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AD-AOG8 799 cORPS OF ENGINEERS BALTIMORE MD BALTIMORE DISTRICT F/6 13/13NATIONAL DAM INSPECTION PROGRAM? WYE MILLS DAM, (NOI-NJMBFR-MD---ETC(U)
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PKASEf I INSPECTION REPORT.
NATioNAL DAM iNspECTiON PROGRAM
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*UPPER CHESAPEAKE BAY BASIN
,WYE MILLS DAM.QUEEN ANNES COUNTY, MARYLAND
(N-,=--D --6O0029) .A ~r f -~
)HASE I .NSPECTIONAEPORT, /A*OAL DAM -S*FEW~- PR60@AM (
Prepared for: DEPARTMENT OF THE ARMYBaltimore District, Corps of EngineersBaltimore, Maryland 21203
Prepared by: WATER RESOURCES ADMINISTRATIONDepartment of Natural Resources
Tawes BuildingAnnapolis, Maryland 21401
Date: / .ay _ 7_ ,
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PREFACE
This report is prepared under guidance contained in the "RecommendedGuidelines for Safety Inspection of Dams," for Phase I Investigations.Copies of these guidelines may be obtained from the Office of Chief ofEngineers, Washington, D.C. 20314. The purpose of a Phase I Investigationis to identify expeditiously those dams which may pose hazards tohuman life or property. The assessment of the general condition of thedam is based upon available data and visual inspections. Detailed investigation,and analyses involving topographic mapping, subsurface investigations, testing,and detailed computational evaluations are beyond the scope of a Phase IInvestigation; however, the investigation is intended to identify any needfor such studies.
In reviewing this report, it should be realized that the reported conditionof the dam is based on observations of field conditions at the time ofinspection along with data available to the inspection team. In cases wherethe reservoir was lowered or drained prior to inspection, such action, whileimproving the stability and safety of the dam, removes the normal load onthe structure and may obscure certain conditions which might otherwise bedetectable if inspected under the normal operating environment of thestructure.
It is important to note that the condition of a dam depends on numerousand constantly changing internal and external conditions, and isevolutionary in nature. It would be incorrect to assume that the presentcondition of the dam will continue to represent the condition of the damat some point in the future. Only through frequent inspections canunsafe conditions be detected and only through continued care and maintenancecan these conditions be prevented or corrected.
Phase I Inspections are not intended to provide detailed hydrologic andhydraulic analyses. In accordance with the established guidelines, thespillway design flood is based on the estimated "Probable Maximum Flood"for the region (greatest reasonably possible storm runoff), or fractionsthereof. The spitlway design flood provides a measure of relative spillwaycapacity and serves as an aid in determining the need for more detailedhydrologic and hydraulic studies, considering the size of the dam, its generalcondition and the downstream damage potential.
Accession For
NTISDDC TABUn mounced
iut fiVt i
Di _ _ al
PHASE T TNSPECTION REPORT
NATIONAL DAM INSPECTION PROGRAM
NAME OF DAM: Wve Mills DamSTATE: Maryland
COUNTY: Oueen Annes
STREAM: Wye East RiverDATE OF INSPECTION: March 26, 1979
ASSESSMENT: Based on the evaluation of the conditions as they existedon the date of the inspection and as revealed by visual observajio.:s,the conditiLcn of Wye Mills Dam is assessed to be good.
Cht, spiilwav capacity (95 per cent PMF) is classified as inadequate b,-
cause it -.,It not pass the recommended spillway design flood of fullProbabl. Maximum Flood (PMP) according to the recommended critoria.
However, It Is believed that the dam will safely pass PMF without , -dangering life and property and, therefore, additional detailed hvIro-
logic qtudles are nnt warranted.
Operatlion and m.anten, ce procedures are unwritten and should be dWe':n'enA forri1l warntg 'vstem should be Implemented to alert dowiistreal 'Iroaq
the ewon' of emcrgencies.
SUBMITTED BY: WATER RESOURCES ADMINISTRATIONDAM SAFETY DIVISION
Date
APPROVED BY:'..q ,",e I~7 7__________
Date ( KWITRbe Colonel, Corps of EngineersDistrIct Engineer
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TABLE OF CONTENTS
PAGE
SECTION I - PROJECT INFORMATION 1
1.1 General 11.2 Description of Project 11.3 Pertinent Data 2
SECTION 2 - ENGINEERING DATA 4
2.1 Design 42.2 Construction 72.3 Operation 72.4 Evaluation 7
SECTION 3 - VISUAL INSPECTION 9
3.1 Findings 93.2 Evaluation 10
SECTION 4 - OPERATIONAL PROCEDURES 11
4.1 Procedures 114.2 Maintenance of Dam 114.3 Maintenance of Operating Facilities 114.4 Warning System 114.5 Evaluation 11
SECTION 5 - HYDRAULICS AND HYDROLOGY 12
5.1 Evaluation of Features 12
SECTION 6 - STRUCTURAL STABILITY 13
6.1 Evaluation of Structural Stability 13
SECTION 7 - ASSESSMENT AND RECOiMENDATIONS/REMEDIAL 15MEASURES
7.1 Dam Assessment 157.2 Remedial Measures and Recommendations 15
iv
I
APPENDICES
Appendix A - Check List - Visual Inspection, site sketch Phase IAppendix B - Check List, Engineering Data, Design, Construction,
Operation, Phase IAppendix C - Location Map and PlansAppendix D - AnalysesAppendix E - PhotographsAppendix F - Geology Report
9v--
PI!ASE ' INSPECTION REPOPTNATTONAL DkM INSPECTION PROGRAM
WYE MILLS DAM
NDT NO. WiD 00029
SECTION iPROJECT INFORMATION
1.1 General
a. Authority. The inspection was performed pursuant to theauthority granted by the National Dam Inspection Act, Public Law 92-367,to the Secretary of the Army, through the Corps of Engineers, to condu
inspections of dams throughout the United States.
b. Pur.ose. The purpose of this inspection is to detervine i ti,
dam constitutes a hazard to human life or property.
1.2 Description of Project
a. Dam and Appurtenances. The Wye Mills Dam consists of io ear':fill embankment with a timber sheet core appro.:imately 26 feet hih and
832 feet iong. Twin concrete box culverts 12 feet by 13 feet connect toa "U-shaped" concrete ogee spillway 107 feet long near the right -4but-mront of the dam. Downstream the twin box culverLs discharge to a 19'7Foot long channel 14 feet wide which carries flow under M) Route 4"I.The upstrean and downstream dam embankment slopes rise at a rate c'3H:IV with a top width, of 10 feet. The u1 ,str/nm face of the eriblk-Ment (_onsists of concrete slab protection from 10.87 feet above MTL tou2C.5 feet above MSL. 1.5 Feet below the top cf the daw. The ogeetype spillway has a crest elevatlo,, of 14.29 .eet or 7.71 feet below th,t,, -f the dam, which is at elevation 22.00. The foundation base ex-
-eads ai~prox1ratelv 4 feet below MSL.
h. Lcatlon. The Wye Mills Dim Is located on the Wye East Riverdividing Talbt and Oucen Annes Counties In the toen of Wye Mills, Maryl.o)The structure is less than .25 miles from tidal influences of t!- WveT':a st River.
C. Size Classification. The maximum height of the dam is 24 -,:
The reservoir volume to the top of the dam at elevation 22.00 is 1224 u r,
feet. Therefore, the dam is in the "intermediate" size category.
d. Hazard Classification. Loss of life and property would lkk1,.
result from a failure of the dam. Also loss of State Road #404 wouldlikely result. Based on the above, the dam is classified in the highhazard category.
1 4
e. Ownership. The Wye Mills Dam is owned by the State of Maryland,Department of Natural Resources, Annapolis, Maryland 21401.
f. Purpose of Dam. The primary purpose of the dam is to provide areservoir for recreation. The Old Wye Mill is put into operation annuallyduring the summer months.
g. Design and Construction History. The present structure is locatedat the site of old mill dams dating back to the late 1600's. In 1953, theState of Maryland acquired the dam and lake. A breaching occurred, probablyas a result of Hurricane Connie in 1955. As a result, the Maryland Cameand Inland Fish Commission and their consultant, Mr. Thomas F. Comber,designed a new dam at the same location with construction beginning onOctober 21, 1957. Construction was completed by the William Dunn Constru-tion Company on May 16, 1958.
h. Normal Operating Procedures. No formal operating procedures exist
1.3 Pertinent Data
a. Drainage Area The Wye Mills Reservoir has a drainage area of10.21 square miles.
b. Discharge at Dam Site The maximum discharge at the dam sitethrough the ungated spillway at elevation 14.29 is 4930 cubic feet/sec.The maximum flood at the dam site is unknown.
c. Elevation (feet above mean sea level)
Top of dam - 22.00Spillway Crest - 14.29Normal Tailwater - 4.0Streambed at centerline of dam - 2.0
d. Reservoir
Length of maximum pool - 1.5 milesLength of recreation pool - 0.95 miles
e. Storage (acre-feet)
Normal pool - 302 acre ft. at elevation 14.;Top of dam - 1224 acre ft. at 22.00
2
f. Reservoir Surface (acres)
Top of dam - 168.8 acresNormal pool - 61.5 acres
g. Dam
Type - EarthfillLength (feet) - 832Height (feet) - 24Top width (feet) - 10
Side Slopes -
Upstream and Downstream: 3H:IV
Impervious core - Wakefield
sheeting top elevation - 17.0Cutoff - Sheeting extends to
elevation - 7.5
h. Diversion and Regulating Tunnel - None
i. Spillway
Type - Concrete ogee, U-ShapedLength of weir (feet) - 107Crest elevation (feet M.S.L.) - 14.29Gates - NoneDownstream channel - Ogee connected to a twin 13 x 12 foot high
90 foot long reinforced concrete box culvert which discharges to anexcavated channel, 197 feet long.
J. Regulating Outlets - Two 24" Armco Slide Gates, Model 20-10CStyle B stems; one located in ogee (drain), invert elevation 2.0; onelocated near the left side of the dam, upstream face (mill headrace), invertelevation 11.5.
3
SECTION 2ENGINEERING DATA
2.1 Design:
a. Data Available. The present Wye Mills Dam was designedduring 1956 and constructed in 1957. This structure encompassed anearlier earthen embankment and impoundment which supplied a mill racefor the historic Wye Mill dating to the middle 17th century. In allprobability, engineering data was never generated for the earlier damand-none was found during the data review for this report.
Design plans including limited subsurface data, structuralcomputations, specifications, special provisions, and a final reportwere prepared for the present dam configuration. The plans are presentedin Appendix "C", and the remaining data is available in the files of theMaryland Department of Natural Resources, Water Resources Administration.The only hydrologic and hydraulic information consists of the designhigh water of 2.8 feet above spillway crest used in the structuralcalculations.
b. Design Features.
1. Embankment - The construction drawings indicate the embank-ment to consist of rolled earth fill with 3H:IV upstream and downstreamslope configurations. The project specifications require the fill materialto be A-l, (clean sand), A-2 (sand and fines), and/or A-3 (sand) classifiedin accordance with Maryland State Roads Commission Specifications. Theembankment was to be placed in lifts not exceeding 6 inches in compactedthickness, rolled with a 1000 pound minimum sheeps foot roller for atleast 6 passes, and compacted to a dry density not less than 105 poundsper cubic foot as determined by A.A.S.H.O. Method of Test T-99.
A treated timber sheetpile cutoff wall, designated as WakefieldSheeting, was to be provided along the centerline of the dam from the leftto right abutments. According to the subsurface explorations and the designdrawings, the core wall was to extend from design high water at el. 17 tolevels corresponding to a clay layer between el. +2.5 and el. -7.5. The damembankment was to be constructed to el. 17 before the sheet piles weredriven. The final tip elevations were to be determined in the field duringconstruction by the Engineer.
Slope protection consisting of concrete panels, six inches illthickness, was to be placed on the upstream face of the embankment. Theprotection was shown to extend from el. 20.5 to approximately el. 11. Thecontractor was given the option of installing either 30-inch square precastblocks or 36-inch square cast-in-place blocks. The bases of the concreteblocks at el. 11 bear against tongue and groove sheetpiling, 8 feet inlength, driven along a narrow bench on the upstream embankment.
4
2. Appurtenant Structures - The overflow spillway consists of a"U" shaped reinforced concrete ogee weir located at the right side of thedam with the crest level designed to be at el. 14.29. The bottom of thebase slab was not specified on the drawings, but the designers intention wasto support the structure on stiff clay. The final foundation level was tobe determined during construction by the engineer.
A drain opening, 24 inches in diameter and fitted with an Armcoslide gate on the upstream side, was to be provided through the right sideof the spillway with invert at el. +2.0.
Flow over the spillway is carried through the embankment by areinforced concrete twin cell box culvert, each cell measuring 12 feethigh by 13 feet wide with wall thicknesses of 1.2 feet. The embankment atthe. outfall of the box culvert is retained by reinforced concrete walls, 14feet in maximum height, with a wall thickness of 1.2 feet. Foundationlevels for the box culvert and retaining walls were to be determined bythe Engineer during construction. All masonry joints were designed tobe waterproofed with copper flashing and/or membrane waterproofing onthe inundated/backfill side and all construction joints are shown on thedrawings to be keyed within the spillway, box culvert, and retaining wall'structures.
An inlet structure was provided on the left side of the embankmen 4
to supply an existing concrete raceway for the Wye Mill. This structureconsists of a 24 inch extra strength reinforced concrete pipe which ispositioned on the upstream embankment slope with an inlet invert at +11.5,extends through the embankment at a 1.75% grade, and outfalls at a concrete
headwall at the raceway. The inlet is encased in a concrete headwall andis provided with an Arrnco slide gate to regulate flow to the mill. Openingsin the Wakefield sheeting cut-off wall for the 24-inch pipe and aroundthe perimeter of the box culvert are provided with copper water stops andbituminous waterproofing.
c. Design Data
1. Hydrology and Hydraulics - The only data available consistsof the design high water level of 2.8 feet above spillway crest found inthe structural computations.
2. Embankment - Data for embankment design is limited to thatwhich appears on the construction drawings and contract documents. Sub-surface data consisting of seventeen auger probes and three drive testswere obtained for the project, but no geotechnical interpretation of thedata relative to foundations, seepage potential, slope stability, oravailability of suitable embankment materials was found durng the datta
review. The drive tests were performed by driving a three-quarter inchpipe, 20 feet in length with a 12 pound maul through the enmbankment whenthe fill had reached el. 17. The numbers of blows per foot were recordedand were apparently used as an indication of the penetration resistancefor the Wakefield sheeting core wall.
Si
3. Appui tenant Structures - Structural analyses for the over-flow spillway, the box culvert, and the retaining wall were available inthe DNR files. The anaylsis of the spillway was concerned primarily withresistance to uplift and computation of internal stresses through varioussections of the base slab for reinforcing steel proportioning. A summaryof the results of these computations appears on SHEET 4 of the contractdrawings and were derived with the following assumptions:
1. The weir and slab structure was analyzed as a unitfor resistance to uplift.
2. Structural dead loads were computed for concrete witha density of 150 pounds per cubic foot.
3. Full uplift of 955 pounds per square foot actedupon the base.
4. Case I considers a total horizontal water (design highwater) and silt load of 383 kips and a vertical dead,water and silt load of 2,085 kips.
5. Case II considers a total horizontal water (normal pool),silt and ice load of 579 kips and the same vertical loadas Case I.
Case II was considered by the designer to be the critical loadingcondition and reinforcing steel design was based upon this assumption.Moments for reinforcing steel content in the base slab, as contained inthe design computations, were apparently computed utilizing an upliftpressure distribution of 100 per cent hydrostatic pressure (normal pool)at the heel and zero at the toe. The sections through the base which wereanalyzed were located at the toe of the ogee weir and at the centerlineof the weir-slab structure.
The box culvert was designed for the dead load of structure based upona concrete unit weight of 150 pounds per cubic foot, earth pressure computedfrom an equivalent fluid load of 35 pounds per cubic foot, and live loadfrom an H-20-44 truck. Hydrostatic pressure was not considered in the designThe retaining walls on either side of the box culvert outfall were designedfor an earth pressure derived from an equivalent fluid loading of 35 poundsper cubic foot and hydrostatic pressure for seven feet of groundwate. behindthe wall. All reinforced concrete design for the spillway, box culvert andretaining walls was based upon the working stress method with steel strengthequal to 18 ksi and concrete strength of 3000 psi (Class A concrete). Allmaterials were assumed to conform to Maryland State Roads Specifications.
6
2.2 Construction. The construction data available consist of the contract
drawings and specifications, special provisions and final report. The finalreport is very general in nature and addresses primarily the final financialstatus of the project. Brief references infer that the contractor wasWilliam Dunn of Denton, Maryland, the project was completed on May 16, 1958,the consulting engineer was Thomas F. Comber, and the inspection serviceswere provided by the Maryland Game and Inland Fish Commission and theEngineering Branch of the Federal Aid Division of the U.S. Fish and WildlifeService. Periodic construction reports, material quality control tests,and other information which may have been pertinent to construction were notfound. With the exception of foundation levels for the appurtenantstructures and cut. off wall which were to be determined in the field,the contract drawings appear to accurately depict the completed project.
2.3 Operation. Formal operating records have not been maintained. Theonly known operational procedures at the dam are seasonal use of the inletvalve for the mill raceway.
2.4 Evaluation:
a. Availability. Construction drawings, contract specifications andspecial provisions, structural computations for appurtenant structures, anda final report constitute the design information. This information is avail-
able in the files of the State of Maryland Department of Natural Resources.
b. Adequacy.
1. Hydrology and Hydraulics - The only reference to
hydrologic and hydraulic design data is the design highwater of 2.8 feet
above the spillway crest which by itself is not considered adequate to
access spillway adequacy. Refer to Section 5, Hydrology and Hydraulicsand Appendix D for complete discussion.
2. Embankment - The construction documents and design data
address the embankment configuration only. Although subsurface data wasobtained, no interpretation of the data relative to soil strengths,
foundation capacities, slope stability or seepage potential was performed.
The provision for a treated timber core wall extending to impervious claymight ordinarily lessen the need for a detailed seepage analysis, butthe as-built tip elevations of the timber sheet piles are not available.The only references to the density of the completed embankment are the resultsof the "drive test" which are highly variable and non-standard methods oftest.
3. Appurtenant Structures - The construction drawings and
specifications appear to adequately address the structural detailing for
the reinforced concrete spillway, box culvert, and retaining walls. Someelements of the design procedure considered standard for dam analysis are
not present in the design computations for this project. Sliding along thefoundation and overturning of the ogee spillway are not directly addressed.
7
The resultant of forces for the weir-slab unit is shown on the plans to fallwithin the middle third of the slab area precluding overturning of thespillway as a unit. However, the resultant falls outside the limits of theogee section and tension appears to 'xist at the heel of weir at the jointwith the slab. Although apparent vertical tension reinforcing steel hasbeen provided between the slab and weir at the heel, no stress analysis orsteel content design was available for review. The ogee section was notanalysed for uplift and sliding along this joint nor along a joint 6.7feet above the top of slab. The structure was also not evaluated for anempty condition.
With the exception that hydrostatic loading was not included in thebox culvert design, the structural computations for the culvert and retainingwalls appear complete and in accordance with accepted engineering practice.The earth loading for these structures apparently utilized active pressuretheory with a soil unit weight of 120 pounds per cubic foot and 4 equal to33 degrees, values well suited to the compacted sand backfill specifiedin the contract documents.
c. Operating Records. There are no formal operating records forreview.
d. Post Construction Changes. The downstream channel, subsequentto completion of the dam in 1958, was lined along the banks with treatedtimber sheetpiling from the end of the retaining walls at the culvertoutlet of the dam to the culvert for Maryland Route 404, approximately180 feet downstream. No drawings, specifications or design analyses wereavailable for this feature.
e. Seismic Stability. The dam is located within Seismic Zone 1and static stability with normal safety factors should be sufficient towithstand minor earthquake induced dynamic forces. No calculations orstudies have been made to confirm this opinion.
8A
SECTION 3VISUAL INSPECTION
3.1 Findings
a. General. The dam and its appurtenant structures were foundto be in good overall condition at the time of the inspection, March 26,1979. The complete visual inspection check list is presented in AppendixA.
b. Dam.
1. There is no cracking, sloughing or other appreciablemovement in the embankment.
2. The vertical alignment is good with no evidence of settle-ment.
3. Erosion exists on the downstream face, right of the over-flow spillway, and has been aggravated by foot traffic.Sparse vegetation exists on the embankment crest in thevicinity of the spillway.
4. The concrete overflow spillway and twin concrete boxculvert are in excellent condition with no cracks,spall{ne or movement noted. Expansion joint materialat the top of both downstream wingwalls of the boxis missing.
5. Upstream concrete slope protection is in excellentcondition.
6. A wet area exists downstream of the toe, left of thedischarge area.
c. Appurtenant Structure.
1. The staff gauge on the left side of the spillway backwallis dislodged.
2. Concrete slope protection panels behind the timber sheetpiling on the right side of the discharge channel have beenundermined and have collapsed.
3. The 24" drain gate in the overflow spillway was inaccess-ible, no steam could be located, and uperating personnelstated that divers were last used in 1966 to lower the pool.
4. The 24" gate which operates the mill race appears to bewell maintained and is operated regularly.
9__
d. Reservoir Area. The reservoir slopes are steep to moderatesloping and are well vegetated and wooded. Sedimentation was evidentat the upper end of the pool as viewed from U.S. Route 50.
e. Downstream Channel. The outlet channel and stream channel isfree of debris to the tidal influence. The overbank areas showed heavydeposits of sand and woody debris from recent flooding. In the event of a
dam failure, a few homes, offices of the owner and a general store/postoffice may be inundated. The Maryland Route 404 bridge would also beinundated. The potential for loss of more than a few lives exists. There-fore, a hazard category of "high" appears appropriate for this dam.
3.2 Evaluation.
a. Dam.
1. With the exception of the inoperable drain gate, the dam
and spillway appear in excellent condition.
2. While a wet area exists downstream of the toe, left of thedischarge channel, it is believed to be as a result ofpoor surface drainage.
3. Collapse of the concrete panels adjacent to the timbersheet piling on the right side of the discharge channelappears to have resulted from flood flows returning tothe channel from the overbank area. No adverse effecton the dam is envisioned due to a distance from the toe
to the damaged area of approximately 180 feet.
10_ _ _
.......
SECTION 4OPERATIONAL PROCEDURES
4.1 Procedure. The purpose of this State owned dam is to provide forrecreational fishing. The normal pool is at elevation 14.3 and is controlledby the overflow spillway crest. The Inland Fisheries Division of theMaryland Wildlife Administration (Department of Natural Resources) hasthe responsibility for operation and maintenance of the structure.Students of the Chesapeake College operate the mill on behalf of theSociety for the Preservation of Maryland Antiquities. Controlled dischargesmay be made by operation of the headrace gate (elevation 11.5). Thedrain gate (elevation 2.0) is presently thought to be inoperable.
4.2 Maintenance of the Dam. No specific maintenance program has beenestablished. Present level of general maintenance appears adequate,with the exception of the inoperable drain valve.
4.3 Maintenance of Operating Facilities. The slide gate for the millheadrace is operated regularly during the summer months and periodically
the remainder of the year. The drain gate is the only other operatingfeature of the dam and has not been exercised since 1966. The ownerclaims that operation of 'his gate would be desirable for winter pooldrawdown for fishery conservation. Drain gate operation is alsodesirable for inspection and repair of the overflow spillway, concretebox culvert and discharge channel.
4.4 Warning System. There is no formal warning system in effect althoughfield offices for the owner are at the dam. Additionally, during periods ofheavy rainfall, the Maryland State Highway Administration assigns anobserver to check and close, if necessary, the Route 404 bridge downstream.
4.5 Evaluation. The general operational procedures are satisfactoryexcept that no formal warning system is in effect and maintenance proceduresare unwritten.
11
SECTION 5HYDRAULICS AND HYDROLOGY
5.1 Evaluation of Features
a. Design Data. The Wye Mills Dam has a watershed area of10.21 square miles and impounds a reservoir with a surface area ofapproximately 60 acres. The overflow spillway is located near theright abutment and can safely discharge 4930 cfs. No hydrologic orhydraulic design data were available for the preparation of this report.
b. Experience Data. As previously stated, the Wye Mills Damis classified as an intermediate size dam in the high hazard category.Under the recommended criteria for evaluating emergency spillway dischargecapacity, such structures are required to pass the Probable Maximum Flood(PMF). The maximum flood at the dam site is unknown.
The PMF inflow hydrograph for the reservoir was determined utilizingthe Dam Safey Version of the HEC-I computer program developed by theHydrologic Engineering Center of the Corps of Engineers. The peak ofthe PMF inflow hydrograph is 6139 cfs. The input data and results ofthe program are presented in Appendix D.
c. Visual Observations. On the date of the inspection, noconditions were observed that would indicate that the spillway of thedam could not operate satisfactorily in the event of a flood.
d. Overtopping Potential. Various percentages of the PMF inflowhydrograph were routed through the reservoir to determine the percentageof PMF inflow that the dam can pass without significantly overtoppingthe embankment and causing breaching of the dam. The analyses indicatethat the spillway can pass 95 percent of the PMF without overtopping.Full PMF would overtop the embankment by a maximum of 0.30 foot for atotal duration of overtopping of 4.50 hours. It is believed that thisovertopping would cause some erosion on the embankment; however, totalfailure is considered unlikely.
e. Spillway Adequacy. Since the spillway cannot pass PMF withoutovertopping, the spillway is judged to be inadequate.
12
SECTION 6STRUCTURAL STABILITY
6.1 Evaluation of Structural Stability:
a. Visual Observations. No visible signs of appreciable movements,distress, or deterioration were detected in the earthen embankment orappurtenant structures. Minor ponded water was noted at the toe of theslope near the center of the dam, but this condition is judged to be theresult of poor surface drainage. No indications of active seepage throughthe embankment were found. A portion of the treated timber sheeting whichlines the banks of the downstream channel had been undermined and waspartially collapsed. This condition however, does not affect the stabilityof the dam.
b. Design and Construction Data:
1. Embankment - Stability problems within the earthenembankment of Wye Mills Dam are considered unlikely due to the specificationfor compacted granular fill material placed at a 3 horizontal to 1 verticalslope configuration. The timber sheeting core wall, as designed, shouldadequately control seepage. Although documented foundation treatmentand levels were not available for review, the good visual alignment ofthe crest and slopes suggests that competent foundation levels wereattained. The geology report presented in Appendix F, indicates thatcompetent materials for foundations and termination of sheet pile cutoff walls were available within the anticipated construction levels ofthe project. Although accurate assessment of embankment performance isnot possible for the slight overtopping condition during PMF, total failureis considered unlikely due to the presence of the embedded sheet pilecut off wall and an extremely high tailwater condition.
2. Appurtenant Structures - Although some deficiencies werenoted in the design computations, the good detailing on the plans andthe excellent performance of the reinforced concrete elements suggest thatstructures competent to withstand normal operating loads were achieved.Although final foundation levels are unknown, the lack of any visibledifferential movement and cracking indicates that competent bearingmaterial was reached during construction. The stability of the spillwayduring PMF loading is considered adequate due to a severe tailwater conditionby which the weir will be completely submerged with equal water pressureon both upstream and downstream sides.
c. Operating Procedures. Detailed operating procedures wereunavailable for review and factors which might affect stability couldtherefore not be assessed.
13
d. Post Construction Changes. There exists no known changes oralterations to the facility which might adversely affect the stabilityof the dam (Ref. Section 2.4.d.).
e. Seismic Stability. Wye Mills Dam is located within seismiczone 1 and seismic stability is judged to be adequate based upon observedstatic stability. No computations have been made to confirm staticstability.
14
SECTION 7ASSESSMENT, REMEDIAL MEASURES AND RECOMMENDATIONS
7.1 Dam Assessment:
a. Safety. Based upon visual inspection and review of design andconstruction data, the Wye Mills Dam appears to be in good condition.Preliminary hydrologic and hydraulic analyses indicate the overflowspillway is capable of passing 95 per cent of PMF before the dam isovertopped. Since the dam is not anticipated to fail completely norsignificantly increase loss of life or property damage in the eventof overtopping by PMF, the spillway is judged to be inadequate, butnot seriously inadequate.
b. Adequacy of Information. The available information consists ofconstruction drawings including limited subsurface explorations, structuralcomputations, specifications, special provisions, and a final report. Thisdata is generally adequate to assess the project.
c. Urgency. Although immediate action is not required at this time,the recommendations of this section should be implemented as soon as possible.
d. Necessity for Additional Studies. Although the spillway isinadequate to pass PMF without overtopping, the overtopping is not consideredof sufficient magnitude or duration to cause failure of the dam and additionalstudies are not necessary at this time.
7.2 Remedial Measures and Recommendations:
a. Structures and Appurtenances.
1. Inspect and repair the 24 inch drain in the overflow spillwayas necessary.
2. Repair and stabilize the timber sheet pile lining of thedownstream channel.
3. Re-vegetate foot paths on downstream face of embankment nearbox culvert and attempt to construct barriers or designated pathways removedfrom the embankment slopes.
4. Replace expansion joint material in concrete structures asnecessary.
5. Replace staff gauge on spillway.
b. Operation and Maintenance Procedures.
1. Document operating procedures in writing.
2. A warning system should be developed to warn downstreamresidences of large spillway discharges, during periods of heavy rainfallor runoff or failure of the dam.
15
APPENDIX A
CHECK LIST - VISUAL INSPECTION, SITE SKETCH, PHASE I
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APPENDIX B
CHECK LIST - HYDROLOGIC AND HYDRAULIC ENGINEERING DATA
PHASE I
iI.
DAM NAME: e .iilsID # MD
CHECK LISTHYDROLOGIC AND ITYDRAULIC
ENGINEERING DATA
DRAINAGE AREA CHARACTERISTICS: Sandy and silt loams, mild slopes,
crop and woodland
ELEVATION TOP OF NORMAL POOL(STORAGE CAPACITY): 14.3 (302 Ac-ft)
ELEVATION TOP OF FLOOD CONTROL POOL(STORAGE CAPACITY):
ELEVATION MAXIMUM DESIGN POOL: 17.1 (571 Ac-ft)
ELEVATION TOP OF DAM: 22.0 (1224 Ac-ft)
CRESTS
a. Elevation 14.3b. Type u - shaped ogee near right abutmentc. Width 29 ft. x 49 ft. x 29 ft.d. Lengthe. Location Spillover discharges through embankment via Twin 13x12 ftf. Number and Type of Gates NONE high box culvert
OUTLET WORKS:
a. Type Normal discharges over ogee sections; appropriations to mill vi
b. Location 24" slide gate, left side of dam, atc. Entrance Inverts inv. elevation 11.15d. Exit Invertse. Emergency Drawdown Facilities 24" slide sate inv. 2.0 located
in ogee section
HYDROMETEOROLOGICAL GAGES:
a. Type NONEb. Locationc. Records
MAXIMUM NON-DAMAGING DISCHARGES: 4930 cfs, non-overtopping dischargedischarges exceeding approximately
1000 cfs damage 200 ft. outlet channel
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APPENDIX C
LOCATION MAP & PLANS
.......
' WYE MILLS DAM4
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APPENDIX D
ANALYSES
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6-000 /9L .. 20.4 a.&.4
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The above calculations assume inlet control governs. To checkthe possibility that outlet control governs, the following down-stream controls/conditions must be known:
1. tidal hydraulics2, geometry & roughness downstream of Rte 4043. geometry of Rte 404 and its bridge4. geometry & roughness between Rte 404 and Wye Mills Dam.
Since determination of the above parameters is beyond the scopeof a Phase I study, outlet control has been assessed for a dischargeclose to PMF, assuming that the culvert is flowing full and usinga Bureau of Public Roads outlet control nomograph:
Q = 6000 = 3000 cfs/barrelArea of culvert = 12x13 = 156 ft
2
Square edged entrance, Ke = 0.5
L = 90 ft, S = 0/001 ft/fth= assumedTW on culvert = 12 ft
00HW, headwater depth = H + ho0 - LSo0
at 3000 cfs/barrel, H = 9 ft from nomographHW = 9 + 12 - 90(.001)
= 21 - 0,09 = 20.9 vs 24 from inlet control
.'. at 6000 cfs, with the 12 ft TW assumption, inlet controlgoverns and the previous calculations are consideredvalid for this Phase I study.
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APPENDIX E
PHOTOGRA~PHS
OVERFA)W SI I ILWAY
OVERFLOW SILLHWAYBOX ('11IE t
UP~STREAM FA( IFROM 1. ICFTABIMIN
D)OWNS TR EAM FA(CEFROM R IGHIT ABUITMENTr
DOWNSTREAM CIIANN I:L FIROMMD). RTE.K. 14O04 BR IDGUE
MD). RTE . 404 BR IDGE,
E- 3
APPENDIX F
GEOLOGY REPORT
GEOLOGY REPORT
WYE MILLS DAMQUEEN ANNES COUNTY, MARYLAND
Wye Mills Dam is situated within the general physiographic regionknown as the Atlantic Coastal Plain characterized by deep unconsolidatedsediments overlying crystaline bedrock. The depth of sediments reaches2500 feet in the vicinity of Wye Mills. At the dam site, the sedimentsoutcropping at the surface are of the Calvert Formation of MioceneAge within the Chesapeake group and consist of clay, sandy clay, sand,marl, and diatomaceous earth. The Calvert Formation is of marine originand in Queen Annes County is exposed primarily in stream valleys whereoverlying pleistocene deposits have been removed through erosion.
Subsurface data obtained for the design of the dam typically penetrated"tight blue to gray clay and marls" of the Calvert Formation betweenelevations +2 and -5. Due to the eroded overlying sediments, these claysare stiff, overconsolidated, relatively impervious and should providecompetent foundation material within reasonable depths. Sheetpile cut offwalls embedded in these clays should prove effective in controlling seepagethrough the dam. Although the subsurface explorations only penetrated theclay layer a few feet and did not define its thickness, recent well logsin this formation in the area immediately adjacent to the dam indicate the"hard clay" stratum to range in thickness between eighteen and forty-fivefeet. Granular borrow material conforming to the project specificationsshould have been readily available in the region surrounding the dam siteabove the stream valley in the pleistocene deposits. j
Although the dam is located in seismic zone 1 and earthquakes areanticipated to be relatively rare, a slight earth movement with itsepicenter at Wilmington Delaware occurred in February, 1973. The seismicactivity reached VI on the Modified Mercali scale at its epicenter, butthe magnitude at the dam site is unknown. No detrimental effects werereported at the dam after the tremor.
F-1
QUEEN ANNE S COUNTY GEOLOGICAL MAPscal im.
010
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f0rilia' ona a.
0CMC
F-2
REFERENCES
1. Maryland Geological Survey, Queen Annes County, 1926.
2. Department of Geology, Mines, and Water Resources,The Water Resources of Cecil, Kent, and Queen AnnesCounties, Bulletin 21, 1958.
P-
