AD-A144 768 NAIIONAL PROGRAM FOR INSPECtION OF NON-FEDERAL DAMS 1/.tCOLUMBIA LAKE DAM ICI..IUI CORPS Of ENGINEERS WALIHAMMA NEW ENGLAND DIV SEP 70

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MICROCOPY RESOLUTION TEST CHART

NATIONA, OURCA OF STANOAtOS-1N65- A

THAMES RIVER BASINI COLUMBIA, CONNECTICUT

COLUMBIA LAKE DAMI' CT 00520

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PHASE 1. INSPECTION REPORTNATIONAL DAM INSPECTIONPROGRAM

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_9 3 84

AI

IINQ~ Ae,-TTrfSECURITY CLASSIFICATION OF THIS PAGE (When Di* knIteod)

REPORT DOCUMENTATIoN PAGE READ INSTRUCTIONSBEFORE COMPLETING FORM

I. REPORT NUMBER 2. GOVT ACCESSION NO. 2. RECIPIENT'S CATALOG NUMBER

CT 00520 !)I / _-_4 TITLE (and S46b610e) a. TYPE Or REPORT a PERIOD COVERED

Columbia Lake Dam INSPECTION REPORT

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

DAMS7. AUTHOR(.j 8. CONTRACT OR GRANT NUMBER(*)

U.S. ARMY CORPS OF ENGINEERSNEW ENGLAND DIVISION

9. PERFORMING ORGANIZATION NAME AND ADORESS t0. PROGRAM ELEMENT PROJECT TASKAREA M WORK UNIT NUMBERS

#I. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

DEPT. OF THE ARMY, CORPS OF ENGINEERS September 1978NEW ENGLAND DIVISION, NEDED 12. NUMBEROF PAGES

424 TRAPELO ROAD, WALTHAM, MA. 02254 .9014. MONITORING AGENCY NAME h AODRESS(I/ dItewI Iftm ,VUOJiAOi 011160) IS. SECURITY CLASS. (of LJo ftport)

UNCLASSIFIEDISa. DEC ASSI PIC ATION/ DOWNGRADING

ISCaDU LE

III. DISTRIBUTION STATEMENT (el sIhd aRort)

APPROVAL FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED

17. DISTRIBUTION STATEMENT (of Ih obetrota entered In S41 0, II 411110mIlem ReW)

IS. 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.

IS. KEY WORDS (Cnte".e on ftr*& sid iO nefo.mp md IdenuIt I ek Rmw )

DAMS, INSPECTION, DAM SAFETY,

Thames River BasinColumbia, Connecticut

20. ABSTRACT (Ceoihgn en eoogro aid. II 0de 807 E I OIFP 6 ,101 114t)

Columbia Lake Dam is an earth dam which is-approximately 295.0 ft, long (includincspillway) and has a maximum height of 28,0 ft, The dam is considerqd to be inpoor condttion. A spillway design test flood outflow of 1418 cfs ( the PMF) willovertop the dam by approximately 0.93 ft.

DD, ,,N9 1473 EITION 0, 1NOV 0 IS OBSOLETE

I COLUMBIA LAKE DAM

CT 00520

I THAMES RIVER BASIN

COLUMBIA, CONNECTICUT

PHASE 1 INSPECTION REPORTNATIONAL DAM INSPECTION PROGRAM

h( been approved

rpi I J'c d sale; itsdiIb : ,j nint-d

NATIONAL DAM INSPECTION PROGRAM

PHASE 1 INSPECTION REPORT

Identification No.: CT 00520

Name of Dam: Columbia Lake Dam

Town: Columbia

County and State: Tolland County, Connecticut

£ Stream: Unnamed Stream

Date of Inspection: 18 May, 1978I

BRIEF ASSESSMENTIColumbia Lake Dam is an earth dam which was constructed

in 1865. The dam has a maximum height of 28.0 ft. and is

approximately 295.0 ft. long (including spillway). The

embankment slopes are approximately 2.5 H : 1.0 V. The

crest and downstream slope are grassed and the upstream

I face is riprapped above water level and to a depth of 3.0

ft. below water surface. The spillway is located on the

extreme left abutment of the embankment and is a curved conver-

Iging type contained between vertical rubble masonry walls.It is 26.0 ft. wide by 260.0 ft. long with a rubble stone

bed that was filled with dumped concrete. The spillway

1 flows discharge into a narrow natural stream bed leading

to a 6.0 ft. x 4.5 ft. concrete box culvert beneath

I41i

m m a m a I I I I

Route 87 immediately downstream from the dam. There are

I no plans, specifications or computations available from

the Owner, County or State offices regarding the design,

construction or repairs of this dam.

I Due to its age, Columbia Lake Dam was neither de-

signed nor constructed by approved state of the art meth-

I ods. Based upon the visual inspection at the site, the

lack of engineering data available, and no operational or

maintenance evidence, there are areas of concern which must

be corrected to assure the long term performance of this

dam. Therefore, based on existing information, this dam is

1 considered to be in poor condition.

There are several visible signs of distress which

indicate a potential hazard at this site: undermining and

J erosion beneath the spillway bed, deterioration of the

outlet gate to the point where its operation is difficult

i and unreliable, erosion holes adjacent to the operating

mechanism which may indicate leakage or seepage along the

outlet conduit, emerging seepage along the downstream toe of

the dam, dislodged stonework and obstructed downstream

spillway channel and a general lack of proper, regular main-tenance.

I

IHydraulic analyses indicate that the existing spill-

l way can discharge a maximum flow of 624.0 cfs at Elev.

! 502.0 (top of Dam). -A spillway design test flood outflow of

1418 cfs (one-half of the probable maximum flood) will

I overtop the dam by approximately 0.93 ft. Due to the po-

tential for overtopping, it is recommended that a definite

I plan for surveillance and a warning system be developed

for use during periods of unusually heavy rains and runoff.

It is recommended that the Owner immediately engage the

services of an engineer experienced in the design of dams

to accomplish the following: develop and implement a pro-

I gram of redesign for the dam to provide adequate spillway

capacity, freeboard, riprip protection, and outlet works

capacity using current hydrologic criteria; institute re-

pair and/or rehabilitation of the present outlet works gate

in order that control of the water be maintained; examine

Ithe present seepage and surface erosion holes and designa system for collection of the flow and monitoring; initiate

short term repairs to the spillway; develop and implement

I procedures to remove the rotting stumps and roots on the

dam slopes; and institute a limited subsurface boring and

Itesting program to accomplish the above. It is recommended

II

iiiT

Ithat the Owner also begin a regular program of inspection

I and maintenance including a plan of action for emergency

l situations.

The above recommendations should be implemented

I within 180 days after receipt of the Phase 1 Inspection

Report. The alternative to these recommendations would

Ibe to drain Columbia Lake and maintain the water surfaceat a reduced level.

!C-E MAGUIRE, INC.

Iby 01 ON,

i card . Long, P.2. NO. s595Vice President s

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I

IThis Phase I Inspection Report on the Columbia Lake Dam has beenreviewed by the undersigned Review Board members. In our opinion,the reported findings, conclusions, and recommendations arecons i stent wi th the ReLQL~g_nd d Lii1e-5_ fof eu. Inspection

of Dams, and with good engineering judgment and practice, and isI hereby submitted for approval.

CHARLES G. TIERSCH, ChairmanChief, Foundation and Materials BranchEngineering Division

i FRED J. S, r., Memb erChief, De gn BranchEngineering Division

Chief, Water Control BranchEngineering Division

!

I APPROVAL RECOMMENDED:

I j-6 TRYAR.Chief, Enqineering Division SEP 29 1978

Iv!VIi'

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, ' I

PREFACE

This report is prepared under guidance contained in theI Reconmmended 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 dam is based upon availabledata and visual inspections. Detailed investigation, and analysesinvolving 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 dam is based on observations of field conditionsat the time of inspection along with data available to the inspectionteam. In cases where the reservoir was lowered or drained prior toinspection, such action, while improving the stability and safety ofthe dam, removes the normal load on the structure and may obscurecertain conditions which might otherwise be detectable if inspectedunder the nonial operating environment of the structure.

It is important to note that the condition of a dam depends onnumerous and constantly changing internal and external conditions,

Iand is evolutionary in nature. It would be incorrect to assume thatthe present condition of the dam will continue to represent thecondition of the dam at some point in the future. Only throughcontinued care and inspection can there be any chance that unsafeconditions be detected.

Phase I inspections are not intended to provide detailed hydrologicand hydraulic analyses. In accordance with the established Guidelines,the Spillway Test flood is based on the estimated "Probable MaximumFlood" for the region (greatest reasonably possible storm runoff). orfractions thereof. Because of the magnitude and rarity of such a stormevent, a finding that a spillway will not pass the test flood shouldnot be interpreted as necessdrily posing a highly inadequate condition.The test flood provides a measure of relative spillway capacity andserves as an dide in detenining the need for more detailed hydrologicand hydraulic studies, considering the size of the dam, its generalcondition and the downstream daiimge potential.

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i I I

TABLE OF CONTENTS

LETTER OF TRANSMITTAL

J BRIEF ASSESSMENT i

REVIEW BOARD SIGNATURE SHEET v

PREFACE vi

TABLE OF CONTENTS vii

OVERVIEW PHOTO ix

LOCATION PLAN

REPORT

SECTION 1 - PROJECT INFORMATION

1.1 General 11.2 Description of Project 21.3 Pertinent Data 8

SECTION 2 - ENGINEERING DATA

2.1 Design 132.2 Construction Records 132.3 Operation Records 132.4 Evaluation of Data 13

SECTION 3 - VISUAL INSPECTION

3.1 Findings 143.2 Evaluation 17

vI

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Ivii . ....

TABLE OF CONTENTS

Page

SECTION 4 - OPERATIONAL PROCEDURES

4.1 Procedures 174.2 Maintenance of Dam 184.3 Maintenance of Operating 19

Facilities4.4 Description of Any Warning System

in Effect 194.5 Evaluation 20

[ SECTION 5 - HYDRAULIC/HYDROLOGIC

5.1 Evaluation of Features 20

SECTION 6 - STRUCTURAL STABILITY

6.1 Evaluation of StructuralStability 24

SECTION 7 - ASSESSMENT, RECOMMENDATIONSAND REMEDIAL MEASURES

7.1 Dam Assessment 277.2 Recommendations 317.3 Remedial Measures 32

APPENDIX

A Visual Inspection Check List1B Records, Inspection, Sketches, Drawings

C Selected Photos

D Hydrologic Computations

E Information as Contained in the National Inventoryof Dams

II

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W4tchoster-_ LOCATION PLANhas or COLUMBIA LAKE DAM

MIN mug Stall I "a 2.0 milesHas PLATE NQ I

.DA POND

PHASE I INSPECTION REPORT

COLUMBIA LAKE DAM CT 00520

I SECTION 1

. GPROJECT INFORMATION

1.1 General

a. Authority. Public Law 92-367, August 8, 1972,

authorized the Secretary of the Army, through the

ICorps of Engineers, to initiate a national programof dam inspection throughout the United States.

The New England Division of the Corps of Engineers

Ihas been assigned the responsibility of supervi-

sing the inspection of dams within the New England

i Region. CE Maguire, Inc., has been retained by

1 the New England Division to inspect and report on

selected dams in the State of Connecticut.

f Authorization and notice to proceed was issued to

C-E Maguire, inc., under a letter of 26 April,

11978, from Ralph T. Garver, Colonel, Corps of

ii Engineers Contract No. DACW33-78-C-0300 has been

assigned by the Corps of Engineers for this work.

j b. Purpose

(1) Perform technical inspection and evaluation

I of non-Federal dams to identify conditions

I1 1

II

I which threaten the public safety and thus

I permit correction in a timely manner by non-

Federal interests.

1 (2) Encourage and assist the States to initiate

g quickly effective dam safety programs for

non-Federal dams.

1 (3) To update, verify and complete the National

Inventory of Dams.

11.2 DESCRIPTION OF PROJECT:a. Location: Columbia Lake is located in the She-

tucket River watershed of the Thames River Basin,

I approximately 1.5 miles northwest of Columbia,

Connecticut, in Tolland County. Columbia Lake

I has a surface area of approximately 270.0 acres,

an average depth of 17.0 feet and a shoreline

length of about 7.6 miles. The watershed of 3.1

I square miles drains a rolling terrain which con-

sists of swampland, woodland and farmland. The

dam is located in the northwest corner of the lake

parallel to, and approximately one hundred and

eighty feet from, the highway embankment for

Connecticut Route 87.

b. Description of Dam and Appurtenances: Based on

I visual inspection, the dam is an earth embankment

2

Ar. .. . - _2 "2 .. . . . . . . . . . . . . . . . ... . 1 II . . . . . .

1 with a crest length of 295.0 feet (including

I spillway.) The upstream and downstream slopes are

approximately 2.5 H : 1.0 V. The crest and the

I downstream slope are grassed. The upstream side

m is riprapped above water level and to a depth of

at least 3.0 ft. below the water level. At th,.

time of inspection, the water level was 1.1 feet

below the crest.

I The spillway is located on the extreme left side

of the embankment and is a converging type con-

tained between vertical rubble masonry walls. It

I is 26.0 feet wide by 260.0 feet long with a rubble

stone bed that was filled with concrete. The

I right training wall is of grouted rubble and

ranges from a height of 4.0 feet upstream to about

1.5 feet on the downstream side. The left train-

fi ing wall is of dry rubble construction with an

average height of 9.0 feet. The spillway dis-71 charges from a rubble stone channel to a rela-

gi tively small natural stream bed leading to a

concrete box culvert 6.0 feet wide by 4.5 feet

I high under Route 87.

The intake gate for the outlet works is located

I on the outside face of a pier consisting of

II 3

I

I vertical stone walls which have apparently been

I filled with earth. The pier is located to the

right of center of the dam embankment, and it

I extends approximately 60.0 feet out into the lake.

The gate is manually operated. The mechanical

works are positioned on the extreme upstream end

I of the pier (see Photo C-6). The downstream end

of the outlet is an 18-inch diameter cast iron

I pipe which discharges into a 40-inch wide by 16-

inch high stone box culvert (see Photo C-7). The

downstream channel is a natural streambed. It

flows to the box culvert beneath Route 87 (see

Photo C-8).1C. Size Classification: The dam is classified as

intermediate in size because the impoundment at

I crest elevation is 3370 Ac.-Ft. which exceeds

1000 Ac.-Ft., the limiting criteria for intermedi-

Iate size.

d. Hazard Classification: The dam is classified as

a significant hazard potential because it is lo-

I cated in a predominantly rural or agricultural

area where failure may damage isolated homes,

I secondary highways and some public utilities.

!'

4

II A"INN 9O

e. Ownership: Town of Columbia, Connecticut. The

dam was built around 1865 by the Willimantic

Linen Company to augment their water supply.

m Ownership was transferred to the Willimantic

Linen Company (now called the American Thread

Company) in 1898 and in 1933 the title was trans-

I ferred to the present owner.

I f. Gate Tender: Mr. Marshal NuhferNuhfer DriveColumbia, Connecticut 06237(203)-228-3018

g. Purpose of Dam: Columbia Lake is presently used

I solely for recreation.

h. Design and Construction History: Columbia Lake

is an entirely artificial body of water. In the

early 1800's, a small millpond was built near the

present outlet to provide water power for a

I sawmill. In 1865, the Lake as it appears today

was created when the Willimantic Linen Company of

Willimantic, Connecticut (now the American Thread

( Company) built the currently existing larger dam.

For the next 68 years (until the water rights

were purchased in October, 1933, by the Town of

I

I Columbia) the lake was used as a back-up source

I of water power. As manufacturing in Columbia

slowly declined, the importance of the lake as a

I recreational attraction steadily increased.

In November, 1939 (as a result of the performance

I of the dam during the hurricane of September,

1938), following a directive from the State Board

of Supervision of Dams for Connecticut, the dam

I was modified. The spillway was doubled in width

from 13.0 feet to 26.0 feet and lined with "stone

I pavers." Records of that time also indicate that

it was recommended that a 12-inch cut-off wall be

installed beneath the spillway, penetrating 3.0

I feet to 4.0 feet into hard material.

I In April, 1963, it was recommended by a consultant

g to the State of Connecticut that all trees be

removed from the embankment, debris cleared from

I the spillway, and an emergency spillway be

excavated in natural ground at the right end of

I the embankment. An inspection of the dam in

g March, 1966, indicated that the trees and debris

had been removed, but no emergency spillway had

Ibeen excavated. In February, 1968, material was

6

NOW

added to the downstream slope above the toe wall

3 and seeded. The top of the dam embankment was

leveled, and an emergency spillway started. In

1 August, 1968, the State of Connecticut, fearing

possible overtopping of the dam based upon the

performance of the dam during storms in March,

g1968, directed that the emergency spillway be

refilled to its former height.

I Raising of the embankment 1.7 feet to provide

additional freeboard, the addition of riprap on

the upstream face, repairs to the spillway dis-

Icharge and removal of trees and brush were recom-mended in September, 1971, by a consultant to the

Water Resource Commission of the State. There

were no observations made during visual inspection

that would indicate that the dam has been raised

Isubsequent to the 1971 recommendations. Therefore,

the height of the dam now is apparently the same

I as in 1865.

i. Normal Operational Procedures: Water surface

levels in Columbia Lake are normally lowered

I approximately 6.0 to 8.0 feet around October 1 of

each year, after the recreational season ends, to

Iprotect shoreline docks and piers from ice damage.

77 o

__m.. . , ,r-- ____ __,_____ I.'g

This reduced level is maintained until late

spring when ice is no longer a problem. At this

time, the gate is closed and the run-off collected

for the next recreational season. Normal pool

elevation is 498.0 NGVD (National Geodetic Verti-

cal Datum).

1.3 PERTINENT DATA

a. Drainage Area: The Columbia Lake drainage basin,

t located in eastern Connecticut, is generally

elongated in shape and has a length of about 3.0

miles, an average width of 1.0 mile, and a total

drainage area of 3.1 square miles. The topography

is generally rolling hills with hilltops at

Elevation 700+. Basin slopes are generally flat

to moderate. A large swamp area (0.2 square

miles) in the upper reaches of the watershed

tends to dampen the effect of surface run-off

from the steeper slopes of the wooded hillsides.

A general basin map is enclosed, see Appendix D.

b. Discharge at Dam Site: The largest storm experi-

enced at the Columbia Lake Dam was the September,

1938 hurricane. Calculations prepared by the

State of Connecticut in 1968 indicate that with

the spillway 13.0 feet in width and the water level

8

approaching the top of the dam, the estimated

Idischarge was 270 cfs during the 1938 hurricane.It is estimated that 960 cfs will flow into the

I reservoir due to a 100 year frequency storm

event. This peak inflow rate is reduced by

storage to produce an outflow of 132 cfs at the

spillway, which is now 26.0 feet wide as computed

by the Soil Conservation Service technique. The

I spillway design test flood (1/2 Probable Maximum

Flood) as calculated in Appendix D is 3120 cfs and

1418 cfs as inflow and outflow, respectively

I based upon 1000 CSM as inflow value. Listed below

are discharge data for spillway and outlet works:

1. Outlet works (conduit) size 18 inch diameter.

Cast iron pipe with invert Elevation 471.0+

2. Maximum known flood at dam site 270 cfs in

1 1938.

3. Spillway capacity at maximum pool level

I(Elevation 502.0) - 624 cfs.

4. Gated outlet capacity at normal pool eleva-

tion with an open 18-inch diameter cast-iron

pipe 73.0 cfs, with reservoir, at Elevation

498.0 and tail water at Elevation 471.0.

9

I 5. Gated outlet capacity at maximum pool level

3 (Elevation 502.0) - 77 cfs.

6. Total discharge (spillway and outlet) capa-

I city at maximum pool level (Elevation 502.0) -

701 cfs.

I c. Elevations: (feet above NGVD)

1. Top of Dam - Elevation 502.0

2. Maximum pool-design surcharge - 4.0 feet

I with no freeboard

3. Full flood control pool - Elevation 502.0

I with no freeboard

n 4. Recreation pool - Elevation 498.0

5. Spillway crest - Elevation 498.0

6. Upstream invert of intake structure - Ele-

vation 471.0 (estimated) - 27 feet + below

n normal pool level

i 7. Estimated elevations of streambed at center-

line of dam upstream 471.0, downstream 470.0

I 8. Maximum tailwater - not computed

d. Reservoir Lengths: (feet)

i 1. Length of maximum pool - 5,600

2. Length of recreational pool - 5,600

3. Length of flood control pool - 5,600

I

I 10

N

e. Reservoir Storage: (acre-feet)

1. Recreation pool - 3,370 at Elevation 498.0

2. Flood control pool - 1,080 at Elevation 502.0

I 3. Surcharge - 1,080 between Elevation 498.0

and 502.0.

4. Top of dam - 4450 at Elevation 502.0.

J 5. Flood control pool of 1080.0 Ac.-Ft. repre-

sents 6.50 inches of runoff from the 3.12

1Sq. Mi. Basin.

f. Reservoir Surface: (acres)

1. Top of dam - 270

2. Maximum pool - 270

3. Flood-control pool - 270

4. Recreational pool - 270

i 5. Spillway crest - 270

6. One foot of surcharge represents 1.62 inches

I of runoff from its drainage area of 3.12 Sq.

Mile.

I g. Dam

1 1. Type - Probably earth, because emergency

spillway excavation was apparently made in

earth and exposed surfaces are of earth.

IIi

J _ m| 11

I2. Length - 295.0 feet (including spillway)

1 3. Height - 28.0 feet from streambed (downstream)

4. Top Width - 16.0 feet

I 5. Side slopes - 1 vertical on 2.5 horizontal

(scaled)

6. Zoning - Unknown

7. Impervious Core - Unknown

8. Cut-off - Unknown. Correspondence indicates

i that a concrete cut-off 3 to 4 feet deep may

exist beneath the spillway)

9. Grout curtain - Unknown

I 10. Other Dry, cut-stone toe wall 6 to 10 feet

high

I h. Spillway

1. Type - Curved, converging, broad-crested,

overflow spillway

2. Length of weir - 26.0 feet maximum normal to

the flow converging to 16.0 feet

I 3. Crest elevation - Elevation 498.0

I 4. Gates - None

5. Upstream Channel - Straight, natural bed

i. Regulating outlet

1. Invert Elev. 471.0+

2. Size - 18" dia.

I 3. Description - Cast Iron Pipe

4. Control Mechanism-Manually operated vertical

slide gate

Ii 5. other- -

12* I I. I.. I~ * .~

I I_________________

SECTION 2

IENGINEERING DATA

2.1 DESIGN

I A topographic survey of the dam embankment conducted

by T.A. Brindamour in June, 1968 is the only engineering

I data available. Elevations indicated on the topo-

graphic map resulting from this survey were not veri-

I fied during this Phase I study.

2.2 CONSTRUCTION RECORDS

No data available.

2.3 OPERATION RECORDS

No data avilable.

I 2.4 EVALUATION OF DATA

I a. Availability - Limited to data menticned in 2.1.

b. Adequacy - Not adequate

J c. Validity - Not verified

I

III

i 13

,I! I , I ° II I I I

I SECTION 3

IVISUAL INSPECTION

1 3.1 FINDINGS

a. General: At the time of the inspection, it ap-

peared that the dam had recently been trimmed of

brush and undergrowth and the downstream channel

and terrain cleared. Fencing at the entrance to

I the access road and private property abutting the

damsite has prevented surface erosion from tres-

pass. It was observed that an attempt had been

I made in the past to repair the spillway bed using

dumped concrete, but undermining of that slab is

I apparent. The masonry of the spillway training

walls, particularly at the downstream ends, was

dislodged and obstructing the bed of the spillway.

I Surface erosion holes in the crest of the outlet

gate pier structure were observed. In general,

it appeared that the condition of the dam was

declining and not being properly maintained.

b. Dam: Seepage at rates ranging up to several

Igallons per minute was observed emanating fromthe downstream side of the dam at locations

I indicated on Plate No. 3 and shown in Photographs

Nos. C-5 and C-10.

n14

INumerous stumps and, hence, rotting roots wereIpresent on the upstream and downstream slope.

Photographs were taken of some stumps and appear

Iin Photograph No. C-9.

An emergency spillway that was excavated on the

dam crest, according to correspondence, appears

to either have been incompletely backfilled or

settled, as there is a definite low spot at pre-

I sent at that location.

The outside perimeter of the 18 inch diameter

cast-iron-pipe outlet conduit at the base of the

Idam was wet, indicating that seepage may be

occurring along its perimeter.

I c. Appurtenant Structures: Surface erosion holes up

to 2.75 feet deep were found on the upbtream end

of the gate support structure. See Plate No. 3

I for locations and Photograph No.C-ll.

Surface erosion holes were also found along the

I westerly spillway wall immediately west of the

stonework. These are very likely due to loss of

soil from openings between stones resulting from

Iinadequate filter material between the stoneworkand the soil. The spillway was found to be seri-

I ously undermined and inadequate in size. Training

15

A- I Ii I

IIwalls were collapsed and dislodged on the down-

stream discharge slope of the spillway.

IThe intake control of the outlet works was repor-

Itedly leaking severely, requiring alternate means

to stop the leakage. These alternate means were

Ireported to be dumped cinders adjacent to thegate.

d,. Reservoir Area: Gneiss bedrock was exposed 50

feet upstream from the right abutment of the dam

embankment. At this location it is planar and

j dips at an angle of 108 in the direction N 800 W.

A one-half inch wide nearly vertical joint in the

I rock is exposed. Its intersection with the hori-

zontal plane strikes N 500 W, toward the highest

part of the dam. The alignment of this joint

I with the main embankment intersects at a point

which projected to the downstream toe lies near

I the seep area indicated on Plate No. 3 and could

be the cause of that flow.

e. Downstream Channel: The downstream channel is

1 irregular and overgrown with trees. The bed of

the channel is stained with a rust colored deposit.

I Several channels have been formed by the

I flowing water that emanates from the downstream

I 16

side of the dam. The beds of these channels are

also rust-stained.

3.2 EVALUATION

I Visual observation made during the course of the

inspection did not indicate any conditions of an im-

mediate critical nature. Several of the deficiences

I observed and discussed above require attention and

should be corrected before further deterioration de-

I velops a hazardous condition. Recommended measures

1 are discussed in Section 7.

SECTION 4

I OPERATIONAL PROCEDURES

4.1 PROCEDURES

Ia. Normal Operating Procedures: Columbia Lake is

presently used primarily for recreational purposes.

Regulation of the water level in the lake is syn-

j chronized with the summer boating and bathing

season. Operation of the control outlet gate

I (which is always locked) is accomplished by a

1 lake-front resident, Mr. Marshal Nuhfer, for the

Town of Columbia. Generally, around the beginning

1 of October the water level is lowered from Eleva-

tion 498.0 (Spillway Crest) approximately six to

I eight feet and held at that reduced level by

117

I#

i intermittent gate openings until the danger from

J ice damage to shorefront docks and piers has

passed in the spring. Depending on the severity

i of the winter, the gates are closed on or about

mid-March in order to raise the level back to its

summer use stage. There are no other outlets to

i the impoundment.

b. Emergency Operating Procedures: Impending in-

iI tense rainfalls from approaching storms are moni-

tored by the gate tender, the Town road foreman

and the Selectmen through local radio or tele-

vision forecasts or direct contact with the

weather bureau. Keys to the control gate are

held by the gate tender and the road foreman. No

formal procedure exists for emergency situations.

The necessary control is based on a judgment made

Iby the keyholders or by the Selectmen. No records

or graphs exist indicating past discharge or

Iwater levels.

i 4.2 MAINTENANCE OF DAM

Maintenance of the dam has been neglected and has

I occured generally only when directed by the State as a

result of their inspections.!

18 V.

Ma.

1 4.3 MAINTENANCE OF OPERATING FACILITIES

I Monitoring the need for maintenance of the gate control

is generally the responsibility of the gate tender.

I The intake control mechanism is an aged mechanical

structure exposed to weather and vandalism. Problems

with closing the gate and leakage through the outlet

1 pipe have been reported annually. Proposals for

repairing the gate were requested by the Town in 1972,

but no action was taken. On the downstream side, the

outlet lies within the embankment toe and could be

blocked or completely obstructed by the occurrence of

j a small slide or dislogement of stones.

4.4 DESCRIPTION OF ANY WARNING SYSTEM IN EFFECT

INo formal warning system is used, but rather the gate

operator, using public weather forecasts, judges the

emergency and operates the gate accordingly. There is

Ino pre-planned effective warning system for the failure

of Columbia Lake Dam. An emergency action plan must

Ibe developed in order that operating personnel can

notify authorities for mobilization of State and local

emergency forces, organize remedial measures to mini-

Imize or prevent complete failures when possible andhave an awareness of the locations of standby equipment

Iand materials.

I19

1 19I

4.5 EVALUATION

I The dam and its appurtenances have been seriously neg-

lected. There is no record of a formal program of

I inspection or maintenance conducted by the Owners nor

is there a definitive contingency plan for emergency

situations.

jSECTION 5

HYDRAULIC/HYDROLOGIC

1 5.1 EVALUATION OF FEATURES

a. Design Data: No specific design data is avail-

able. In lieu of existing design information,

I[ the U.S.G.S. topographic maps (Columbia Lake

Quadrangle) were used to develop hydrologic

Iparameters. Outflow for the Spillway DesignFlood was developed using approximate routing

parameters with the lake at spillway crest level

f (see Appendix D). Pertinent hydraulic design

data was obtained and/or confirmed for the spill-

I way, outlet and other appurtenant structures by

(actual field measurements. The dam failure

profile was developed from the above mentioned

I topographic mapping. Surcharge storage was

approximated assuming that the lake surface area

I remained constant above spillway crest elevation

(as required by Corps) The results of the flood

routing are as follows:

I1 20%

0 E-

0 'o r

0 ~ 0.E14 0 4(n Enr4

'o rqr -r- 4 0 ~ 41 0-'0 .) >) :3r

::) E4 Z V 4) UE(n 44 r I 4 -I0 0

>1 &U>

ON 414c H%.0 0 No 0 ) ~ 4in r-4 cnr, -4 0 0 0 4.) 413~-Cz~. i - 4 rli .- 0 "q

z 4j0 It) u

U)~~: 4. 4 .1.0 w0 0N1

E44 0 '1 4-) 44 0 0

I'4.3 4) 43

U) 0 4341 q w 0 41

u ad 44141 0. ..10- 41 0 IU .4. (D 04 4

10 0o :3 4w'L 0

41 0 4.) 0

1-4 4110 :"Jg- H 0U 0 0 >- 4*r-" 4 U 4J 0t' '

w44 19Z %-4 V-4 0 m-t o0z (A NJ -H. 0 01'04 ONr~ V- 0 041. '

'' -4i 0 U) 'E-iZ V'4-4 N. 0 cto4 *- 0 v-4

4 0 v 0. 0 U 41 0

r-4 Ln 00 'U 0) a0 .E4 z 041 0u V Q -.-4 4j uUW00 tv 0 44 4U"E-4)4- H'. 0z r- v) ( 1AQ 4'Qi 4J M 0 '.4 0t 'rq us w -4 &C 'U- E V 'U

41z z Uo r -~II ~9a VO ' 0 ,-d AE- m) 0- 41 N U i - .01- 0 (n 0 N4 U) '44 CO) WC4 ~ ~ . 9 -4IVI

4rq0 Id uI

iv 0 N l

b. Experience Data

1. Spillway:

1938 Flood Q outflow = 270 cfs

Surcharge = 2.75 feet (esti-

mated)

The Dam was sandbagged to prevent overtopping.

Water levels approached within one foot of the dam

crest elevation. As a result of this flood the

spillway was doubled in size.

1955 Flood No records available

1968 Flood Q outflow = 65 cfs (estimated)

Surcharge = 0.75 feet

2. Outlet and Intake Structure: A vertical

pier which extends approximately 60 feet out

into the lake is oriented normal to and

flush with the top of the embankment and

(contains the control mechanism for the

outlet. This consists of an old manual

hoist, which, through a series of gears,

lifts vertically an 8.0 inch wooden gate post.

The only information available for te

assembly in which the gate seats is a sketch

made by a diver in May, 1968. This sketch

indicates that the gate rides in a tapered

I~22

slot on the face of the pier. The gate

seats in front of the outlet conduit. A

timber trash rack in front of the gate was

in bad disrepair according to the diver

survey. (See attached sketches - Appendix

B). Seating of this gate has become a

serious problem.

c. Visual Observations:

1. Spillway bed is undermined and in poor con-

dition.

2. Spillway training walls are eroded, dislodged

and collapsed on the downstream slope.

3. Intake control structure is in urgent need

of repairs.

4. Emergency spillway was refilled and no

longer exists, but filling was incomplete or

settlement of the placed material has occurred,

leaving a low spot in the crest of the dam.

d. Overtopping Potential: Spillway is hydraulically

inadequate and structurally unsafe to pass the

Spillway Design Flood. The surcharge created by

this Flood will overtop the lowest point on the

dam crest by approximately 0.90+ feet. The 100-

I

23

II

year storm event with hurricane-type winds will

produce wave set-up and ride-up that would be

dangerous to the dam because of inadequate free-

board. The upstream face of the dam requires

additional slope protection for wave action. The

maximum discharge capacity of the spillway without

overtopping the dam is 624 cfs which is 44% of the

test flood outflow discharge of 1418 c.f.s. See

Appendix D for Spillway Rating Curve.

SECTION 6

STRUCTURAL STABILITY

6.1 EVALUATION OF STRUCTURAL STABILITY

a. Visual Observations: There were several signs of

structural distress evident during the visual

inspection that are discussed in various sections

of this report (seepage, spillway slab, spillway,

training walls, outlet works pier, etc.)

b. Design and Construction Data: No such data are

available and an evaluation cannot be made.

C. Operating Records: The gatekeeper has indicated

that 12-inch size stones with mortar on them

passed out of the 18-inch cast iron discharge

conduit. No evidence of such major damage was

visible at the time of the inspection. The

24

F

I surface erosion holes mentioned in Section 3.1

5 (c) may be related to such losses.

d. Post-Construction Changes: Available correspond-

I ence indicates that sandbags were placed on the

crest during the 1938 hurricane, but that those

sandbags were not found to be needed. After the

I hurricane, the spillway was widened from 13.0

feet to its present 26.0 feet and a concrete

1 cutoff 3 to 4 feet deep was apparently placed

beneath the spillway channel at an unrecorded

location.

I An emergency spillway was cut into the right side

of the dam. The bottom of the channel, which was

I unlined, was 2.0 feet above the present spillway

channel, according to the correspondence. This

emergency spillway was subsequently filled with

I earth of an unspecified type in an unspecified

manner by Town of Columbia work crews.

Trees up to 20 inches in diameter were allowed to

grow in substantial numbers on the upstream and

downstream sides of the dam. Subsequently, these

j trees were cut, leaving stumps and roots that are

now rotting. The brush was most recently cleared

I from the downstream face of the dam in the fall

of 1977, so that at the time of the inspection,

1 25

IP

i there was no brush present, only grass and low

I growth up to about 18 inches in height.

The downstream face of the dam was, according to

I the correspondence, flattened to its present

slope by adding fill. The fill type was not

specified, nor was the method of placement. The

I fill was added in a wedge from the crest to the

top of the toe wall in an apparent effort to make

i the dam more stable. Placement of such additional

weight above the toe wall reduces the stability

of the downstream slope. If this fill is less

1 pervious than the embankment itself, then the

stability of the downstream slope would be re-

1 duced. Only if the fill were equally or more

pervious than the embankment, and if it extends

down beyond the toe wall, would the downstream

I slope stability be improved.

e. Seismic Stability: This dam is in seismic Zone

J 1 and, hence, does not have to be evaluated

for seismic stability according to the Recom-

mended Guidelines.

II1 26

I.

I A

1I SECTION 7

ASSESSMENT, RECOMMENDATIONS & REMEDIAL MEASURES

7.1 DAM ASSESSMENT

a. Condition: Based on the visual inspection,

records available of the site and past opera-

tional performance, the dam is judged to be in

poor condition. A review of the limited data

available reveals that there are areas of

concern which must be corrected in order to

assure the long term performance of the dam.

These concerns are as follows:

1. The spillway bed is undermined over a

substantial area, has steep, unprotected

downstream slopes with loose rubble

masonry which is generally dislodged,

I settled or eroded. Prior patching with

dumped concrete has been ineffective.

I High impoundment levels cause flow be-

neath the spillway floor slab. These

flows could produce serious undermining

I and erosion and could lead to subsequent

failure of the dam.

1 2. Surface erosion holes adjacent to the

I operating mechanism at the upstream end

1 27

L

iI of the gate support structure may be due

J to erosion through holes in the masonry

or into the discharge conduit. Observable

I evidence at the site does not indicate

which way the material is being lost.

Loss of material through the outlet would

be dangerous to the integrity of the dam.

3. It was reported that closing the gate of

I the outlet works has become increasingly

difficult with leakage and possible

clogging occurring. In April of this year

I it was reported that, to prevent this

leakage, cinders were dumped immediately

9 upstream of the gate face. Unless imme-

diate repair to the gate is undertaken,

I water levels cannot be controlled.

g 4. Large trees were allowed to grow on both

embankment faces and were subsequently

I cut. Roots of these trees located on

both the upstream and downstream dam

slopes continuously rot and form increas-

I ingly dangerous discontinuities in the

embankment where seepage and erosion

I

I128 -

I "-I.I

may concentrate. These stumps should be

J given special attention during future

inspections to watch for any signs of

I developing seepage, until a program for

their subsequent removal has been devel-

Ioped. It is particularly important that

embankment slopes be well maintained in

order that inspectors can closely discern

I changes that may occur.

5. significant seepage was observed exiting

I from several locations along the down-

I stream toe of the dam and from the abut-

ments. Seepage was observed and reported

to flow under the spillway floor slab and

to exit on the downstream slope of that

Ichannel. The zone outside of the 18 inchI diameter discharge conduit on the down-

stream end was wet. Although these

seepage conditions may have been occurring

for many years, continued seepage aggra-

vated by a rise in the water level behind

m this dam may, over a period of time, lead

to internal erosion (piping) of the dam.

" II

6. The spillway capacity does not satisfy

J the screening criteria established by the

Corps of Engineers for the Spillway

I Design Flood. The adopted storm event

(1/2 Probable Maximum Flood) overtops

this dam. The freeboard allowance is

I also inadequate for the 100-year recur-

rence interval storm event (see Appendix

I D).

7. Both east and west spillway training

walls on the downstream slope show signifi-

I cant signs of wear with stones dislodged,

or collapsed into the spillway bed.

1 8. There is no proper and regular maintenance

and inspection program for the dam, nor

is there a formal warning system for

I emergency situations.

B. Adequacy of Information: The information

I available is such that the assessment of the

condition of this dam must be based primarily

on the visual inspection and the past operation-

j al performance of the structure.

C. Urgency: It is considered that the recom-

I mendations suggested below be implemented

II30"''

I a

within 180 days of receipt of this Phase 1

J report.

D. Need for Additional Information: There is no

Ievidence that formal engineering analyses wereever performed for this dam. The visual

inspection and operational history indicate

Ithat attention should be given to the collec-

tion of current data in order that the recom-

I mendations listed below may be implemented.

7.2 RECOMMENDATIONS

a. Facilities: In view of the concerns for the

condition of Columbia Lake Dam, and the lack

of engineering backup data, it is recommended

I that the following measures be undertaken by

the Owner.

1. Engage the services of an engineer experi-

enced in the design of earthen dams to

collect, analyze and develop designs to

I accomplish these recommendations.

2. Institute immediately an analysis for the

short term repair and/or rehabilitation

I of the present outlet works gate in order

that control of the water level can be

I maintained.

I,3

I . .. .. _ . . . . . . . . .. __ -_ i L .. . _F k1 1

M 3. Initiate an examination and design to

I develop and implement short term repairs

to the spillway to prevent further under-

I mining and potential erosion.

i 4. Examine the present seepage emanating

from the downstream toe and design a

I system for collection and monitoring this

flow in order that changes in flow quantity

i and sediment transport can be detected.

5. Investigate the cause and correct the

surface erosion holes on the gate mechanism

I pier.

6. Redesign and reconstruct the dam to

I provide adequate spillway capacity,

i surcharge storage capability, freeboard,

slope protection and outlet works capacity

using current hydrolic criteria.

7. Implement immediately a limited subsurface

I boring and testing program to accomplish

i the above items.

7.3 REMEDIAL MEASURES

a. Alternatives: As an alternate to the immediate

commencement of studies to upgrade the struc-

I ture Columbia Lake water surface levels should

I32

ii be lowered and maintained at a level well

below the spillway crest. That reduced level

should be controlled to provide storage for

Jstorm events.

b. Operations and Maintenance Procedures: While

Ithe dam has had some maintenance, it is consid-

1ered important that the following items be

attended to as early as is practical:

1 1. Develop and commence a regular inspection

and maintenance schedule for the 2acility.

2. Incorporate in the above program monitor-

I ing of the seepage and examination of the

tree stumps on the slopes. Once a pro-

Icedure has been developed for the removal

m of the rotting stumps and roots, incorpo-

rate this procedure into the regular

m maintenance program.

3. Develop a system for the recording of

m data with regard to items such as: water

m levels, discharges, time and drawdown to

assist those responsible for the monitor-

I ing of the structure.

4. Prepare an "Emergency Action Plan" to

m prevent or minimize the impact of failure,

II 33

I _ _ _ _ _,

listing the expedient action to be taken

I and authorities to be contacted.

5. Because of the concerns for this dam and

Ithe limited data available, an around-the-

clock surveillance should be instituted

during periods of high precipitation.

IIIIIIIIIIII 34

I O

p__!E

II1I1I

I APPENDIX A

VISUAL INSPECTION CHECK LIST

11I

I11II

I __

-

I ___

VISUAL INSPECTION CHECK LISTI PARTY ORGANIZATION

PROJECT COLUMBIA LAKE DAM DATE 18 MAY 1978

TIME 0830 - 1630

IWEATHER CLOUDY -RAIN

W.S. ELEV. _____U.S.____D.S.

I PARTY:I. R.W. LONG CEM 6. STrAN CEM

I 2. E. A. REED CEM 7. ____________

3. S. POULOS GE 1 8. ____________

4. R. BROWN CEM 9

I . V. GALGOWSKI STATE OF CONN. 10 _____________

PROJECT FEATURE INSPECTED BY REMARKS

1.

3.

I 6.

7.

I 8.

10.

_ A-i1 .

PERIODIC INSPECTION CHECK LIST

l PROJECT COLUMBIA LAKE DAM DATE 18 MAY 1978

INSPECTOR DISCIPLINE

I INSPECTOR DISCIPLINE

AREA EVALUATED CONDITION

I DAM EMBANKMENT

Crest Elevation Elevation 502.0

I Current Pool Elevation Elevation 498.0

i Maximum Impoundment to Date See Section 1

Surface Cracks None observed

I Pavement Condition No pavement, grass covered

Movement or Settlement of Crest Depression about 6' to right of spillwaywall on top of crest. About 3" below upand downstream crest line.

I Lateral Movement None olbserved

Vertical Alignment Surface is too irregular to judgealignment. No pronounead misalignment

Horizontal Alignment observable.

I Condition at Abutment and at At right abutment dumped fill used toStructures seal emergency spillway. Slight depres-

sion in this zone. Fill could be loose.Left abutment is spillway wall.

I Indications of Movement of StructuralItems on Slopes None observed.

Trespassing on Slopes Free Access. Crest grass is worn thin.

Sloughing or Erosion of Slopes orAbutments Downstream slope very slightly gullied

by surface erosion. One animal holedownstream just above toe wall.

I Rock Slope Protection - Reprap Failures Riprap sloughing to left of upstreamjetty. Slope is eroded from wave action.

I Unusual Movement or Cracking at ornear Toes None Observed

A-2 4

dA-2 * ~• -, .J

I PERIODIC INSPECTION CHECK LIST

I PROJECT COLUMBIA LAKE DAM DATE 18 May 1978

INSPECTOR DISCIPLINE

I INSPECTOR DISCIPLINE

AREA EVALUATED CONDITION

DAM -4BANKENT

I Unusual Embankment or DownstreamSeepage Several seeps downstream on left and

right sides. All appear to be siltfree

Piping or Boils None observed

Foundation Drainage Features None

I Toe Drains None

Vegetation Several old stumps on both faces. RottingIInstrumentation System A-2 None

IIIIIII

I"A-3 ,

IPERIODIC INSPECTION CHECK LIST

PROJECT COLUMBIA LAKE DAM DATE 18 MAY 1978

INSPECTOR DISCIPLINE

i INSPECTOR DISCIPLINE

AREA EVALUATED CONDITION

i OUTLET WORKS - SPILLWAY WEIR, APPROACHAND DISCHARGE CHANNELS

a. Approach Channel Riprap apron

General Condition Poor to fair

Loose Rock Overhanging Channel None observed

Trees Overhanging Channel None observed

I Floor of Approach Channel Natural w/riprap apron grouted

b. Weir and Training Walls

General Concition of Concrete Dry rubble walls westerly side goodexcept for downstream end.Grouted rubble wall easterly side goodexcept for downstream end.Slab - Grouted stone, poor conditionundermined.Downstream end bad

Rust or Staining None observed

Spalling N/A

Any Visible Reinforcing None observed

Any Seepage or Efflorescence None observed

I Drain Holes N/A

' c. Discharge Channel

General Condition Poor

Loose Rock Overhanging Channel Yes - Retaining wall (not natural rockcut).

I Trees Overhanging Channel Recently cleared + overhanging trees.

Floor of Channel Natural- Partially obstructed withboulders

Other Obstructions Downstream hi~hwav culvert

IPERIODIC INSPECTION CHECK LIST

I PROJECT COLUMBIA LAKE DAM DATE 18 MAY 1978

INSPECTOR DISCIPLINE

I INSPECTOR DISCIPLINE

AREA EVALUATFED CONCITION

i OUTLET WORKS - CONTROL PIER

a. Concrete and Structural

General Condition Dry rubble construction earth filledpoor to fair.

Condition of Joints Open Joints ungrouted

Spalling N/A

Visible Reinforcing N/A

Rusting or Staining or Concrete None observed

Any Seepage or Efflorescence Sinkholes around gate controlMechanism

I Joint Alignment N/A

Unusual Seepage or Leaks in GateChamber Considerable leakage noticed on

downstream face in area of outlet pipe

could be unseated gate, or cracks inpipe, etc.

Cracks None observed

I Rusting or Corrosion of Steel Rusting observed in discharge wateror downstream face.

I b. Mechanical

Air Vents Manually operated gate. Locked.Exposed to weather. Rusted.

Float Wells Last operated in April, 1978 andproblems in seating occurred. Finally

Crane Hoist sealed by dumping cinders. Gates andtrash rack are wooden and reportedly in

Elevator need of repair or replacement.

I Hydraulic System

Service Gates

A-5

IPERIODIC INSPECTION CHECK LIST

I PROJECT COLUMBIA LAKE DAM DATE 18 MAY 1978

INSPECTOR DISCIPLINE

I INSPECTOR DISCIPLINE

AREA EVALUATED CONDITION

OUTLET WORKS - CONTROL PIER (cont.)SkEmergency Gates None

Lightning Protection system None

I Emergency Power System None

Wiring and Lighting System in None} gatehouse.

IIIIIIII

I

A-6_

' [ ' "' , " -i I

PERIODIC INSPECTION CHECK LIST

PROJECT COLUMBIA LAKE DATE 18 MAY 1978

I NSPECTOR DISCIPLINE

INSPECTOR DISCIPLINE

AREA EVALUATED CONDITION

OUTLET WORKS - INTAKE CHANNEL ANDINTAKE STRUCTURE

a. Approach Channel

Slope Conditions Not observed. Below water.

Bottom Conditions Not observed. Below water.

Rock Slides or Falls Not observed. Below water.

Log Boom None.

I Debris Not observed. Below water.

Condition of Concrete Lining Not observed. Below water.

Drains or Weep Holes Not observed. Below water.

b. Intake Structure Stone faced, earth filled pier onupstream face jutting out intoColumbia Lake. Trash rack, and gatej mechanism located in southerly tipof pier. Inspected as part of dam.

Condtion of Concrete Not observed. Underwater.

Stop Logs and Slots In wet well of chamber. Not observed.

I!I

I

. I -

PERIODIC INSPECTION CHECK LIST

PROJECT COLUMBIA LAKE DATE 18 MAY 1978

INSPECTOR DISCIPLINE

INSPECTOR DISCIPLINE

AREA EVALUATED CONDITION

OUTLET WORKS - CONDUIT

General Condition of Concrete Conduit - 18" diameter cast iron pipeat downstream end. Appears to berusted and mishapen at the outleton the downstream face.

Rust or Staining on Concrete

Spalling

Erosion or Cavitation

Cracking

Alignment of Monoliths

Alignment of Joints

Numbering of Monoliths

III

I___ __ __ ___ __ __ __ ___ __ __ _ _ __ __ __ ___ __ __ ___ __ __ __

PERIODIC INSPECTION CHECK LIST

PROJECT COLUMBIA LAKE DATE 18 MAY 1978

INSPECTOR DISCIPLINE

INSPECTOR DISCIPLINE

AREA EVALUATED CONDITION

OUTLET WA)RKS - OUTLET STRUCTURE ANDOUTLET CHANNEL

General Condition of stone masonry Dry stone box culvert 16" x 40"

Rust or Staining Considerable rust staining from outlet

Spalling

Erosion or Cavitation

Visible Reinforcing Dry rubble construction enclosinga pipe.

Any Seepage or Efflorescence Considerable seepage noted.

Condition at Joints

Drain holes

Channel Natural earth channel

Loose Rock or Trees OverhangingChannel Yes

Condition of Discharge Channel Poor to fair

IA-II

- - A-9

• ' ,, 1im | |

APPENDIX B

I. Records for dam can be found at:

1. Town Hall, Box 165, Columbia, CT 06237

2. Department of Environmental Protection

State of Connecticut

State Office Building

Hartford, Connecticut 06115

Attention: Mr. Victor Galgowski,

Dam Safety Engineer

Water and Related Resources Unit

II. Inspection Correspondence

III. Sketches, Drawings

i

'I

II ii mm/

MOZZOCHt ASSOCIATES G17ON6U8A.16 .. 0402

CIVIL, ENGiN 'RS p,4temg 63.40t

POIVItgCMCg a. 3. Q-03%tlo WeV80884lr'r III~I

PAR 'iR Sptcmber 22, -1971 P"Oute 411-420

J OHMN 6.iJCMS. .1*STVART -. UECX MAN

.RV.Y To. Glastonbu_"y....liam H. O'Brien, IIICivil Engineer STATE WATER "URC-W';ater Resource ComissionState Office SuildingHarfr, Conlnecticut 06L113 aEP 23971

AN I ' *........ Re- Columbia Lake DamRE E"D Columbia, Connecticut

_ _ _ _ _ _ _Our Fil ;*57 -73 43

Dear Mr. O'Brien:

Reference is made to our report of Aoril 17th, 1970, for this dan.This letter reported on thr hydraulics of the present structure withseveral reccmmendations.

I revisi ted the site on. September 7th, 1972 and noted theI following :

1. Several la:ge trees were un-rooted by the recent strongI winds (August 28th, 1971). "

2. The spillway is paxtially clogged with branches fr-om atree that was felled and cut up recently on property to thewest of the spillway.

3. Growth is beginning to reappear on the e.bankment. Sassaf--as,wild cherry and other trees are taking root.

4. The area at the easterly end of the emtan=ent , which oncequalified as a crude emergency spillway, has been filled .n &:-dis presently higher than the rest of the embankment.

5. Exit channel below Level control section de---io-a:.n-

:he hydraulics for -his st--ctu-e were checked again and din-:I to ,e corrac,. In 1igh- of your letter to check the s:tbilizy of :heelicz:ency seoi-lz.ayv and my. -acen" visit, ".h iowng s a

I.

I

I A

made:

I 1. Raise embankment 1.7 feet :o provide 3 r freeboard and add

rira protection.

1 2. Exit channel below control level section should be repa4.:ec.It is recommended that concrete be _,sed -o -il voids bet.eentIe stones (as has been done on t:he control section) to hold inposition. Velocity vaies from 9 to 1. feet per second dictati4ngadditional protection.

I 3. Remove fallrn trees and brush from the downstream a=ea.

i4.Initiate a maintenance program for the st-ucure.

IVery truly yours,

I M ZZPC4 C ASSC II:ATS

I ~~By /'John Luchs, Jr., Senior r-.er

I

II

MQ7.7CH I ASSOCIATES ftLPfCC85r"UCIVIL. rNG1NC:1VS M64

Pq"yVIOCMCt'. 'a. 1:94Is# *ggwvaVITt I,11gB?

rAWXP.vt April 1.7, 1.970 .. AzI.QA2

JOHN L.UCHGO JR.

Ra-,Y TO, .4-t~~~j

R, c Co2.i"7,ilin Lake CamnC-CL Connecticut

Our 7'.v 457-73*4L3

Dear Mr. :-iu

cI' cl - n 1 9 7 " Itof v rr:~ Z ~ f i i f F

~ t Uli14tw-14.1 -! 1.6' top

f' C. Il C, -3~t h: -ie --- l a 2~ nd

and bi ~ ~ ~ '' rt UfLG:' o rz!)L y t.j2' C:O11t.

±12 0 -..- '. v.*nt ri" .L::"_;o to c-ontrol t"-ewatc!- 0- ac

of'' c Usi'-- ,rwj tcC,

Floo c%-' the12~ ~s~~~ o~ lo.

ax'6- 'z 012Th-: .n.

al I, :-I

. .........

Ins H. O'Brien, III- - AprL 17, 1970

I DEIrCT %!AX,.WAT7:1 SURFACZTY:?Z OPP RAIN'FALL !UN-OFF -ZVATIO: ABOVESVE- (inches) (inches) CRTLWAY CC.ST r

50 y2z:tor- 4.5 2.9 2.. 2.6lir. durution

ICO yr itorm 5.1 3.5 1.9 2.3

1.5 x 100 yr storm 7.6 4-.9

6 arn Ouri tion

I With s fetch of L.mile of open weter, a minimum of 3? of riprepedfr ?cbcard i-3 pndent rind some corrcctive oesures are required to :=taithis. Refcring to Mozzochl's lettcr dr ted April 25, 1963, the fcllo-irrecommencndtLona are in Cub.nintiai ngrecinart.

1. Provide addition.il .pi.y on the easterly end of dam orrni.c top of Jnr,..

2. Clean dnbris from area between dam embankment and roodembonknent to prevent clogring of the 41x6l box cu lvert under

i th. rend.

I : "

I Vory truly yours,

MOZZOCHZ A30C rATES

By khcn J. e a >!.

, I]

INTERDEPARTMENT MA;. Z DECSMBSEM 7. 1;67T'O ! : PAATM lUST

FI I I I

E.'

O-PARTM I?4T

?i. O'rRIr

f ="LUNIBIA LA, E:A:A. C- LUAST,%

I On Decembez 6, 1967, the undersigned visited the above dam and made tha

following observations:

1. The -water level had been lowered several feet oelow normal, 1 asse to

allow property owners to make repairs to docks, etc.

2. It appeazed that some w;rk had been done in constructing an emergency

spillway on the east end of the dii'e. rn any event, there was a low

area at the extreme easterly section d the dan which was approximately

I 2 feet in width and at an elevation approxi.atel'y 2 feet above nor.al

pond level. However, there was a pile of dirt in the iddle of this

Isiill-may" and there was no protection of the side slopes of this

spillway. The intent of suggesting an ewrg ency spillway in this area

was apparently to take advantage of a low area for-mod by the access road

I to'the damn from Route *87. In fact, with suitable srosion prtaction,

part of this roadwmay could be used as pa t of the emergency spillway

channel. :n any event, t he emergency spillway was in no way complete,

but it appear*ed that it could be Vh a minimum of effort. "

1 3. Thoere was a 12 inch tree growing very .close to the out'et end of t"he

dx-3wdown st-jctzr- :.hich should ce cit down.

4. There was a ;-at deal of de ris in the lower principal scil lay :hannel

such as fa ken r-cks, and small trees a.d some :-s. Th4s s.,uld a

C-1 anac .p.

1 * ;;pa:rent! no Irx in :-san;n" dow-r-s-.jsa sl.ce -ad a*en acne.

, AI-

I JOHN J. MOZZOCHI AND ASSOCIATES QLSTrONOUNY. CONNI.317 "11m3110" POSM

CIVIL,, NGiNrERS pot* 633.&AGo

PROV10104ez S. R. I.jamf4N J. 341 CN 1" =1 1 1"S,.S.SOCIAM March 11, 1966 1 1041444 G ,4o=rao

i CWa4 J. WHrlrJams* LAMM 4fl.JaQ I-41VANA&4NSN R=LY Too Glastonbury

W'"iam H. O'Brien, IUWater Resources Comm-ssionState Office Buildi.ni ar-ord, Connec cu: 06115 O

I Re: Our P11. 57-73-43

Columbia Lake Dam

Dear Mr. O'Brien:

In accordance with your Lnstucotons of March 7th, I re-inspected thereferenced dam on March Sth and found that Items No. 1, Remove all tees rom the

i embnk=en:, and I tam No. 2, Remove aLL debris Lrom spillway, (as called !or in =yreport of April Z5, 1963) have been accomplished satisfactorily. The other itemscalling for an emer-ency spillway and flattening of the downsteam slope hav'e notoeen acComphjshad. a

I sug-est tha this =ar.er be called to the Town's atte .cn, as soonI as Possible.

Very truy yours,

I "ohnJ. MozzachL..ahd Associatesj .Itik Civil. Engineers'

I _ S _ ; I

I

I _ I II *iI

JOHN J. ,'vIOZZOCHI AND ASSOCITSS " - . LAoNU,'.CON-.

CIVIL ENGINEERS 1 111 ;'BRO ,cu

JOHN .J. -40=ZCXI "V oe ~c, _____________April 2S, 1963' - .. .......... .... ,,, A8 .MC ,,= 1."203

,ASSOC. AlTS. .....................

ow ed J. W 14i'z ... ......... ...... .. ... ,

JOM 6UC344. JR..EC * ,.. 41,VA"41HNI R1, t Glastonu--

I Wi.Liam S. iVise-D-iectarWater Resources CommissionState Office 3uilci.nq

I nart-ord !5, Conect:.cut Re: Our File S7-73-43Columbia Lake DamColumbia, Connecticut

I Dear Mr. Wise:

As per instuctions received !rom Robert McCabe, I contacted Mr. Clair Robinson,First Selectman of Columbia, and made an inspection of the referenced dam on APr.1L 4th.This is a town-ownd str'ucture.

Mr. Robinson has been selocTman in Columbia for 42 years and is very well acquain:-=with the recent historr of the dam. He Lforms me that in 1938, the dam was sand-baggedto prevent it -from boing overtopped and that a wash-out occurred at the eastaery end of thee.-bankrnent. This washout was refilled but ap arently to an aievation that is now 'huqherthan the -a=.

I ~ This is an aarthen dam about 260' long with a maximum heght of about ZS - 30 feet.it has a splU.w-ay about Z' wide and 40' long 'with a freeboard of 4 feet. The lake has anarea of about Z70 acres and a clear reach of about a m-ila south of the -an. The town has

I t-p-aped the lake side of the dam against wave action. There is an excellant sod coveron top of ;e .dam but thre are also numerous large diameter -ees. rowing thereon. Thedownstream slope of the dam appears to be steeper than a 2 to 1 slope. A drawdown gateis n ;ood operat.ng :oanditcn and is opened each Fall to lower the pond level through "..winter. However, the discharge opening downstream is only 1-1/2' x Z' and therefore addsonly sl ghtly to the capacir of the spillway.

I Wih a min--imum freeboard of . foot, I calculated the discharge Capaci-t lf the s.:i-way at 360 C..?.S. For a total drainage area of 3. 1 sq. -riles, 1 belleve th.is s. '-I'zv hasnst.;4c an: capac-:t as already Ldicated by e axerenca in '228.

: . .--.e. the :olowi.-.g acons be i:s rad:

I .. -e.ov3 ai.l.. 3es -om he m:an.:nen-z;2. ".e-ve all deris "rom :he .'i ,zy

3. ":zava:a an emcr-ency sp-L±w-ay at :he easz en o4 :he ka .-. _ "' .,.......... .t =y *-e at a an ale'.-a.:-n Z: abc'"u: .- e ao- 3 ..e .. s. ,''=.=

I

I A:

I 4. Flatten tl7e downstream slope of "he dam to a slope of 3 horizontal : 1 vertical.

The only alternate to (3) above would be to raise the dam at least 3 2eet to !provideaddit.onal Ieeboard. I beiave the emergency spillway vould e more economical and

i safer. .......

L accordance with our phone discussion, I am =ansmirrting a copy of this lettarD o Mr. Robinson to expedita s :%port to a Town Meetl-ag on Saturday, April 27th.

IVery truly yours,

/John I. Mozochi and AssoclatesITM~~k / /Civil Znginners;

IIIIIIII

I! I I I II

#1i OThayer

.Yovelier 6,LZ

I ~* . R~ obimsom

froz :. tapo ;rnp'ical .-4 t;-.!t tae a~i Co-4. co ut:Lr_ to theib- iz bot .-cur scu-, e ::±-lez buzt.6 'L ~i". re "Ot ;:tc:,ystaep

;n you..0 ......vc a...~ pond. Yo rc-_g.t est~±~i

-==-c ent 5=44-t so t:- ou "e't o.±Ued t- P.Laceb. ... C~ : Uc trerr edg'a. Ma a= Q -'L ama c*: of a~ eIa:T%-._

z-o~n v; tze ra~ves.

I~~~ Jnt ~ ~1~y .s =y recom"n-&-t-ln t.''t t 12111-e d n. n_.- the ~ i' tn. pre-uent s~lllwy of 122 'Vet and wi4 ;.a- iou=,a

I.~ iaut 6 Xe-e: -It doei'..ot co=& to our za :lzaents. 7here Vwas; o.e ication an llze grcu~d tb..Jit t.*e spillwaiy il.ad ot~e -. rro-,d ,I;, eitz'.0u;:Z ;0:7 .cxdou~tt ti4-1.z bein, dzn,K±!'or it Is iirc. to wi,.vv i ~t sl;ou.a.± be-'-y rcoazmcatc lz~t.it N.x .oubl u:) the -e .t. of !, :PI2.&.*ay " irinmne %ut-ents Ln a3~ihZ2±e as -cu Sujeaz.", u~I i±t :ect t-Ie S:e:

of't: exist-In: cnnnne!k: 'ihe new spi.31;.ay, unless -It cones ca l.ed~e,I S-cem. 4L-ta~ble, shou.Ld be paved as,.u su,_o1st ~itiStone pvr"cut !.V" deep. 'xou. "_so reco:=end, un-less -...e =Lpll is extrse::*>

rd I e :r-w section -,L t~i -- tp wayou nu-. an 2.L" cancrete cutz...e- .'..ct-Ion wr- ;. z V2. zz Vo~ n_ 4

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LEGEND

bDENOTES SEEPAGE ZONES

SUJRFACE EROSION HQL.E

AREA OF~ DtSLOUGEO MASONRY hkN -

-OBSTRUCT=P SPILLWAY IMP

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C-IOKN ATA ONTEMSOEDMEBNMN

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IC -2 LOOKING WEST ATONTRESLOE DAM EMBANKMENT

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C-7 STONE BOX CULVERTOUTLET AT EMBANK-MENT TOE

NOTE: RUST STAINING

IU

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C- TM TTO ALO ONSRA AEOEMAKMN

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IIIiII'IIIIII'III?

C - 10 SEEPAGE AREA AT DOWNSTREAMTOE

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IIIIIIIIIIIII C-Il SINKHOLES AT GATE MECHANISM

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IAPPENDIXD

HYDROLOGIC COMPUTATIONS

III

I!

IIIJ I,

'0 0

~C U

COvLUMBIA LAKE DRAINAGE BASIN

Drainage Area -3.1 sq. mi.I j Datum- N. GV D. PLATE NO. 4

A. Size Classification

Height of Dam = 27.0 feet; Hence SMALL

at crest elevation reservoir storage = 'S370 AC-ft., hence L

adopted size category INJIflMEiDlAT9

IB. Hazard Potential

~AM S L.ATRD jn AN AkGA THAT IS NdW PRTkMIWAWTLV RUCAL.

I FAILJPE OF THO DA.i im TE NEAP._ FW..kc MAY Nor _AUs b-kA4_ "it

UFQ cc Ko .4_S u T Wiu.L i)n.uva APPZC1ALe C-.5.hpMIn , L.OSS

12&--,A&IOvw4AL FACILIi5 . 1'Hr AiL.OV HAS A MisTIN.T :RITIAL,

I wAsHws~a~ na-l 12o-rr a7 Abmfl I1F-4 uMILIT ADb.3Ac1 1 IT

1It is estimated from the rule of "thumb" failure hydrograph as follows:

Category Loss of Life Economic Loss

1 Homes - D

Buildings NIL.I ___Farms

. Miscellaneous =YE

Jh I .I T ________NOME Highways or roads YFS

1 C. Hazard Size "Test Flood" or Spillway Design Flood

I"MfIAl IaRM ATOR - YA i0 NIM

AdoptedS.D.F. (test flood) = 4 PA . I00 ,

l Adcpted value of test flood due to watershed characteristics = 000 CSM __

0I 4 Lb.A

10

-.) 1) 10

C) E-:

o ~ t 'U 4

.~ -4-4

001 -

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to 03.) 4 -4

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al 00 Ci0U 4) t

'I K ~ -M 0 -E0 0 $ C0 4 1

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to ) sig Cc

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tic 0.

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-4 4)c

0 ~ ~ .4' 4 1

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o 0 40bol C. ri

L. 4) 'cd

0 -4to

A4_ 3c_ _

4.3 C. ca -

0 a'rgg~~0

"Rule of Thumb Guidance for EstimatingDownstream Dam Failure Hydrograph"

I BASIC DATA

Name of dam C -o01v1z.4 6Az L2A Name of town -

Drainage area = 3 1- .Lq.mi. Top of dam 502 ,0

ISpillway type =YA/tO/OLL4F 6O/IPLOW Crest of spillway '

Surface area at crest elevation = -2. 7 o 0 ot

Reservoir bottom near dam - +7L' 0 7 o M V

Assumed side slopes of embankments = 2.

Depth of reservoir at dam site .- Lu Yo= 7. 0 ft.

jMid-height elevation of dam = 4f-B + so /Iavv'

Length of dar at crest -_ 6 o

Length of dam at mid-height = 2. 0_

4o% of dam length at mid-height = = S 2 rt.

Stream height of dam 52 ; + _

Hydraulic height of dam = 2 7

l Step 1:

1 1R E S E e9 Va' RElevation Estimated Storage

.S.L. In AC-ft. -5' Remarks

" L f- 9 9 . o o o - . . . . 3 3 7 o

" 5oo o C -- 3 -(aj0- .0 I -. ..- "I 2.. " . . . 9 " 5 "

Step 2:

p312I . 2Yo b y3/2 13 3 7 G ,F ,

I

ISteP 3:

ILengthReach in Feet Stage Discharge Remarks

SL Soo 9o r7 0 1 o

~-z. Lf7o -z.

I ... •5

!

1

Notes -

.I.

Step h:Ste 5:

IReach Length 1-2 Reach Length 2-3

A) ", = t 13-9 CFS 2 3oo cFS

Stage L 7 Stage _ _ 'I I. I_

Area = ^.-1 JJ! sq. ft. 0Q.LAC-dI Area-- $ .psq. ft. =-_,_07.9AC-.m

Length - L1 -2 = n_ __ ft. Length = L2_ 3 -__--______ ft.

V1 c _u. ft. - 4jjLAC-ft. V2 _ _cu. ft. AC-ft.

L s -L ' 2.- o AC-ft. s= +72-O AC-ft.

v , less than 0.5; O.K. v- - 0 0 '+7 less than 0.5; O.K.

B) %p2 (Trial) = Q1 (1 - asV_II . O3CFS __-3 (Trial) = Qp-2 (1 - V2) = ctOoCFS

C, Stage for %-2 = ' -7 8 Stage for '- 3 3 ___'90 ____

Area a0 sq ft. Area __ _______sq. :ft.

_1-2 = length a _3 0 _ _ft. L2 -3 = length =P ft.

S2 = " AC-ft. v3 0 ____AC-ft.

s L- r2- 0 AC-ft. S= L"7?- AC-ft.

Y2 less than 0.5; O.K. ;3 = ,01S less than 0.5; O.K.

+ S -S

D) X - = __ _ _AC-ft. V2 avg 70 AC-ft.

- " -: -avg) %-3%-2 (1 - vavg)

* 13oaCiS 0 (0 0 _CiSIStage for %-2 - L71,80 Stage for *-3

I

2.

Me L ", o... .. E V;t ,

AD A14 766 NA I I ONA PF f all IO 1M C I m ON O ON IIf11 11,6 DAMS.COLUISIA tiau DAM ICI fiw CORPS oau,.s WA0tHA

Al A N4 A "IV tWillANl DIV SIP is

111 1 .0 11. 2 8 11.5

11111 1.1 14. IIIII

MICROCOPY RESOLUTION TEST CHART

NATIONAL BUREAU OF STANDAROS- 9E3

-A

IStep 4 (con't): Reach Length 3-4 Step 5 (con't): Reach Length 14-5

AJ S-. CFS qp- -______ _ CS

I Stage . _ .-. 91_ . 4_ 1 _ Stage -

Area- 1 2-0 sq. ft. - AC-40. Area = sq. ft. = AC-ft.

Lengtha = _3-4 _0_ ft. Length = L _5 = ._._ft.

V3 a cu. ft. - 77,3AC-ft . V4 = -fcu. ft. = AC-ft.

s9 72- AC-ft. s AC-ft.

Y3= ,. 0 0 b less than 0.5; O.K. Y4 _ _ less than 0.5; O.K.S S

(ial) - Vp- (Io 8 3FF (Trial) =. 0.- S4 F

Stagq for Qp-4 2 .'~* Stage for P 5 =

Area = 1..O Area _

L3 _4 __________ft. L _ _5 __ft.

7 7. AC-ft. v u AC-ft.V4 5s - __ t 72-0 AC-ft. S AC-ft.

iV-4 DOI( les tan 05; .K.______less than 0.5; O.K.

1) ss- than 0. ;. r5 VAC-ft.2 v 2 avg

E ... . ' c

I (Eg,,v.,-. o

I

IC

0~

4 to£7 -1

2 0

Naa

C 4i In 1U)

U 41 r45 0 *- 11 01

10 = = 4 I I

- N I"'D-7

i Storage Elevation Estimation Procedure

j Depth Area Storage CapacityEIvation in Feet Acres AC-ft.

Increment Cumulation

I ~.oZ- Z70o 3370

| S'I .Qo ,L "

5 r.- I,

I ~

I!

1I.N

I,

PRO.'CCT -6i/I/ ~k A~ACC. NO. / 2t2a Ijg L iIELPC RTL SHEECT map.-OP...

COMP. ___________ __C"ECK_____________ CONT. NO._____

FAILURE: 4-s1cA/.ojC 93 z7 c.c

Lj 5'1 q~- 71-7 (~ 7

~406,50PROCL e?75 35"5 3.5, 9c

II

&C1.-R 4 D,7.Ac

IOvertovping Potential

Spillway crest elevation = 4 5. 00 M.S.L.Top of dam elevation 5 02.00 M.S.L.

Maximum discharge capacity of )Spillway without overtopping 4 o C.F.S.

"Test flood" outflow discharge = i4 C.F.S.

] % of "Test flood" carried by -44% 1Spillway without overtopping

"Test flood" outflow discharge = 74 C.F.S.which flows over the dam

j - 64.0% of "Test flood" 2

Ii 1 + 2 = 100%

III

II

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SPILLWAY RATING CURVEJ COLUMBIA LAKE DAM

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APPENDIX E

INFORMATION AS CONTAiNED iN

THE NATIONAL INVENTORY OF DAMS

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