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AD-AI56 372 NATIONAL PROOIAfl FOR INSPECTION OF NON-FEDERAL DAMS 00 itfBROOK DAN (NN O01..UI COPS OF ENGINERS WALTHAN EMNEW E:NGLAND DIV NOV 78
UNCLASSIF IEO Fil 13/13 NLIII III-ElI"''11
W-N 1 1.-0 JL
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MICROCOPY RESGLUTION TEST CHART
NATIONAL BUREAU Of STANDARDS 1963 A
i.
I
I CONNECTICUT RIVER BASIN
N SPRINGFIELD, NEW HAMPSHIRE
I
IBOG BROOK DAM
1 NH 00189
I NHWRB 220.12
I PHASE I INSPECTION REPORT
U NATIONAL DAM INSPECTION PROGRAMIO
I DTIC
I id JUL 0
IDEPARTMENT OF THE ARMY
I NEW ENGLAND DIVISION, CORPS OF ENGINEERS
I WALTHAM, MASS. 02154DISTRIBUTION STAr,-MEN A~
1978 Appxoved fox public releaos
NOVEMBER Distxibution Unlimited
I 11FILE COPY 85 06 14 117
" ,-'JB
DISCLAIMER NOTICE
THIS DOCUMENT IS BEST QUALITYPRACTICABLE. THE COPY FURNISHEDTO DTIC CONTAINED A SIGNIFICANTNUMBER OF PAGES WHICH DO NOTREPRODUCE LEGIBLY.
M~ I-ROLPCL U AT GOVERNMENTr FXPEN4SE
SECURITY (LI ASIIAcTNOFP1 S PAG f~olbl &Rooted)
REPORT DOCUMENTATION PAGE READkEINSTRUCTIONS
I mgF!8"T NUMBER 1. GOVT ACCESSION NO. 3 RECIPIENT'S CATALOG. MUMMER
Nil 00189 2PAII6 14TITL fd h.bI4eI) S. TYPE OF REPORT a PERIOD COVERED
Bog rookDamINSPECTION REPORT
NATIONAL PROGRAM FOR INSPECTION OF NON-FEDERAL iPaRrFORMiNG ORG. REPORT NuftoERDAMS
7 AU I 4ORI 4) S1. CON4TRACT oR GRANT MNGERo)
U.S. ARMY CORPS OF ENGINEERSNEW ENGLAND DIVISION
9 PERFORMING ORGANIZATION NAME AND ADDRESS 10- PROGRAM ELEMENT. PROJECT, TASKAREA a WORK UNIT NUmOeRS
It CONTROLLING OFFICE NAME ANO ADDRESS 12. REPORT DATE
DEPT. OF THE ARMY, CORPS OF ENGINEERS November 1978NEW ENGLAND DIVISION, NEDED Is. RUNNER OF PAGES
424 TRAPELO ROAD, WALTHAM, MA. 02254 47IS. MiONITORIN.. AGENCY NAME & AOORISS d~i.,ma beem QmwehMftd% 00906) Is. SECURITY CLASS. (wfg awe
UNCLASSIFIEDIgo. o9CL ASSI PIC ATIONID~OI1AIIIwG
SCHRIOU L
I6. DISTRIBUTION STATE1MINT (el I*S* *0orl
APPROVAL FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED '17. OISTRINUTION STATEMENT (ofsh ~aof Me* 101d in 810411 ". It 41Ibe6Mt Raw AwOW)
IS, SUPPLEMENTARY MOTES
Cover program reads: Phase I Inspection Report, National Dam Inspection Progris;however, the official title of the program is: National Program for Inspection. ofNon-Federal Dams; use cover date for date of report.
19. K EY @0605 (Cinmwe aft Peewm. SS eee m mE~f of' 0~6rM AkrO bdl ee 1114)
DAMS. INSPECTION, DAM SAFETY,Connecticut River BasinSpringfield, New HampshireBog Brook
20ASRC CR em.sd la..epm s~~ ~Se*ibe
-The dam is a 289 ft. long earthfill structure which incorporates 71 ft. of freeeverfall spillway and two 4 ft. wide sluiceways with stoplogs. It is inter-mediate in size with a low hazard potential. The dam is in good condition atthe present time.Only minor operations and maintenance type procedures arerequired to correct the deficiencies.
DD 1473 slvIioN OF I sOV a is1 oRSOLEYE
II
Acc9ssion For
NTIS GRA&I
DTIC TABU1fnnounced 0]
BOG BROOK DAM JustifioctioNH 00189 ' -
Distributioa/
Availability Codes
aveil and/or
Dist 1Special
CONNECTICUT RIVER BASIN
SPRINGFIELD, NEW HAMPSHIRE 0
PHASE I INSPECTION REPORT
NATIONAL DAM INSPECTION PROGRAM
III
I
II
NATIONAL DAM INSPECTION PROGRAM
PHASE I REPORT
Identification No.: NH 00189NHWRB No.: 220.12Name of Dam: BOG BROOK DAMTown: SpringfieldCounty and State: Sullivan County, New HampshireStream: Bog BrookDate of Inspection: September 20, 1978
BRIEF ASSESSMENT
Bog Brook Dam is a 289 foot long earthfill structure whichincorporates 71 feet of free overfall spillway and two 4 footwide sluiceways with stoplogs. The embankment portions ofthe dam are approximately 7 feet high and contain a concretecore wall. The gravity concrete spillway and sluiceway sectionis founded on bedrock and has a maximum height of approximately13.5 feet. The dam was constructed in 1957 by the New HampshireFish and Game Department for wildlife management purposes.
The dam lies on Bog Brook and receives runoff from 12.1 squaremiles of steeply sloping, heavy forest. The dam's maximumimpoundment of 2500 acre-feet places it in the INTERMEDIATEsize category, while the absence of any downstream hazard fora distance of at least 3 miles indicates a LOW hazard potentialclassification.
Based on the size and hazard potential ratings and in accord-ance with the Corps' guidelines, the Test Flood (TF) is in therange of the 100 year flood to one half the Probable MaximumFlood (PMF). An inflow TF of 5000 cfs yields a maximum dis-charge at the dam of approximately 3100 cfs, which wouldresult in overtopping on the order of 0.5 feet. The maximumdischarge capacity of the dam without overtopping is approxi-mately 2840 cfs. Thus, it is recommended that further hydro-logic studies of the spillwa.y adequacy be made.
3The dam is in GOOD condition at the present time. Only minoroperations and maintenance type procedures are required tocorrect the deficiencies noted.I
I
Included in these tasks are monitoring of a wet spot on thetoe of the embankment, increased brush clearing and the
repar ofrodent holes, repair of some eroded concrete joints,remvalof debris and overhanging trees from the downstreamchanelremoval of debris and sediment from behind the dam,
installation of a gage and the provision of a device forsecuingstoplogs in place.
The above recommendations and remedial measures should beimplemented within two years of receipt of this report bythe owner. Based on the dam's GOOD condition, periodictechnical inspections should be scheduled every two years.
Nc 9.5~
, -r
William S. T 'no Robert MinutoliNew Hampshire Registration 3226 Massachusetts Registration 29165
IThis Phase I Inspection Report on Bog Brook Damhas been reviewed by the undersigned Review Board remwbers. In ouropinion; the reported findings, conclusions, and recoa. ndations arc 3A. t -ih th-: ?&-orricended Guidelines for Safi v Inscti.
-F -m . a,,J L-ng-,reering Judgiwno and an..'. , ,i.,,ittA for approv i.
CHARLES G. TIERSCH, ChairmanChief, Foundation and Materials BranchEngtneering Division
-FRED J. *IVJNS, Jr., Member
Chief, De rgn Branch -Engineerin.g -.Divi sion
SAUL COOPER, Member_Chief,. Water Control BranchEngineering Division
APPROVAL RECOMMENDED:
5JOE B-. FRY ARChief, Engineering Division
SI'I
iii
mmm m m m
PREFACE
This report is prepared under guidance contained in theRecommended Guidelines for Safety Inspection of Dams forPhase I Investigations. Copies of these guidelines may beobtained from the Office of Chief of Engineers, Washington,D.C. 20314. The purpose of a Phase I Investigation is toidentify expeditiously those dams which may pose hazards tohuman life or property. The assessment of the general con-dition of the dam is based upon available data and visualinspections. Detailed investigation and analyses involvingtopographic mapping, subsurface investigations, testing, anddetailed computational evaluations are beyond the scope ofa Phase I investigation; however, the investigation is inten-ded to identify any need for such studies.
In reviewing this report, it should be realized that thereported condition of the dam is based on observations offieldi conditions at the time of inspection along with dataavailable to the inspection team. In cases where the reser-voir was lowered or drained prior to inspection, such action,while improving the stability and safety of the dam, removesthe normal load on the structure and may obscure certainconditions which might otherwise be detectable if inspectedunder the normal operating environment of the structure.
It is important to note that the condition of a dam dependson numerous and constantly changing internal and externalconditions, and is evolutionary in nature. It would beincorrect to assume that the present condition of the damwill continue to represent the condition of the dam at somepoint in the future. Only through continued care and inspec-tion can unsafe conditions be detected.
Phase I inspections are not intended to provide detailedhydrologic and hydraulic analyses. In accordance with theestablished Guidelines, the Test Flood is based on theestimated "Probable Maximum Flood" for the region (greatestreasonably possible storm runoff), or fractions thereof. Be-cause of the magnitude and rarity of such a storm event, afinding that a spillway will not pass the Test Flood shouldnot be interpreted as necessarily posing a highly inadequatecondition. The Teut Flood provides a measure of relativespillway capacity and serves as an aid in determining theneed for more detailed hydrologic and hydraulic studies,considering the size of the dam, its general condition andthe downstream damage potential.
iv
TABLE OF CONTENTS
Page
LETTER OF TRANSMITTAL
BRIEF ASSESSMENT
REVIEW BOARD SIGNATURE SHEET
PREFACE iv
TABLE OF CONTENTS V
OVERVIEW PHOTOS vii
LOCATION MAP i
SECTION 1 - PROJECT INFORMATION
1.1 General 1-11.2 Description of Project 1-21.3 Pertinent Data 1-4
SECTION 2 - ENGINEERING DATA
2.1 Design Records 2-12.2 Construction Records 2-12.3 Operational Records 2-12.4 Evaluation of Data 2-1
SECTION 3 - VISUAL INSPECTION
3.1 Findings 3-1
3.2 Evaluation 3-3
SECTION 4 - OPERATIONAL PROCEDURES
4.1 Procedures 4-14.2 Maintenance of Dam 4-14.3 Maintenance of Operating
Facilities4-4.4 Description of Any Warning
System in Effect 4-14.5 Evaluation 4-1
V
Table of Contents - Cont. Page
SECTION 5 -HYDRAULIC/HYDROLOGIC
5.1 Evaluation of Feature 5-15.2 Hydraulic/Hydrologic Evaluation 5-35.3 Downstream Dam Failure Hazard
Estimate 5-3
SECTION 6 -STRUCTURAL STABILITY
6.1 Evaluation of StructuralStability 6-1
SECTION 7 -ASSESSMENT, RECOMMENDATIONS ANDREMEDIAL MEASURES
7.1 Dam Assessment 7-17.2 Recommendations ri-i
7.3 Remedial Measures 7-1
APPENDICES
APPENDIX A - VISUAL INSPECTION CHECKLIST A-i
APPENDIX B - FIGURES AND PERTINENT RECORDS B-1
APPENDIX C - PHOTOGRAPHS C-1
APPENDIX D - HYDROLOGIC AND HYDRAULICCOMPUTATI ONS D-i
APPENDIX E - INFORMATION AS CONTAINED INTHE NATIONAL INVENTORY OF DAMS E-1
vi
IML
Overview of dam from left abutment
Overview of dam from left spillwayI endwall
vii
IIIIIIIIIIII Overview of dam from upstream right
side
IIII1I
viii
-Sf t
4?,
Oct.
AA
4C to4
f
V. 4 I T N
- SCALE'-0 1/2 12s
SCfSEomggwAUCp AUOcU~ J.SAlMY ENGIEER ON NEW ENGLANDFROM: USGS MASCOMA,N.H. mwnUm FALNIWLTfi.ASO
QUADRANGLE M~AP
NATIONAL PROGRAM OF INSPECTION OF NON-FED DAM
4D LOCUS PLANcu
z0 0 BROK D NEW HAMPSHIRE
I~ SCALE AS NOTEDI D?t SEPT 1918
Ix
PHASE I INSPECTION REPORT
BOG BROOK DAM
SECTION 1
PROJECT INFORMATION
11 General
(a) Authority
Public Law 92-367, August 8, 1972, authorized theSecretary of the Army, through the Corps of Engineers,to initiate a national program of dam inspection through-out the United States. The New England Division of theCorps of Engineers has been assigned the responsibilityof supervising the inspection of dams within the NewEngland Region. Goldberg, Zoino, Dunnicliff & Associates,Inc. (GZD) has been retained by the New England Divisionto inspect and report on selected dams in the State ofNew Hampshire. Authorization and notice to proceedwas issued to GZD under a letter of August 22, 1978from Colonel Ralph T. Garver, Corps of Engineers.Contract No. DACW 33-78-C-0303 has been assigned by theCorps of Engineers for this work.
(b) Purpose
(1) Perform technical inspection and evaluationof non-federal dams to identify conditions whichthreaten the public safety and thus permit cor-rection in a timely manner by non-federal inter-ests.
(2) Encourage and prepare the states to initiatequickly effective dam safety programs for non-federal dams.
(3) Update, verify and complete the NationalInventory of Dams.
(c) Scope
The program provides for the inspection of non-federal dams in the high hazard potential category basedupon location of the dams and those dams in the signifi-cant hazard potential category believed to represent animmediate danger based on condition of the dam.
1-1
I
1.2 Description of Project
(a) Location
The Bog Brook Dam is located on George Hill Roadat the intersection designated Washburn Corner. Thispoint is 4.2 miles south of the junction of George HillRoad and Route 4A, which, in turn, is 1.5 miles southof Enfield Center on Route 4A and 5.5 miles south ofthe town of Mascoma at the intersection of Routes 4 and4A. The portion of the USGS Mascoma, NH quadrangle onpage ix shows this locus. Figure I of Appendix B pre-sents a site plan developed from the map and the siteinspection.
(b) Description of Dam and Appurtenances
This dam is basically a 289 foot long earthfillstructure incorporating two 4 foot wide sluiceways withstoplogs and 71 feet of free overfall spillway (Pg. B-3).The embankment portions of the dam, 77 feet long onthe right side and 130 feet long on the left side, areapproximately 7 feet high and contain a concrete corewall to a height approximately 2 feet above the permanentspillway crest (Pg. B-4).
Beginning at the right side, the concrete portionof the dam consists of a concrete endwall extending upand downstream, a 4 foot wide sluiceway structure withprovision for stoplogs and an invert 2 feet below thespillway crest, a 20.5 foot section of gravity concretespillway, another sluiceway identical to the previousone but with an invert 7.2 feet below the spillwaycrest, a 50.5 foot section of spillway with a V config-uration and an endwall on the left side. The endwallsare approximately 4.3 feet higher than the spillwaycrest. The entire gravity concrete structure is foundedon hard, generally competent schist and has a maximumheight of approximately 13.5 feet above the streambed.
(c) Size Classification
The dam's maximum impoundment of 2500 acre-feetfalls within the 1000 to 50,000 acre-feet range whichdefines INTERMEDIATE size category as defined in the"Recommended Guidelines."
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fmm m m mm l m m m m m
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(d) Hazard Potential Classification
The dam is located in a sparsely populated areaand is at least 3 miles upstream of the nearest popu-lation center. These facts, when combined with thestructure's fairly broad downstream channel, indicatea LOW hazard potential classification.
(e) Ownership
The New Hampshire Fish and Game Department(NHFGD), 34 Bridge Street, Concord, New Hampshireowns the dam. The Department's phone number is(603) 271-3421.
(f) Operator
The Engineering Section of the NHFGD controls theoperation of the dam. Mr. Stephen A. Virgin is theDepartment's responsible engineer and he can be reachedat the phone number given above.
(g) Purpose of Dam
The dam was constructed for the purpose of wild-life management.
(h) Design and Construction History
Construction of the dam was completed in 1957.The Fish and Game Department designed the dam and con-structed it by force account.
(i) Normal Operational Procedures
Day to day operation of the dam rests with localconservation officers who adjust the water level asnecessary to accomplish wildlife management goals.Operation for any other purpose would be directed bythe chief engineer and accomplished by the local conser-vation officer; no operations of this nature are onrecord or can be recalled by the Engineering Section.
1-3
I1.3 Pertinent Data
(a) Drainage Area
The pond impounded by Bog Brook Dam receives run-off from 12.1 square miles of steeply sloping, heavilyforested terrain. Bog Brook and several smaller streamscarry runoff into the impoundment. There is no develop-ment around the shores of the pond.
(b) Discharge at Damsite
(1) Outlet Works
The dam's only outlets are the two 4 footwide sluiceways. The sluiceway at the right endof the spillway has its invert at El. 1092.7,while the invert of the other sluiceway is atEl. 1087.5.
(2) Maximum known flood at damsite
No data on experienced peak flood flows orpond levels are available for this dam.
(3) Spillway capacity at maximum pool elevation:
2110 cfs at El. 1099
(4) Sluiceway capacity at normal pool elevation:
295 cfs at El. 1094.7
(5) Sluiceway capacity at maximum pool elevation:
730 cfs at El. 1099
(6) Total discharge capacity at maximum poolelevation:
2840 cfs at El. 1099
(c) Elevation (feet above MSL based upon New HampshireDepartment of Public Works and Highway Bench Mark4190020 located on crest of dam)
(1) Top of dam: 1099.0 +
(2) Maximum pool: 1099.0 +
1-4
I
(3) Recreational pool: 1094.7 +
(4) Spillway crest: 1094.7 +
(5) Streambed at centerline of dam: 1085.5 +
(6) Maximum tailwater: Unknown
(d) Reservoir
(1) Length of recreational pool: 2 miles +
(2) Storage - recreational pool: 1000- maximum pool: 2500 acre-feet +
(3) Surface area - recreational pool: 330 acres +
(e) Dam
(1) Type: Earth embankment with concrete gravityspillway
(2) Length: 289 feet
(3) Height: 7 feet +
(4) Top Width: 8 feet +
(5) Side slopes - U/S 3:1- D/S 2:1
(6) Impervious Core: 1 foot thick concretecore wall from ledge to El. 1096.5
(7) Zoning, cutoff and grout curtain: Unknown
(f) Spillway
(1) Type: Concrete gravity, free overfall
(2) Length of weir: 71 feet
(3) Crest elevation: 1094.7 feet +
(4) U/S channel: Shallow approach from pond
(5) D/S channel: Broad and rocky
1-5
F
I
(g) Regulating outlets
As mentioned previously, the dam's only regulat-ing outlets are the two 4 foot wide sluiceways withmanually installed and removed stoplogs. The sluicewayat the right end, which has its invert at El. 1092.7can accommodate 2 feet of stoplogs. The second sluice-way, with invert at 1087.5, provides for installatin n ofup to 7.2 feet of stoplogs.
1-6
WOO
SECTION 2 - ENGINEERING DATA
2.1 Engineering Records
The design of this dam is quite simple and incorporatesno unusual features. No original design drawings or calcula-
tions are available.
2.2 Construction Records
Plans for the construction of the dam are included inAppendix B. Page B-3, which presents a plan of the dam, wasaltered to reflect the as-built configuration of the struc-ture.
2.3 Operational Records
The owner operates the dam in a manner consistent withits intended purpose and engineering features.
2.4 Evaluation of Data
(a) Availability
The absence of design drawings and calculations isa significant shortcoming, but is somewhat mitigated bythe availability of the construction plans. An overallmarginal assessment for availability is, therefore,warranted.
(b) Adequacy
The lack of in-depth engineering data does notpermit a definitive review. Therefore, the adequacy ofthe dam cannot be assessed from the standpoint of review-ing design and construction data. This assessment is thusbased primarily on the visual inspection, past perform-ance and sound engineering judgement.
(c) Validity
Since the observations of the inspection teamgenerally confirm the information contained in the con-struction drawings, with modification, a satisfactoryevaluation for validity is indicated.
2-1
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SECTION 3 - VISUAL OBSERVATIONS
3.1 Findings
(a) General
The Bog Brook Dam is in GOOD condition at thepresent time and requires only minor routine maintenancefor continued safe operation.
(b) Dam
(1) Embankment
The dam's embankment is divided into twosections, one 130 feet long and one 77 feet long,by the spillway and sluiceways. Both sections areapproximately 7 feet high and tie into high groundon either side of the dam. The internal construc-tion of the embankments is not know, but existingplans do show a concrete core wall on both sidesof the spillway from ledge to El. 1096.5. The corewalls tie into the spillway endwalls and into natu-rally rising ground at the dam's abutments.
Inspection of the embankments revealed noevidence of vertical or horizontal movement. Nodeficiencies were noted at the junctions with thespillway endwalls or with the natural slopes ateither side. The embankments are covered with athick, low brush which appears to have been recentlytrimmed. There was no evidence of any sloughing,erosion or cracking of the earthfill. Severalsmall rodent holes were noted, however.
There are no obvious signs of active seepagealong either of the embankments. However, at adistance of 95 feet from the left spillway endwall,a wet area approximately 10 feet by 20 feet in planand 3 to 6 inches deep was noted at the toe ofthe left embankment some 40 feet from the center-line. There was no evidence of flow or of turbi-dity, although the water was discolored. Basedupon the topography of the area, this locationcould be a natural ponding point for storm runoff.No obvious deficiencies in the earthfill were notedin this area.
3-1
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(2) Spillway
The gravity concrete spillway is founded onbedrock which appears to be a hard, generally com-petent schist. While there is some nearly verticaljointing in the rock at essentially right anglesto the dam centerline, the low head behind the damindicates that these joints are not a significantconcern.
Observations of the spillway crest revealedno evidence of erosion, spalling, cracking orefflourescence of the concrete. Similar observa-tions apply to the two concrete endwalls.
(3) Sluiceways
Both sluiceways show evidence of erosionalong the construction joints between their side-walls and the buttress supports on the spillwaysides of these structures. Efflourescence andfine random cracking is evident along the samejoint on the inside face of both sluiceways.Minor erosion was observed on the concrete sillin the sluiceway located at the right spillwayendwall. The stoplogs in place in the sluicewaysare in good condition.
(c) Appurtenant Structures
This dam has no appurtenant structures.
(d) Reservoir
Observation of the reservoir shore revealed noevidence of movement or other instability. A smallamount of sedimentation was noted behind the spillway.Examination of the surrounding area revealed no workin progress or recently completed which might increasethe flow of sediment into the pond. Additionally, therewere no changes to the surrounding watershed whichmight adversely affect the runoff characteristics of thebasin.
(e) Downstream Channel
The immediately downstream channel is very rockyand has many overhanging trees.
3-2
Some trees are also growing in the channel itself. Addi-tionally, there is a large, corrugated metal archculvert under the road some 100 feet downstream of thedam which could create a hydraulic constriction in theevent of the Test Flood. Since the dam has only limitedoperational features, these obstructions do not limitIthe operation of the dam. They could, however, createflow restrictions at a time when such a situation isleast tolerable.
3.2 Evaluation
Because most of the dam's key features are readilyaccessible for observation, the visual inspection provided asatisfactory basis upon which to assign a GOOD evaluation forthe majority of those items which affect the safety of thestructure.
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SECTION 4 -OPERATIONAL PROCEDURES
4.1 Procedures
Based upon information provided by Mr. Virgin of theFish and Game Department, the water level in the reservoirdoes not vary much during the year and little manipulation ofstoplogs has been necessary for as long as he can remember.Local conservation officers could make adjustments if theirperiodic inspections deemed such action necessary.
4.2 Maintenance of Dam
The local conservation officers visit the site periodi-cally and report any observed deficiencies back to the Depart-ment. Additionally, an engineer from the Department inspectsthe dam semiannually and upon notification of a problem bythe local conservation officers. The engineer then initiatesany necessary maintenance activity.
4.3 Maintenance of Operating Facilities
The stoplogs require no maintenance other than periodicinspection and replacement, if necessary.
4.4 Description of Any Warning System in Effect
There is no warning system in effect for this dam.
4.5 Evaluation
The established operational procedures are adequate forBog Brook Dam. The good condition of the dam reflects well onthe Department's maintenance program. Due to the absence ofnearby downstream development, the lack of a formal warningsystem is not a significant concern.
4-1
SECTION 5 - HYDROLOGY/HYDRAULICS
5.1 Evaluation of Features
(a) Design Data
The only data sources available for Bog Brook Damare two construction drawings dated January 1956 and someassociated hydraulic calculations. These data have beernchecked and updated by information acquired in the field.Changes to the original design include the addition ofa 4 foot wide stoplog weir on the right end of the spill-way and a change in the configuration of the left portionof the spillway. The original spillway capacity calcula-tions are only of value as an approximate check of presentcalculations, since the dam as actually built differsappreciably from the original design.
(b) Experience Data
No data on experienced peak flood flows or lake
levels is available for Bog Brook Pond.
(c) Visual Observations
Bog Brook Dam is an earth embankment and core wallstructure built on ledge and with concrete gravity out-let works. The dam has an overall crest length of about289 feet at El. 1099. The top width of the dam averages8 feet with two to one and three to one slopes on theembankments.
The dam's control features consf'st of a 71 footlong broad-crested spillway at elevation 1094.7 and-tw~o adjustable four-foot long stoplog weirs. One of theweirs has a permanent concrete base 2.0 feet below thespillway crest, while the permanent base of the otheris 7.2 feet below the spillway. At the time of theinspection, both stoplog weirs were set at the sameheight as the spillway and the pond was at approximatelythe same level, resulting in only a trickle of flowthrough the outlet.
Just downstream of the dam is a constricted channelsection due to a high roadway embankment with a crestabout 2.8 feet higher than the spillway crest. Thestream at this location passes through a large 18 footby 11.5 foot elliptical, corrugated metal culvert.Beyond the culvert, the stream resumes a normal channeland passes through an area having very little, if any,development.
5-1
I
(d) Overtopping Potential
The hydrologic conditions of interest in thisPhase I investigation are those required to assess theovertopping potential of the dam and its ability tosafety allow an appropriately large flood to pass. Thisrequires using the discharge and storage characteristicsof the structure to evaluate the impact of an appropri-ately-sized Test Flood.
Guidelines for establishing a recommended TestFlood based on the size and hazard potential classifi-cations of a dam are specified in the "RecommendedGuidelines' of the Corps of Engineers. As shown inthese Guidelines. the apprnpriate Test Flood for a damclassified as INTERMEDIATE in size with a LOW hazardpotential would be between the 100-year frequency floodand one-half of the Probable Maximum Flood (PMIF).
The magnitude of the 100-year peak inflow to BogBrook Pond is estimated using a regression relationshipprovided by the USGS in Water Resources Investigations78-47, "Progress Report on Hydrologic Investigations ofSmall Drainage Areas in New Hampshire." This equation,which uses the drainage area, main channel slope and the24-hour, 2-year frequency precipitation to estimate peakinflow, yields a 100-year peak flood flow of 1560 cfs forthe Bog Brook Dam basin. A check of the spillway capacityby the New Hampshire Water Resources Board in 1957 de-rived a 100-year flood flow of 2000 cfs.
The chart of "Maximum Probable Peak Flow Rates"obtained from the Corps of Engineers, New England Divi-sion is used to determine the PMF. For the 12.1 squaremile drainage area above Bog Brook Dam, which has a hillytopography, the curve for "rolling" terrain gives aPMF flow of 1600 cfs per square mile. This results ina total PMF of 19,400 cfs or a one-half PMF flow of9.700 cfs.
The "Guidelines" further suggest that if a rangeof values is indicated for the Test Flood, the magnitudemost closely related to the involved risk should beselected. Since the risk is towards the lower end ofthe LOW category, a Test Flood of 5000 cfs is used asinflow to the Bog Brook impoundment.
jThe attenuation of the peak, due to storage, isestimated using the procedure suggested by the Corpsof Engineers, New England Division for "Estimating theEffect of Surcharge Storage on Maximum Probable Dis-charges."
5-2
p I
The Storage-Stage Curve used for these calculations isdeveloped assuming that the surcharge storage availablein a pond is equal to the surface area of the pond timesthe depth of surcharge. No spreading or increase insurface area with increasing depth is considered. Useof the recommended procedure shows that the pond storagedoes have a significant attenuating effect on the magni-tude of the peak flow, since the calculations result ina corrected Test Flood flow of about 3100 cfs, or athirty-eight percent reduction in the pond inflow.
The Stage-Discharge Curve is developed by definingdischarge as the sum of the flows over the spillway andstoplogs, flow over the dam crest, and the flow over theslopes at the ends of the dam. Since it is possiblethat stoplogs might not be pulled in the event ol theTest Flood, these calculations assume that stoplogsremain in place throughout the flood at spillway level.Thus. the sluicewavs are assumed to act as weirs. Para-graph 1.3 presents the discharge capaL ies assumingthat stoplogs were removed.
5.2 Hydrologic/Hydraulic Evaluation
The results of the hydrologic and hydraulic calculationsindicate that the outlet capacity of Bog Brook Dam is insuffi-cient to pass the applicable Test Flood of 3100 cfs withoutovertopping the dam crest. Flow over this portion of the damis not desirable since the crest is formed by a simple earthenembankment and is not intended to carry flow. Even if it werepossible to remove all stoplogs in the event of a major storm,the capacity of the existing outlet works would be only 2800cfs with the water level at the dam crest. Thus, additionaloutlet capacity, possibly in the form of an emergency spillway.would be required to safely pass the recommended Test Floodflow.
5.3 Downstream Dam Failure Hazard Estimates
The flood hazards in downstream areas resulting from afailure of Bog Brook Dam are estimated using the proceduresuggested in the Corps of Engineers, New England Division's"Rule of Thumb Guidelines for Estimating Downstream DamFailure Hydrographs." This procedure accounts for the attenu-ation of dam failure hydrographs in computing flows and fl(od-ing depths for downstream reaches.
5-3
N For these calculations, failure is assumed tooccur as soon as the damn crest is overtopped at a pondelevation of 1099.0 feet. This corresponds to a heightI of 13.5 feet above the stream bed. If the breach widthis assumed to be thirty feet, the resultant peak dis-charge due to dam failure is 2400 cfs.
Downstream of the dam the stream may be consideredin four reaches for these calculations. Below these fourreaches is a swamp and pond that would dampen out theeffects of any dam failure flows.
The first reach covers the region between the damand a highway bridge about 100 feet downstream. Due toits short length and well defined channel, this reachpasses the peak discharge downstream with no attenuation.At the bottom of this reach, an 18' by 11.5' corrugatedmetal culvert beneath the roadway controls the dischargepassing on to Reach 2.
The flow capacity of the culvert was determinedusing a nomograph shown in the Handbook of Steel Drainageand Highway Construction Products (American Iron andSteel Institute, 1971). The capacity was computed fora 13.5 foot depth in the reach to be 2200 cfs.
Reach 2 covers a section of stream about 2300feet long in a well defined channel. This reach wouldexperience a 4.3 foot stage increase while offeringlittle or no attenuation in the peal, discharge. Theflow passed to Reach 3 is 2190 cf's.
In Reach 3, which covers the next 3500 feet ofstream, the channel is wider and flatter than the firstreaches, and would develop a flood flow depth of about5.3 feet. In passing through this reach, the peak flowwould be reduced to about 2140 cfs. Reach 4 is a wide,flat swampy area about 8000 feet lorng that would experi-ence a flow depth of about 5.8 feet, while attenuatingthe peak flow to about 2000 cfs.
There is no development along any of these fourreaches that would be affected by the computed depthsof flooding.
5-4
SECTION 6 -STRUCTURAL STABILITY
6.1 Evaluation of Structural Stability
(a) Visual Observations
The field investigation revealed no significantdisplacements or distress which warrant the preparationof structural stability calculations based on assumedsectional properties and engineering factors.
(b) Design and Construction Data
While no design drawings or calculations areavailable, the construction drawings would be of con-siderable value to a stability analyses were one deemednecessary.
(c) Operating Records
There are no formal operating records for thisdam. Thus, no information concerning the stability ofthe dam during periods of high flow is available.
(d) Post-Construction Changes
There have been no post-construction changesas of the date of this report.
(e) Seismic Stability
The dam is located in Seismic Zone No. 2 and, inaccordance with recommended Phase I guidelines, doesnot warrant seismic analyses.
6-1
I SECTION 7 - ASSESSMENT, RECOMMENDATIONS
AND REMEDIAL MEASURES
7.1 Dam Assessment
(a) Condition
The Bog Brook Dam is in GOOD condition at thepresent time.
(b) Adequacy of Information
The lack of in-depth engineering data does notpermit a definitive review. Therefore. the adequacy ofthe dam cannot be assessed from the standpoint of review-ing design and construction data. This assessment isthus based primarily on the visual inspection, pastperformance and sound engineering judgement.
(c) Urgency
The remedial measures recommended below shouldbe accomplished within two years of receipt of thePhase I Inspection Report by the owner.
(d) Need for Additional Investigation
No additional investigations are indicated atthis time.
7.2 Recommendations
Since the discharge capacity of the dam is insufficientto pass the selected Test Flood, it is therefore recommendedthat further hydrologic studies of the spillway adequacy bemade.
7.3 Remedial Measures
The Bog Brook Dam requires the following operating andmaintenance improvements:
(1) Monitor the wet area at the downstream toe ofthe left embankment to determine the source ofthe water. If the water is seepage through theembankment, institute appropriate measures toprotect the toe of the fill from erosion.
7-1
(2) Fill all rodent holes in the embankment.
(3) Conduct a more vigorous program of brush clearingon the embankments, as the vegetation appears togrow rapidly.
(4) Rake out eroded construction joints and packthe joints with high strength mortar.
(5) Remove all debris and sediment from behind thedam.
(6) Clear all vegetation and debris from the down-stream channel and trim or remove all treesoverhanging the chant~el.
(7) Install a gage at the dam and institute a programof regularly recorded readings to provide somehistorical performance data for the dam.
(8) Provide a method of securing stoplogs in placeto preclude unauthorized removal.
(9) Perform a technical inspection of the dam everytwo years.
7.4 Alternatives
There are no viable alternatives to the accomplish-
ment of the following operations and maintenance tasks.
7-2
APPENDIX A
VISUAL INSPECTION CHECKLIST
A-i
I
INSPECTION TEAM ORGANIZATION
Date: September 20, 1978
NH 00189BOG BROOK DAMSpringfield, New HampshireBog BrookNHWRB 220.12
Weather: Sunny and warm
INSPECTION TEAM
Robert Minutoli Goldberg, Zoino, Dunnicliff &
Associates, Inc. (GZD) Team Captain
William S. Zoino GZD Soils
Nicholas Campagna GZD Soils
Andrew Christo Andrew Christo Engineers(ACE) Structural
Paul Razgha ACE Structural
Richard Laramie Resource Analysis, Inc. Hydrology
A-2
Bog Brc ,K Dam September 20, 1978Springfield, New Hampshire NH 00189
CHECK LISTS FOR VISUAL INSPECTION
AREA EVALUATED BY CONDITION & REMARKS
EMBANKIIENT
Vertical alignment and "'. No deficiencies notedmovement
Horizontal alignment and No deficiencies noted; topmovement width variable
Condition at abutments No deficiencies noted
Trespassing on slopes No evidence
Sloughing or erosion ofslopes or abutments None noted: thick, recently
trimmed growth over entireembankment; some small rodentholes
Rock slope protection None
Unusual movement orcracking at or near toe None noted
Unusual downstreamseepage I Wet area 10' x 20' in plan
95 feet along crest from leftspillway endwall and 40 feetdownstream of centerline:water is 3-6 inches deep,appears stagnant and shows noevidence of turbidity; noflow noted: based on localtopography, could be ponding.area for storm runoff; noother significant observations
Piping or boils None noted
Foundation drainage fea-tures Unknown, but none shown on
drawings and unlikely
A-3I
"" "f" €
Bog Brook Dam September 20, 1978Springfield, New Hampshire NH 00189
CHECK LISTS FOR VISUAL INSPECTION
AREA EVALUATED BY CONDITION & REMARKS
OUTLET WORKS
a. Approach Channel
Slope conditions Broad approach from pond withvery low banks
Bottom conditions Some siltation behind dam
Rock slides or falls No rock in vicinity
Log boom None
Control of debris Small amount of debris sub-merged behind dam
Trees overhangingchannel None
b. Spillway
Condition of concrete
General condition Good
Erosion or cavitation None noted
SpalIing None noted
Cracking None noted
Condition of joints No deficiencies noted
Rusting or staining None noted
Visible reinforcing None noted
Sec age or efflour-escence None noted
A-4
Bog Brook Dam Sep ..iter 20, 1978Springfield. New Hampshire NH k.)189
CHECK LISTS FOR VISUAL INSPECTION
AREA EVALUATED BY CONDITION & REMARKS
Foundation conditions A- Spillway founded on bedrockwhich appears to be hard,generally competent schist;near vertical jointing atright angles to centerline ofdam
c. S luiceways
C ndition of c.n krete
General condition Good
Erosion or cavitation Some erosion of constructionjoints between sidewalls andbuttress supports on thespillway sides of the sluice-ways; minor erosion on con-crete sill in sluiceway adja-cent to right abutment
Spal Ii n None noted
Cracking Fine random cracking alongthe construction jointsmentioned above on the insideface of both sluiceways
Condition of joints Good except as mentionedabove
Rusting or staining None noted
Visible reinforcing None noted
Seepage or efflour-escence Some efflourescence along
construction joints mentionedabove
Condition of stoplogs - Good
IA-5
I
-*9. *3* __ ___ ___ ____ ___ ____ ___ ___ ____ ___ ___
B(. Brook Dam September 20, 1978Springfield. New Hampshire NH On189
I CHECK LISTS FOR VISUAL INSPECTION
AREA EVALUATED BY CONDITION & REMARKS
Adequately secured ,)(tamperproof) Stoplogs not locked in place
d. SpillNway Endwalils
Condition of concrete
General condition Good
ELrfsion or cavitation None noted
Spal I ing None noted
Cracking None noted
Condition of joints No deficiencies noted
Rusting or staining None noted
Visible reinforcing None noted
Seepage or efflour-escence None noted
d. Outlet Channel (immedi-ate area)
Slope conditions Downstream area generallygently sloping bedrock: lowbanks with heavy overgrowth
Rockslides or falls None noted
Control of debris Small amount of debris inchannel
Trees overhangingchannel Heavy overgrowth on both
sides which does extend overchannel: some small treesgrowing in channel
A-6
Bog Brook Darn September 20. 1978Springfield. New Hampshire NH 00189
CHECK LISTS FOR VISUAL INSPECTION
AREA EVALUATED BY CONDITION & REMARKS
Other obstructions Large corrugated metal, mul-tiplate arch under road 100feet downstream of dam
c. Existence of gages None at dam
RESERVOIR
a. Shoreline
Evidence of slides None noted
Potential for slides Shoreline stable
b. Sedimentation Some noted immediately behindd am
c. Upstream hazard areas inIthe event of backflood-1ng None
d. Changes in nature ofwatershed (agriculture.logging, construction, N
etc.) None noted
DOWNSTREAM CHANNEL
Restraints on dam oper-ation 4 None given dam's limited
operational capacit:.
Potential flooded area No development within 3 milesof dam
A-7
Bog Brook Dam September 20, 1978Springfield. New Hampshire NH 00189
CHECK LISTS FOR VISUAL INSPECTION
AREA EVALUATED BY CONDITION & REMARKS
OPERATION AND MAINTENANCEFEATURES
a. Reservoir regulationplan
Normal procedure Maintain water level forwildlife management: little
or no manipulation of stop-logs required
Emergency procedures No emergency situation everencountered since construc-tion: local conservationofficer could pull logs ifnecessary
Compliance with
designated plan Satisfactory
b. Maintenance
Quality No 0 & "I type deficienciesnoted
Adequacy Dam inspected semi-annuallyby engineers: no problemswith maintenance evident
A-8
!
APPENDIX B
Page
FIGURE 1 Site Plan B-2
Plan, elevation and sections of
dam B-3
Topographic map of dam site B-4
List of pertinent records not
included and their location B-5
B-i
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2 TCHIA COSLAT CO P FENIE R
N4EWTON UPPER FALLS. MASS.
NATIONAL PROGRAM OF INSPECTION OF NON-FED. DAMSFIGURE I
SITE PLAN0
LBOG BROOK DAM NEW HAMPSHIREVCALE NO SCALE
LLDATE NOV 1970
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The New Hampshire Water Resources Board, 37 Pleasant Street,Concord, New Hampshire has in its files two pages of hydrau-lic calculations dated September 3, 1957. The Board may bereached at phone number (603) 271-3406.
The New Hampshire Fish and Game Department maintains recordsconcerning the construction of the dam, including the changeorder directing the angling of the spillway and the additionalsluiceway. The Department's address and phone number arepresented in subparagraph 1.2(e).
B-5
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II
APPENDIX C
SELECTED PHOTOGRAPHS
C-1
- ,DIRT ACCESS
LAN
OVERVIEW PHOTOSGOLDBERG, 70141, OUNNICLli-fV ASSOC , U.SARMY ENGINEER DIV N~EW ENGLANdGEOTEC4NICAL CONSULTANTS CORPS Of EV4BiNEERS-4> APENDX C POTOSNEWTON UPPER FALLS, MASS.
NATIONAL PROGRAM OF INSPECTION OF NON-FED) DAMS
LOCATION AND ORIENTATIONc~j OF PHOTOS
zLu BGBOKAM NEW HAMPSHIELA. SC ALE NO SCALE'I ___ ___ ___ ___ ___ __I DATE NOV 1978
C-2
IY
I 1. View of right sluiceway showing bedrock foundationunder concrete portions of dam
.
2. Detail of Photo 1 showing erosion of constructionjoint between sluiceway sidewall and spillwaybuttress support
C- 3
I
I
3. View of center sluiceway showing erosionbetween sluiceway sidewalls and spillwaybuttress supports
II
I
III ,I /
4. View from channel between dam and roadI showing bridge culvert
C-4
._,
| I
I
APPENDIX D
HYDROLOGIC/HYDRAULIC COMPUTATIONS
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DEPTH ELEU AREA WPER HYD-R AR2/3 00.0 1890.0 0.0 0.0 0.0 0.0 8.00.5 1090.5 7.8 19.1 8.4 4.2 27.41.0 1891.8 19.0 26.2 0.7 15.3 99.81.5 1091.5 33.8 33.3 1.0 34.1 219.92.0 1092.0 52.0 40.3 1.3 61.6 397.42.5 1092.5 73.8 47.4 1.6 99.0 638.73.0 1093.0 99.0 54.5 1.8 147.4 958.93.5 1893.5 127.8 61.6 2.1 207.8 1340.64.0 1094.0 168.0 68.7 2.3 281.2 1814.44.5 1894.5 195.8 75.8 2.6 368.6 2378.55.0 1895.0 235.0 82.9 2.8 471.0 3038.85.5 1095.5 277.8 90.0 3.1 589.? 3801.36.0 1096.0 324.0 97.0 3.3 724.1 4671.76.5 1096.5 373.8 104.1 3.6 876.6 5655.57.0 1097.0 427.0 111.2 3.8 1047.5 6758.27.5 1097.5 483.8 118.3 4.1 1237.6 7965.08.8 1898.0 544.8 125.4 4.3 1447.8 9341.28.5 1098.5 607.8 132.5 4.6 1678.9 10&31.99.0 1099.0 675.8 139.6 4.8 191.5 12462.09.5 1899.5 745.8 146.6 5.1 2286.6 14236.518.8 1100.8 820.0 153.7 5.3 2504.7 16160.210.5 110.5 897.8 160.8 5.6 2826.8 18237.9I1.0 1101.0 979.0 167.9 5.8 3173.4 20474.311.5 1101.5 1063.8 175.0 6.1 3545.3 22873.912.8 1102.8 1152.0 182.1 6.3 3943.2 25441.312.5 1102.5 1243.8 189.? 6.6 4367.9 28161.113.0 1103.0 1339.0 196.2 6.8 4819.9 3109?.?13.5 1103.5 1437.8 203.3 7.1 5300.1 34195.414.0 1104.0 1540.0 210.4 7.3 5808.9 37478.514.5 1104.5 1645.8 217.5 7.6 6347.2 40951.4
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D-21
APPENDIX E
INFORMATION AS CONTAINED IN
THE NATIONAL INVENTORY OF DAMS
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