AUDADOA AO BLACK AND VEATCH KANSAS CITY MO FIG 13/1n

NATIONAL DAM SAFETY PROGRAM. GILFORD LAKE DAM (MO 31137), MISS--ETC(U)

NOV A0 E R BURTON, H L CALLAHAN DACW43-8D-C-0074

U) CLA$ISIFIED NL

IEEEEEEEE

LEVEL ~AT4

MISSISSIPPI-KASKASKIA-ST. LOUIS BASIN

GUILFORD LAKE DAM '

ST. LOUIS COUNTY, MISSOURI

MO 31137

PHASE 1 INSPECTION REPORTNATIONAL DAM SAFETY PROGRAM

United Stat.. ArmyCorps of Engineers

.. Smng the Army~St. the Nauiof

S.Louis District

PREPARED BY: U.S. ARMY ENGINEER DISTRICT. ST. LOUIS

FOR: STATE OF MISSOURI -ilC

NOVEMBER 1960 o11 2 C031

UNCLASSIFIEDSECURITY CLASSIFICATION OF THIS PAGE (Mhen Dot Entered)

REPORT DOCUMENTATION PAGE READ INSTRUCTIONSBEFORE COMPLETING FORM

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

14. TITLE (and Subtitle) S. TYPE OF REPORT & PERIOD COVERED

Phase I Dam Inspection ReportNational Dam Safety Program Final ReportGuilford Lake Dam (MO 31137) 6. PERFORMING ORG. REPORT NUMBER

St. Louis County, Missouri1. AUTHOR() 4. CONTRACTOR GRANT NUMSER(e)

Black & Veatch, Consulting Engineers

DACW43-80-C-007 /

'. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASK

U.S. Army Engineer District, St. Louis AREA & WORK UNIT NUMBERS

Dam Inventory and Inspection Section, LMSED-PD210 Tucker Blvd., North, St. Louis, Mo. 63101

1I. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATEU.S. Army Engineer District, St. Louis November 1980Dam Inventory and Inspection Section, LMSED-PD I3. NUMBER OF PAGES

210 Tucker Blvd., North, St. Louis, Mo. 63101 Approximately 4514. MONITORING AGENCY NAME & ADDRESS(II different from Controlllng Offlco) IS. SECURITY CLASS. (of thl report)

UNCLASSIFIEDISa. DECL ASSI FI CATION/DOWNGRADING

SCHEDULE

IS. DISTRIBUTION STATEMENT (of tel Report)

Approved for release; distribution unlimited.

17. DISTRIBUTION STATEMENT (of the abesract entered In Block 20, If different from Report)

IS. SUPPLEMENTARY NOTES

IS. KEY WORDS (Continue on teverse side It necesslary nd identify by block number)

Dam Safety, Lake, Dam Inspection, Private Dams

20, ABSTRACT (kthwe - evae WhI nm myI -d ideO bY block number)This report was prepared under the National Program of Inspection ofNon-Federal Dams. This report assesses the general condition of the dam withrespect to safety, based on available data and on visual inspection, todetermine if the dam poses hazards to human life or property.

01JII*W3 EM ONDFIo., 501190ETIM 72 NUNCLASSIFIED

SECURITY CLASSFICATIOn OF THIS PAGE (When Date Enotred)

SECURITY CLASSIFICATION OF THIS PAOE(ftm Deem sheee4)

at

"Abs.shouldtide SMaea

dates

aswe

orderof the

Of.I

carn

of

tiN

it

SECURITY CLASSIFICATION OF THIS PAGEIWhei beta Entlered)

MISSISSIPPI-KASKASKIA-ST. LOUIS BASIN

GUILFORD LAKE DAM

ST. LOUIS COUNTY, MISSOURI

MO 31137

PHASE 1 INSPECTION REPORTNATIONAL DAM SAFETY PROGRAM.

Gvilford Lake Dwn (MC( 3113)Mississippi - Kaskaskia - ?LLouis Basin,St. Louis County, Missouri. Phase IInspection Report.

United Status ArmyCrsof Engineers

Serving the Army.. evng the Nation

St. Louis Distri-t.. -9 Final rept.

15 DACW43-80-C-0074

10/ Edgn R.L ~~~

PREPARED BY: U.S. ARMY ENGINEER DISTRICT. ST. LOUIS

FOR: STATE OF MISSOURI

I MW

_ DEPARTMENT OF THE ARMYST. LOUIS UISTRICT. CORPS OF ENGIINERS

210 TUCKER BOULEVARO. NORTHST. LOUIS. MISSOURI 63191

SUBJECT: Dam Phase I Inspection Report

This report presents the results of field inspection and evaluationof the Guilford Lake Dam (MO 31137).

It was prepared under the National Program of Inspection of Non-Federal Dams.

This dam has been classified as unsafe, non-emergency by theSt. Louis District as a result of the application of the followingcriteria:

a. Spillway will not pass 50 percent of the Probable MaximumFlood without overtopping the dam.

b. Overtopping of the dam could result in failure of the dam.

c. Dam failure significantly increases the hazard to loss oflife downstream.

SIGNED Q'" "iSUBMITTED BY: S

Chief, Engineering Division Date

APPROVED BY: SIGNLL., 3o APR t IColonel, CE, District Engineer Date

| IIII 0 0

0

GUILFORD LAKE DAM

p ST. LOUIS COUNTY, MISSOURI

MISSOURI INVENTORY NO. 31137

PHASE I INSPECTION REPORT

NATIONAL DAN SAFETY PROGRAM

PREPARED BY:

BLACK & VEATCHCONSULTING ENGINEERS

KANSAS CITY, MISSOURI

UNDER DIRECTION OF

ST. LOUIS DISTRICT CORPS OF ENGINEERS

FOR

GOVERNOR OF MISSOURI

NOVEMBER 1980

9PHASE I REPORT

NATIONAL DAM SAFETY PROGRAM

Name of Dam Guilford Lake DamState Located MissouriCounty Located St. Louis CountyStream Tributary of Fox CreekDate of Inspection 19 November 1980

Guilford Lake Dam was inspected by a team of engineers from Black &Veatch, Consulting Engineers for the St. Louis District, Corps of Engi-neers. The purpose of the inspection was to make an assessment of thegeneral condition of the dam with respect to safety, based upon avail-able data and visual inspection, in order to determine if the dam poseshazards to human life or property.

The guidelines used in the assessment were furnished by the Depart-ment of the Army, Office of the Chief of Engineers and developed withthe help of several Federal and state agencies, professional engineeringorganizations, and private engineers. Based on these guidelines, thisdam is classified as a small size dam with a high downstream hazardpotential. According to the St. Louis District, Corps of Engineers,failure would threaten lives and property. The estimated damage zoneextends approximately two miles downstream of the dam. Within the esti-mated damage zone are eight dwellings, several farm buildings, and StateHighway 100. Contents of the estimated downstream damage zone wereverified by the inspection team.

Our inspection and evaluation indicates that the spillway does notmeet the criteria set forth in the guidelines for a dam having the abovesize and hazard potential. The spillway will not pass the probablemaximum flood without overtopping but will pass 15 percent of the probablemaximum flood. The spillway will pass the flood which has a one percentchance of occurrence in any given year (100-year flood). The spillwaydesign flood recommended by the guidelines is 50 to 100 percent of theprobable maximum flood. Considering the hazard zone and the volume ofwater stored, the spillway design flood should be 50 percent of theprobable maximum flood. The probable maximum flood is defined as theflood discharge which may be expected from the most severe combinationof critical meteorologic and hydrologic conditions which are reasonablypossible in the region.I

It

Based on visual observations, this dam appears to be in good condi-tion. Deficiencies visually observed by the inspection team were poorerosion protection on the embankment, erosion of the right (southwest)bank of the spillway channel, erosion of the left (northeast) abutment,and erosion of the right (southwest) abutment below the spillway.Seepage and stability analyses required by the guidelines were notavailable.

There were no observed deficiencies or conditions existing at thetime of the inspection which indicated an immediate safety hazard.Future corrective action and regular maintenance will be required tocorrect or control the described deficiencies. In addition, detailedseepage and stability analyses of the existing dam, as required by theguidelines, should be performed. A detailed report discussing each ofthese deficiencies is attached.

Edwin R. Burton, PEMis un E-10137

afyL. Callahan, PartnerBlack & Veatch

PHASE I INSPECTION REPORTNATIONAL DAM SAFETY PROGRAM

GUILFORD LAKE DAM

TABLE OF CONTENTS

Paragraph No. Title Page No.

SECTION 1 - PROJECT INFORMATION

1.1 General 11.2 Description of Project 11.3 Pertinent Data 2

SECTION 2 - ENGINEERING DATA

2.1 Design 52.2 Construction 52.3 Operation 52.4 Geology 52.5 Evaluation 5

SECTION 3 - VISUAL INSPECTION

3.1 Findings 63.2 Evaluation 7

SECTION 4 - OPERATIONAL PROCEDURES

4.1 Procedures 84.2 Maintenance of Dam 84.3 Maintenance of Operating Facilities 84.4 Description of Any Warning System in Effect 84.5 Evaluation 8

SECTION 5 - HYDRAULIC/HYDROLOGIC

5.1 Evaluation of Features 9

SECTION 6 - STRUCTURAL STABILITY

6.1 Evaluation of Structural Stability 11

SECTION 7 - ASSESSMENT/REMEDIAL MEASURES

7.1 Dam Assessment 12

7.2 Remedial Measures 12

TABLE OF CONTENTS (Cont'd)

LIST OF PLATES

Plate No. Title

I Location Map

2 Vicinity Topography

3 Dam Plan

4 Dam Cross Section and Dam Crest Profile

5 Spillway Profile and Spillway Cross Section

6 Photo Index

LIST OF PHOTOGRAPHS

Photo No. Title

i Upstream Face of Dam Looking South

2 Upstream Face of Dam Looking North

3 Crest of Dam Looking South

4 Crest of Dam Looking North

5 Downstream Face of Dam Looking South

6 Downstream Face of Dam Looking North

7 Inlet to Spillway Channel

8 Spillway Channel Looking Downstream

9 Erosion on Abutment Slope Downstream ofSpillway Channel

10 Stream Channel Below Dam

11 Void in Fill at Old Stream Channel Below Dam

12 Erosion at Left Abutment

TABLE OF CONTENTS (Cont'd)

LIST OF PHOTOGRAPHS

Photo No. Title

13 Erosion on Downstream Slope of Dam

14 Livestock Tracks and Overgrazed Area

APPENDIX

Appendix A - Hydrologic and Hydraulic Analyses

SECTION 1 - PROJECT INFORMATION

1.1 GENERAL

a. Authority. The National Dam Inspection Act, Public Law 92-367,authorized the Secretary of the Army, through the Corps of Engineers, toinitiate a program of safety inspection of dams throughout the UnitedStates. Pursuant to the above, the District Engineer of the St. LouisDistrict, Corps of Engineers, directed that a safety inspection of theGuilford Lake Dam be made.

b. Purpose of Inspection. The purpose of the inspection was tomake an assessment of the general condition of the dam with respect tosafety, based upon available data and visual inspection, in order todetermine if the dam poses hazards to human life or property.

c. Evaluation Criteria. Criteria used to evaluate the dam werefurnished by the Department of the Army, Office of the Chief of Engi-neers, in "Recommended Guidelines for Safety Inspection of Dams." Theseguidelines were developed with the help of several Federal agencies andmany state agencies, professional engineering organizations, and privateengineers.

1.2 DESCRIPTION OF PROJECT

a. Description of Dam and Appurtenances.

(1) The dam is an earth structure located in the valley of atributary to Fox Creek (See Plate 1). The watershed is an area of lowhills with fairly steep slopes consisting of about 65 percent timberlandand 35 percent grassland pastures. There are several large houses inthe drainage area. The dam is approximately 350 feet long along itscrest and is constructed with a curved alignment. The dam is about 32feet high and is 11 feet wide at its crest. The downstream face of thedam has a nonuniform slope from the crest to the valley floor below.

(2) The spillway is an unlined open channel cut in the naturalmaterial of the right abutment. The material excavated from the spillwaychannel forms a dike along the left bank of the spillway. The spillwaychannel is nonuniform in width and cross section with an approximateaverage depth of 4 feet and an approximate average bottom width of 7feet. Flow through the spillway channel discharges to the natural slopeof the abutment then to the stream channel below the dam.

(3) Pertinent physical data are given in paragraph 1.3.

b. Location. The dam is located in western St. Louis County,Missouri, as indicated on Plate 1. The lake formed by the dam is in anarea shown on the United States Geological Survey 7.5 minute seriesquadrangle map for Eureka, Missouri in Section 19 of T44N, RO3E.

c. Size Classification. Criteria for determining the size classi-fication of dams and impoundments are presented in the guidelines refer-enced in paragraph l.lc above. Based on these criteria, the dam andimpoundment are in the small size category. A small size dam is classi-fied as having a height less than 40 feet, but greater than or equal to25 feet and/or a storage capacity less than 1,000 acre-feet, but greaterthan or equal to 50 acre-feet.

d. Hazard Classification. The hazard classification assigned bythe Corps of Engineers for this dam is as follows: The Guilford LakeDam has a high hazard potential, meaning that the dam is located wherefailure may cause loss of life, and serious damage to homes, agricul-tural, industrial and commercial facilities, and to important publicutilities, main highways, or railroads. For the Guilford Lake Dam theestimated flood damage zone extends approximately two miles downstreamof the dam. Within the estimated damage zone are eight dwellings,several farm buildings, and State Highway 100. Contents of the estimateddownstream damage zone were verified by the inspection team.

e. Ownership. The dam is owned by Mr. Charles F. Guilford, RuralRoute 5, Pacific, Missouri 63069.

f. Purpose of Dam. The dam forms a 4.5-acre lake used for recre-ation and as a livestock water supply.

g. Design and Construction History. Data relating to the designand construction were not available. The dam was constructed in 1976 byKenneth Pointer with design assistance from the Soil Conservation Service.

h. Normal Operating Procedure. Normal rainfall, runoff, trans-piration, evaporation, and overflow through the uncontrolled spillwayall combine to maintain a relatively stable water surface elevation.

1.3 PERTINENT DATA

a. Drainage Area - 26 acres

b. Discharge at Damsite.

(1) Normal discharge at the damsite is through an unlined, openchannel spillway.

2

(2) Estimated experienced maximum flood at damsite - Unknown.

(3) Estimated ungated spillway capacity at maximum pool elevation60 cfs (50 Percent Probable Maximum Flood Pool El. 690.9).

c. Elevation (Feet above m.s.l. Approximated from USGS Map contours).

(1) Top of dam - 690.0 (see Plate 3)

(2) Spillway crest - 689.0

(3) Streambed at toe of dam - 658.5

(4) Maximum tailwater - Unknown.

d. Reservoir.

(1) Length of maximum pool - 790 feet + (Probable maximum floodpool level).

(2) Length of normal pool - 590 feet + (Spillway crest).

e. Storage (Acre-feet).

(1) Top of dam - 52

(2) Spillway crest - 46

(3) Design surcharge - Not available.

f. Reservoir Surface (Acres).

(1) Top of dam - 5.7

(2) Spillway crest - 4.5

g. Dam.

(1) Type - Earth embankment.

(2) Length - 350 feet

(3) Height - 32 feet +

(4) Top width - 11 feet

(5) Side slopes - upstream face 1.0 V on 3.4 H, downstream facevaries between 1.0 V on 2.5 H and 1.0 V on 5.0 H (see Plate 4).

3

(6) Zoning - Unknown.

(7) Impervious core - Unknown.

(8) Cutoff - Unknown.

(9) Grout curtain - Unknown.

h. Diversion and Regulating Tunnel - None.

i. Spillway.

(1) Type - Unlined, open channel with an approximate 7-foot bottomwidth and 4-foot height.

(2) Crest elevation - 689.0 feet m.s.l.

(3) Gates - None.

(4) Upstream channel - Unlined earth channel.

(5) Downstream chaznel - Spillway discharges to natural slope,then to the natural stream downstream of the dam.

j. Emergency Spillway - None.

k. Regulating Outlets - None.

4

SECTION 2 - ENGINEERING DATA

2.1 DESIGN

Design data were not available. Design assistance was provided bythe Soil Conservation Service.

2.2 CONSTRUCTION

Construction records were unavailable. The dam was constructed by

Kenneth Pointer.

2.3 OPERATION

Operational records and documentation of past floods were unavail-able.

2.4 GEOLOGY

The site of the dam and reservoir is located in a shallow, broad,steep-sided valley. The dam impounds a very short, intermittent tribu-tary of Fox Creek.

There were no data available on the soils in the area of the damand reservoir. The bedrock consists of limestone of the Osage series ofthe Pennsylvanian System according to the Geologic Map of Missouri.

2.5 EVALUATION

a. Availability. No engineering data were available.

b. Adequacy. No engineering data were available. Thus, an assess-ment of the design, construction, and operation could not be made.Seepage and stability analyses comparable to the requirements of the"Recommended Guidelines for Safety Inspection of Dams" were not avail-able, which is considered a deficiency. These seepage and stabilityanalyses should be performed for appropriate loading conditions (includ-ing earthquake loads) and made a matter of record.

c. Validity. The validity of the design, construction, and opera-tion could not be determined due to the lack of engineering data.

5

SECTION 3 - VISUAL INSPECTION

3.1 FINDINGS

a. General. A visual inspection of Guilford Lake Dam was made on19 November 1980. The inspection team consisted of Edwin Burton, teamleader; Robert Pinker, geologist; Gary Van Riessen, geotechnical engi-neer; and John Ruhl, civil engineer. The dam appeared to be in goodcondition. Specific observations are discussed below. No observationswere made of the condition of the upstream face of the dam below thepool elevation at the time of the inspection.

b. Dam. The inspection team observed the following conditions atthe dam. No cracking, sliding, sloughing, unusual irregularities, orother signs of instability or settlement were observed. The grass coveron the dam was very thin to nonexistent in spots. Numerous tracks ofcattle and horses were observed which would indicate heavy grazing.There were no trees on the embankment. Small riprap (approximately 3-6inches in size) has been placed on the upstream face at the waterline.The soft upstream face for several feet above the waterline would indi-cate that the water level had been higher a short time before the inspec-tion. Erosion exists along the left abutment where runoff from the roadand hillside drains into the lake and on the right abutment below theend of the spillway channel. Minor erosion was observed on the down-stream slope of the embankment. No areas of seepage were observed.Although the old stream channel was very green, the inspection teambelieves that this is due to surface drainage rather than seepage. Avoid exists in the fill material in the old stream channel. There wereno animal burrows observed on the embankment. Although the owner statedthat the dam was overtopped in 1978 there were no visible signs ofovertopping.

c. Appurtenant Structures. The inspection team observed thefollowing items pertaining to the appurtenant structures. The spillwaywas in good condition. The right bank of the spilIway channel is erodingfrom hillside runoff. Although the grass cover is unsatisfactory, therehas been no erosion of the channel floor. There was no development inthe spillway area which would suffer damage due to flow through thespillway.

d. Geology. The soils observed in the area of the dam and reser-voir consist of silty clay formed in residuum from limestone. Forengineering purposes the soils are classified as clayey silt or siltyclay of low plasticity. No outcrops were observed in the area. Howevernumerous fragments of chert were present in the soils and on the embank-ment. A sample of the material in the embankment was taken with anOakfield sampler near the center of the downstream crest. The materials

6

sampled consisted of silty clay and were visually classified for engi-neering purposes as silty clay of low plasticity (CL). Based on thesesamples, it is surmized that the embankment is constructed of silty clay(CL).

e. Reservoir Area. No slumping or slides of the reservoir bankswere observed. Drainage into the reservoir is primarily runoff from thesteeply sloping hills around the lake with little defined channelizedflow. There was no noticeable lake siltation.

f. Downstream Channel. The spillway discharges to the naturalslope, then flows overland to the natural stream channel downstream ofthe dam. The stream channel has been filled for approximately 200 feetdownstream of the toe of the dam.

3.2 EVALUATION

The various deficiencies observed at the time of the inspection arenot believed to represent an immediate safety hazard. They do, however,warrant monitoring and control.

The thin grass cover on the embankment and in the spillway haspermitted the erosion of the right spillway bank, the right abutmentbelow the spillway, and the left abutment. Each of these areas oferosion should be repaired and adequate erosion protection should bemaintained.

7

SECTION 4 - OPERATIONAL PROCEDURES

4.1 PROCEDURES

The pool is primarily controlled by rainfall, runoff, evaporation,transpiration, and capacity of the uncontrolled spillway.

4.2 MAINTENANCE OF DAM

According to the owner, the dam was overtopped in 1978 due toblockage of the spillway. Subsequently, the blockage was removed andthe embankment was redressed and seeded. No other maintenance has beenperformed.

4.3 MAINTENANCE OF OPERATING FACILITIES

No operating facilities exist.

4.4 DESCRIPTION OF ANY WARNING SYSTEM IN EFFECT

There is no existing warning system or preplanned scheme for alert-ing downstream residents for this dam.

4.5 EVALUATION

A maintenance program should be established to provide adequateerosion protection of the spillway and embankment.

SECTION 5 - hnDRAULIC/HIYDROLOGIC

5.1 EVALUATION OF FEATURES

a. Design Data. No design data were available.

b. Experience Data. The drainage area and the lake surface areaare developed from the USGS Eureka, Missouri Quadrangle Map. The damlayout is from a survey made during the inspection.

c. Visual Observations.

(1) The spillway appears to be in good condition. The lake levelat the time of the inspection (El. 685.0) was below the spillway crestlevel. There were no obstructions to flow in the downstream channel.

(2) There is no emergency spillway for this dam.

(3) Large spillway discharges will probably erode the spillway andcould erode the embankment.

d. Overtopping Potential. The spillway will not pass the probablemaximum flood without overtopping the dam. The probable maximum floodis defined as the flood discharge that may be expected from the mostsevere combination of critical meteorologic and hydrologic conditionsthat are reasonably possible in the region. The spillway will pass 15percent of the probable maximum flood without overtopping the dam. Thespillway will pass the one percent chance flood estimated to have a peakoutflow of 19 cfs developed by a 24-hour, one percent chance rainfall.According to the recommended guidelines from the Department of the Army,Office of the Chief of Engineers, a high hazard dam of small size shouldpass 50 to 100 percent of the probable maximum flood. Considering thedownstream hazard, and the volume of water stored, the appropriatespillway design flood should be 50 percent of the probable maximumflood. The portion of the estimated peak discharge of 50 percent of theprobable maximum flood overtopping the dam would be 150 cfs of the totaldischarge from the reservoir of 210 cfs. The estimated duration ofovertopping is 5.6 hours with a maximum height of 0.9 feet. The portionof the estimated peak discharge of the probable maximum flood overtoppingthe dam would be 420 cfs of the total discharge from the reservoir of530 cfs. The estimated duration of overtopping is 7.2 hours with amaximum height of 1.4 feet. The embankment could be jeopardized shouldovertopping occur for these periods of time.

According to the St. Louis District, Corps of Engineers, the effectfrom rupture of the dam could extend approximately two miles downstreamof the dam. Within the estimated damage zone are eight dwellings,several farm buildings, and State Highway 100. Contents of the estimated

9

downstream damage zone were verified by the inspection team. Floodplain regulations under the National Flood Insurance Program restrictdevelopment in the flood plain of Fox Creek which is downstream of thedaiq.

10

SECTION 6 - STRUCTURAL STABILITY

6.1 EVALUATION OF STRUCTURAL STABILITY

a. Visual Observations. Visual observations of conditions whichaffect the structural stability of this dam are discussed in Section 3,paragraph 3.1b.

b. Design and Construction Data. No design data relating to thestructural stability of the dam were found. Seepage and stabilityanalyses comparable to the requirements of the "Recommended Guidelinesfor Safety Inspection of Dams" were not available, which is considered adeficiency.

c. Operating Records. No operational records exist.

d. Postconstruction Changes. Repair of erosion due to overtoppingincluded redressing and seeding the embankment crest and slopes. Therepairs were made in 1979.

e. Seismic Stability. The dam is located in Seismic Zone 2 whichis a zone of moderate seismic risk. A properly designed and constructedearth dam using sound engineering principles and conservatism shouldpose no serious stability problems during earthquakes in this zone. Theseismic stability of an earth dam is dependent upon a number of factors:embankment and foundation material classifications and shear strengths;abutment materials, conditions, and strengths; embankment zoning; andembankment geometry. Adequate descriptions of embankment design para-meters, foundation and abutment conditions, or static stability analysesto assess the seismic stability of this embankment were not availableand therefore no inferences will be made regarding the seismic stability.An assessment of the seismic stability should be included as part of thestability analysis required by the guidelines.

11

SECTION 7 - ASSESSMENT/REMEDIAL MEASURES

7.1 DAM ASSESSMENT

a. Safety. Several conditions observed during the visual inspec-tion by the inspection team should be monitored and/or controlled.These are erosion on the left abutment, the right abutment below thespillway, and the right bank of the spillway, and the poor erosionprotection on the embankment. Seepage and stability analyses comparableto the requirements of the "Recommended Guidelines for Safety Inspectionof Dams" were not available, which is considered a deficiency.

b. Adequacy of Information. Due to the absence of engineeringdesign data, the conclusions in this report were based only on perfor-mance history and visual conditions. The inspection team considers thatthese data are sufficient to support the conclusions herein. Seepageand stability analyses comparable to the requirements of the "RecommendedGuidelines for Safety Inspection of Dams" were not available, which isconsidered a deficiency.

c. Urgency. It is the opinion of the inspection team that aprogram should be developed as soon as possible to implement remedialmeasures recommended in paragraph 7.2b. If the safety deficiencieslisted in paragraph 7.1a are not corrected, they will continue todeteriorate and lead to a serious potential of failure. The item recom-mended in paragraph 7.2a should be pursued on a high priority basis.

d. Necessity for Phase II. The Phase I investigation does notraise any serious questions relating to the safety of the dam nor doesit identify any serious dangers which would require a Phase II investi-gation. However, the additional analyses noted in paragraph 2.5b arenecessary for compliance with the guidelines.

I e. Seismic Stability. This dam is located in Seismic Zone 2.Adequate description of embankment design parameters, foundation andabutment conditions, or static stability analyses to assess the seismicstability of this embankment were not available and therefore no infer-ences will be made regarding the seismic stability. An assessment ofthe seismic stability should be included as part of the recommendedstability analysis.

7.2 REMEDIAL MEASURES

a. Alternatives. The spillway size and/or height of the dam wouldneed to be increased or the lake level would need to be permanentlylowered to increase available flood storage in order to effectively passthe recommended spillway design flood.

12

b. Operation and Maintenance Procedures. The following operationand maintenance procedures are recommended and should be carried outunder the direction of a professional engineer experienced in the design,construction, and maintenance of earth dams.

(1) An adequate grass cover should be maintained on the embankmentand in the spillway to prevent erosion. Overgrazing by cattle should beprevented.

(2) The erosion of the right spillway bank, the left abutment, andthe right abutment below the spillway should be backfilled with suitablematerial and compacted. A paved ditch or some other means of slopeprotection may be required to control the concentrated runoff at theleft abutment.

(3) Seepage and stability analyses should be performed.

(4) A detailed inspection of the dam should be made periodicallyand the results documented and made a matter of record. More frequentinspections may be required if additional deficiencies are observed orthe severity of the reported deficiencies increase.

13

GUILFORD94 LAKE

DAM

DD .1 1

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VICINITY MAPSCALE 101 WILCS

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GUILFORD LAKE DAMLOCATION MAP

SCALE IN MILES1- 1 -L -T0 1 2 3 4

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GUILFORD LAKE LEVEL AT TIME OF INSPECTION. EL. 685.0

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689.6

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PHOTO 1: UPSTREAM FACE OF DAl LOOKING SOUTH

PHOTO 2: UPSTREAM FACE OF DAM LOOKING NORTH

PHOTO0 3: CREST OF DMN LOOKING SOUTH

PHOTO 4: CREST OF DX4 LOnOKTNG NORTH

PHOTO 5: D0OWNSTREAM FACE OF DAN LOOKING SOUTH

PHOTO 6: DOWNSTREAM~ FACE OF DAM LOOKING NORTH

PHOTO 7: INLET TO SPILLWAY CHANNEL

PHOTO 8: SPILLWAY CHANNEL LOOKING DOWNSTREAM

PHOTO 9: EROSION ON ABUTMENT SLOPE DOWNSTREAM OF SPILLWAYCHANNEL

PHOTO 10: STREAM CHANNEL BELOW DAM

PHOTO 11: VOID IN FILL OF OLD STREAM CHANNEL BELOW DAM

PHOTO 12: EROSION AT LEFT ABUTMENT

PHOTO 13: EROSION ON DOWNSTREAM SLOPE OF DAM

PHOTO 14: LIVESTOCK TRACKS AND OVERGRAZED AREA

APPENDIX A

HYDROLOGIC AND HYDRAULIC ANALYSES

HRDROLOGIC AND HMDRAULIC ANALYSES

To determine the overtopping potential, flood routings were per-formed by applying the Probable Maximum Precipitation (PMP) to a synthe-tic unit hydrograph to develop the inflow hydrograph. The inflow hydro-graph was then routed through the reservoir and spillway. The over-topping analysis was determined using the computer program HEC-I (DamSafety Version) (1).

The PMP was determined from regional charts prepared by the NationalWeather Service in "Hvdrometeorological Report No. 33" (IDM-33) (2).Reduction factors were not applied. The rainfall distribution for the24-hour PMP storm was determined according to the procedures outlined inHMR-33 and EM 1110-2-1411 (3). The St. Louis, Missouri rainfall distri-bution (5 min. interval - 24 hours duration), as provided by the St.Louis District, Corp of Engineers, was used when the one percent chanceprobability flood was routed through the reservoir and spillway.

The synthetic unit hydrograph for the watershed was developed bythe computer program using the Soil Conservation Service (SCS) method.(1 and 4). The parameters for the unit hydrograph are shown in Table 1.Lag time and time of concentration were calculated by two differentmethods. The results used in the analyses were obtained by using theKirpich formula.

The SCS curve number (CN) method was used in computing the infil-tration losses for the rainfall-runoff relationship. The CN valuesused, and the result from the computer output, are shown in Table 2.

The reservoir routing was performed using the Modified Puls Method.The initial reservoir pool elevation for the routing of each storm wasdetermined to be equivalent to the crest elevation of the spillway atelevation 689.0 feet m.s.l. in accordance with antecedent storm condi-tions preceding the one percent probability and probable maximum stormsoutlined by the U.S. Army Corps of Engineers, St. Louis District (5).The hydraulic capacity of the spillway and the storage capacity of thereservoir were defined by the elevation, surface area, storage, anddischarge relationships shown in Table 3.

The rating curve for the spillway is shown in Table 4. The flowover the crest of the dam and through the spillway was determined usingthe non-level dam crest option ($L and $V cards) of the HEC-I program.The program assumes critical flow over a broad-crested weir.

The result of the routing analysis indicates that a 15 percent PM!1flood will not overtop the dam.

A-I

A summary of the routing analysis for different ratios of the PNFis shown in Table 5.

The computer input data and a summary of the output data are pre-sented at the back of this appendix.

TABLE 1

SYNTHETIC UNIT HYDROGRAPH

Paramet- -s:

Drainage Area (A) 26 acres

Hydraulic Length of 0.16 milesWatercourse (L)

Difference in Elevation (H) 90 feet

Time of concentration (Tc) 0.05 hours

Lag Time (L ) 0.03 hours

Duration (D) 0.4 minutes(use 5 minutes)

Time (Min.) Discharge (cfs) *

0 05 236

10 6615 1320 325 0

From HEC-I computer output

FORMULAS USED:

T = [(11.9 x L3)/H]0 .385 (6)c

D = 0.133 T

L = 0.6 Tg c

A-2

TABLE 2

RAINFALL-RUNOFF VALUES

Selected Storm Storm Duration Rainfall Runoff LossEvent (Hours) (Inches) (Inches) (Inches)

PMP 24 32.89 31.31 1.5850% PMP 24 17.18 15.65 1.53

1% Probability 24 6.97 4.13 2.84

Additional Data:

1) No information on soil associations was available for thiswatershed.100 percent of the drainage area was assumed to be in hydrologicsoil group C.

35 percent of the land use was grassland.65 percent of the land use was timberland.

2) SCS Runoff Curve CN = 88 (AMC III) for the PMF.3) SCS Runoff Curve CN = 75 (AMC II) for the one percent

probability flood (4).

TABLE 3

ELEVATION, SURFACE AREA, STORAGE, AND DISCHARGE RELATIONSHIPS

Elevation Lake Surface Lake Storage Spillway(feet-msl) Area (acres) (acre-ft) Discharge (cfs)

*689.0 4.5 46 0690.0 5.7 52 21

*Spillway Crest Elevation**Top of Dam Elevation

The relationships in Table 3 were developed from the Eureka, Missouri.7.5 minute quadrangle map and the field measurements.

A-3

TABLE 4

SPILLWAY RATING CURVE

Reservoir SpillwayElevation (ft-msl) Discharge (cfs)

*689.0 0

689.5 4689.8 12

*":%-690.0 21

*Spillway Crest Elevation" Top of Dam Elevation

METHOD USED:

Spillway releases were computed by HEC-I from spillway geometrydata input on $L and $V cards. Discharges through the spillwayfor the probable maximum flood and for 50 percent of the probablemaximum flood were determined by the equations for flow over anon-level crest.

dc = 2/3 (Hm + 1/4 AY)

A = 1/2 T (2d - Ay)c

Q = (A3g/T)0 .

5

where:

d = critical depth (feet)C

H = available specific energy which is takento be the height of the water surface in the

reservoir above the bottom of the section (feet)AY = change in elevation across the section (feet)A = flow area (sq. ft.)T = top width (feet)Q = flow (cfs) 2g 32.2 ft/sec = acceleration due to gravity.

A-4

TABLE 5

RESULTS OF FLOOD ROUTINGS

Ratio Peak Peak Lake Total Peak Depth Durationof Inflow Elevation Storage Outflow (ft.) (hrs.)PMF (cfs) (ft.-msl) (ac.-ft.) (cfs) Over Top Over Top

of Dam of Dam

0 *689.0 46 0 - -

0.15 114 690.0 52 21 0 0

0.50 379 690.9 57 212 0.9 5.6

1.00 757 691.4 59 531 1.4 7.2

Spillway Crest Elevation

A-5

BIBLIOGRAPHY

(1) U.S. Army Corps of Engineers, Hydrologic Engineering Center, FloodHydrograph Package (HEC-I), Dam Safety Version, July 1978, Davis,California.

(2) HMR-33, Seasonal Variations of Probable Maximum Precipitation, Eastof the 105th Meridian for Areas 10 to 1000 Square Miles and Durationsfrom 6 to 48 Hours, U.S. Department of Commerce, NOAA, NationalWeather Service, 1956.

(3) EM-llI0-2-1411, Standard Project Flood Determinations, U.S. ArmyCorps of Engineers, 26 March 1952.

(4) U.S. Department of Agriculture, Soil Conservation Service, NationalEngineering Handbook, Section 4, Hydrology, August 1972.

(5) U.S. Army Corps of Engineers, St. Louis District, Hydrologic/Hydraulic Standards, Phase I Safety Inspection of Non-Federal Dams,12 December 1979.

(6) U.S. Department of the Interior, Bureau of Reclamation, Design ofSmall Dams, 1974, Washington, D.C.

(7) U.S. Department of Agriculture, Soil Conservation Service, SoilSurvey Interpretations and Field Maps, 1980.

(8) Mary H. McCracken, Missouri Division of Geological Survey, GeologicMap of Missouri, 1961.

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