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D-Ai42 986 NATIONAL PROGRAM FOR INSPECTION OF NON-FEDERAL DAMS I/iHIEMLOCI(S RESERVOIR DR._(U) CORPS OF ENGINEERS WALTHAMMR NEWI ENGLRND DIV RUG 78

UNCLASSIFIED F/G 3/13 NL

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MICROCOPY RESOLUTION TEST CHARTNATIONAL BUREAU OF STANDARo-Ig3-A

(D CNNECICUTWESTERN COASTAL AREA

I FAIRFIELD ,CONNECTICUT

I HEMLOCKS RESERVOIR DAMCT 00018

PHASE I INSPECTION REPORT

NATIONAL DAM INSPECTION PROGRAM

cl.~ JUL 9 1984

Uj A'S Thi- do-'Imerlt has been approved-

I r Pubi-Ic release and sale; its

DEPARTMENT OF THE ARMYNEW ENGLAND DIVISION. CORPS OF ENGINEERS

WALTHAM, MASS. 02154

AUGUST 1978M

84 '06 29 065

d -&I A-* 1

DEPARTMENT OF THE ARMY-. ,:.e ~NEW ENGLAND DIVISION. CORPS OF ENGINEERS

., .424 TRAPELO ROAD:% WALTHAM, MASSACHUSETTS O2154

REPLY TOATTENTION OF:

NEDED

SEP 2 8 1978.....'

Honorable Ella T. GrassoGovernor of the State of Connecticut

"1 State Capitol."., iHartford, Connecticut 06115

., Dear Governor Grasso:

I am forwarding to you a copy of the Hemlocks Reservoir Dam Phase I In-spection Report, which was prepared under the National Program for In-

*spection of Non-Federal Dams. This report is presented for your use andis based upon a visual inspection, a review of the past performance anda brief hydrological study of the dam. A brief assessment is includedat the beginning of the report. I have approved the report and support

'e. the findings and recommendations described in Section 7 and ask that youkeep 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 torwarded 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.The Bridgeport Hydraulic Company, 835 Main Street, Bridgeport, Connect-icut 06604.

Copies of this report will be made available to the public, upon request,by this office under the Freedom of Information Act. In the case of this

- report the release date will be thirty days from the date of this letter.

I wish to take this opportunity to thank you and the Department of Envi-FRI. ronmental Protection for your cooperation in carrying out this progra'.

Sincerely yours,

%

S.>Inl J01N P. CHANDLERA : 'As stated . lonel, Corps of Engineers-iivision Engineer "" "

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HEMLOCKS RESERVOIR DAM

CT 00018

CONNCTICT WSTER COSTALARE

FARIED CONCIU

57

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PHASE I REPORT

NATIONAL DAM SAFETY PROGRAM

Name of Dam: HEMLOCK RESERVOIR DAM

State Located: Connecticut

P County Located: Fairfield County

Stream: Cricker Brook

Date of Inspection: 21 JUNE 1978

BRIEF ASSESSMENT

'The Hemlock Reservoir Dam is a linear concrete gravity damabout 700 feet long with an earth embankment concrete conesection comprising the west side of the dam. A concretespillway section about 120 feet long is located at the east-ern side of the dam. The dam is 64 feet high. Based on thevisual inspection of the site, review of available informa-tion and the past performance of the dam, the dam is judgedto be in good condition.

The project will not pass the test flood without overtoppingthe dam, and therefore the spillway capacity is inadequate.As the spillway will pass more than 50 per cent of the testflood without overtopping, the spillway is not judged serious-ly inadequate. The overflow will be 0.9 feet above the top ofthe dam.

Horizontal and vertical cracks should be repaired to every ex-tent possible to prevent seepage and continuing deterioration.Additionally, since the degree and extent of spalling is some-what excessive, the areas affected should be repaired. Due tothe potential for overtopping, it is recommended that a defin-ite plan for around the clock surveillance be implemented bythe owner during periods of unusually heavy rains and a formalwarning system should be developed.

S Giavara, P.E.rinc ipal

Registered, CT 7634

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This Phase I Inspection Report oni Hemlocks Reservoir Dam has been" : reviewed by the undersigned Review Bodrd memjbers. Ii our opinion, - -the reported ftindings, conclusions, dnd recomIunnddtions dreconsistent with the Recoyiended Guidelies for Safety Inspectionof 0Mins, dnd with 9o eniineer1i. Jud4miitindpractice, onn-F-

"eri - ubmittd for opprovdl.

44 4

RSCH, Chaimni-.

Chief, Foundation and Materials Branch

Chief, DO gn BranchEngi neering! Divif on "--

.1 nVinverloV DiVision

APPROVAL RECOftNODD:

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Chief, Engineering Division

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PRE FACE

This report is prepared under guidance contained in theReconoiended Guidelines for Safety Inspection of Dams, for Phase IInvestigations. copies of these guidelines may be obtained fromthe Office of'Chief of Engineers, Washington* D.C. 20314. Thepurpose of a Phase I Investigation is to identify expeditiouslythose dams which may pose hazards to human life or property. Theassessment of the general condition of the darn is based upon availabledata and visual inspections. Detailed investigation, and analyses

involving topographic mapping. subsurface investigations. testing#and detailed computational evaluations are beyond the scope of aPhase I investigation; however. the investigation is intended toidentify any need for such studies.

In reviewing this report. it should be realized that thereported condition of the darn is based on observations of field conditionsat the time of inspection along with data available to the inspectionteam. In cases where the reservoir was lowered or drained prior toinspection. such action, while improving the stability and safety ofthe dam, removes the normal load on the structure and may obscurecertain conditions which might otherwise be detectable if Inspectedunder the normal operating gnvirprnent of the structure.

*.--

It is important to note that the condition of a damn depends onnumerous and constantly changing internal and external conditions,and is evolutionary in nature. it would be Incorrect to Assume thatthe present condition of the dar will continue to reprent thecondition of the damn at some point in the future. Only through

Scontinued care and inspection can there be any chance that unsafeconditions be detected. oe

Phase I inspections are not Intended to provide detailed hydrologicand hydraulic analyses. In accordance with the established Gdeline"the Spillway Test flood is basod on the estimated "Probable MaximumFlood" for the region (greatest reasonably possible storm runoff). orfractions thereof. Because of the magnitud and rarity of such a stormnd beinterpreted as necessarly inga highly inadequate 4ondition.

The test flood provides a measure onvelate spillway capacity andserves as an aide in determining the need for more detailed hydrologicand hydraulic studies. considering the size of the dam. its generalcondition and the downstream damage potential.

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TABLE OF CONTENTS

Section Page

Letter of Transmittal

- Brief Assessment

Review Board Signature Sheet

* Prefacei

1 * Table of Contents ii -iv

Overview Photo v

Location Map vi.

1. PROJECT INFORMATION

1.1 General 1

a. Authority 1b. Purpose of Inspection 1

1.2 Description of Project 1

-~a. Description of Dam and Appurtenances 1 4

-~?b. Location 2Ac. Size Classification 2

d. Hazard Classification 2qe. Ownership 2

f. Purpose of Damn 2g. Design and Construction History 2h. Normal Operational Procedure2

1.3 Pertinent Data 2-4

. 2. ENGINEERING DATA

2.1 Design

2.2 Construction

2.3 Operation

2.4 Evaluation

* . , .o. . . j . . ,. - ; , . ., . j = . . ' . .. .-.

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Section Page-! ...-

3. VISUAL INSPECTION

3.1 Findings 6

a. General 6b. Dam 6 IC. Appurtenant Structures 6-7d. Reservoir Areae. Downstream Channel 8

3.2 Evaluation 9-

4. OPERATIONAL PROCEDURES h

" *4.1 Procedures 10

4.2 Maintenance of Dam 10

4.3 Maintenance of Operating Facilities 10

4.4 Description of any Warning System 10in Effect

4.5 Evaluation 10

5. HYDRAULIC/HYDROLOGIC

5.1 Evaluation of Features 11

a. Design Data 11b. Experience Data 12C. Visual Observation 12

; d. Overtopping Potential 12

*6. STRUCTURAL STABILITY

6.1 Evaluation of Structural Stability 13

a. Visual Observation 13b. Design and Construction Data 13c. Operating Records 13d. Post-Construction Changes 136. Seismic Stability 13

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5Section Page j7. ASSESSMENT, RECOMMENDATIONS AND REMEDIAL MEASURES

7.1 Dam Assessment 14

5' a. Condition 14," b. Adequacy of Information 14'- c. Urgency 14

d. Need for Additional Investigation 14

7.2 Recommendations 14 "--

-". 7.3 Remedial Measures 14

a. Alternatives 14'..! ..* b. Operation and Maintenance and Procedures 15

LIST OF APPENDICES

.. ...

Appendix Description

* '*' I Photographs

, Hydrologic Computations

III Visual Inspection - Check List

IV Engineering Data - Check List

V Drawings

VI Information as Contained Inthe National Inventory of Dams

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". PHASE I INSPECTION REPORTHEMLOCKS RESERVOIR DAM CT 00018

SECTION 1 - 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 inspection

• *.i* throughout the United States. The New England Division of' .. the Corps of Engineers has been assigned the responsibility

of supervising the inspection of dams within the New EnglandRegion. Flaherty Giavara Associates, P.C. has been retainedby the New England Division to inspect and report on selecteddams in the State of Connecticut. Authorization and notice

- to proceed was issued to Flaherty Giavara Associates, P.C.under a letter of 25 April 1978 from Ralph T. Garver, Colonel,Corps of Engineers. Contract No. DACW33-78-0309 has beenassigned by the Corps of Engineers for this work.

-, b. Purpose: 7

1) Perform technical inspection and evaluation ofnon-federal dams to identify conditions which threaten the.public safety and thus permit correction in a timely mannerby non-federal interests.

2) Encourage and assist the States to initiate .-.quickly effective dam safety programs for non-federal dams.

3) To update, verify and complete the NationalInventory of Dams.

1.2 DESCRIPTION OF PROJECT:

a. Description of Dam and Appurtenance. The HemlockReservoir Dam is a linear concrete gravity dam about 700 feetlong, with an earth embankment, concrete core segment 300 feetlong on the west side. A concrete spillway section is on theeast side of the dam and is 120 feet in length. The spillwayhas an ogee crest. The dam section is 64 feet high, with avertical upstream face and a downstream slope of 0.7 horizontalto lvertical. The earth embankment section has a slope of2 horizontal to 1 vertical with a shelf and then a flatter

- .~ slope to the entrance roadway. Upper and Lower gate housesprovide for take off to two 48-inch supply mains and 10 and36-inch blow off lines. -.tft

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* SECURITY CLASSIFICATION OF THIS PAGE (When Date Enteed)

REPOT DCUMNTATON AGEREAD INSTRUCTIONSREPOT DCUMNTATON AGEBEFORE COMPLETING FORM

I. REPORT NUMBER 12. GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER

CT 00018 ___________

4. TITLE (and Subtdil) S. TYPE OF REPORT A PERIOD COVERED

Conn. Western Coastal Area, Fairfeild Conn. INSPECTION REPORTHemlocks Reservoir Dam ________________

NATIONAL PROGRAM FOR INSPECTION OF NON-FEDERAL S. PERFORMING ORG. REPORT NUMBER

-' fl~AMS _ _ _ _ _ _ _ _ _ _ _ _ _ _

7. AUTmOR(aj 11- CONTRACT OR GRANT NUMUER(.)

U.S. ARMY CORPS OF ENGINEERSNEW ENGLAND DIVISION

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASKAREA & WORK UNIT NUMBERS

11. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

DEPT. OF THE ARMY, CORPS OF ENGINEERS August 1978NEW ENGLAND DIVISION, NEDED 13. NUMBER OFPAGES

* ~424 TRAPELO ROAD, WALTHAM, MA. 02254 cc

14. MONITORING AGENCY NAME & AODRESS(if different fto ContrJIAaa Office) IS. SECURITY CLASS. (of tMle report)

UNCLASSIFIEDIts. OECL ASSI PIC ATION/ DOWNGRADING

SCHEDULE

* ISW DISTRIBUTION STATEMENT (.1 UiC Report)

APPROVAL FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED

17. DISTRIBUTION STATEMENT (of Me obelrao; Mooed in Rj..& 2o. of diifeI how Roeatu)

C. 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 of

* Non-Federal Dams; use cover date for date of report.

Io. KEY WORDS (Cmontinao tmi revere aide of inoetym md ad IneeDt? by Me"0 MaMbo.)

DAMS, INSPECTION, DAM SAFETY,Western Coastal Area, Fairfeild Conn., Hemlocks Reservoir Dam

20. ABSTRACT (Centme an revee mid@it ROG...wP Ad O&ONIOOV 6? WOOJI mambe4 The Hemlock Reservoir Dam is a linear concrete gravity dam about 700 ft. long witlan earth embankment concrete cone section comprising the west side of the dam. Aconcrete spillway section about 120 ft. long is located at the eastern side of the dam.The dam is 64 ft. high. Based on the visual inspection of the site, review of avai ableinformation & the past performance of the dam, the dam is judged to be in fair goolcondition.

DD IA7 'j*"* 147% .EITION 001 1Oe No IS 1 OBSOLETE

* .-.. *

b. Location. The dam is located on Cricker Brook 1.5 ".[ * miles north of its junction with the Mill River within the

Connecticut western coastal area. The dam is located in the- -iTown of Fairfield, 1/2 mile north of the Merritt Parkway and4-1/2 miles north of Mill Plain.

c. Size Classification. The applicable guidelines indi-cate that for an intermediate category the storage in acre/feetfor the impoundment must be greater or equal to 1,000 and lessthan 50,000. The height must be greater or equal to 40 feet

IP and less than 100 feet. The top of dam storage is 11,635 arce- .feet and the height of dam is 75 feet. Therefore, based onboth the storage capacity and height of dam the size classifica- -

tion is intermediate.

d. Hazard Classification. The dam is designated as hav-ing a high hazard potential. There are more than 50 dwellingsless than 10 feet above the riverbed along the first 3 miles ofthe downstream river channel. The Merritt Parkway would alsobe damaged by a flood produced by a dam failure.

e. Ownership. Hemlock's Dam is owned and operated by the. Bridgeport Hydraulic Company, of Bridgeport, Connecticut. *

f. Purpose of Dam. The dam's function is to impoundwater for the Hemlock Reservoir. This reservoir forms part

, .of the water company's distribution system and supplies amajor portion of the demand.

g. Design and Construction History. The dam was designed ""and constructed in 1914. Both the designer and contractor whoconstructed the dam are unknown. %%

izedh. Normal Operational Procedure. The reservoir is util-

ized for drinking water purposes by taking water through theupper gate house to two 48-inch supply lines. A 36-inch anda 10-inch pipe provide for blow off. To augment supply, water.

from the Aspetuck and Saugatuck River watersheds are diverted -

to Hemlock's Reservoir as needed.

1.3 PERTINENT DATA:

a. Drainage Area - 5.3 sq. miles

b. Discharge at Dam Site -

Maximum Known Flood UnknownWarm Water Outlet Not ApplicableDiv. Tunnel Low Pool Outlet Not ApplicableDiversion Tunnel Outlet Not ApplicableGated Spillway Not ApplicableUngated Spillway at Max. Pool 4,700 CFS -Total Spillway Cap. at Max. Pool 4,700 CFS 77

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Top of Dam 230.1 Max. Design Pool Unknown

Full Flood Control Pool Not ApplicableRecreation Pool Not ApplicableSpillway Crest Ungated 225

* Upstream Portal Invert Div. Tunnel Not ApplicableDownstream Portal Invert. Div. Tunnel Not ApplicableStreambed at Centerline of Dam 155Maximum Tailwater 165+ .

d. Reservoir -Length of Max. Pool 13,000 Ft.Length of Recreation Pool Not AvailableLength of Flood Control Pool Not Available

e. Storage -Recreation Pool Not Applicable

-. ". Flood Control Pool Not ApplicableDesign Surcharge UnknownTop of Dam 11,635 Acre-Feet

f. Reservoir Surface (acres) -

Top of Dam Not AvailableMax. Pool Not ApplicableFlood Control Pool Not ApplicableRecreation Pool Not ApplicableSpillway Crest 437

g. Dam-Type: 700' concrete gravity dam, 400' earth

embankmentLength: 1,100 feetHeight: 75 feetTop Width: 11 feetSide Slopes: Concrete

Upstream: VerticalDownstream: 0.7 Horizontal/l Vertical

Zoning: Earth embankment, downstream slope:2 Horizontal/l Vertical

Impervious Core: Concrete CoreGrout Curtain: Unknown

h. Diversion and Regulating Tunnel -

Type: No tunnelLength: Not ApplicableDiameter: Not ApplicableAccess: Not Applicable . .,-.

Regulation: Not Applicable

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i. Spillway\. Type: Oe

Length of Weir: 116 feetCrest Elevation: 225Gates: UngatedUpstream Channel: Reservoir perimeter, stone bottomDownstream Channel: Concrete training wallSpillway is founded on rock

*2 j. Regulating Outlets-4Intake Structure: 8 - sluice gates, 3' x 51-6"'

2- 48" dia. water supply mains1 -36" dia. reservoir drain-

blow off1. 110" dia. gate house drain-

blow off

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SECTION 2 - ENGINEERING DATA

2.1 DESIGN:

The designer of the dam is unknown. Two drawings were utilizedduring this study entitled as follows:

a. "Hemlock's Dam Gate Houses" - not dated

b. "Gate House Details" - not dated

2.2 CONSTRUCTION:

A rock and earth profile developed for the site of Hemlock'sDam has been reviewed. The data and accuracy of the profileare unknown.

2.3 OPERATION:

j & No operation records were made available for use during thisinvestigation.

2.4 EVALUATION:

a. Availability. Only plans showing some of the dimen-sional features are available. Specifications indicating theproperties of the materials used and construction proceduresare not available.

b. Adequacy. Information available is adequate forPhase I purposes.

C. Validity. There is no reason to question the validity ,-of the documents reviewed.

44-

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SECTION 3 - VISUAL INSPECTION.,%, .** . .

3.1 FINDINGS:

a. General. The dam is composed of two sections, a con-crete core wall earth embankment on the west and a concrete damwith downstream earth berms on the east. The concrete sectionwas gunited in 1964 and is spalling at several locations. Somestaining is occurring, however, the source of water is unknown.The earth embankment sections were well maintained and did not

pI show any evidence of sloughing, erosion, or wet spots.

b. Dam.

1) Gravity Concrete Section

a) Upstream Face - For the full length of the damhorizontally about two feet above the water line there is anarea of scour exposing the fine aggregate in the concrete. Atalmost every joint in the dam there is a larger space where

~ ~.*, deterioration has taken place and concrete is absent. Generally,there are some minor areas of spalling along the U/S face of thedam, however, at the panel adjacent to the gate house (west side)there is an area of severe spalling nearly the full length ofthe panel about one foot thick (approximately one foot above thewater line). In the panel on the east side of the gate housethere is an area of deep scour (one foot thick) for nearly itsfull length. Generally, there is some spalling of the jointsat the coping.

b) Downstream Face - The joints are generally in

* . poor condition. At the joint at Station 4+71 just above theground surface a large area of gunite has spalled off exposingthe wire mesh. At the joint at Station 5+31 there is a bubblefor about the middle third of the exposed portion of the jointand a deep, narrow spalling of the gunite at the bottom thirdof the joint. There is efflorescence for most of the joint at -.Station 5+91 and a large wet spot near the ground surface. Thejoint at Station 6+51 has spalling and considerable rust stains.The panel between Station 6+51 and Station 7+11 has several W .

.* areas of surface cracks, efflorescence and bubbles. Near thebottom of the joint at Station 7+11 there is an area of spallingseveral inches deep which exposes the wire mesh. A short dis-tance down from the top of the dam horizontally across this

* joint there is a large bevel and just below a depression,probably due to guniting. In the panel between Station 7+11 Fand Station 7+71, near the bottom there is a large area of sur-face spalling. Also, in this panel near the bottom is a large

- bubble and some spalling and below this, an area of surface

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cracks. Near the joint at Station 7+71 close to the ground, .%i surface is an area of deep spalling and efflorescence. In

the panel at the gate house between Station 7+71 and Station8+01 there is a large spalled area close to the top of thedam. At Station 8+01 the joint shows cracking for nearlythe full depth and a bubble and small spalled area near theground surface. Slight seepage was noted at several joints.

c) Spillway - The area of the spillway adjacentto the dam has severe spalling and the wire mesh is exposedat what appears to be the uppermost horizontal constructionjoint with water seeping through and evidence of efflorescence.There are several areas of cracking and spalling and alsoseveral places showing evidence of water seeping through atthe horizontal joints.

d) Earth Embankment - The downstream berm is. generally in good condition with no sloughing or wet spots

noted. The berm appeared to be relatively shallow in thevicinity of the downstream concrete gate house.

Mica schist bedrock is exposed about 30 feet downstream fromb the face of the dam in the vicinity of Station 6+00. Several

, large outcrops appear to strike N35oW and dip 100 west.Additional stone inlets were located in the downstream bermat Station 4+90 adjacent to the access road, Station 5+25 onthe berm and one near Station 9+70 on the left side of the dam.The outlet for the later stone inlet could not be located dur-ing the visual inspection.

2) Core Wall Embankment Dam Section -

a) Upstream Slope - The upstream slope was ex-posed for a distance of approximately 6 feet. (The reservoirwas about 1 foot below the spillway crest.) The riprap ex-tended to within 1 foot of the embankment crest and generallyappeared in good condition. Some small windows were exposed

- through the riprap and there was some evidence of differentialweathering of the mica schist riprap at a few locations. .P

b) Crest - The crest of the dam consisted of thetop of the earth embankment, 30 feet wide. The core wall, 10 .feet wide, is exposed only at the junction with the concrete dam,Station 3+89. A small test pit was excavated at Station 2+30which uncovered the top of the concrete core wall about 9 inchesbelow the roadway surface.

c) Downstream Slope - The portion of the downstreamslope above the lower access road is grassed and had been re-cently mowed. It did not show any evidence of sloughing, ero-

- ' sion or wet spots. There are several stone inlets (stone wasnot removed) on the upstream side of the lower access road at

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approximately Stations 1+37, 2+57, and 3+44. The inlets ap-pear to connect to culverts which are laid underneath theaccess road and which connect into a grassed drainage channelon the downstream side of the road. All the culverts weredry except for a small trickle of water flowing from theIculvert under the road at Station 1+37. Below the road, theslope is heavily wooded, and it is difficult to observe anymovement.

There are a few holes made by burrowing animals on the slope.

, C. Appurtenant Structures.

1) Upper Gate House - The upper gate house was cleanIS and neat. The gate controls appeared to be easy turning and

are exercised once a year. A recent diver's report is purportedto have indicated that two of the stem guides were broken.(Report not released by Bridgeport Hydraulics Company.) A re-quest by the inspection team to operate the blow offs to ensureproper functioning was not met. The filtration screens for thewater supply mains have electrical power hoists in good condi-tion. Electrical equipment for the hoists, interior light, damfloodlights, and deicer pumps appeared in good condition. ' Allinterior wiring was enclosed in conduits free of corrosion anddirt.

2) Lower Gate House - Generally good condition.

d. Reservoir Area. The reservoir perimeter has well vege-tated banks at moderate to steep slopes. There was no evidenceof slides or sloughing. No noticeable debris or obstructionswere seen in the vicinity of the upper gate house. The depthof sediment, and rate of accumulation in the reservoir, is

, unknown. However, sediment has accumulated in the eastern endof the reservoir at the spillway (reaching the crest).

e. Downstream Channel.1) Spillway Discharge - The spillway channel is in

good condition. The low concrete and stone wall on the rightside of the channel is also in good condition. Mica schistbedrock is exposed about 150 feet downstream from the spillwayweir. At this location, it is planar, and strikes N10°W anddips 100 west. There are minor obstructions on the bottom ofthe channel consisting of small bushes, tree branches and grassgrowing at various locations along the bottom. The spillwaychannel has a large crevice near the end of the low concretewall which has been created by differential erosion along thefoliation of the exposed mica schist.

8'..

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2) Blow-Off Discharge Channel -The channel*is becoming obstructed with sediment at its junction with the

spillway discharge channel.

1 3.2 EVALUATION:

The dam appears in good condition, and there are no visual in-dications of the dam being unsafe. The gunite repair (1964)has deteriorated and a program of concrete maintenance iswarranted.

The spillway channel contained debris and obstructions on the -

bottom and it is important it be maintained to allow unob- .

structed flow during peak discharge periods. Some trees im- -

mediately adjacent to the left side of the spillway channelcould also adversely effect capacity.

' ' 5

;2I,11

9. 4

SECTION 4 - OPERATIONAL PROCEDURES

4.1 PROCEDURES:

Water is withdrawn through the upper gatehouse service gatesand treated at a plant just downstream of the dam. Two 48-inchsupply lines service customers in the greater Bridgeport region.

4.2 MAINTENANCE OF DAM:

. ". The dam and associated structures are generally well main-tained with a regular program of grass mowing and generalmaintenance in effect. Yearly routine inspections are carriedout by Bridgeport Hydraulic Company staff. A consultant washired to perform a cursory inspection of Bridgeport HydraulicCompany dams during November 1976. It was recommended thatspalling concrete at Hemlock's dam be repaired.

4.3 MAINTENANCE OF OPERATING FACILITIES:

The operating valves were inspected recently; although theresults of the inspection are not available, generally thevalves/valve stems need some repair.

4.4 DESCRIPTION OF ANY WARNING SYSTEM IN EFFECT:

There was no warning system of any kind in effect at the time.r. of the inspection.

p 4.5 EVALUATIONS:The Hemlock's Reservoir, which is approximately 70 years old,

is well operated and maintained. Although not designed for ..rapid drawdown, it should be noted that, if the need shouldarise, drawdown could be effected by the following procedures:

a. Allowing for maximum discharge through the 36-inchand 10-inch blow-offs.

b. Allowing for discharge through the two 48-inch %supply mains.

The blow-off was not operated during the site inspection, there-fore comments on the serviceability cannot be made. The valve

- should be tested on a periodic basis to insure that it couldbe operated if required. .

10 -

%p _ %.. 22

SECTION 5 - HYDRAULICS/HYDROLOGY;.-.'. .-

5.1 EVALUATION OF FEATURES:

a. Design Data. There is no available information on thehydraulic design criteria for this dam and appurtenances. Underestablished criteria (OCE Guidelines) the recommended spillwaytest flood for the size (intermediate) and hazard potential(high) classification is the probable maximum flood (PMF). ThePMF is the flood that may be expected from the most severe com-bination of critical meteorologic and hydrologic conditions

~. .~that are reasonably possible in the region.

;.' An estimate of the magnitude of the test flood at the site isbased on an analysis of several sets of regional flood frequencydata as presented in Appendix II.

As a conservative approach to the investigation, the most criti-cal design hydrograph was used throughout (peak discharge of9,600 CFS).

is A stage-discharge relationship was calculated for the spillwayand indicates the following flows, based upon a coefficient of3.6 and a length of 116 feet.

Stage - Discharge Relationship

Stage Head, Ft. Discharge Rate, CFS

225 0 0. 226 1 420

227 2 1,180228 3 2,170

a229 4 3,340T a230 5 4,670

the peak inflow rate of the test flood. (Compare 9,600 CFS

with 4,670 CFS.) In order to determine the effect of the reser-voir storage capacity, a h .rograph of the test flood was routedthrough the reservoir.

t- The hydrograph was formed by assuming the test flood had a dura-tion of 24 hours, with the peak of 9,600 CFS occurring at 8 hoursfrom the beginning of runoff. The rising and falling' limbs of

~. .~. the hydrograph were assumed to be changing at a constant rate,forming a triangle. The routing operation indicated that thepeak rate of discharge would be reduced to 8,800 CFS, resultingin a stage elevation of 230.9 feet.

4- . "

,,,.............................-........-....v... ....,-.-,,:.:...'..-..,

b. Experience Data. Discussion with water company per-" :"" :, sonnel indicates that since the early 1950's the dam has not

. " been overtopped.

C. Visual Observations. The on-site inspection of thedam provided the data for the hydraulic evaluation of thespillway.

d. Overtopping Potential. The peak rate of discharge

from the test flood will overtop the dam and embankment (0.9 LAfeet). The maximum spillway capacity is however equal to morethan one-half of the test flood.

id

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SECTION 6 - STRUCTURAL STABILITY

6.1 EVALUATIONS OF STRUCTURAL STABILITY:

a. Visual Observations. No evidence was observed that-would indicate structural instability. The concrete surface(gunite) has deteriorated, and some water was seeping at thejoints. Monitoring of this seepage should be initiated.

b. Design and Construction Data. The design and con-struction data available are not sufficient to formally

" evaluate the stability of the dam. In particular, there isno available information concerning the embankment and bermmaterials and construction documentation nor the foundationmaterial for the core wall and the concrete gravity section.The drawing suggests that the gravity section was placed inan excavation. It is now known whether bedrock was reachedand, if so, what was the in-situ properties of the bedrock.

c. Operating Records. There are no available recordswhich indicate evidence of stability problems since the damwas constructed in 1914. As the Hemlock Reservoir Dam wasdesigned and constructed as a water supply dam and has beensubjected to a full head of water a majority of the time

. since construction, its stability could be considered tobe adequate based on past performance.

d. Post-Construction Changes. A lime feed and storage

tank was constructed downstream of the dam west of the treat-ment facility. A large diameter gas main was also constructeddownstream of the dam south of the entrance roadway. Neitherof these changes affects the structural stability of the dam.

p e. Seismic Stability This dam is in Seismic Zone 1and hence does not have to be evaluated for seismic stability.

14

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SECTION 7- ASSESSMENT, RECOMMENDATIONS AND-" -" REMEDIAL MEASURES 'v

7.1 DM ASSESSMENT:

a. Condition. Based on the visual inspection, recordsavailable and past operational performan.e, the dam is judgedto be in good condition.

The project will not discharge the test flood without overtop-P ping the dam, and therefore the spillway capacity is inadequate.

The spillway capacity is not judged seriously inadequate, asthe project will pass one-half the test flood without overtop-

.*4 ping the dam.

b. Adequacy of Information. The information and dataavailable were adequate for performance of this investigation. -

c. Urgency. The recommendations and remedial measurespresented should be carried out in the near term.

d. Need for Additional Investigation. Additional inves-tigations to further assess the adequacy of the dam and appur-

i. 42 tenant structures do not appear necessary.

7.2 RECOMMENDATIONS:

It is recommended that the following measures be undertaken bythe owner: '-.

1) Horizontal and vertical cracks should be patched toevery extent possible to prevent seepage -and continuing de-terioration.

2) Since degree and extent of spalling is considered ex- .-.-.cessive, the areas affected should be repaired. "..-4

3) Sediment accumulation in front of spillway section(east side) should be removed and hauled away.

4) Defective valves and stems should be repaired toinsure that if required, they could be operated to lower thewater level in the reservoir.

7.3 REMEDIAL MEASURES:

* ,Although the dam is generally maintained in good condition, itis considered important the the following items be accomplished: -

a. Alternatives. Not applicable.

.9 -14-

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-' b. Operation and Maintenance and Procedures.

1) An operation and maintenance manual for the pro-.. ject should be prepared.

2) Animal bore holes should be filled and plugged.

.. "3) The blow-off valve should be exercised periodi-cally.

-: -4) Due to the potential for overtopping, it is re-commended that a definite plan for around the clock surveillancebe implemented during periods of unusually heavy rains and aformal warning system be developed for use in the event of anemergency.

.4.P

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APPEDIX

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APPENDIX II

HYDROLOGIC COMPUTATIONS

p. P .. F "-

A An-quj "Lln -W -9A7 24 4.7-IV oL7%7 4. - K -

NMONROEREDDING -

- EASTONRESERVOIR

SAUGATUCK0RESERVOIR EA NTRUMBULL

ASPETUCI(RESERVO/IR

HEMLOCK -? N -

WESTON -

44

DRAINAGE AREA MAPSCALE IN MILES HEMLOCK RESERVOIR DAM

FAIR FIELD, CONNECTICUT0 2

K- . - - - - - --7. -

LhM- v-nFLAHERTY-GIAVARA ASSOCIATES SHEET NO. OF 2\1 c ENVIRONMENTAL DESIGN CONSULTANTS BY ~ .C\DATE C-I~i

U gONE COLUMBUS PLAZA. NEW HAVEN. CONN 06610/20317W1-260 CHK..BYC-!'L.DATE&429..

PMF PEAK FLOW/ ESTIMATZ

*WATP-R~j-JF-r AR-A,, IS S.?.7 -SQUAFEM L-

RMFF- ro PR LUIAZY GUIANCE F=OP,

NE.V. ENGLANL4 1:WY(SI04 CZOPPS OFENG(,IF

uNi7 FLO /87-0 oFS/i (IoLLAJG)

SAY IG. C QF3

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MEFAN A/V/ JAL PLOE ZS (FIG. I-S

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PA.AF Sx5 ( SOO 7500 O-FS

.~IpFOR," SPA1LWV~AY EVAN )ATIO06 \Jss- 1(Oco CF'sI

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i NO H2031WI26 CHKr.BAT: DAEII/

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APPENDIX III

.~ *4.j

4.--.4

VISUAL INSPECTION

CHECK LIST

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.4, -~ - ~ 4.; ~ 44

PERIODIC INSPECTION CHECK LIST

.'ROJECT Hemlocks Reservoir DATE June 21, 1978

INSPECTOR Anthony Rummo DISCIPLINE Structural

INSPECTOR DISCIPLINE_________

AREA EVALUATED CONDITION

CONCRETE DAM STRUCTURE

General Condition Concrete Gunite surface severely spalledSurfaces

Movement or Settlement of NoneCrest

Vertical Alignment Good

Horizontal Alignment Good

Condition at Abutment andOther Structures

Structural Cracking None observed

Spalling Major spalling of surface(gunite) "9.

Visible Reinforcing Wire mesh, exposed (gunite)

Rusting or Staining of Yes, at some jointsConcrete .-?..

Condition of Monolith/ Joints in poor conditionConstruction Joints

. Drains - Foundation, NoneJoint, Faces

Major efflorescence observed andAny Seepage or Efflorescence seepage noted at joints rFoundation Damage, Undermining None

,. Water. Passagesu.met

abutmnts .>

! ' :#~ ~ .~~P4 S 5' ~ .* fE:.:.:.'.,~AA

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77- ;.


SPROJECT Hemlocks Reservoir DATE June 21, 1978

INSPECTOR Richard Murdock DISCIPLINE Geotechnical -N PECTO DISCIPLINE__________

,...


DAM EMBANKMENT

-. Crest Elevation El. 225

Current Pool Elevation El. 224

: Maximum Impoundment to Date•

Surface Cracks None observedPavement Condition Ruts evident in roadway

Movement or Settlement of None observed. Crest

SLateral Movement None

Vertical Alignment Good

Horizontal Alignment Good

Condition at Abutment and at GoodConcrete Structures

Indications of Movement of NoneStructural Items on Slopes

Trespassing on Slopes Few small animal holes

Sloughing or Erosion of NoneSlopes or Abutments

Rock Slope Protection - Good, some minor deteriorationRiprap Failures present --.

.. Unusual Movement or Cracking None observedat or near Toes , *..

Ususual Embankment or Down- Nonek istream Seepage

. . ... .

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,',, ' , ' '.,.. ." ",' "." ''."''.-.".-.. .' "V . ' " , .; " .- ' .., ,. .". . " ." '...


PRJECT Hemlocks Reservoir DATE June 21, 1978

INSPECTOR Richard Murdock DISCIPLINE Geotechnical

INSPECTOR DISCIPLINE_ _ _


DAM EMBANKMENT - (continued)

Piping or Boils None

Foundation Drainage Features None IToe Drains None

Instrumentation System None

...a,.-

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?~.ROJCT Hemlocks Reservoir DATE June 21, 1978

I=SPECTOR Anthony Rummo DISCIPLINE Structural

INSPECTOR__James MacBroom DISCIPLINE Hydrology


.OUTLET WORKS - CONTROL TOWERGenerally in good condition,

a, Concrete and Structural some erosion

-D General Condition

Condition of Joints

SpallingMinor spalling noted

Visible Reinforcing No visable reinforcing

Rusting or Staining ofConcrete

Any Seepage or Efflorescence

Joint Alignment

Unusual Seepage or Leaks inGate Chamber

Cracks No cracks noted

5Rusting or Corrosion of None*:: : ~ Steel

b. Mechanical and Electrical

* Air Vents

Float Wells Good condition

Crane Hoist

ulevator

Xydraulic System None

-S\ ~

kA .a~ M Z LA

'.4.


" -sROECT Hemlocks Reservoir DATE June 21, 1978

INSPECTOR Anthony Rummo DISCIPLINE Structural .4

Hydraulics/INSPECTOR James MacBroom DISCIPLINE Hydrology


OUTLET WORKS - CONTROL TOWER(continued)

Service Gates Good condition

Emergency Gates

Lightning Protection System Satisfactory

Emergency Power System None

Wiring and Lighting System Electrical, good conditionIn Gate Chamber -,

.V

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S:PROJECT Hemlocks Reservoir DATE June 21, 1978

INSPECTOR_____________ DISCIPLINE__________

P INSPECTOR____________ DISCIPLINE_ ________

~.:AREA EVALUATED CONDITION

-vOUTLET WORKS - INTAKE CHANNEL AND.~ INTAKE STRUCTURE

r .a. Approach Channel- Water travels from the reservoir

Slope Conditions directly into the intake struc-ture.

~: Bottom ConditionsRock Slides or Falls-

Log Boom

Denditio of Concrete

Drains or Weep Holes

bi. Intake Structure

Condition of Concrete

Stop Logs and Slots

II

PERIODIC INSPECTION C HECK LIST

PROJECT Hemlocks Reservoir DATE June 21, 1978

J.' INSPECTOR Anthony Runimo DISCIPLINE Structural

INSPECTOR- Richard Murdock DISCIPLINE Geotechnical

James MacBroom Hydraulics/Hydrology

- ~ AREA EVALUATED CONDITION

O-UTLET WORKS -SPILLWAY WEIR,

" APPROACH AND DISCHARGE CHANNELS

a. Approach ChannelSediment has accumulated at

General Condition .eastern end of approach to . -

Channel

j Trees Overhanging Channel

Floor of Approach Channel

~Weir and Training Walls

General Condition of Concrete Severe spalling r7

Rust or Staining Yes

~::~*Spalling Yes

Any Visible Reinforcing Wire mesh exposed

Any Seepage or Efflorescence Some seepage and efflorescence

4, Drain Holes None observed *.

a. Discharge channel

%* ~ 4

General Condition Good

'~:~ Loose Rock Overhanging None* observedChannel

Tree OvrhagingChanelA few trees in close proximity/9 to left wall.

Floor of Channel Good condition

Other Obstructions Brush, grass, a few wood pieces

! % %


t 'ROJECT Hemlocks Reservoir DATE June 21, 1978

INSPECTOR_________ DISCIPLINE__________

ZNPECTOR_________________ DISCIPLINE___________

*1,4AREA EVALUATED CON15ITION

' OTLET WORKS - SERVICE BRIDGE

Super. Structure Nn

-~ .~ Anchor Bolts

::~ jBridge Seat' Longitudinal Members

Under Side of Deck

Secondary Bracing

Deck

~ Drainage System

Railings

Expansion Joints

.4 Paint

jb xbutments &Piers

GenralCondition of Concrete

WI Alignment of Abutment

Approach to BridgeI Condition of Seat &Backwall

*. -0%

RUSK- w W' 4w*J

*4 * *-~ ~ ' .


PRJC elcsReservoir DATE June 21, 1978

ISPECTOR__________ ___ DISCIPLINE__________

ISPECTOR______________ DISCIPLINE__________


O UTLET WORKS -TRANSITION AND

COfNDUIT

S' General Condition of Concrete

Rust or Staining on Concrete

Spalling

-~Erosion or Cavitation

Cracking

SAlignment of Monoliths

SAlignment of Joints

Numbering of Mooliths

'i

A

C N


,%?p~jECT Hemlocks Reservoir DATE June 21, 1978Hydraulics!

INSPECTOR James MacBroom DISCIPLINE- Hydrologry

SINSPECTOR_____________ DISCIPLINE_________


O ~UTLET WORKS - OUTLET STRUCTURE4 AND OUTLET CHANNEL

~' General Condition of Concrete

-Rust or Staining

M Spalling

'~Erosion or Cavitation

Visible Reinforcing

,~Any Seepage or Efflorescence

Condition at Joints

Drain Holes

Channel:7 1'Generally good condition; some

Loose Rock or Trees Over- sediment collected at junctionhanging Channel with spillway discharge channel

Condition or Dischargehannel

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EAM ELEVATION OF DAMNTS

HEMLOCKS RESERVOIR DAMMILL RIVER

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APPENDIX VI

INFORMATION AS CONTAINED IN

THE NATIONAL INVENTORY OF DAMS

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