the upstreamtoe of the dam. A rock foundation drain fills the bottom ofthe valley to a depth of about 30 feet from a point about 200feet downstream of the cutoff walls to the concrete arch toedam at the downstream toe of the dam. The concrete toe damis provided with three 4 ft. x 6 ft. weep holes to allow exitof foundation drainage. Topsoil was stripped up to 125 feetwide and a concrete cutoff wall was placed to a depth of atleast five (5) feet into sound ledge rock across the valley andup to an elevation of 955. A second cutoff wall was placedacross the valley bottom up to an elevation of about 765. Inaddition, extensive foundation grouting was carried out alongthe cutoff walls. Sluiced hydraulic fill was placed up toabout elevation 945 and a puddled core up to elevation 956.The upstream and downstream embankment slopes were designedand constructed with variable slopes which begin fairly flat atthe toe and increase in steepness toward the top of the dam.The embankment slopes vary from 1 on 4.72 and 1 on 4.52 atlow levels to 1 on 1.5 above about elevation 959. The designdrawings (Appendix B) indicate the design top of dam elevationwas 965, however, during construction this was increased anda roadway was constructed across the top of the dam. Damembankment construction was carried up to elevation 969.5and road construction completed the embankment to elevation973. Measurements made during this inspection indicate thatthe lowest point along the top of the dam is presently aboutelevation 972±.

1-2

Substantial rock fills were provided at both upstreamand downstream toes of the embankment. The upstream facewas covered with five (5) feet of rock to elevation 910 and 15feet of rock above that elevation. The downstream face wasprovided with a five (5) foot thick cover up to elevation 860.Then the rock cover thinned to two feet thick from elevation910 to elevation 956. Above elevation 956 the rock facebecame thicker as the sides were steepened to raise the topfrom design elevation of 965 to final top of road at elevation973.

2) Spillway (B-i, B-1i, B-12, B-13, and B-14)

The spillway is an open rock cut up to fifty (50) feetdeep and fifty (50) feet wide at the bottom. A reinforcedconcrete overflow weir 135 feet long controls overflow. Weircrest is at elevation 952.0 feet NGVD. Concrete abutmentsrise six feet above the weir crest which stands six feet abovethe sand floor approach channel and concrete lined spillwaychute. The concrete lined spillway chute narrows to aboutfifty (50) feet wide at the roadway bridge which is 175 feetdownstream from the weir and extends past the bridge to apoint about 210 feet downstream from of the weir.

The spillway bridge is an elliptical concrete arch thirty(30.00) feet wide with a sixty (60) foot span at spring lineand an elevation of 967 NGVD at the soffit of the crown.

(3) intake (B-16, B-17, B-18, and B-19)

The intake control tower is a 32 ft. x 28 ft. reinforcedconcrete structure housing 20 ft. x 20 ft. trash rack androller gate and hoisting machinery. The structure also con-tains a six (6) foot diameter control valve and its emergencyhydraulic operating pump, as well as a 7 ft. x 13 ft. air ventand tunnel access shaft. Principal operating power is electric,remotely controlled at the powerhouse and filter plant.Emergency power for the roller gate hoist is a battery at anupper level of the control tower. Emergency operation of the6 ft. diameter valve is by a hand operated hydraulic pump.

A 10.0 ft. wide x 11.5 ft. high concrete lined tunnelwith an invert at elevation 830 and 218 feet long connects thecontrol tower with the reservoir. A concrete lined tunnel10.0 ft. wide x 9.33 ft. high and 6350 ft. long connects thecontrol tower to a 10 ft. diameter steel power plant inlet thatdelivers water to the hydroelectric power house at the IntakeReservoir.

(4) Diversion (B-i5)

A concrete lined 10.5' x 10.5' horseshoe section tunnel1600 ft. long allows stream diversion and reservoir draining

1-3

around the dam embankment. The tunnel floor at the reser-voir inlet is at elevation 754. Control is via two 42 in.diameter steel pipes and valves at elevation 753.25 ft. MSL atcenterline. Each pipe is fitted with a 39-3/4 inch rotaryvalve by Escher-Wyss with 4 in. bypass and then a 42 in. x30 in. Lamner-Johnson discharge regulator discharging througha brick wall into the discharge tunnel which has an air ventand separate stairway from the valve room to the surface.The valves are operated by hand wheels from an operatingfloor above the valve room.

(c) Size Classification

Both the structural height of 250 feet and capacity of 96,500acre feet put this dam in the LARGE size classification.

(d) Hazard Classification

The extensive flooding and great loss of life in Westfield andWest Springfield that would result from failure of this dam placesit in the HIGH hazard classification. There is a high potential forseverely damaging hundreds of homes with the attendlent possibleloss of hundreds of lives as well as numerous highway and railroadbridges, industrial and commerical areas, and other structures.

(e) Ownership

Cobble Mountain Reservoir Dam is owned by the City ofSpringfield, represented by its Board of Water Commissioners.The address is as follows:

City of Springfield Water DepartmentCity Hall, Court SquareSpringfield, Massachusetts 01105Tel: 413-787-6060

(f) Operator

Cobble Mountain Reservoir Dam is operated by the City ofSpringfield, acting through its Water Department.

The operator at the dam site on a daily basis is:

Mr. William YorkBorden Brook ReservoirGranville, Massachusetts 01034Tel: 413-357-8733Emergency Tel: 413-787-6206

(g) Purpose of Dam

The purpose of Cobble Mountain Reservoir Dam is to providea water supply reservoir for the City of Springfield, Massachusetts.The reservoir also provides for hydroelectric generation.

1-4

(h) Design and Construction History

Cobble Mountain Reservoir Dam was designed by Mr. AllenHazen of New York and built during the period 1927 to 1932 undermultiple construction contracts,

Notes of Mr. James L. Tighe who reviewed the design andconstruction for the Hampden County Commissioners indicate thatclose control was maintained over the quality of the material beingsluiced into the hydraulic fill core. On May 20, 1930 sluicingoperations were stopped because of excessively fine material.Construction methods and borrow areas were reorganized andconstruction resumed on September 20, 1930. Construction pro-ceeded steadily thereafter with adjustments of borrow material fromtime to time and, on occasion, removal of unsatisfactory materialfrom the core. Core construction was completed October 17, 1931and rock paving was completed on January 30, 1932 when thereservoir water leve( was at elevation 832. Diversion tunnel gateswere closed on August 25, 1931 to start reservoir filling. TheCity of Springfield started using water from Cobble MountainReservoir on December 1, 1931. Road construction was completedat a later date.

A seepage weir with a crest length of 4.0 feet was constructeddownstream of the dam. James L. Tighe's notes indicate thatseepage increased as the reservoir filled. The reservoir reachedan elevation of 938.7 on January 31, 1933 when flow over theseepage weir was 0.98 ci's. Seepage flow during 1933 and 1934correlated closely with reservoir levels. On June 16, 1934 withthe reservoir at elevation 939.6, the seepage flow was 0.86 cfs.

The dam was designed to have a top elevation of 965.0 feetMSL, a top width of 50 feet, and variable embankment slopes witha maximum slope downstream of 1I on 2a and 1 on 2-3/4 upstream.The top of the dam was raised during construction to a finalelevation of 969.5 before road construction by increasing thesteepness of the upper part of the dam to 1 on 11- both upstreamand downstream.

The spillway was designed to have a crest in the concretefloor at elevation 945.0 with flashboards mounted on steel pipesseven feet high to elevation 952.0. The concrete spillway weir wasactually constructed to an elevation of 952.0 with no provision forflashboards. At the same time, the concrete spillway abutmentswere raised from elevation 955.0 to elevation 958.0.

Maintenance grouting has been carried out in the diversiontunnel to control seepage. In 1973, the spillway weir wall wasreconstructed and the concrete outflow channel floor and side wallswere resurfaced and weepholes were installed.

1-5

(i) Normal Operating Procedures

The dam, intake works, supply tunnel, diversion tunnel anddiversion control structure are owned and maintained by the Cityof Springfield. Daily operation of the power plant which regulatesreservoir level is under control of Northeast Utilities. The operatingagreement specifies minimum reservoir levels for each month of theyear based on annual water demand by the City of Springfield.Minimum daily discharge required to meet the requirements of theCity of Springfield is released. Within these limits the powercompany operates to use all inflow to the reservoir. Normallythere will be no flow over the spillway. Normally, the reservoirwill be within about a foot of the spillway crest in late spring andat its lowest level in late fall. There are no special operations forflood control purposes.

1.3 Pertinent Data

(a) Drainage Area

The drainage area tributary to this dam is about 45.8 squaremiles including 8 square miles tributary to Borden Brook Reservoirwhich is upstream of Cobble Mountain Reservoir. Most of the areais steep and mountainous with good forest cover.

Controlled flow from the watershed of the Littleville Flood ControlDam can be diverted to the Reservoir via a pumping station locatedin Russell.

(b) Discharge at Dam Site

1) Outlet Works

Normal discharge from the reservoir is via a ten (10)foot diameter concrete lined tunnel which delivers water to ahydroelectric powerhouse. The invert of the tunnel intake isat elevation 830.0 MSL. Inlet controls consist of a 6 footdiameter valve and a 20 ft. x 20 ft. steel roller gate whichare installed in series with the steel roller gate on the upstreamside of the intake structure. The intake tunnel has a capacityof approximately 1120 CFS with the reservoir level at thespillway test flood elevation of 967.3.

A reservoir drain and diversion tunnel consisting of a10 - ft. x 101 ft. concrete lined tunnel has inlet invert atelevation 754.0 feet MSL. Control is via two 42 in. diametersteel pipes. Each pipe discharges through two valves inseries into the outlet tunnel. The diversion tunnel has acapacity of approximately 3780 CFS with the reservoir level atthe spillway test flood elevation of 967.3.

1-6

2) Maximum Known Flood

The maximum flood record at this site occurred on August19, 1955. Peak inflow has been estimated to be about 19,600cfs. Peak outflow via spillway and intake tunnel has beenestimated at 12,850 cfs. The reservoir stage reached amaximum elevation of 959.1 feet NGVD, which is 7.1 feetabove the spillway crest.

3) Ungated Spillway Capacity at Top of Dam

The capacity of the spillway above the crest elevation(952.0 feet NGVD) to the top of the dam (elevation 972.± feetNGVD) is about 55,000 cfs.

Elevation 972± is the low point along the roadway overthe top of the dam as field measured during this inspection.

4) Ungated Spillway Capacity at Test Flood

The capacity of the spillway above the crest elevation(952.0 feet NGVD) with the reservoir at test flood elevation(967.3 feet NGVD) is about 38,000 cfs.

5) Gated Spillway Capacity at Normal Pool

None

6) Gated Spillway Capacity at Test Flood

None

7) Total Spillway Capacity at Test Flood

The capacity of the spillway above the crest elevation(952.0 feet NGVD) with the reservoir at test flood elevation(967.3 feet NGVD) is about 38,000 cfs.

8) Total Project Discharge at Top of Dam

Total project discharge including spillway, intake tunneland diversion tunnel with reservoir at top of dam elevation(972 feet NGVD) is about 60,000 cfs.

9) Total Project Discharge at Test Flood

Total project discharge including spillway, intake tunneland diversion tunnel with reservoir at test flood elevation(967.3 feet NGVD) is about 42,900 cfs.

(c) Elevation (feet above MSL NGVD)

1) Stream bed at toe of dam: 722±

1-7

2) Bottom of cutoff: 710±

3) Maximum tailwater: Unknown

4) Normal pool: 952.0

5) Full flood control pool: not applicable

6) Spillway crest: 952.0

7) Design surcharge: 958.5Based on:

a) Design spillway crest 945.0

b) Design top of dam 965.0

8) Top of dam

a) as built 973

b) existing low point 972t

9) Test flood surcharge: 967.3

(d) Reservoir (length in feet)

1) Normal pool (952.0 NGVD): 21,000

2) Flood control pool: Not applicable

3) Spillway crest pool (952.0 NGVD): 21,000

4) Top of dam (972 NGVD): 22,600

5) Test flood surcharge (967.3 NGVD : 22,300

(e) Storage (acre-feet)

1) Normal pool (952.0 NGVD): 70,000

2) Flood control pool: Not applicable

3) Spillway crest pool (952.0 NGVD): 70,000

4) Top of dam (972 NGVD): 96,500

5) Test flood pool (967.3 NGVD): 91,200

(f) Reservoir Surface (acres)

1) Normal pool (952.0 NGVD): 1134

2) Flood control pool: Not applicable

1-8

3) Spillway crest pooi (952.0 NGVD): '1134

4) Top of dam (972.1 NGVD): 1445

5) Test flood pool (967.3 NGVD): 1385

(g) Dam

'1) Type: Hydraulic fill between rock toes

2) Length: 730 feet

3) Height: 250 feet

4) Top width: 50 feet

5) Side slopes: upstream: 1:4.72 to 1:1.5downstream: 1:4.52 to 1:1.5

6) Zoning: sluiced hydraulic corerock fill toe upstream and downstreamrock facing upstream and downstreamrock riprap upstream upper zone

7) Impervious core: sluiced hydraulic fill

8) Cutoff: 3 ft. wide x 3 ft. high concrete at least 5 ft.deep in good rock. One wall full width ofdam, one wall across valley bottom

9) Grout curtain: 15 ft. deep full valley width and 8 holes25 feet deep

h) Diversion and Intake Tunnels

Diversion Intake

1) Type: concrete lined concrete linedrock bore rock bore

2) Length: 1550 feet 7500 feet

3) Closure: Concrete Inlet control48 feet long structure

4) Access: Gatehouse shaft Gatehouse shaft

5) RegulatingFacilities: 2-42"1 steel pipes 20' x 20' steel

each with 1 roller gaterotary valve and 6' diam. valve &1 retracting plug turbine controlsvalve @ power plant

1-9

i) Spillway

1) Type: Concrete wall 6 ft. high, 4 in. x 4 in. chamferedfront corner, rounded downstream corner of3 ft. wide top.

2) Length of weir: 135.0 feet

3) Crest elevation: 952.0 NOVO

4) Gates: none

5) Upstream channel: sand and gravel

6) Downstream channel. concrete linedfor 210 ft.then rock cut

7) General: Channel floor drops 15 ft. in 200 ft. andnarrows from 135 ft. to 50 ft., then 1%slope in rock cut.

()Regulating Outlets

Diversion Intake

1) invert 754.0 830.0

2) Size 2-42 in. 20 ft. x 20 ft.in parallel 6 ft. diam.

3) Description 40 in. rotary roller gateretracting plug valve

4) Control mechanism handwheels electric hoisthydraulic operator

1-10

SECTION 2 - ENGINEERING DATA

2.1 Design Data

Design data shown on eighteen sheets of design plans and reportsof the County Commissioner's Engineer and Review Board indicate thedam was designed in accordance with good engineering practice of thetime.

The site was well mapped and investigated for foundation andembankment material. Project facilities were located to assure maximumintegrity of the dam embankment. There were no abrupt changes inthe regular "V" shaped valley profile that would indicate potentialproblems. Drainage was specifically provided for. Generous spillwaycapacity for that time - 20,000 cfs - was provided at a site removedfrom the embankment. Generous, secure diversion and intake workswere provided.

2.2 Construction Data

The diary and notes of James L. Tighe who inspected the work forthe Hampden County Commissioners, other review commission reports,and published reports indicate that construction was carefully supervisedto assure that good quality material was properly placed during con-struction.

2.3 Operation Data

The dam, intake works, supply tunnel, diversion tunnel anddiversion control structures are owned and maintained by the City ofSpringfield. Daily operation of the power plant which regulates reservoirlevel is under the control of Northeast Utilities. The operating agreementspecifies minimum reservoir levels for each month of the year based onannual water demand by the City of Springfield. Minimum daily dischargerequired to meet the requirements of the City of Springfield is released.Within these limits, the power company operates to use all inflow to thereservoir. Normally there will be no flow over the spillway. Normallythe reservoir will be within about a foot of the spillway crest in latespring and lowest in late fall. There are no special operations for floodcontrol purpose.

Maintenance records are available from the City of Springfield.Detailed records of operation including reservoir elevation, discharge,etc., are available from Northeast Utilities, the power plant operatior.

2.4 Evaluation of Data

(a) Availability

Plans of the dam as built and basic information were readilyavailable from the Springfield Water Department. Additional reportswere readily available in publications of the New England WaterWorks Association. Notes and design plans and reports were

2-1

obtained from the files of Tighe & Bond/SCI, Easthampton, Massa-chusetts. Records of materials placed during construction areavailable from the Springfield Water Department.

(b) Adequacy

The data and information was adequate, when combined withvisual inspection and engineering experience and judgment, toevaluate the safety of Cobble Mountain Reservoir Dam under normaloperating conditions. The data examined for this report was notadequate to evaluate the safety of Cobble Mountain Reservoir Damunder seismic load conditions. There may not be adequate existinginformation for seismic analyses, including the potential for liquifactionof the hydraulic fill.

(c) Validity

Since visual inspection observations confirm the available dataand reports from several independent sources concur on constructionprocedures, it is concluded that the data is valid and reliable.

2-2

SECTION 3 - VISUAL INSPECTION

3.1 Findings

(a) General

Cobble Mountain Reservoir Dam is in GOOD condition at thepresent time.

(b) Dam (see photos in Appendix C)

The dam embankment was found to be covered with rock.The upstream face had a thick layer of rock that obscured anyobservation of underlying material. The downstream face was notas thickly covered and gravel and sand were at the surface insome areas. Brush growth on all faces of the dam had been cutand was obviously well controlled. Drainage through the concretetoe dam was clear and free from silt though red iron oxide sludgewas present in the bottom of pools. Rock debris filled the bottomof the valley nearly to the top of the weep holes. There was nosign of leakage from the face of the dam above the toe dam. Theconcrete toe dam showed weather deterioration up to 2 inches deepon all exposed faces. There was minor seepage from the face ofthe toe dam near the right abutment. The road across the top ofthe dam was in good condition. The road at the center of the damwas observed to be about 1 .8 feet lower than the approaches tothe dam.

This difference is believed to be due to a combination ofminor settlement of the dam embankment and the formation of avertical curvature in the roadway with the abutment areas beingbuilt up forming the roadway approaches. The abutment areas arebelieved to be somewhat higher than elevation 973 due to theroadway construction.

(c) Appurtenance Structures

The spillway was found to be in good condition. The spillwayweir wall was found sound and in good condition with only minorhairline cracks. Concrete sidewalls and floor had been repaired.Minor seepage was apparent at some joints. Weep holes appearedto be functioning. The spillway bridge was found in excellentcondition. The lower part of the spillway with natural rock wallswas found with considerable growth of brush up to 2 inches indiameter that would have no detrimental effect on the operation ofthe spillway.

The intake control building was found in excellent condition.Submerged portions of Lhe structure and equipment were notinspected. Equipment appeared to be in good condition except fora leaky hand hydraulic pump and a jerry-rigged float well fordepth indication. Emergency operating facilities appeared to beadequate. The diversion tunnel access building was found in good

3-1

condition. Window-,s were boarded for security against vandalism.Only minor leakage and efflorescence was observed in lower portionsof the access shaft. The valve operating floor was in good conditionwith operating handwheels for all valves in position and no signifi-cant deterioration. The valve chamber was found in good conditionwith no significant deterioration. All valves appeared to be operable;no operation was tested. The valves are frequently operated aspart of the powerhouse operation and for routine inspection andmaintenance. The diversion tunnel was found in good condition.Some debris from trespass intruders was observed, but none thatwould prevent normal function. Some leakage and efflorescencewas observed in the 340 feet of tunnel nearest the outlet end.Grout holes and evidence of grouting work was noted. The outletportal showed weather deterioration up to 2 inches deep. A steelgrate barrier had been installed but was not maintained closed.

(d) Reservoir Area

The reservoir and shore line appeared to be reasonably clearup to spillway elevation with only scattered brush and minordebris noted at any location.

(e) Downstream Channel

In the valley bottom downstream of the dam to the powerhousethe only flow is leakage through the dam and rare spillway overflowsbelow the spillway. The valley floor was found to have a substantialgrowth of brush and small trees up to 3 inches in diameter.

3.2 Evaluation

The dam and appurtenances are generally in excellent condition.The maintenance staff is to be complimented.

The following deficiencies or problems may warrant attention:

1. A proper float well and depth indicator should be installed.

2. The hand operated hydraulic pump should be replaced orrepaired and located above possible high water.

3. The diversion tunnel outlet gate should be removed if it isnot to be maintained secure to avoid the possibility thatdebris inside the tunnel may partially block the Outlet andcause back pressure at the valve chamber.

4. The present elevation and profile of the top of the dam shouldbe determined.

3-2

SECTION 4 - OPERATION AND MAINTENANCE PROCEDURES

4.1 Operation Procedures

See Section 1.2(i), page 1-5, for a general description of operatingprocedures.

There are no special operations for flood control purposes or otherdam failure contingencies. The Springfield Water Department has an"Emergency Operations Plan" for dealing with general emergenciesconcerning the water supply and distribution system.

4.2 Maintenance Procedures

Regular maintenance is performed by a full time staff under thesupervision of a foreman who lives at the reservoir. Daily visits aremade to the intake control building and darn site. Regular maintenanceincludes:

Cleaning, lubrication and maintenance of intake control equip-ment;

Cleaning and maintenance of intake control building anddiversion tunnel control building;

Clearing brush from dam, spillway and reservoir area;

General maintenance and debris removal from the reservoir,public areas, and City-owned watershed areas; and

An annual shutdown inspection and maintenance of powerfacilities and intake tunnel.

No formal program of technical inspections by tie Springfield WaterDepartment of the dam, spillway, and diversion tuni-e! is in effect.

4.3 Evaluation

The framework of normal operating procedures is adequate exceptfor the following deficiencies:

1. A downstream emergency flood warning system should bedeveloped and put into operation.

2. Generation and release operations responding to storm orflood warnings should be developed and put into practice.

3. A biennial program of technical inspections by a registeredprofessional engineer qualified in dam design and inspectionshould be developed and put into practice.

4-1

SECTION 5 - EVALUATION OF HYDRAULIC/HYDROLOGIC FEATURES

5.1 General

Cobble Mountain Reservoir Dam is located in Russell, Massachusettson the Little River about 13 miles above its confluence with the WestfieldRiver in Westfield, Massachusetts. The reservoir is about eight mileswest of Westfield at the eastern margin of the Berkshire Hills. Thedrainage area of about 45.8 square miles is in mountainous terrain thatvaries to areas of rolling terrain in upper elevations. Bedrock is micashist covered with glacial deposits of great variety and generally of lowpermeability. About 80% of the watershed is covered with good forest.

Downstream of the dam, the Little River valley has a steep gradientof about 2% and a steep "V" shaped ravine of about 1:2 to 1:1.2 slope.This valley extends downstream past the power house and intake damabout eight (8) miles to the eastern escarpment of the Berkshire uplandat the rolling valley floor of the western part of Westfield. From thispoint, the river flows through a flood plain by the south margin of theCity about five (5) miles to the Westfield River at the east end of theCity of Westfield. The Westfield River winds about 3 miles across aflood plain until it enters the water gap between East Mountain andProvin Mountain at the West Springfield town line. For the next 5 -miles the Westfield River flows through a narrow channel betw"een WestSpringfield and Agawam to the west edge of the Connecticut River floodplain. The Westfield River then flows more than a mile across theConnecticut River flood plain to empty into the Connecticut River lessthan a mile upstream from the Springf ield- Longmeadow town line.

The spillway of the dam is a reinforced concrete wall standing six(6) feet above the approach and discharge channel floor. The spillwayweir is 135 feet long. The discharge chute converges to 50 feet wideand drops in elevation about 15 feet in 200 feet and flows through adeep rock cut 50 feet wide to discharge into the Little River valleyabout half a mile below the toe of the dam.

The flow into the Cobble Mountain Reservoir can be augmented bywater pumped from the Littleville Dam impoundment via a pumpingstation and pipeline to Cobble Mountain. The pumping station is locatedwithin the Town of Huntington and presently is equipped with 3 pumpshaving a combined capacity of about 45 MGD (million gallons per day).Provisions have been made for the future installation of a fourth pumpwhich would increase the capacity by an additional 15 MGD.

5.2 Design Data

Design plans provide a spillway discharge profile and hydrauliccalculations for a flow of 20,000 cfs, reported to be 31- times recordflow prior to design date. Page B-l1 of Appendix B indicates a designwater elevation of 958.5 feet at a 20,000 CFS discharge rate. Reportsindicate that model studies were made of the proposed spillway andmodifications indicated thereby were adopted. The design plans providefor a concrete crest threshhold flush with the spillway floor in an

5-1

unlined rock channel. The spillway was actually constructed withconcrete lining for about 200 feet from the crest through the bell mouthconstruction past the bridge. The six foot high concrete weir wall wasconstructed at a later date. A detailed technical analysis of downstreameffects due to dam failure was not carried out in conjunction with thedesign of this dam based on records available for review.

5.3 Experience Data

Reports made at the time of design indicate flows of about 5700 cfshad been reported at this site and the storm of December 1878 w,,asreported to yield runoff of about 150 cfs per square mile on the WestfieldRiver.

A report by the Springfield Water Department on the storm ofAugust 1955 indicates that the maximum inflow to the reservoir wasabout 19,600 cfs and the maximum discharge was about 12,850 cfs. Thereservoir surface was 7.1 feet above the spillway crest wall. (ReservoirStage = 959.1 NGVD)

5.4 Test Flood Analysis

The objective of the test flood analysis is to assess the capacity ofthe dam to safely pass a severe runoff event of a size commensuratewith the size of the dam and the downstream hazard to life and property.

Guidelines for establishing a test flood are specified in "RecommendedGuidelines" of the Corps of Engineers. The height of this dam (250feet) and storage volume (96,500 acre-feet) put this dam in the LARGEsize classification. The potential for flooding most of the City of Westfieldbelow the elevation of Noble Hospital puts this dam in the HIGH hazardclass. Table 3 of the Corps of Engineers "Recommended Guidelines"indicated that the spillway test flood for a LARGE size, HIGH hazarddam should be the probable maximum flood. The spillway test floodapplied was PROBABLE MAXIMUM FLOOD.

Storm runoff of a maximum probable flood was estimated based onU.S. Corps of Engineers, New England Division "Preliminary Guidancefor Estimating Maximum Probable Discharges." A discharge of 1440 cfsper square mile on the drainage area of 45.8 square miles gives a peakinflow of 66,000 cfs. Routing the probable maximum flood through thereservoir and spillway by preliminary methods assuming the initialreservoir level at spillway crest elevation (952.0 ft. NGVD), results ina maximum reservoir stage of about elevation 967.3 feet NGVD or about4.7 feet below the top of the dam. Maximum discharge over the spillwaywould be about 38,000 cfs.

Analysis was made to evaluate the possibility of overtopping CobbleMt. Dam if Borden Brook Reservoir Dam failed. If Borden Brook Damfailed during a storm with Cobble Mt. Reservoir at elevation 960 (8 feetabove 'he spillway and higher than any past reservoir elevation) themaximum stage of Cobble Mt. Reservoir would be elevation 966.7 ft.NGVD which is 14.7 ft. above spillway crest, and 5.3 ft. below top ofdam. Maximum discharge would be about 35,800 cfs over the spillway.

5-2

It is concluded that the spillway capacity is adequate to preventovertopping of the dam due to a Probable Maximum Flood event.

5.5 Dam Failure Analysis

The hazards and potential damages resulting from failure of CobbleMountain Reservoir Dam were evaluated assuming reservoir level at testflood elevation (967.3 feet NGVD) by the procedures suggested in NewEngland Division, Corps of Engineers "Rule of Thumb Guidelines forEstimating Downstream Dam Failure Hydrographs." No allowance wasmade for" possible clogging of waterways caused by trees and debris.The length of the dam at mid height and the height of the dam weretaken from the plans of the dam provided by the Springlield WaterDepartment. The distance across the valley was taken as 370 feet atelevation 850 and the dam height as 250 feet. The peak dischargeusing the suggested "Rule of Thumb" is 904,000 cfs. This flow wasrouted downstream to the Connecticut River.

The PMF discharge via the spillway of 38,000 cfs will flow downthe Little River canyon at a depth of about 19 feet and velocities ofabout 24 fps. This flow would overtop the Intake Dam non-overflowsections by about six (6) feet probably causing considerable damagethough not complete collapse. There would probably be some damage tothe powerhouse. Dam failure flow could be as much as 90 feet deep inthe valley and would probably destroy the powerhouse and possibly theIntake Dam at hazard area (2).

At Northwest Road - hazard area (3) - the PMF spillway dischargewould probably flood the road across the valley about eight (8) feetdeep and flood two (2) houses and about 250 acres of land. Damfailure flow would inundate Northwest Road as deep as 31 feet, floodingabout six (6) houses and 400 acres.

At Horton's Bridge, where Granville Road crosses Little River' -hazard area 4 - the PMF spillway discharge would probably flow overthe road three (3) feet deep flooding the factory and about five housesabove the dam there. Cobble Mountain Dam failure would result inwater over the road to a depth of about 41 feet and the flooding of themill and about 110 houses.

At the Route 202 bridge over the Little River - hazard area 5 - thePMF spillway flow of about 38,000 cfs from the Little River could resultin flood water reaching the top of the road with little damage. CobbleMountain Dam failure would result in flood waters up to about 12 feetabove the road, flooding the mill and about 125 houses.

At hazard area 6, the former New Haven railroad embankment andbridge constitutes such a barrier and restriction that the PMF spillwayflow would probably flow through the center of Westfield at depths ofas much as five feet above some of the City streets. About 400 acresof the City might be flooded, the water reaching an elevation of about149 feet MSL. The failure of Cobble Mountain Dam would create a floodwave about 19 feet higher than the PMF flood. This failure would floodas much as 600 acres, reaching elevations of about 168 feet MSL, nearlythe elevation of Noble Hospital (Elev. 170).

5-3

At hazard area 7, the PMF spillway flow would rise as high asabout elevation 125 feet MSL before it could pass through the water gapat the West Springfield - Westfield town line. This would inundateabout 800 acres in Westfield and Southwick. Cobble Mountain Damfailure would result in water rising to elevation 157 feet MSL, inundatingup to 3600 acres in a wide area.

At Dewey Street and Westfield Road - hazard area 8 - the PNMFspillway flow would possibly rise to three feet above the road and flood12 houses and buildings in the area. Dam failure could result in waterup to eighteen feet deep over Route 20, Westfield Road, flooding about30 houses and buildings.

At Front Street in West Springfield - damage area 9 - damagewould probably be light as even the dam failure flood would be wellbelow the railroad at Front Street and Bridge Street.

At the Memorial Drive bridge to Agawam - hazard area 10 - hePMF spillway discharge from the dam would pass satisfactorily but thedam failure peak flow would probably overtop the Westfield River floodprotection dike by about two feet which could result in flooding about210 acres of low land near the Eastern States Exposition.

Failure of Cobble Mt. Reservoir Dam would probably c,-,ise con-siderable flooding of low lying areas along the Connecticut River thatare not protected by dikes - hazard area 10.

The information reviewed above is summarized in the followingtable of "Downstream impacts of Dam Failure," the "Location and HazardMap," and more fully developed in the computations in Appendix D.

In summary, a Cobble Mountain Dam failure would result in extensiveflooding and great loss of life in Westfield and West Springfield. Thereis a high potential for severely damaging hundreds of homes with attendlentpossible loss of hundreds of lives as well as numerous highway andrailroad bridges, industrial and commercial areas, and other structures.

5-4

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STATESDRAINAGE AREA MAP

ZEECOBBLE MOUNTAIN RESERVOIR DAM (MA 00068) RUSSELL~ JHAMPDEN COUNTY MASSACHUSETTS

THIS map- LOCATION SCALE : AS NOTED4 ~ DATE :MARCH 1980

SECTION 6 - EVALUATION OF STRUCTURE STABILITY

6.1 Visual Observation

Visual inspection of Cobble Mountain Dam did not r'-veal any signsof abnormal or alarming movement of the structure; nor igns of anysignificant leakage that should be cause for concern.

6.2 Design and Construction Data

Design and construction data and published reports provide infor-mation on the nature and arrangement of materials in the dam. Thereports and information examined were not adequate to make a modernanalysis of stability of the embankment or to evaluate seismic suscepti-bility of the dam. The plans and reports indicate that the best practiceof the day was followed and no signs of distress have been observed.

6.3 Post Construction Changes

Near the end of construction, the slopes of the upper, 14 to 17 feetwere steepened from 1 on 2.25 and 1 on 2.75 to 1 on 1.5 to increasethe height of the dam by seven (7) feet to elevation 973 feet MSL.

Sometime after construction was complete the flashboards werereplaced with a reinforced concrete wall seven (7) feet higher than thedesign crest. This reduced the freeboard safety and ability to nasssevere storms without overtopping the dam. It is estimated that evenso, the project can pass a probable maximum flood safely.

Other post construction work, namely, diversion tunnel groutingand spillway concrete repair, have not altered the characteristics of theproject, but have been carried out to maintain them in good condition.

The diversion tunnel outlet portal barrier grate which was installedto prevent trespass has not been successful.

The Massachusetts Division of Waterways' most recent inspectionreport dated May 2, 1978 was not available for review.

6.4 Seismic Stability

The dam is located in seismic zone No. 2. According to the recom-mended Corps of Enginers Guidelines, a seismic analysis would notnormally be warranted. However, due to the susceptibility of hydraulicfill dams to failure due to earthquake motion and to the extremely highhazard to downstream communities in the event of dam failure, it isrecommended that seismic stability studies including the potential forliquifaction of the hydraulic fill be undertaken.

6-1

SECTION 7 - ASSESSMENT, RECOMMENDATIONSAND REMEDIAL MEASURES

7.1 Dam Assessment

(a) Condition

Cobble Mountain Reservoir Dam is generally in good condition.Leakage is not excessive nor is there any sign of piping or seepagethat should be cause for concern. Maintenance is good and theproject condition is excellent. No sign of structural distress wasobserved. However, due to the lack of a seismic stability analysisfor this hydraulic fill dam, it has been rated as FAIR.

(b) Adequacy of Information

Information on soil and rock embankment materials in placethat would be adequate to perform modern stability analyses orseismic analysis was not available. Information concerning designand construction was otherwise complete and adequate. informationregarding the current post construction elevation of the top of thedam was not available.

(c) Urgency

The recommendation for a seismic stability analysis should beinitiated within one (1) year from receipt of this report by theOwner.

The remedial measures described herein should be implementedwithin two (2) years.

7.2 Recommendations

It is recommended that the following items be investigated underthe supervision of a qualified registered professional engineer:

1. Determine the strength and stability of the embankment especiallywith respect to seismic loading conditions, including thepotential for liquifacton of the hydraulic fill.

7.3 Remedial Measures

The following remedial, maintenance and operation procedures arerecommended:

1. Develop an "Emergency Action Plan" that will include aneffective pre-planned downstream warning system, locations ofemergency equipment, materials and manpower, authorities tocontact and potential areas that require evacuation.

2. Determine the current elevation and profile of the top of thedam.

7-1

3. Install a secure, reliable depth measurement float.

4. Correct leak and relocate hand hydraulic pump to an upperfloor.

5. Remove diversion tunnel outlet security gate.

6. Institute a biennial technical inspection by a registered pro-fessional engineer qualified in dam design and inspection.

7.4 Alternatives

There are no practical alternatives to the above stated Recommenda-tions and Remedial Measures.

7-2

APPENDIX A

INSPECTION CHECKLIST

INS17ECTION CLECK LIST

C' Cobble Mountain Reservoir Dam 11/15/79

T h 8:30

,,:E-. - Clear, breezy

... . 936 U.S. MSL .s.

Tighe & Bond/SCI Based on design elevations of

structures

.-John W. Powers, Project Manager 6. Omer H. Dumais, Civil

Hydrology/

2. George H. McDonnell, Hydraulics 7.

3. Edward A. Moe, Soils/Hydraulics- .,

4. David M. Lenart, Civil 9.

. Howard A. Koski, Civil 1O.

1. All project features were inspected by all party members.

L

7.

9.

:O.

Present for the Owner: Francis Broderick, William York

tS

?.KCo-T Cobble Mountain Dam rA'"E 11/15/79

pRj -'.u Embankment I A,.C Tighe & Bond party

AP- EVALUATED c '

Crest Elevation 972.1+ (35.8' + above water level)

Current -ool -l vaion 936.3 + (15.7' + below spillway crest)

.inm'a. Izo'nient to Date 959.1 (7.1' above spillway crest)

,urface Cracks None Concrete toe wall shows surfaceweathering & deterioration up to

ave ent Condition 2" deepRoad pavement - good

I-overrent or Settlement of Crest 0.9' based on recon. levels1.8' based on road grade observations

,- .. l. . : , :v ne t None evident

Good

zrizcrtal ,~...Good

Conition at Ab-er.ent and at Concrete ood, only minor erosion

Structures

Lications of Movement of Structural one. variations in downstream slope rockitems on Sl o )n gravel bed appears to be as built, not

-t ." ubsequent movement.

resnas sing on Slopes es, some debris, no damage.r S;omall brush. Maintenance clearing is good.Vegitation on Slopes No sloughing. Moss on rock & gravel indi ateSlouhing or Erosion of Slopes or stability. Minor localized erosion alo(n

A.butme.ts rock pocket at abutment.

Rock Slone Protection - Riprap Failures Good condition both faces.

Unusual Movemen or Cracking at or Nonenear Toes

Unusual .. an.. t or Dow.nstream o seepage at surface. Maximum passingSeepage lam estimated at about I cfs. Minor

geepage through toe wall near rock face..-?_:ing or Boils 4one. No silt in outflow.

undotion Drr.aS e ...- eattures ock foundation drain to toe wall & weepholes appear to be functioning well.

,: . r, s 3-6' wide weep holes - tops seen aboverock. Outflow clear - no silt, some

.r'Ste... iron oxide sludge.NonetI

Cobble Mountain Dam . 11/15/29

F 2 EE -J Diversion tunnel control tower Tighe Bond party

1.,it'D.

a. r,3nrt .... and! ..... Str, - US~ra

General Conaiti On Excellent

Cor...t-.on of J enr Good

.- .. .. Nonle

NoneMiziblc ? eiri'orcinz None

atincor Ce-'-'-n of ... .. None

S ee_-a or ' .... Minor leakage & efflorescence belowLe,.-1 8

-- ,- . - Good. Brick wall around Lamer-Johnsondischarge nozzles

U". -- -or .. No. Only minor leakage

None

.or Orrozic C Steel None

.r Vcr.:zs Good - 10'x4'-8" vent & hoist shaft

Float Wells None

Crane Koist None fixed

-1.- :at- r None

-- None

Sc G- 2-42" pipe & 42" x 30" Larner-John;on

discharge regulators... .cGy Ct z 2-39-3/4" Escher-Wvss rotary valves & 4"

bypa:s

.... :, - te -: 2....n None

-.-- y .c. ..... . Valves are hand w1hee operated from I ou,: 10a0bove

; _.. Lf. ., in ~* None Cxccpt temporarv drop ligh-. r a "2; -.' a.

" -'-'* Cr1,ithhl., ,mrrt in Dam - 1l/ 7

S'Divrsio TunneL .'- Ji T e & Bond party

ic

- . . . ... :.- CuDi S F.' -_vo - .. g'

. .Good at gate chamber to fair at outlet

portalNone

Minor, less than 11" deep at so:me jointin last 430'

-" - -or Cavi-atin- None

None

Some last 430'. Gets worse toward outend. Local ized near joints. Grout

- -o holes evident.

None

Z3 3 I ,:! -C r Cr _ C .... T--t--r,

----.- No

C .- n o C e Rocky & brushy wiLh trees less than

Outlet Portal Steel grate barrier & door, not locked.Concreto shows genera.1l surface

deterioration

-h

-'Z Cobble Mountain Dam . 11/15/79

F. ' , Spillwav.X-2. Tighe & Bond party

AREA EWAL-UD T c C: I2 2

-..... - "- . Concrete abutment top 6.0' above spillwacrest.

Crest of spillway weir wall is 6.2'+ aboesand approach channel

-nra- Ocnin Good. Some minor hairline cracks .of sur aceconcrete at 8'-10' spaces

~C~se Rock Dvernan:rg No

.... Q-er.n mr. Cir-.~elNo

- of Ar ch Chanl Sand & gravel floor, ledge sides

. .e -- -- -- 135' long crest

Gw'a1 Condition of C znrete Good. Recent surface repair

Minor under bridge

Minor less than !" deep of surface repaiplaster at some joints of training tlls'

e in None

.or " - C-;

-ce Minor at some joints & cracks

D:_-.H ce s Recent 212 ' 0 plastic, 5' above floor

Older T.," 0 steel, I' above floor.

- Cc: . on Good. Wall joint sealer sagging in some

joint ;

Lsze Rock c'. -.... ,....1None

Trees O':erha.n~z Chnz=c1 Soe up to 5" 0 down!;tream of bridr,

Feer of Charr.el Concrete past bridge ledge I)yond

that0iber Obtru;cion: Brush up to 2" 0 more than 100' below

bridge to outlet end

z:2' Cobble Mountain Dan .-. _- 11/15/79

C -C Tillway Bridge Tighe & bond party

None -eliptiral arch structure

rBota None

r - None..- ° ... ...... Minor effiorescence & seepage at joint.

between 3 segments of arch.

.. ... . . NonleNoii

d Bituminous concrete paved. Random

cracks at 8' +

spring line

Susrfc abtmn 7eep hoeSnConcrete in good condition

-.- z Good

None

b. Ab =n 6Per

G~r- a .. CZo flt , ^-Good

. .C .... Good

SCrch to -ridic Good

Crt f S nt)--7-Mi! --- weep holes are functioningSoihe seepage

S.- -- Cobble Mountain Dam .2. 11/15/79

- '' Power Tunnel intake Tower i. Tighe & Bond artv

AREA D~r C C:cc:- r.=CL

"

R* - -- Cz :3r.2t . St.,z-xicTu ,.,a

Cener. Condition Excellent

Condit-icn of Joints Good

S -l -- None

Tizib2 c Reinforcirng None

-i or S,-:ni; O-f Concrete None

Sear or 2 C Ce None

jhnt ...- ~-- No joints evident

.ercNot observed - it is submergedU- ': - a I S eerTae oz- LeksinGte

Chaf:er

Cr :-: None

or o Steen None

A..r ",ent s

Float Wells In corner of inlet we] l

C:ne Foit Fixed stop log hoist in place. Electricdrive controlled at powerhouse or filter p la

4a o r Battery stand by power

Noneyr'-ic .-- Good. For !;ervice gate. Emnergency

lhand pump60" 0

E-'rfecy Gates 20' x 20' steel roller gate

--. "t~ ~"None-i--r.n i-.. Z=*~ct~n ... t,"

.... -..... "" Battery & hand hydaul-ic pump

'" . ...- None

-_, .... . C, CK - '

Cobble Mountain Dam-'-- 11/15/79

- -- Power Tunnel Intake j:AC Tighe & Bond party

a. -raeh Char-.

S. .Submerged

BnCt C- - .cti ons Submerged

eck Siides o Faz - s None evident

70 BOCm None

br 4- SNone

Czairish of Concrc e -. :- Submerge. All concrete observed

was in excellent condition.

%-Cnditin af Cc-c -- Excellent

Stzc and Good

Trash screen 3" spaces

L.--

APPENDIX B

ENGINEERING DATA

Design and construction information is available at the following locations:

Item Location

Construction plans City of Springfield Water Department

Construction records City of Springfield Water Department

Report on Construction New England Water Works AssociationVol. XLVI No. 4, December 1932

Notes of James L. Tighe Tighe & Bond/SCI, Easthampton, MAInspector for Commissionersof Hampden County

Plans of Spillway Repairs, 1973 City of Springfield Water Department

Inspection Reports Mr. John Hannon, Mass. D.E.Q.E.Waterways Division, 100 Nashua St.Boston, MA

Plans attached:

General As Built Plan Attached hereafterDesign Plans (18 sheets) Attached hereafter

B-1

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APPENDIX C

PHOTOGRAPHS

____ (PHTOS NO.22,23 tI& 41

2 -=Z 1 E SO TUN

-~ PORTAL

TOE WALL

W E

COBBLE MOUNTAINRESERVOIR

-~OVERVIEW (AERIAL) NATIONAL PROGRAM OF INSPECTION OF NON-FED. DAMS

-f APPENDIX C LOCATION AND ORIENTATIONOF PHOTOS I

COBBLE MOUNTAIN RESERVOIR DAM (MA 00068) RUSSELLHAMPDEN COUNTY MASSACHUSETTS

CALE' NONE

____________________________ jDATE MARCH f9@1O

SPILLWAY DISCHARGE CHUTE

W E

COBBLE MOUNTAINRESERVOIR

INTAKE CONTROL SHAFT(PHOOS O. S S20)

NATIONAL PROGRAM OF INSPECTION OF NON-FED. DAMS

APPENDIX C LOCATION AND ORIENTATIONOF PHOTOS 2

COBBLE MOUNTAIN RESERVOIR DAM (MA 00068) RUSSELLHAMPDEN COUNTY MASSACHUSETTS

S CALE: NOME

DATE: MARCH 1990

lily'

Phonto 4

Dow;nstream face o' dam,ule)r part, looking south.....a t rioh-t end

44.-A

Photo 5

Downstream face of dam, ~mid height, show-ing4 rock,. .'

s~nauls and orowthl*.- SZ,':

Do,': ; fjcC r) . r! md(A--lil of rock ;1ir,,ico

.4~

ek

Photo 10

Downstream face of toe damand weep hole tap

Photo 11

Toe dam weep hole

Photo 12

View looking north from intak-eA Astructure at sp-lav dr is

bevond left end of mountain,left of sruillway.

71 tC

SnIw-Cet ,I r

I 5uhit

Photo 14

Northwest end of spil lwav;crest wall 5-howinq a--roach

7ond bridge over spilIra?channei showing, repairedconcrete surfaces & ween holes

Photo 16

F£oillway rock cut, lonkingc~Yitramti:.ard rcg

Photo 17

Spillwa/ disclharU&e s102Dfefrom ond of rock cut into

Little River Canyon

Photo 18

Intake gatehouse frcmn southwest

Photo 19

Maximum reservoir levelsAug. 1955, and Oct. 1955;at intake gatehouse, showingtypical good condition

Photo 20

Hand hydraulic pump foremergency operation of mainintake valve at intake gatehouse.

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7: 1 t

APPENDIX D

HYDROLOGIC AND HYDRAULIC COMPUTATIONS

APPENDIX D

HYDRAULIC AND HYDROLOGIC COMPUTATIONS

INDEX

Spillway Capacity 1-3/10Stage Capacity Curves 4/10Size Classification 5/10Hazard Classification 5/10Spillway Test Flood 5/10Spillway Test Flood Summary 6/10Maximum Probable Flood Curves 7/10Diversion Tunnel Capacity 8/10Intake Tunnel Capacity 9-10/10Borden Brook Dam Analysis 11/11Dam Failure Conditions 1/17Dam Failure Flood Routing 2-16/17Dam Failure Summary 17/17Downstream Hazard Map 18

D-1

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AD-A145 564 NATIONAL PROGRAM FOR INSPECTION 0F NON-FEDERAL DAMSCOBBLE MOUNTAIN RESER,.U) CORPS 0F ENGINEERS WALTHAM

UMA NEW ENGLAND DIV MAR D0

% 84

1 ---- 2--3. 2

11111-111L8'--~l L 1136 IIII

1.25 jl. 4 jflj 1.6

MICROCOPY RESOLUTION TEST CHART%AT ONAL BAACAU OF STANDARDS-1963-

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APPENDIX E

INFORMATION AS CONTAINED IN THENATIONAL INVENTORY OF DAMS

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