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AD-A142 782 NATIONAL DAM INSPECTION PROGRAM PEMBERWICK DAM (CT 1/208842) SOUTHWESTERN CO..(U) CORPS OF ENGINEERS WALTHAMMA NEN ENGLAND DIV FEB 88UNCLSSIFIED FFGt3/3 NL
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MICROCOPY RESOLUTION TEST CHARTNATIONAL BUREAU OF STANDARDS- I963-A
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SOUTHWESTERN COASTAL BASIN
k I GREENWICH, CONNECTICUT
• PEMBERWICK DAMCT 00042
PHASE 1 INSPECTION REPORTNATIONAL DAM INSPECTION PROGRAM
4.
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-JUL05 6194
I E:L.J DEPARTMENT OF THE ARMY
NEW ENGLAND DIVISION, CORPS OF ENGINEERSWALTHAM, MASS.
PEDlRUARY, 1980
.:: 1 84 07 02 048S.-.. . . . ...*."k" , ". ", -, -,- . k ,*9 ',i'
4 IINCI ASSITEDSECURITY CL ASSIFICATION OF TeqIS PAGE tWhen LUce. EntafedI
REPOR DOCMENTTIONPAGEREAD INSTRUCTIC)NSREPOR DOCMENTAION AGEBEF~ORE COMPLETING FORM1. REPORT NUMBER 2.GOVT ACCESSION NO.3 RECIPIENT'S CATALOG NUMBER
-, ~~CT 00042 4'''I4 TITLE fend Suebuitle) S. TYPE Of R4EPORT 6 PERIOD COVERED
outhwaestern Coastal Basin INSPECTION REPORT'.' renicConn. jmberwick Dam 6_PERFORMING_____REPORTNUMBE
NATIONAL PROGRAM FOR IN SPECTION OF NON-FEDERAL B EFRIGOGEOTNME
I. AUTI4ORI.) S. CONTRACT OR GRANT NUMDER(a)
.0U.S. ARMY CORPS OF ENGINEERSNEW ENGLAND DIVISION
9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASKAREA a WORK UNIT NUMBERS
11. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE
DEPT. OF THE ARMY, CORPS OF ENGINEERS Feb. 1980NEW ENGLAND DIVISION, NEDED13NUBROPAE424 TRAPELO ROAD, WALTHAM, MA. 02254 *110
14. MONITORING AGENCY N4AME & AODRESS(iI different from Controlling Offce) 1S. SECURITY CLASS. (of chip report)
UNCLASSIFIED&~a. DECLASSIPICATIONIDOWNGRADING
SCHEDULE
1S. DISTRIBUTION STATEMENT (of this Report)
APPROVAL FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED A
17. OIST016UTION STATEMENT (of rho ebstract eitered In Riock 30. It different hoe 1111410r0)
'iv _e"
% 1. SUPPLEMENTARY NO0TESCover program reads: Phase I Inspection Report, National Dam Inspection Program;however, the official title of the program is: National Program for Inspection ofNon-Federal Dams; use cover date for date of report.
19 CE WORDS (Coninue on, rovee lo itso neceem and idenifyS by' block number)
DAMS, INSPECTION, DAM SAFETY, -4* Southwestern Coastal Basin
Greenwich, Conn. -
Pemberwick Dam20. AMSTRMAC T (Cotinuwe on reverse side #I nlecessary' ad 0~111yI, by' block number)
* This dam is masonry arch approx. 115 ft. long, 45 ft. high with an average top ofdam width of 8 ft. The dam was built about 1867 and presently serves no function ..
* except an aesthetic one. The test flood for this dam is the Probable MaximumFlood. The test flood has an outflow discharge equal to 25,6000 cfs and will overto the ~-dam by 17.0 ft. in stillwater condition. The maximum outflow capacity of the spillw yunder a stillwater condition is 1,100 cfs, which is 4 percent of the test flood.
~DID , 14731 &OITION, 0f, I OV 691 IS 0SOLIEVE
. . . . . . . . . . . . . .
.. **-
. ~ DEPARTMENT OF THE ARMY
NEW ENGLAND DIVISION, CORPS OF ENGINEERS
424 TRAPELO ROAD
SWALTHAM. MASSACHUSETTS 02154
REPLY TOATTENTION OF
- -. NEDED MAR 2 1 1S:,
Honorable Ella T. Grasso
Governor of the State of ConnecticutState Capitol
"- Hartford, Connecticut 06115
Dear Governor Grasso:
Inclosed is a copy of the Pemberwick Dam Phase I Inspection Report,which was prepared under the National Program for Inspection of
Non-Federal Dams. This report is presented for your use and is basedupon a visual inspection, a review of the past performance and a brief
hydrological study of the dam. A brief assessment is included at the
beginning of the report. I have approved the report and support thefindings and recommendations described in Section 7 and ask that youkeep me informed of the actions taken to implement them. This follow-up
action is a vitally important part of this program.
A copy of this report has been forwarded to the Department of Environ-
mental Protection, the cooperating agency for the State of Connecticut.In addition, a copy of the report has also been furnished the owner,Fairfield Associates, Inc., Greenwich, Connecticut.
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 ofEnvironmental Protection for your cooperation in carrying out thisprogram.
Sincerely,
Mmd
I jIncl i iSCEER
As stated Colonel, Corps of EngineersIWDivision Engineer
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SOUTHWESTERN COASTAL BASIN
0 mGREENWICH, CONNECTICUT
PEMBERWICK DAM
CT 00042
l U
. PHASE I INSPECTION REPORT
NATIONAL DAM INSPECTION PROGRAM
.., ;
.° 4.
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NATIONAL DAM INSPECTION PROGRAM
PHASE I - INSPECTION REPORT
Identification No.: CT 00042
Name of Dam: Pemberwick Dam
Town: Greenwich
County and State: Fairfield, Connecticut
Stream: Byram River
U Date of Inspection: November 12, 1979
BRIEF ASSESSMENT
This dam is a masonry arch approximately 115 feet long. 45 feet high with an average topof dam width of 8 feet. The dam was built about 1867 and presently serves no function ex-cept an aesthetic one.
Based on the visual inspection and past operational performance, the dam is judged to be inFAIR condition. Seepage was noted on the downstream face. The emergency outlet worksare inoperable and there is no method of lowering the water level.
This dam is classified as INTERMEDIATE in size and a HIGH hazard potential structure in ac-.., cordance with recommended guidelines established by the Corps of Engineers.
*The test flood for this dam is the Probable Maximum Flood (PMF). The test flood has an-. outflow discharge equal to 25,600 cfs and will overtop the dam by 17.0 feet in a stillwater
condition. The maximum outflow capacity of the spillway under a stillwater condition is1,100 cfs, which is 4 percent of the test flood.
It is recommended that the following items be studied further: The downstream leakage,. the toe and the upstream face, and the spillway capacity.
"o"4.. " . ° . " . . - " . - • • " - • % • .= % ", . = N " % "," . % • % . .
Recommendations and remedial measures that should be implemented by the Owner witnin
I one year period after receipt of this Phase I Inspection Report, are further described in Sec-tion 7.
JAMES P. PURCELL ASSOCIATES, INC.
.,,1 . - (*r ."" ."".''. ,' -. ', .
~yj..jJ~K~ A-~1~R NAOI
""" Sudhir A. Shah, P.E. \ ' '
Vice-President '... 0 NA- ,(;,.
Connecticut P E No. 80182
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This Phase I Inspecton Report on Pemberwick Dambe@a been trevieved by the uders igned Review Board swers * In ouropinion. the reported findings, conclusions, and recommendations areconsistent with the Recomended Guidelines for SafetT Inspection ofPlIE and wiLth good engineering judgment and practice, and is herebysubmitted for approval.
.CARNEY H. TERZIAN, KEBERDesign BranchEngineering Division
-RICHARD DIE NOKMEWater Control BranchEngineering Division
ARAMAST HAHTESIAN, CHAIRMAN-. - Foundation & Haterials Branch
Engineering Division
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",-,'-.Chief *gisenriv Divisin
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PREFACE
This report is prepared under guidance contained in the Recommended Guidelines forSafety Inspection of Dams, for Phase I Investigations. Copies of these guidelines maybe obtained from the Office of Chief of Engineers, Washington, D.C. 20314. The pur-pose of a Phase I Investigation is to identify expeditiously those dams which may posehazards to human life or property. The assessment of the general condition of the damis based upon available data and visual inspections. Detailed investigation, andanalyses involving topographic mapping, subsurface investigations, testing, anddet. iod computational evaluations are beyond the scope of a Phase I Investigation.However, the investigation is intended to identify any need for such studies.
In reviewing this report, it should be realized that the reported condition of the dam is-' -based on observations of field conditions at the time of inspection along with data
'. -available to the inspection team. In cases where the reservoir was lowered or drained. ~prior to inspection, such action, while improving the stability and safety of the dam,
removes the normal load on the structure and may obscure certain conditions which
,- might otherwise be detectable if inspected under the normal operating environment ofthe structure.
It is important to note that the condition of a dam depends on numerous and cons-tantly changing internal and external conditions, and is evolutionary in nature. It wouldbe incorrect to assume that the present condition of the dam will continue to represent
"., -the condition of the dam at some point in the future. Only through continued care andinspection can there by any chance that unsafe conditions be detected.
Phase I inspections are not intended to provide detailed hydrologic and hydraulicanalyses. In accordance with the established Guidelines, the spillway test flood is
-%7 based on the estimated "Probable Maximum Flood" for the region (greatest reasona-bly possible storm runoff), or fractions thereof. Because of the magnitude and rarity ofsuch a storm event, a finding that a spillway will not pass the test flood should not beinterpreted as necessarily posing a highly inadequate condition. The test flood pro-vides a measure of relative need for more detailed hydrologic and hydraulic studies,considering the size of the dam, its general condition and downstream damage poton-tial.
The Phase I Investigation does not include an assessment of the need for fences,gates, no-trespassing signs, repairs to existing fences and railings and other itemswhich may be needed to minimize trespass and provide greater security for the facilityand safety to the public. An evaluation of the project for compliance with OSHA rulesand regulations is also excluded.
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TABLE OF CONTENTS...- .
Section Page
Letter of Transmittal
Brief Assessment
Review Board Page
Pref ace
Table of Contents ii-iv
Overview Photo v
Location Map vi
REPORT
1. Project Information
1.1 General
a. Authorityb. Purpose of Inspection
1.2 Description of Project
" a. Locationb. Description of Dam and Appurtenances',
." x * c. Size Classification5," -'- d. Hazard Classification
e. Ownership5 f. Operator
g. Purpose of Damh. Design and Construction Historyi. Normal Operational Procedure
O.. 1.3 Pertinent Data 3
2. Project Information
2.1 Design 3
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-7. :
TABLE OF CONTENTS (Cont'd)
Section Page
- 2.2 Construction 7
2.3 Operation 7
2.4 Evaluation 7
3. Visual Inspection
3.1 Fingings 8
a. Generalb. Damc. Appurtenant Structuresd. Reservoir Areaa. Downstream Channel
3.2 Evaluation 10
4. Operational and Maintenance Procedures
if 4.1 Operational Procedures 11
4.2 Maintenance of the Dam 11
4.3 Maintenance of the Operating Facilities 11
4.4 Description of Any Warning System in Effect 11
4.5 Evaluation 11" . 5. Evaluation of Hydraulic/Hydrologic Features
5.1 General 12
5.2 Design Data 12
5.3 Experience Data 12
5.4 Test Flood Analysis 13
' *. 5.5 Dam Failure Analysis 13
%iii
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TABLE OF CONTENTS (Cont'd)
Section Page
S 6. Evaluation of Structural Stability
6.1 Visual Observations 14
, 6.2 Design and Construction Data 14
6.3 Post-Construction Changes 14
6.4 Seismic Stability 14
7. Assessment, Recommendations and Remedial Measures
%J"4.r '. 7.1 Dam Assessment 15
a. Conditionb. Adequacy of Informationc. Urgency
'.- 7.2 Recommendations 15
3 7.3 Remedial Measures 15
a. Operation and Maintenance Procedures
7.4 Alternatives 16
APPENDIXES
Appendix A - Inspection Checklist A-1
Appendix B - Engineering Data B-1
Appendix C - Photographs C-1
Appendix D - Hydrologic and Hydraulic D-1Computations
Appendix E - Information as Contained in the E-1National Inventory of Dams
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OVERVIEW PHOTO - PEMBEPWICK DAM-S
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LOCTIO PLAN
1PAT NO I
NATIONAL DAM INSPECTION PROGRAM
PHASE I - INSPECTION RE'ORT
NAME OF DAM: PEMBERWICK DAM
SECTION 1
PROJECT INFORMATION
1.1 General.-
- a. Authority: Public Law 92-367, August 8, 1972, authorized the Secretary ofthe Army through the Corps of Engineers to initiate a national program of daminspection throughout the United States. The New England Division of theCorps of Engineers has been assigned the responsibility of supervising the in-
--' spection of dams within the New England Region. James P. Purcell Associates,Inc. has been retained by the New England Division to inspect and report on
- dselected dams in the State of Connecticut. Authorization and notice to proceedUwas issued to James P. Purcell Associates, Inc., under a letter from William E
Hodgson, Jr., Colonel, Corps of Engineers. Contract No. DACW33-80-C-00022K". has been assigned by the Corps of Engineers for this work.
b. Purpose of Inspection
" 1. Perform technical inspection and evaluation of non-Federal dams to iden-tify conditions which threaten the public safety and thus permit correc-tion in a timely manner by non-Federal interests.
2. Encourage and prepare the States to initiate quickly, effective dam safetyV. programs for non-Federal dams.-,":
3. To update, verify and complete the National Inventory of Dams.
1.2 Description of Project
"' a. Location: Pemberwick Dam is located in Fairfield County, Connecticut, ap-proximately 0.4 miles north of the village of Pemberwick on the Connecticut -New York state line (See Plate No. 1). The dam impounds water from the
SByram River and is located approximately 3.5 miles upstream of Long IslandSound. The impoundment is situated in a north-south direction, with the dam
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located at the southern end. The latitude is 410 -0l'-42" and the longitude is730 -39'-48".
b. Description of Dam and Appurtenances: The Pemberwick Dam is an archdam, built between ledge rock abutments, creating an impoundment in the nar-row gorge with nearly vertical sides. The downstream face is nearly vertical
with a plan radius of 180+/- feet and is constructed of coursed ashlar maso-1 , nry. The date of construction of the dam is approximately 1867.
A 63 foot long spillway is located in the center of the dam.
The outlet works, consisting of pipes through the dam, have been inoperablefor many years. The high level outlet was sealed in 1978 to control leakageand the inlet for the low level outlet is suspected to be below the present sedi-
-* ment level.
c. Size Classification: The dam is classified as an INTERMEDIATE structure asperthe criteria set forth in the Recommended Guidelines forthe Safety Inspec-tion of Dams by the Corps of Engineers. The impoundment storage at the topof the dam is 60 ac. -ft. (within the "small" category range of 50 to 1000 acre-feet) and the maximum height of the dam is 45 feet (within the "intermediate"
*? - category range of 40 to 100 feet). The size classification is governed by the3 •height criteria.
d. Hazard Classification: The dam is classified as a HIGH hazard potentialstructure as per the criteria set forth in the Recommended Guidelines for theSafety Inspection of Dams by the Corps of Engineers. It is located just
3 upstream of a residential development, a day school, and an industrial facilitywhere failure discharge may cause the loss of more than a few lives and ex-cessive damage due to high velocity impact from debris and flooding. Theestimated water depth will inundate the school by approximately 10 feet andcause flooding of structures along the banks in the village of Pemberwick of
a.* approximately 3 to 5 feet.
-. The failure of an upstream dam (the American Felt Dam), located approx-
imately 3000 feet upstream, might have a potentially hazardous effect on thePemberwick Dam.
e. Ownership: The Pemberwick Dam is presently owned by Fairfield Associ-ates, Inc., 100 Putnam Street, Greenwich, Connecticut 06830. The propertywas acquired in 1979 from the GAF Corporation, Wayne, New Jersey, as adevelopment investment. Subsequent to the development of the property, the
4, owners will be a condominium association.
b
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f. Operator: The operator and caretaker for Pemberwick Dam is:
John Koslowski, Maintenance SuperintendentFairfield Associates, Inc.
, 6 Glenville StreetGreenwich, CT 06830Tel: (203) 531-1822 (mill)
, " 531-9093 (home)
g. Purpose of Dam: The Pemberwick Dam impounds water from the Byram
River. The original purpose of this dam is unknown, and its purpose now is%. ' ." only aesthetic.
- h. Design and Construction History: The Pemberwick Dam was constructedafter the Civil War in 1867. Reportedly, the dam failed in a flood of 1877 and
-N4 -was rebuilt shortly thereafter. No information on the extent of the damage or
rebuilding is available. This dam was probably never used for power genera-
tion. No construction plans are known to be in existence.
i. Normal Operating Procedures: The dam, as it is presently used, requires no-* " attention for normal operating procedures.
51.3 Pertinent Data
a. Drainage Area: The Pemberwick Dam is located in Fairfield County, Con-
necticut. The drainage basin lies 0.4 miles north of the village of Pemberwick.The basin is generally rectangular in shape having a length of 11.8 miles andan average width of 2.2 miles. The total drainage area to the dam is 26.2
• , square miles (see drainage basin map in Appendix D). The topography is
generally rolling to moderate terrain, with elevations ranging from a high of740 feet to 76.5 feet at the spillway crest. Stream and basin slopes are flat to
moderate having average grades of 0.9 percent to 1.2 percent, respectively.
The pond has a normal surface area of 5.5 acres, which is 0.03 percent of the" I .watershed.
All elevations used in this report are based on the National Geodetic VerticalDatum (NGVD). Elevations are based on a spillway crest elevation of 76.5 feetestimated from available mapping.
- b. Discharge at Dam Site: Discharge records are limited to estimated flows forthe 1938 and 1955 storms (refer to Section 5.3 - Experience Data). Listedbelow are calculated discharge values for the spillway:
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1. Outlet works: N/A (inoperable)
2. Maximum known flood at dam site: Estimated by unknown source to havebeen 3200 cfs in October 1955.
3ad.
3. Spillway capacity at top of dam: 1100 cfs at elevation 80.0.
ai 4. Spillway capacity at test flood: 1 5800 cfs at elevation 97.0.
5. Gated outlet capacity at normal pool elevation: N/A
6. Gated outlet capacity at test flood elevation: N/A
7. Gated outlet capacity at top of dam elevation: N/A
8. Total project discharge at top of dam: 1100 cfs at elevation 80.0.
9. Total project discharge at test flood elevation: 15800 cfs at elevation97.0.
c. Elevation (Feet above NGVD)
1. Streambed at toe of dam 35.0
** " 2. Bottom of cutoff Unknown
3. Maximum tailwater Unknown
• - 4. Recreation pool N/Af...- .5. Full flood control pool N/A
6. Spillway crest 76.5
7. Design surcharge Unknown
(original design)
8. Top of dam 80.0
9. Test flood level 97.0
5"* - d. Reservoir (Length in Feet)
1. Normal pool. 1500
- . , 4
,.-..;...
2. Flood control pool N/A
. 3. Spillway crest pool 1500
4. Top of dam 3000
5. Test flood pool 3000
3. Storage (Acre-Feet)
.-. 1. Normal pool 41
. , 2. Flood control pool N/A
3. Spillway crest pool 41
. 4. Top of dam 60
5. Test flood pool 223
f. Reservoir Surface (Acres)
1. Normal pool 5.5
,, ,2. Flood control pool N/A
3. Spillway crest 5.5
4. Top of dam 7.0
5. Test flood pool 11.0
g. Dam
1. Type Stone masonryarch dam
2. Length 115 ft.
3. Height 45 ft.
4. Top width 8 ft.
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5. Side slopes Upstream: Verticalabove spillwayDownstream: 1 H:1QV
6. Zoning Unknown
7. Impervious core Unknown
8. Cutoff Unknown
9. Grout curtain Unknown
h. Diversion and Regulating N/ATunnel
i. Spillway
• 1. Type Overflow broad
crested, uncon-trolled weir
2. Length of weir 63 ft.
3. Crest elevation 76.5
4. Gates None
5. U/S Channel Natural bed
6. DIS Channel Natural bed,floodwall oneast bank.
*-.' *. j. Regulating Outlets (inoperable)
1. Invert N/A
2. Size N/A
3. Description N/A
4. Control mechanism N/A
.1
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- SECTION 2
" iENGINE77RING DATA
2.1 Design
There are no available records presenting design information for the construction ofIL mthe Pemberwick Dam. A plan made during a previous inspection in 1938 is included
in Appendix B of this report.
2.2 Construction
There are no available records of the construction of the dam and it appears that the
above referenced drawing illustrates the "as built" condition. The high level outlet
was plugged in 1978.
2.3 Operation
No forma! records of operation are kept for this facility. The dam is inspected-.-. weekly by personnel from Greenwich Associates, Inc., developers of the surround-
ing property inclusive of the Pemberwick Dam. The dam has only an aesthetic use atthis time.
2.4 Evaluation
a. Availability: The information noted above for this facility is available in theVfiles of the Department of Environmental Protection, Water and Related
I Resources Unit, Dam Safety Engineers, State Office Building, Hartford, Con-necticut, and Greenwich Associates, Inc., Greenwich, Connecticut.
b. Adequacy: The lack of indepth engineering data did not allow a definitivereview. Therefore, the adequacy of this dam could not be assessed from thestandpoint of reviewing design and construction data, but is based primarily
"" on the visual inspection, the dam's past performance, and sound engineering"5 judgment.
_ c. Validity: The validity of the limited information available must be verified.
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SECTION 3
VISUAL INSPECTION
3.1 Findings
a. General: The visual inspection of the Pemberwick Dam was conducted onNovember 12, 1979 and a copy of the visual inspection check list is containedin Appendix A of this report.
The following procedure was used:
1. Inspection of the upstream reach of the river which was impounded bythe dam.
2. Visual inspection of the face and the top of the dam and spillway for
at cracks, loose stones, leakage, otc.
- 3. Inspection of the outlet works and other appurtenances as to their exis-tence, location and operability.
4. Review of procedures that could be utilized in the event of an emergencysituation.
5. A check of the downstream area for seepage, piping, boils or other in-dications of abnormal conditions. The downstream hazard potential inthe event of dam failure was investigated.
6. Photographs of the general area of the dam and of specific items of note.1, -were taken and are included in Appendix C of this report.
5 -: I Before the inspection, the available existing data and aerial photographswere studied and reviewed.
b. Dam
I. Crest: The top of the dam is constructed of granite capstones with noevidence of settlement or misalignment (Photo C-1). Grass is growingbetween some of the stones. The dam's east crest supports the gear liftmechanisms for the outlet works, and a metal pipe railing around theperimeter, which appears in good condition (Photo C-5). The western topof the dam was not accessible, but appears to be in a similar condition.The top of the dam has a width of approximately 8 feet.
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2. Upstream Face: The upstream face of the dam is stone masonry with avertical face above the water level at the time of the inspection, which
. was approximately 31 inches below the top of the dam. Grass was grow-ing in the joints between some of the stones.
3. Downstream Face: The downstream face is also stone masonry with anearly vertical face. See Appendix B for a typical cross section through
5 the dam. Grass and small shrubs were growing in joints between some of. -_ the stone blocks. Leakage was noted from several masonry joints at and
adjacent to both ends of the spillway (Photos C-3, C-4). The dam appearsto be founded on bedrock.
c. Appurtenant Structures
1. Spillway: The spillway is a 63 foot long and 8 foot wide broad crested
weir with a free drop of approximately 33 feet to the tailwater (PhotoC-6). It is constructed of capstones which overhang the downstream face
I~ of the dam by approximately 6 inches. Water was flowing over the spill-
way at the time of inspection, and leakage was noted between the stone"s'. :comprising the vertical ends of the spillway and the masonry dam em-
,'5 bankment. Two logs, each approximately 15 inches in diameter and 30feet long, were resting on the spillway crest at the time of inspection(Photo C-2). It is probable that they will wash over the crest during thenext high discharge, possibly creating an impact or blockage hazarddownstream.
2. Low Level Outlet: The information provided by the representatives ofthe owner, and record photographs, indicate the presence of a low leveloutlet located approximately in the center of the dam. The slanted gearlift mechanism on the dam's east crest apparently regulated flow through
i ithis outlet, which is suspected to lead through the dam. The present levelI of silt and sediment on the upstream side of the dam, and the owner, indi-
cate that the intake is covered and, therefore, inoperable.
3. High Level Outlet: The high level outlet is located on the east side ofthe dam and was controlled by a valve attached to the vertical gearmechanism. The threaded bar for the mechanism has been sheared, red-nering the valve inoperable (reportedly in the open position). The horizon-tal outlet pipe from the downstream face of the dam to the vertical shaftin the center of the dam was filled with concrete in 1978 by the S. E.Minor Company.
* ~ d. Reservoir Area: The impoundment created by the dam is a narrow floodedportion of the natural river bed. The valley walls are fairly steep at the dam and
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".- become less steep 1500 to 2000 feet upstream. Bedrock appears to be at or
near the surface. No geologic features were detected that could be expected toadversely affect the dam.
Trespassing on the dam is prohibited and the dam site is fenced and locked on,' ".' the east side and fenced on the west side, reducing the potential for trespass-
S' ing and vandalism. The fence on the west side has collapsed on the upstreamend (Photo C-2), but protection against access to the site is still afforded.
e. Downstream Channel: Immediately downstream of the dam is a continua-
tion of the steep valley walls on the west side, and a building (Mead School)and flood wall on the east side (Photo C-7). Numerous trees are overhangingthe channel in this section. Further downstream, the channel is lined with
.. ,*' ,..- riprap and is a fairly straight uniform trapezoidal channel (Photo C-8).
3.2 Evaluation
. IBased on the visual inspection, the Pemberwick Dam appears to be in fair condition
. ,overall, and there were no major areas of distress noted. Specific items of concern'- that were noted are:
", The inability to draw down the pond level due to the inoperability of the outlet
works.,-.4
The presence of leakage on the downstream face and the vegetative growth on the
S --. faces of the dam.
The structural integrity cannot be evaluated due to the unknown conditions withinand below the dam.
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SECTION 4
S OPERATIONAL AND MAINTENANCE PROCEDURES
4.1 Operational Procedures
Thereare presently no operational procedures for the Pemberwick Dam. It has onlyan aesthetic purpose at this time.
4.2 Maintenance of the Dam
There is no regular maintenance schedule for this dam. The downstream channel islined with riprap for erosion protection and is free of vegetation growth. Upstreamof the dam, the tree-lined channel has natural steeply sloping rock walls not requir-ing any maintenance.
4.3 Maintenance of the Operating Facilities
- No maintenance of the outlet works is presently performed. The high level outletwas plugged in 1978 and the low level outlet is apparently covered with sedimentand is inoperable.
4.4 Description of Any Warning System in Effect
.- No formal emergency or contingency plan is in effect to reduce or minimizedownstream damage in emergency situations.
4.5 Evaluation0
. -To insure the safety of the residents and industries immediately downstream, aregular inspection and maintenance program should be developed and imple-mented.
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SECTION 5
EVALUATION OF HYDRAUILIC/HYDROLOGIC FEATURES
",'. " 5.1 General
The Pemberwick Dam, built across the Byram River, creates a narrow impoundmentwith a total storage capacity of 41 ac.-ft. at the spillwa-; elevation of 76.5 or 0.03percent of the watershed area of 26.2 square miles. Each foot of depth in the pondabove the spillway crest can accommodate approximately 5.5 ac.-ft. The spillway
: ". is a 63 foot long by 8 foot wide broad crested uncontrolled weir. Stream and basinslopes are flat to moderate having average grades of 0.9 percent and 1.2 percent,respectively.
5.2 Design Data
. a. Flood calculations were done by the State of Connecticut in November, 1955and yielded a 100-year frequency flood of 3390 cfs for the Pemberwick Damsite.
>N. To supplement this data, U.S.G.S. topographic maps (scale 1 "=2000') were
utilized to develop hydrologic parameters such as drainage areas, reservoirm, surface areas, basin length, time of concentration and other runoff charac-
teristics. Elevation-storage relationships for the reservoir were approximated.
Surcharge storage was computed using U.S.G.S. maps. Some of the pertinenthydraulic design data was obtained and/or confirmed by actual field measure-
ments at the time of the visual field inspection.
b. Outflow values (routing procedures) and dam overtopping analyses were com-,- %puted in accordance with the guidelines developed by the Corps of Engineers.
4.. %Judgment was used in calculating final values outlined in this report, which arequite approximate and should not be considered a substitute for actualdetailed analysis.
5.3 Experience Data
Historical data for recorded discharges at the dam site is limited to the followingapproximations derived in 1955 from an unknown source:
July and September 1938 - 2400 cfsOctober 1955 - 3200 cfs
From the spillway capacity and dam overtopping analysis calculations, both ofthese floods overtopped the dam by at least 2 feet.
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5.4 Test Flood Analysis
.. Recommended Guidelines for the Safety Inspection of Dams by the Corps ofEngineers were used for the selection of the "Test Flood". This dam is classified asa HIGH hazard and an INTERMEDIATE size structure. Guidelines indicate that theProbable Maximum Flood (PMF) be used as the test flood for these classifications.The watershed has a total area of 26.2 square miles. Snyder's lag was calculated tobe 7.31 hours and a Snyder peaking coefficient of 0.625 was used. The 200 squaremiles - 24 hour Probable Maximum Precipitation (PMP) is 22 inches. The flood hy-
* ... drograph package, HEC-1 computer program, developed by the Corps of Engineerswas utilized to develop the inflow hydrograph, route the flood through the reservoir,and for the dam overtopping analysis. A test flood inflow equal to the PMF wascalculated to be 25600 cfs. The inflow of 1/2 PMF is 12800 cfs.
The spillway capacity is hydraulically inadequate to pass the test flood (PMF) andovertopping of the dam will occur. The maximum outflow capacity of the spillwaywithout overtopping the dam is 1100 cfs. This corresponds to 4 percent of the testflood and a storage above the spillway level of 19 ac.-ft. The maximum outflow dis-charge value for the test flood is 25600 cfs corresponding to a depth of flow over
the top of the dam of 17.0 feet and a storage above the spillway level of 182 ac.-ft.The outflow value for 1/2 PMF is 12800 cfs. A spillway rating curve and a reservoirsurface area - capacity curve are included in Appendix D of this report.
There are no operating outlet works and all flow must be discharged over the spill-
,- -way or top of the dam. Storage for impending flood conditions cannot be providedif the pool level is high.
r 5.5 Dam Failure Analysis
This dam is classified as a high hazard structure. Failure discharge can causedamage due to high velocities, impact from debris, and flooding to over 5 residen-tial homes, a school and a commercial building. The calculated dam failure dis-charge is 8350 cfs at a pool level equal to the top of the dam. At this level, theprefailure flow in the downstream channel will be 1100 cfs corresponding to adepth of flow of approximately 5 feet. Failure will produce a water surface level of
approximately 11.5 feet immediately downstream from the dam. The failure dis-charge will affect downstream areas for a distance of 3000 feet from the dam. Atthis distance the water surface level will be approximately 1 to 2 feet above normal
observations. Beyond 3000 feet, the effects of the failure discharge will be reducedas it enters an unnamed pond. Water surface elevations due to the failure of thedam are listed in Appendix D. Probable consequences including the prime impact
areas, are also listed in Appendix D.
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S-.SECTION 6
* EVALUATION OF STRUCTURAL STABILITY
6.1 Visual Observation
The visual inspection revealed no signs of major physical distress in the structure.However, leakage was noted on the downstream face.
6.2 Design and Construction Data
There is insufficient design and construction data to permit a formal evaluation ofstability.
6.3 Post-Construction Changes
- No post-construction design data pertinent to the embankment or foundation isavailable. It is believed that the original dam failed in October 1877 and the presentdam rebuilt shortly thereafter. The extent of the damage due to the failure or infor-mation concerning the rebuilding is unavailable.
The high level outlet was sealed in 1978. The low level outlet is suspected to be-u below the present sediment level.
-' 6.4 Seismic Stability
The dam is in Seismic Zone 1 and, hence, does not require evaluation for seismic- Istability according to the Corps of Engineers Recommended Guidelines.
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SECTION 7
ASSESSMENT, RECOMMENDATIONS AND REMEDIAL MEASURES
7.1 Dam Assessment
a. Condition: Based on the visual inspection, past performance and hydraulic/hydrologic evaluation, the Pemberwick Dam and appurtenances are judged tobe generally in FAIR condition. Items of concern that should be addressed as aresult of this inspection are listed in Sections 7.2 and 7.3.
b. Adequacy of Information: The absence of existing engineering data did notallow for definitive review. Therefore, the adequacy of the dam is based onvisual inspection, past performance history, and engineering judgment.
- c. Urgoncy: The recommendations and remedial measures described belowshould be implemented by the owner within one year after receipt of thisPhase I Inspection Report.
7.2 Recommendations
fi It is recommended that the owner engage a qualified registered engineer to carry
out the following actions:
. a. A detailed hydraulic-hydrologic investigation to determine the need andmeans of increasing the discharge capacity of the project.
b. The pond be lowered and the upstream face be visually inspected, and the toe
checked for potential undermining.
" "J. 7.3 Remedial Measures
a. Operational and Maintenance Procedures
1. The vegetation should be removed from the joints and the joints re-pointed on the faces and top of the dam.
2. The two logs should be removed from the spillway crest as soon aspossible.
3. The trees overhanging the channel downstream of the dam should be
removed.
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4. The damaged fence on the west abutment should be repaired.
. 5. The seepage on the downstream face should be monitored to note anychange from the existing conditions.
6. The low level outlet should be brough back to an operating condition toallow the pond to be lowered.
7. Institute a program of annual periodic technical inspection with specialemphasis on the joint between the dam and the rock abutments at thevalley walls.
8. Develop a formal flood warning and surveillance plan, including round-
the-clock monitoring during heavy precipitation.
7.4 Alternatives
Remove the dam.
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-. APPENDIX Ah INSPECTION CHECK LIST
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INSPFCTION CIECK LIST
PARTY ORGANIZ'TION
PROJECT PEMBERWICK DAM DATE NOVEMBER 12, 1979
."TIME 10:00 AM - 12:00
WEATHER PARTLY SUNNY
W.S. ELEV. U.S. DN.S.
PARTY:
1. R. JOHNSTON, JPPA 6. D. KNAPFL- GREENWICH ASSOC.
2 R. LYON, JPPA 7.
3. G. SALZMAN, CWDD R.
- 4. 9.
5. 10.
PROJECT FrATURE INSPFCTFD BY RFMARKS
1. Hydraulics R. Johnston
2. Structural R. Lyon
3. Geotechnical G. Salzman
4.
5.
6.
7.
A.1 9.
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.1*. , A
erg INSPECTION CHECK LIST
PROJECT P1M), ERWTCK DAM DATE 11-1.2-79
PROJECT FEATURE_ __ _NAME
DISCIPLINE NAME
AREA EVALUATED CONDITION
DAM E BAN1MFNT
Crest Elevation 80.0 GOOD - STONE CRFST
Current Pool Elevation 76.5 GOOD- 31" BELOW CREST
Maximum Impoundment to Date
Surface Cracks NONE OBSERVED
-[ .Pavement Condition GRASS GROWING BFTWEEN STONES
Movement or Settlement of Crest NONE OBSERVED
Lateral Movement NONE OPSERVED
Vertical Alignment GOOD
9 Horizontal Alignment GOOD
Condition at Abutment and at GOODConcrete Structures
Indications of Movement of NONE OBSERVFDV Structural Items on Slopes
- ' Trespassing on Slopes NOT PFRMITTFDVegetation on Slopes MINOR - GRASS & SM. SHRUBS IN JOIN S
". Sloughing or Erosion of Slopes NONE OBSERVEDor Abutments
Rock Slope Protection - Riprap N/AFailures
a....' Unusual Movement or Crackina at TOE NOT VISIBLE - UNDERWATERor near Toes
Unusual Embankment or Downstream LFAKS AT AND ADJACENT TOSeepage SPILLWAY SILL EDGES
4 Piping or Boils NONE OBSERVED
* ) Foundation Drainage Features NONE OBSERVED
N' 'i Toe Drains NONE OBSERVED
Instrumentation System NONE OPSERVFD
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INSPECTION CHEFCK LlfST
PPOJECT PI'MPEPViriK DAM DATE 1-27
PROJECT FEATURE_________ NAME ______________
I DISCIPLINE____________ NAME_______________
AREA EVALUATED CONDITION
*CUTLET WORKS - INTAKF CHANNELI ANDINTAKE STRUCTURE
a. Approach Channel ENTIRE RIVER BED -UNDERWATERI
b. Intake Structures
pLow Level Outlet NOT VISIBLE -SUSPECTED TO BECONTROLED BY THlE SLANTED GEARLIFT ON THE TOP OF THE DAM .INTAKE SUSPECTED TO BE BELOW
High Level Outlet SURFACE INTAKE OPEN. LOWER INTAKE
- NOT VISIBLE. VERTICAL GE2\R STEMON INOPERABLE (SHEFARED SHAFT).
A-3
INSPECTION CHECK LIST
* PROJECT PFMBEPWTCK DAM DATE 11-]2-79
PROJECT FEATURE NAME
B DISCIPLINE____________ NAME________________
AREA EVALUATED CONDITION
OUTLET WORKS - TRANSITION & CONDUI"
Low Level Outlet TYPE AND CONDITION UNKNOWN.
High Level Outlet A VERTICAL StTAFT LEADS FROM THFSURFACE AND LOWFP INTAKE TO A 36"PIPE WHICH EXTFNDS HORIZONTALLY TOTHE DOWNSTRFAM FACE OF THE DAM.
-' PLUGGED WITH CONCRETE IN 1978.
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INSPECTION CIECK LIST
- . PROJECT PFMPFRWITCK DAM DATE 11-12-79
PROJECT FEATURE NAME
I-IDISCIPLINE___________ NAMIE_____________
"" AREA EVALUATED CONDITION%I
OUTLET WORKS - OUTLET STRUCTUREAND OUTLET CI1ANNFL
" Structure NOT VISIBLE. 12 INCH OUTLET VALVEON DOWNSTREAM FACE OF DAM FOR HIGHLFVFL OUTLFT WAS REMOVED AND OUT-LET SEALED WITI1 CONCRFTE IN 1978.LOW LEVEL OUTLET WAS APPARENTLY A
- PIPE OUTLETTING THROUGH TILE FACEOF TIE DAM.
Channel SEE SPILLWAY DISCIIARGF CHANNFL.
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INSPECTION Ciii;C LIST
PPOJECT P17MBERWTCK DAM DATE 11-12-79
PROJECT FEATURE NAME
SDISCIPLINE_ NME
AREA EVALUATED CONDITION
. OUTLET WORKS - SPILLWAY WEIR,
APPROACH AND DISCIARGF CHANITFLS
a. Approach Channel ENTIRE RIVER BED - UNDER WATFR
General Condition
Loose Rock Overhanging Channel
Trees Overhanging Channel
-5Floor of Approach Channel
-" b. Weir
General Condition of Granite GOOD
Rust or Staining N/A
Spalling NONF OBSERVFD
Any Visible Reinforcing NONE OBSFRVFD
Any Seepage or Efflorescence SPILLWAY FLOWING - NONE VISIBLE
-" Drain Holes NONE OBSERVED
c. Discharge Channel ENTIRE RIVERBED - UNDERWATER
General Condition GOOD
Loose Rock Overhanging Channel NONE OBSERVED
Trees Overhancina Channel YES
Floor of Channel UNDERWATER - APPARENTLY ROCK
Other Obstructions BUILDING AND SURROUNDING CONCRFTE4% * " WALL ON LEFT SLOPE
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pj, APPENDIX B .
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APPENDIX B3-i1
DESIGN, CONSTRUCTION AND MAINTENANCERECORDS AND LOCATION
.Mr. Victor J. GalgowskiDam Safety EngineerWater and Related Resources UnitDepartment of Environmental Protection
id State of ConnecticutState Office BuildingHartford, Connecticut 06115
Greenwich Associates, Inc.100 Putnam GreenGreenwich, Connecticut 06830
I
B-I
' Mr.Victo J. Gagowsk
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. I 7
BUCK & BUCKE N C I N E E It S
98 WADSWOIITI! STEIET., iHAIITFORDI , x)NNJCTICUT O(0OG
a~m~u A. Ti4ThPA(uU ity.r woLrorr flI(
mot . RXUCK D. -5LKLawwzxOUSO? (a. r.avxtCKA%COMM. 5713-131 June 13, 1978
Mr. Victor Galgowski, ,. u.'-:.-Superintendent of Dams,Department of Environmental Protection, F( 2 f- \( V ,-State Office Building,Capitol Avenue,Hartford, Connecticut 06115 ,
Reference: "American Felt Dam"* III Byram River, Greenwich t'IL 5 %i.----
Dear Vic:
We inspected the subject dam on May 19, 1978 and found the dam to be ingood condition and apparently safe. There is a slight leak at spillway level
•U. in the west abutment, but the leak is very minor and nothing to be concernedabout. The dam is a cut stone masonry arch, founded on ledge rock. Mostprobably the abutments also bear against ledge rock. The dam is basically arun of the river type structure which can be overtopped without danger to thedam.
I checked the Corps of Engineers'Flood Plain Information Study" of theByram River, prepared in 1964 and found that the subject dam is called the"Aerotec" dam in that report. The Corps study indicates the dam will be over-topped by a 10-year flood. The study also indicates the downstream channelwill contain a flood flow of 4,300 cfs, which is equal to the flood of record,which occurred in October of 1955.
Although the dam itself is in good condition, we found some of its appur-tenances in bad shape. The protective railing which surrounds the east abut-ment is rusting at the base of each post and a large section on the downstreamside has broken off. The gate mechanism operating wheel has been broken, thestem is badly rusted and it's most probable that the mechanism is inoperable.A gate and section of pipe that had been installed in the old "pipe head race"has broken off, reportedly due to heavy ice loads this last Winter, and wateris spewing freely from the broken pipe. Downstream owners expressed concernabout the flow from this pipe, but it is being deflected by a ledge outcroppingand is causing no damage.
-Reproduced Irom
best available copY.
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B ICK & I'CK ENGINEIFIS
Ir Mr. Victor Galgowski PAo 2.
"TIE June 13, 1978 COMM. 5713-131'7.
I
In summary, the structure is in good condition and appears to be safe.Some of its appurtenances need improvement, but they are all non-structuralmaintenance type items. The owner should be notified of these conditions.
Sincerely yours,
BUCK & BUCK
James A. Thompson4% JAT:fb
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Inventoried INVLNTO 1 DATA! ":i.By t • '
Nw'e of /. ' or Pon /
; O..fl. . "-'.. .. -r ' *..L ~
Bateod No.t"( .
Name of trapajne / mL'C ,
Wlz.1
*One ) ( ~ .. j• ) -
Address /JJ ai
"ond Used For 1I /.dI ii , .. , .. . ,., -
Dimensions of Pond: Width _______Length ________Area 4t
A Total Length of Dam / Length of Spillwav id-
Location of Spillway c..i2'/'5J
Height'of Pond Above Stream Bed *~ ~ iL
Height of Embankment Above Spillway -
Type of Spillway Co-struction -Lze W <A
Type of Dike Construction
Downstream Conditions G2 (4~~''~" c~ \
I.
Surrmary oE File Data . .' '
,* , 1 . - ..
Remarks - " ' I- .
")" Tye I 1pilly Pos1c1on .(3
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.. --Type o Dike onstr ct-o 4 .. 2 - 2,,. - - -- _________..'
"-W ownsFtr m ' Con iion '; ,hi i,z le /bi " / ; ______\ls .._ _
4.. . . . . ;'14 ' ~ 4
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Rerdue.fo%,Remarks~ ~ ~~ ~3- b.est. , ,9il~l c-,,/opy,/, 7/,5 ¢lc
_' .. _' .. ;o ev,,d, ; ,, .. , %
TOWN OF GREENWICH4CONNECTICUT
IDMP. OF PUBLIC WORKS
A7,cr.1c-.n ::cm Coo
!Pes !%zcnir Arrh 'xn: - brr !!vcrDear 1'r. Lc.for-: 1Vc-th o' Conly Ave.
-:-s for+.i'att fo - .'Ir- -. cs '.rcu -nnticnc-1 t~n i:r:r dv ~:T.curconlI)iny a-.i the R... : L .. Xi :-nd th..t ;,cu !-_- dr.-;.n d'.;;n '.!e :al r ;cr
.'thn n-ir-scl or ronai' .n a -~te. f £sunttion of -i; CL--t 1.,z r zr, ; o cver i1 yo irs rot 'kincwn.: rehror nct -,i. coujr in haJccrred
- at 4 4. mlL.Atc in the itr ol poul r- pi1-r(,d o-af --id
hc.-r~.>ot,,,;rn _c:At zt -a, i . cf aa.b~ 'co,>1*Ij-d~ .. l~tL1'J3t ;Az the fo'ind1it~n a: rdi~i~;t i &Sr-
~ - -. o? .'v~ a'. I~rti1'! -11* 1- t.It en'-'.'r c-incrtunity a.:cr.! ~,s:.- i-n pz-rr:1-3a 2i'.'j- to ten Ycars, that lh, pool ',r an'~r d 'dto 07ti:rn.cfl.
j.C r'1- r01 L weta'-:-. -iar in ALn Let ter cud rtn
.t!.i t-v,- (.n '.:.o e-i'd 4'l'Uj- to 1thc. inc ~i-Al, of~ tlhe str~ti-
T c! I rnot rxxin' thr!i~: ~.;2r -cints c~c.:r sInce U-ho n<ole areir.-r: -r : I d X11 not e -re to f'ifl and hrvak a k c An ~'- -cstei to you
-. cv~'r thotc, -.)'one I bi2:it -.-f~ud bo to .;u c-..n:"s intlore3t 3 >'ioth~po~tin to ..cterinoto -.,!:t i~tn '-as delt ckLJ'clate-1. ~LS~3 a1 :,0,
~.*: . are'~ .- ' cri .;d if the nrih~trcrAs teril I-, it Tiould Lr '8c ~r a rioi' ie tl.-ou -h t hC. cu~1~c o :ul'or mo, t La r
a ccomnA.Iion thait -,--It iA_-,-ir the Z;fety of tTf wi. IT c : r,.x a
you too1 Into 1h !isn i ;. 1, 1 1 of :-.'ir- rc;.ilra L. tl2,>L'8 . ;prC;C :2. ." 01kcby- thL-s proce 3 r'ort-ir Is L~hot into thn structure at ccnzidora; le ve? ority.
I wuuIld "beinve alao t!",* thla nrece.-, .;muld olo -is *;ood or a better ACb1 ar.d% -1at c cost t tan th i u suial h atnd rot! -.oJis or poiti'I o.
'.1I undorcotand thait now divin- is not p.--rriittcd from~ tlo !a-'. Ycii willrote In the photo,7raphs a Lizeablo . culder a-mro<LrateV. In t zniiter ofthe pool; it it; a womler that so-zi 1,oy dlid not break his3 neck in the pant.
You will understand of covurse that -7 principal intercst in this strijo-15 &.!O1- to fcclriL; th zt thc T.-'-n 0.-i:., re.z:pons ti ily to the, irth:abi-
% ~ta'.ts in the C.-barrzfick ~I'1pl-tn lelow L:-. 1dim aa well. a.; (Ii-a.:c w croads ard bric1gone
Yours vcry truly, ro
) ~ s vailabe my~
ilkQ~h,..Cn
cc. stata~~.& dot of Da1 Cc -Am - er -
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S. E. MINOR M Co., ,Nc. .C IV I L EN, It#: Rs - .r R S
.,'¢N'r t4WC . CONN. - .:.December 15. 9.B
S Drnina-e CCL'ni3Son, Torn Han
. ,:, Greenwich, Cc, n-onih". Re: byrem River Dams
Gentlemen:-
At the request of your Commission, reprosontin6 the Town of
Greenwich, and other interested parties, en in .pction wns made
*i + : ovembor 2, 1930 of three dams on the Byrem River by a oo ittoo
of this Board consisting of P'essrs. PeIrer, Blair end .done, ,With
particular reforenoe to loss or damage In the Pcberaick flood
area should these de=s break away*
A study of the watershed to determine probable maxi zum run-
oft was made by the writer end field date was obtained under his
supervision.
The dams under consider~tion, in order followinL do;.stroanm
are co=nonly known as the:- Reynolds Dema* ?clt Co. Dar., and
* R. D. :*. Da=, owned respectivcly by rirc-e V. A. Reynolds, The
American Felt Co. end russoll, Burdscll & ;ard Bolt Nut Co.
-Natershed tributary to the Felt Co. d&m is 27.35 sq. mi. and
to the R. tD. & L'. dem. 27.7 5 sq. rl , both .pproxinote. 'later Is
S. diverted from the watershed rit two points; by New York City on the
west branoh of the BIyrem at the Stoto Line ond on the east branch
by the Greenwich ',ater Co. above Old Il1l Roade
Estirated flood flow on July 23, 1938 end Sept. 21, 1938,
both of the same ceenitude, was approximatoly 2000 cubic foot per
second, lied both tunnels been closed, the flow would have been
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Draingo Comisslon
approxziEtely 2200 o.t.s.
. The watershed, from a runoff vicwpoint, i undeveloped.
N" Quokor runoff with higher flood stages is to be oxpooted In thoU
N . - future due to swamp clearance and drainaCe, construction of storm
• .. drains, buildings, pavements, and other impervious surfaces.
Usin; the Fuller form.ula with c watershed oonstaint of 80 and
time frecuenoy of 1000 mnaximum rate of runoff is obteined of
5200 cubic feet per socond or moro thun twice the flood flow of
the floods of July and optember. This is not on unreasonable
*... , flood to erpoct soretime In the future, pnrticularly conaidering
the compnratively small area of the watershed. Had the center of
the hurrioene of JOpte.ber passed alone the Byran watershed, this
flow would have been obtained.
.4 .'. Plans,
No construction plens of the da-s t.re tno.-m to be in exlrtence.
* ' "The Zoynolds and Felt Coo. damsa are evidently by their nppoersnce
quite old, The ori6tna.l . D, & . dam ;uite liikely fniled in the
flood of October 9. 1897 when precipitation was 9,7 inches in 10.5
hours at ,hite Fleins, t. Yo It is roasonable to presume the
present R. B. & ... dMr was built shortly thereafter.
Qo Back profiles or sections of dam, s at naoxzizum heiiht were ob-
.- tained by soundlnG fror, a boat with on iron rod throu.h wvater and
silt, consequently sections are approximeto. Condition of toe of
R. B. & 1. dam was investigated in the same manner.
Reynolds Vs_.,
This dam Is a typical dry rubble overflow dam with vortical
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Drainago Corrission
face, orlainally with a tleht-lino and probably an impact plat-
form* Abutmonts are c~oinat ledge rook*. Headroe ends in a
wooden bulkhoad in poor conditions Old mill has been razed. The
pond formed by the don. is shallow due to silting end impounds
about 5 core feet.
The dam is a small affair in poor condition end unless ro-
paired will Co out during; sorac freshet. Failure will be compara
tively olow; the dam will not Cive way all at once. For this
reason and since only a smll amount of water is retained by the
.! dan, no serious harn will be done.
Felt Co. Dvn*.
This d= is loontod 17001± below the Reynolds dm and 3300'3
U i above the R. B, & :: dam. Principal dimonsions are as follows:-
Crest len;th 200 ' 1!pillvy length 49'Laximum hvi.;ht at spillvy 30'Top width at spillway 13'BOttom width at spillwny 19'EFreeboard 4.75 Aver.Area of pond 2.0 As.
-.- Capacity ot pond (silted) 6± i-o. ft.
The ds.. is constructed of oement rubble masonry with a vortioal
face. The back, iss nearly us could be determined by soundinLa, Is
stopped. The spillway section is arched in plan with a face radius
of 05'0 The east obutment hoe considerable mass and is backed by
a retaining wall$ perpendicular to the dam, with heavy fill in brick
of retaining wall end between dan and mill building. The weat abut-
h 4 ment has not sufficient r.ass nor is the plan proper to take arch
thrust. Consequently the don should bo considered an a Gravity
section disregarding arch action.
B-1ot ; ,,,.; ..- :.. . . -- . .. .. -.. . v . " * *.. -*.* -. -. -" .". . .*~~*.- .." ,-"v -',' - - "." - . W .' -. . ...-. " -. " - - "".
Oreenwich Drainage Cormoasion -4-
Impaot of overflow at spillway In teken by exposed led6a
rook nd thero Is no danaer of concealod undersour. It is be-
lievod the rzain portion of the dam is on ledGe rock* The extreme
ends may not be.
Tho spilliwmy is inndequate. The crest was topped by a few
inches aurine the floods of 198o. If apillriy length re~ains the
same end crest length is hold to 1859 by buildina up ends, it is
probable a future flood would have a still water height of about
2 .5 above crest of dam and about ?.3 above spillway. Length of
spillway should be Increased by extondine sane to the waest.
-U Under the conditions stated above end considered as a Gravity
U section, the resultant of forces acting on the d=c falls well out-
side the niddle third % nd .yhile the dprt ie theoretically safo
-.. egainst overturning, there Is probcble tension in masonry in the
back of the dam. There is not the margin of safety Indicated by
good pructioe, particularly when the condition of-the masonry in
: " the interior of the d . Is unknown, The dan can be strengthened by
additional masonry along the downstrenm faco,
Trees have been nllowecd to 6row on and close to the dam. This
should not be allo'ed eccount of root aotion.
There is i colleotinv_ trouGh alonL the east portion of the
*2. dnm to take overtoppino;. If this was not Included in the ori-
-'- ". ignnl dosiGnp it was built as the result of some exporionce in
the past. The bottom of this #rough should be paved to prevent
scouring.
If the building on the downstreern aide of the west end of
... .. . . . .. .... , ... . . . jZ A.... ....
Greenwich Drainae Goriosion -
N the dnm is to be protected, c similer troush should be con-
struotod clong the west portion of the dame
An oxtraordincry flood would probably out around the endsrWof the de=, partioulnrly thi west ends This mitht result in
I"::T proereasvo underxinin of the ends of tbo don and final failure*
into solid Sround.
There is a leak throuL:h the bottrz of the sluiooway under
the easterly portion of the spill-oy. This should be ropairod.
The old sluicoway in the western portion of the duw is not used
and should be closed with masonry.
The fact thbt a dari hes stood for a lons period of years
should not of itself 6ivo assurance the dam will :Ithstnnd ell
futuro floods. ro refute thin Idea there is the evidonce,
throuthout New :nFlL.nd, of numerouz neglected dam, that havo
-. ;" ffailed. n old dr* row;'trea frequent end thorou ,h maintenance.
Yoreover, it is quite drobeble tho particuler %yatershod ha
not been subject to ti serious flood condition for a period far
"..'-J '.". beyond the no.ory of the oldest irhnbitento
To place the dr. in botter oondition the folloinG is
reeorzended:- Len.;then spillway - 1,dditloncl r.bsonry to In-
. oroase nection - :cnrove trees - Pove east oollooting trou;h -
% Construct similar trough alon, west end - Build up ends of dam
O to prevent end scour - Repair losk - Clone up old sluicoway -
% Careful rnintonnnoe.
., ,. The volume Impoundod b. this dan is snfll, the distonce
p to the 'R 3, & ';, din is 3CO foot nontly still weter, area
B- 12
K . - "-- 71 -7.
I Oreenwioh braineGe Cotrisseon 6
3 of the R. Bi. & 4. pond Is 5*v acres, sur~e would flatten out
quickly an~d still wnter levol. at the T19 U. & .'.* dewm would be
only slightly ralsed. Should the dom fail, loss or damage would
be confined to the AmerIoan Felt Co, and the Pomberwiok flood
plain would not suffer loss or damage.
,* iio 13. & 0 Dln, (PEMBERWICK)
This dam is located 3300'± below the 7elt Co. dam ond im-
mediately above the flood plain section of "Pomberiio"L PrInei-
pal dimensiono are as follows:
Crest length 115'Spillway length 630Maximum heit9ht at spillwny 41'
V... Top width at spillmy 8'Bottom width at spillway 17'±Treeboard 3.5
. -roa of pond 5,5j Ac,Capaoity of pond (silted) .92 Ao. ft.
This is en arch danm botwoen lodge rook abutments, in a
narrow Cor~e with nearly vertical sides* ?"see of dam is vcrticl
and face radius of eroh is leO'±. Vaoe mnsonry is courseC ashlcr
*% .' nd is a wonderful piece of work. i;ntire visible portion of dar.i
is on 1odge rook. As nearly as could be detor-:.inod by soundin.
with iron rods from a bout In the spillariy pool, overflow impact
is taken by ledte roclz snd there was no underscourin, of the da-M
rj that could be found by prodding.
Still water heirht over spillway durine recent floods was
"* 4.3'±. The entire length of the dar. acts as en overflowv dam
'S ~i durinZ floods with no daner of end scour.
.4 The dam is safe in Its present condition end will withntend
00
" .'/ ,, . .. . .... .. ... . .- . .B -1 3
% j . .. . . . . . . . •. •.+. *
Greonwloh brein,,ge Cor isnion - 7 -
any flood it In reasoncble to expect.
The stability of this type of dam, eamong other things,
-Udepends on tight contact with gorge wells and constant Inter-
oonteot of the varlous sections of the darn; and of course, as
with any dam, undorscouring muot be prevented. Consequently
this dm must be Inspected periodically to deter-ino (1) that
Corge walls ere not softening .-nd that no leaks ore developing."
'J X around ends or ulong bottom; (2) that mortar in masonry Joints
has not seriously deteriorated ond is in good condition; (3) that
undersoouring is not taking pl0e.
'o• "It Is rooon-mended thrnt the spillway pool be dewatered durina
the next low water staje of the rivor to determine by visual
inspection the exaot condition or the dam rnd foundcktion at the
too in tho pool, end to determine whether or not repairs are
-" "neoessary*
Conclusion,
It is our opinion that:-
The :eynolda d n is in poor condition and will fail
during some freshet but the Pemborwiok section will not suffer
loss or daemae on cocount of such failure.
,. 4. The Felt Coo der may feil during some future flood
but the Pe.aberytiok Section will not suffer loss or dazage on
account of such failure.
The t. D. & .'1. d:iri in safe at present and will not
' B-14
,2 -T.W
Greenwob DrtinnSo Cormiission -a-
- --
fali under tho notion of any flood It ia reasonvcble to expect,
-- -providcd tho dar, Is maintained in good conditIon.
* "Yours very truly,
State Board of Civil Bneineore
ByJoseph .- 1e
c -=bor for V'ourth Distriot
%JM Concurred in-
!'ember for econd Distriot
°4
Glarnc ZZ1a'Member for Third Distriot
Z
%7
.I "
., 'CB-1
)" . . . . -" -" .: " " " v . , " v v . . " , , ," ." , ' ; , -• ' .-, . • .., ' ' -. , ., 2 , . ' -'
o 4
.1
APPENDIX B-3
:, , RECORD DRAWINGS AND SKETCHES
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I°" i°
k:;: APPENDIX C
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C-I EAST CREST AND SPILLWAY - LOOKING FROMI SLOPEABOVE WEST CRESTI
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C-4 SPILLWAY AND LEAKAGE AT FAST END OF EST.Q
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, .~C-5 OUTLET WORKS CONTROL MECHANISM
C- PLWYLOIGFRMDWSRA NESBAN
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, :.,APPENDIX D
"'. HYDROLOGIC AND HYDRAULIC COMPUTATIONS
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HYDROLOGIC AND HYDRAULIC ANALYSISSUMMARY SHEET
Dam Pemberwick Dam ....... ....
Test Flood PMF
INFLOW HYDROGRAPH DEVELOPMENT
Drainage Area 26.2 sq. mi.
Probable Maximum Precipation24 hour - 200 square mile PMP 22 inches
Initial Railfall Loss 0 InchUniform Railfall loss .' Inch
. Snyder's Lag 7.31 hours
Snyder's Peaking Coefficient .625
- Test Flood Inflow 25600 CFS
PMF Inflow 25600 CFS
RESERVOIR ROUTING AND DAM OVERTOPPING
Test Flood Outflow 25600 CFS
Spillway Capacity at Top of Dam 1100 CPS4 % of Test Flood
Flow Over Spillway at Test Flood 15800 CFS
Spillway Crest Elevation 76.5 FeetTop of Dam Elevation 80.0 FeetTest Flood Elevation 97:0 Feet
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D.1
PEMBERWICK DAM
" A. Size Classification
Height of dam = 45 ft.; hence intermediate
Storage capacity at top of dam (elev. 80.0)= 60 Ac-FT.; hence small
Adopted size classification intermediate
B.i) Hazard Potential
SThis dam is located upstream of Pemberwick, an urbanized
area, Residential homes are located along the downstream
channel. Mead School and a commercial building also are
located along the channel.
ii) Impact of Failure of Dam at Maximum Pool (Top of Dam)
It is estimated from the "rule of thumb" failure hydrograph,that the following adverse impacts are a possibility by the failureof this dam.
a) Loss of homes Over 5b) Loss of buildings 1-2 "c) Loss of highways or roads Noned) Loss of bridges None
The failure profile can affect a distance of 3000 feetfrom the dam.
C. Hazard Potential Classifications
HAZARD SIZE TEST FLOOD RA'1GE
High Intermediate PMF
" Adopted Test Flood = PMF = 1010 CSM
'. = 26500 CFS
D. Overtopping Potential
Drainage Area 16,777 Acres = 26.2 sq. miles
Spillway crest elevation = 76.5 GVD
* Top of Dam Elevation = 80.0 NGVD
Maximum spillway discharge .414 Capacity without overtopping of dam = 1100 CFS
"test flood" inflow discharge = 26500 CFS"test flood" outflow discharge = 26500 CFS
D- 18 "', A:t .. . . . . . .. . .
PEMBERWICK DAM
Dam Failure Analysis
1. Failure discharge with pool at top of dam (clev. 80.0 )= 8350 CFS
2. Depth of water in reservoir at time of failure = 36 ft.
3. Maximum depth of flow downstream of dam 11.5 ft.
4. Water surface elevation just downstream)of dam at time of failure ) = 51.5 NGVD
The failure discharge of 8350 CFS will enter and flow down-
stream 3,000 feet until the brook enters a pond on Byram River.
Valley storage in this 3,000 foot length of brook is substantial in
_reduing the discharge. Also due to roughness ctharacteristics,
obstructions and frictional losses, it is very likely that the
W unsteady dam failure flow will dissipate its wave and kinetic
energy and thus convert to steady and uniform flow obeying Manning's
"" formulae 3000 feet downstream. The failure profile will have
the following hydraulic characteristics:
DISTANCE FROM THE DAI WATER SURFACE ELEVATIO:7 '1GVD KDMARKS
f0' 80.0 Upstream of dam
0' 51.5 Downstream of dam
1000' 1.5
2000' 31.5
3000' 10.0 @ Pond
Beyond 3,000 feet _
failure discharge will flow in the below given channel characteristics:
Q 3158 CFS; S .007
S n = 0.05 ; b = 300 ; d = 3±
Side slopes = 1V or 211.
D1
* D-19
7 AD-AI42 702 NATIONAL DAM'INSPECTION PROGRAM PEMBERWICK DAM (CT
2/2I 88842) SOUTHWESTERN CO..(U) CORPS OF ENGINEERS WALTHAMI MA NEW ENGLAND DIV FEB 88pUNCLSSIFIEDFFG 130 N
[L. 111O2
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MICROCOPY RESOLUTION TEST CHARTNATIONAL BUREAU OF STANDARDS-1963-A
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"Rule of Thumb Guidance for EstimatingDownstream Dam Failure Analysis"
DATA
Name of Dam Pemberwick Dam
Location North of Pemberwick, CT.
Drainage Area 26.2 sq. mi., Top of Dam 80.0 NGVD
* Spillway Type Overflow-broad crest , Crest of Spillway 76.5 NGVD
Surface Area @ Crest Elev. 5.5 Acres = .009 sq. mi.
Pool Bottom Near Dam = 44 ± NGVD-
Assumed Side Slopes of Embankments = i:1
Depth of Pool at Dam (Yo) = 36 Feet
Mid-Height Elev. 62 NGVD
Length of Dam at Crest = 115 Feet
Length of Dam at Mid-Height = 93 Feet
% of Dam Length at Mid-Height = Wb = 23 Feet
Step 1
Storage (S) at time of failure 60 Ac-FT(Equal to top of dam)
- Step 2Peak Failure Discharge
Qpl = 8/ 2 7 Wb V TYo 3 / 2
1.68 Wb YO3/2 8346 cfs
" Failure is assumed to coincide with pool elevation at top of dam.
7.
D-20
.. t W- V xl . Y Vp-- - .
Ui.-4%
No Name Pond is located 3000 feet downstream
of Pemberwick dam. There is a 35 foot
drop into No Name pond which will cause the dissipation
A:- of wave and kinetic energy of the failure discharge. Approximately,
the water surface elevations between Pemberwick dam
• and No Name pond will be as given on Dam Failure
- Analysis. The increase of depth in No Name pond due to
failure of Pemberwick dam is estimated to be 1-2 feet.
4-
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D- 22
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D-25
V RATING CURVE DEVELOPMENT
Pembcrwick Dam
6jSpillway Q C CLI1 2/3
C =2.70
L =63 feet
.4.
D- 26
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' PEMBERWICK DAM
"- D-28 RESERVOIR AREA-CAPACITY CURVE
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APPENDIX E
* INFORMATION AS CONTAINED IN THE
NATIONAL INVENTORY OF DAMS
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