Dams Design

IOWA DEPARTMENT OF NATURAL RESOURCES

Technical Bulletin No. 16

December, 1990

DESIGN CRITERIA AND GUIDELINES

FOR

IOWA DAMS

DNR TB-16 December, 1990Design Criteria and Guidelines for Iowa Dams

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IOWA DEPARTMENT OF NATURAL RESOURCES

TECHNICAL BULLETIN NUMBER 16

FLOODPLAIN MANAGEMENT PROGRAMDESIGN CRITERIA AND GUIDELINES FOR IOWA DAMS*

CONTENTS

Chapter Title Page

I Introduction . . . . . . . 2

II Hazard Classification . . . . . . 2

III Design Floods . . . . . . . 3

IV Hydraulic and Structural Criteria and Guidelines forSpillways . . . . . . 5

V Embankments . . . . . . . 7

VI Special Requirements for Major Dam Structures . . 8

VII Specifications . . . . . . . 9

VIII Dam Breach Wave Analysis . . . . . 9

IX Operating Plan . . . . . . 10

X Lands, Easements, Rights-of-Way . . . . 11

XI Hydrologic and Hydraulic Design References . . 11

* Adopted by reference 567—72.3(1)”a”, Iowa Administrative Code


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CHAPTER IINTRODUCTION

The purpose of this bulletin is to set forth technical designcriteria and guidelines that the Department of NaturalResources will use in reviewing applications to obtain apermit for construction, operation and maintenance ormodification of a dam. Other requirements which must bemet in order to secure such a permit are outlined in theIowa Administrative Code under agency number 567.Several chapters of the department’s administrative rulesin 567 Iowa Administrative Code concern the construction,operation and maintenance of dams as follows:

Chapter 70 contains definitions of terms used inother chapters.

Chapters 50, 51 and 52 concern water permitswhich must be obtained to authorize storage ofwater in surface impoundments.

Chapter 71 explains when approval is required inorder to construct, modify, operate and maintaindams.

Chapter 72 lists criteria for approval of damprojects.

Chapter 73 concerns operational procedures fordams, fluctuation of water levels inimpoundments, abandonment and removal ofdams, inspections of dam sites and dams, anddesignation of unsafe dams. Chapter 73 appliesto all dams whose dimensions or effects exceedthe regulatory thresholds in Chapter 71.

Copies of the department’s administrative rules may beobtained from the Records Center, Department of NaturalResources, Wallace State Office Building, Des Moines,Iowa 50319, upon request.

The above-described rules should be consulted whenplanning to construct or modify a dam, change theoperation or use of a dam, or abandon or remove a dam.This bulletin is part of the above-described rules and isintended for use in conjunction with them. The chaptersentitled “Hazard Classifications” and “Lands, Easements,Rights-of-Way” are substantively identical to rulespublished in the Iowa Administrative Code. These non-technical criteria are repeated in this bulletin for theconvenience of the user.

Minimum requirements in this bulletin are labeled as“guidelines” or “criteria” depending on the frequency withwhich they are likely to be relevant to the safety of aparticular type of structure. The distinction betweencriteria and guidelines is not intended to be rigid. When

the applicability of a criterion or guideline to aparticular project is not clear to the design engineer, theengineer should consult the department. Any permitissued by the department must explain the reasons forwaiving conformity with a criterion or guidelinedetermined to be applicable to the type of structureproposed.

Adoption and Amendment of Bulletin #16. Thisbulletin has been adopted as part of the department’sadministrative rules. Pursuant to Section 17A.6(3),Code of Iowa, this bulletin is not published in the IowaAdministrative Code but copies will be made availableto the public upon request at no more than the cost ofreproduction.

This bulletin may be amended from time to time byrulemaking proceedings. Amended editions of thisbulletin will be identified in Chapter 72 of thedepartment’s rules by reference to the year and monththat the new, superseding edition becomes effective.The user should obtain a copy of current departmentalrules as published in the Iowa Administrative Code andcompare the edition date on the cover page of thisbulletin with the edition date identified in the rules.

CHAPTER IIHAZARD CLASSIFICATION1

Dams shall be assigned a hazard class based on thepotential consequences of failure. Anticipated futureland and impoundment use shall be considered in thedetermination of hazard class. The criteria in thischapter shall be used to determine hazard classregardless of the methodology used in engineeringdesign of a dam. The hazard class shall determine thedesign requirements of the structure as outlined in thisbulletin. The hazard class shall be evaluated using thefollowing criteria.

A) Low Hazard. Structures located inareas where damages from a failurewould be limited to loss of the dam,loss of livestock, damages to farmout-buildings, agricultural lands, andlesser used roads, and where loss ofhuman life is considered unlikely.

B) Moderate Hazard. Structures locatedin areas where failure may damageisolated homes or cabins, industrialor commercial buildings, moderatelytraveled roads or railroads, interrupt

1 This chapter is substantively identical to 567—72.3(2)”a”, Iowa Administrative Code.


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major utility services, but withoutsubstantial risk of loss of human life.

In addition, structures where the damand its impoundment are of themselvesof public importance, such as damsassociated with public water supplysystems, industrial water supply orpublic recreation, or which are anintegral feature of a private developmentcomplex, shall be considered moderatehazard for design and regulatorypurposes unless a higher hazard class iswarranted by downstream conditions.

C) High Hazard. Structures located in areaswhere failure may create a serious threatof loss of human life or result in seriousdamage to residential, industrial orcommercial areas, important publicutilities, public buildings, or majortransportation facilities.

D) Multiple Dams. Where failure of a damcould contribute to failure of adownstream dam or dams, the minimumhazard class of the dam shall not be lessthan that of any such downstreamstructure.

CHAPTER IIIDESIGN FLOODS

A dam will be required to safely accommodate or passcertain minimum flood events. Routings of the floodhydrograph through the impoundment should begin at anelevation no lower than the normal operating level. Themagnitude or frequency of the required flood dischargeswill vary with the hazard classification, size, and drainagearea of the project.

A) Freeboard Design Flood

The specified freeboard design floodrepresents the greatest flood the dammust be designed to accommodate. Theflood must be passed withoutovertopping of the dam and endangeringits safety or the dam must be designed towithstand such overflow. Some erosiondamage in earth emergency spillwayswill be tolerated, provided the safety ofthe dam would not be compromised.

For dams with emergency spillways, thetop of dam elevation after settlementshall not be less than the highest peakpool elevation reached during the

freeboard design flood. For damswithout an emergency spillway, thetop of dam elevation shall be two feethigher than the peak flood elevationexpected to occur during passage ofthe freeboard design flood, unless itis specifically designed to withstandthe overflow.

In the following circumstances, theindicated freeboard design flood willbe used:

1) All high hazard dams: theprobable maximum flood(PMF).

2) All moderate hazard dams,and low hazard damsclassified as majorstructures: one-half (0.5) ofthe probable maximumflood (a flood hydrographproduced by multiplying theordinates of the PMFhydrograph by a factor of0.5).

3) Low hazard dams notclassified as majorstructures:

a. Where the height of theemergency spillwaycrest* measured abovethe elevation of thechannel bottom at thecenterline of the dam(in feet) multiplied bythe total storage volume(in acre-feet) to theemergency spillwaycrest elevation* isbetween 3,000 and30,000, the flood shallcorrespond to therainfall calculated fromthe following formuladeveloped by theUSDA SoilConservation Service.

Rainfall = P100 + 0.12(PMP – P100)

b. Where the height of theemergency spillwaycrest* measured above


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the elevation of the channelbottom at the centerline ofthe dam (in feet) multipliedby the total storage volume(in acre-feet) to theemergency spillway crestelevation* is less than3,000, the flood shall bethat resulting from the 50-year, 24-hour precipitation.

B) Principal Spillway Design Floods andDischarge Capacity

The principal spillway is normally aconcrete or metal conduit or structurewhich conveys water through or aroundthe dam. Its size and discharge capacityare governed primarily by the followingfactors: the need to control flooddischarges downstream from the dam,and the need to limit both the depth towhich floodwaters are impounded andthe length of time for which they areimpounded. Related to these factors isthe need to limit the frequency ofoperation of emergency spillways.

Except where special considerationsmust be addressed, the criteria listedbelow shall apply to the design ofprincipal spillways. The design floodsindicated must be passed by the principalspillway without need for operation of anemergency spillway.

1) Design Floodsa. High hazard dams – the 100-

year flood.

b. Moderate hazard dams – the 50-year flood.

c. Low hazard dams with drainageareas of 250 acres or more – the25-year flood.

d. Low hazard dams with drainageareas less than 250 acres – the10-year flood.

2) The spillway discharge capacityshall be sufficient to evacuate atleast 80% of the volume of watertemporarily stored during theprincipal spillway design floodwithin 10 days.

Where this cannot beaccomplished, the emergencyspillway and freeboard designflood routings shall be madebeginning with the impoundmentlevel at the 10-day drawdownelevation.

3) For dams with emergencyspillways of structural concreteor which are excavated intosound rock, a higher frequencyof use, and therefore a lowerprincipal spillway design flood,may be permitted if flood controlor dam safety would not beadversely affected.

*For dams without emergency spillways, the storagevolume and height shall be determined by measuring tothe top of dam elevation.

C) Rainfall Depth and Distribution

Precipitation values for variousfrequency storm events: 10, 25, 50,100-year and PMP are contained inthe Iowa Department of Agricultureand Land Stewardship publication,Climatology of Iowa Series #2,Revised, Iowa Rainfall Frequenciesby Paul Waite. Ten-day rainfallamounts are contained in theNational Weather Servicepublication, Technical Paper No. 49.

Some acceptable methods ofdistributing the rainfall in Iowa arefound in the U.S.D.A. SoilConservation Service publication,TR-60, Earth Dams and Reservoirs;and the Illinois State Water Surveypublication, Time Distribution ofRainfall In Heavy Storms by F. A.Huff.

D) Rainfall Losses

Conservative loss rates (interception,infiltration, etc.) and antecedentmoisture conditions should be usedin computing rainfall excess. Also,when applicable, snowmelt runoffrates should be estimated.

The Soil Conservation Service (SCS)weighted curve number method isacceptable for determining rainfall


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losses and is explained in NationalEngineering Handbook Section 4Hydrology, SCS, 1972.

E) Storm Duration

Criteria and guidelines for developingdesign storms from rainfall events are asfollows:

1) The critical duration storm orthe storm which results in thehighest water level in theimpoundment, shall be used indetermining the freeboarddesign flood for a high hazarddam.

2) Six hour storms arerecommended for determiningthe freeboard design flood fordams designated in paragraphsA (2) and A (3)”a” of thischapter except where the timeof concentration exceeds sixhours. The 24-hour storm isrecommended for damsdesignated in paragraph A(3)”b” of this chapter.

3) Twenty-four hour (24-hour) or10-day storms arerecommended for developingprincipal spillway designfloods.

CHAPTER IVHYDRAULIC AND STRUCTURAL CRITERIAAND GUIDELINES FOR SPILLWAYS

The following criteria and guidelines are designconsiderations which will be used by the department toinsure that spillway structures are capable of functioningsafely and efficiently and of resisting the forces to whichthey may be exposed during the life of the structure.

A) Spillways should be designed to operatesafely for the life of the structure and atthe discharges and pressures whichwould be experienced under all normalor flood flow conditions including thefreeboard design flood.

B) Anti-seepage collars or other means ofpiping and seepage control (e.g.,drainage diaphragms), anti-vortex

devices, trash racks or other inletdebris control measures, and outletstilling basins should be provided forall conduits unless evidence can bepresented establishing they are notnecessary.

C) For dams where a conduit isproposed to serve as the principalspillway, suggested minimum sizesof the principal spillway conduit forthe indicated type of structure are asfollows:

1) High hazard dams andmoderate dams classed asmajor structures – 36-inchinside diameter.

2) Moderate hazard dams notclassed as major structuresand low hazard dams, whichare classed as majorstructures – 24 inch insidediameter.

3) Low hazard dams notclassed as major structuresbut which have drainageareas of 250 acres or more –18-inch inside diameter.

4) Low hazard dams withdrainage areas under 250acres – 12-inch insidediameter.

These minimum sizes areapplicable to dams withemergency spillways orwhich are designed forovertopping only. For damswithout emergencyspillways, substantiallylarger conduit sizes withspecial provisions againstplugging will normally berequired.

D) Drop inlets (risers) should have aninlet cross-sectional area at least 1.5times that of the conduit and shouldbe constructed of comparablematerials.

E) Conduits and risers should be ofsufficient strength and have adequatejoints to withstand all anticipated


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external and internal pressures withoutdamage or leakage, with provisionsmade for vertical settlement. Conduitsshould be cambered where significantsettlement of the overlying embankmentis anticipated. Articulated or bell jointsshould be provided as necessary toaccommodate the maximum elongationestimated to occur during the life of thestructure. Risers must be designed tocounteract buoyant forces.

F) Corrugated metal pipe conduits andrisers should be close riveted withwatertight connecting bands and shouldbe fiber bonded, asphalt coated, or givenequivalent protection. Cathodicprotection shall be provided in corrosivesoils. Corrugated metal pipe (CMP)conduits are not recommended for highhazard dams, moderate hazard damsclassed as major structures, or where theheight of earth fill over the conduitexceeds 25 feet.

G) Concrete conduit and drop inlet (riser)design using precast pipe sections shouldspecify reinforced concrete pressurepipe.

H) Open concrete spillways, concrete boxconduits, and concrete flumes or chutesshould have longitudinal curbs or raisedjoints which will prevent contact bynormal flows with the construction jointbetween the floor and wall slabs.Seepage barriers, drainage blankets anddrains should be installed where neededto maintain hydraulic flow integritythrough the structure and toaccommodate anticipated settlement orelongation in the longitudinal ortransverse directions.

I) Emergency spillways should be capableof safely conveying excess flood flowsaround or through the dam. They shouldnot operate except at floods greater thanthe principal spillway design flood.

J) Earth emergency spillways should besubject to the following minimumrequirements at the control section:

1) Minimum bottom width – 10feet.

2) On major structures,minimum depth – 3 feet.On other structures,minimum depth – 2 feet.(Elevation of top of damminus elevation ofemergency spillway crest.)

3) The profile through theemergency spillway shouldbe horizontal for at least 30feet through the crestcontrol section.

4) Exit channel slopes shouldnot be less than 1% orgreater than 10%, butshould provide formaintaining critical depthcontrol at the crest.

K) For dams where substantial erosionin the emergency spillway wouldpose the risk of a dam failure, theflow velocities during the freeboarddesign flood should be non-erosive.Where such erosion would pose nosubstantial risk of failure, the flowvelocities should be non-erosive atthe discharge which occurs whenflow through the control section is at30% of the maximum depth. Onvegetated spillways, the non-erosivevelocity should be determinedassuming the vegetation is wellestablished.

L) Emergency spillways should beconstructed in undisturbed soilwherever possible. Where no viablealternative is available, they may beconstructed on fill as a rampspillway.

M) Smooth transitions in horizontal andvertical alignment should beprovided at and between the inlet, thecontrol at the crest and the outletsections of emergency spillways.

N) All spillways should discharge a safedistance from the toe of the dam, andthe inlets and outlets should be solocated and aligned as to minimizerisk of erosion damage to the dam orof damage to downstream buildings,roads, dams or other structures.


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O) An adequate energy dissipation structure(stilling basin) or an alternativeacceptable method should beincorporated at the outlet of all structuralspillways. On major structures, upliftanalysis and arching requirements shouldbe considered.

CHAPTER VEMBANKMENTS

The earth embankment of a dam should be designed andbuilt according to the following criteria and guidelines.

A) Foreslopes and Backslopes.Embankments should be built of suitablematerials and with stable slopes.Foreslopes should not be steeper than 3:1(horizontal to vertical) in till or loesssoils below the permanent water level.Above the permanent water level,foreslopes should not be steeper than2.5:1 in till soil or 3:1 in loess soil.Backslopes should not be steeper than2.5:1 in till soils or 3:1 in loess soils.Steeper foreslopes or backslopes may beused if justified by soil tests and stabilityanalysis.

B) Settlement Allowance. A minimumvertical settlement allowance of fivepercent of the depth of fill should beprovided unless a lesser amount isjustified by soil tests.

C) Top Width. The minimum embankmenttop width should be 14 feet for dams 25feet high or higher. As a rule of thumb,the top width could be reduced by twofeet for every five feet of reduction in theheight of the dam to a minimum width ofeight feet. The top width of dams withroads across the crest should beconsistent with normal roadway designpractices, including roadway andshoulders.

D) Core Trench. Core trenches should belocated approximately along thecenterline (axis) of the earth fill. Itshould be continuous across the base ofthe fill extending into and up the sideslopes of the dam abutments to normalreservoir level. The core trench shouldbe excavated to a minimum depth of fivefeet or until a suitable base material isreached. The base width should be that

which will accommodate excavatingequipment, but not less than eightfeet. The side slopes of the coretrench should not be steeper than 1:1,regardless of depth or width of base.Impervious material shall be used inbackfilling the core trench.

E) Wave Erosion Protection. On theupstream face of the dam, ahorizontal bench or berm at least 10feet wide usually should be providedat the normal pool elevation to limitdamage from wave erosion. Onlarger impoundments, riprap or otherphysical means of protection shouldbe considered whether or not theberm is provided.

F) Site Preparation. All vegetation, sod,stumps, and large roots should beremoved from the embankment site,and the ground surface scarified toprovide bond with the earth fill.Overhanging banks, pits, or holesshould be sloped and graded soslopes do not exceed 1:1, and anyother sharp discontinuities in theground surface shall be smoothed.Special consideration should begiven to the removal of sandy ormucky deposits unless otherwiseprovided for in the design.

In till soils, topsoil should be savedand placed as a surface layer over thefinished embankment to provide anadequate seed base in establishingvegetation.

G) Fill. Fill material should be cleanearth containing no appreciableamounts of vegetation, large rock,frozen material or other foreignsubstances. Fill should not be placedon a frozen foundation or in freezingweather.

Moisture content of the fill should besufficient to assure adequatecompaction. A moisture contentslightly higher than optimum isrecommended. An above optimummoisture content is desirable fromthe standpoint of providing a moreplastic embankment capable ofresisting greater differentialsettlement without experiencing


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potentially hazardous cracking. Unlessotherwise specified after soil testing, fillshould be placed in horizontal lifts notexceeding eight inches extending overthe entire fill area and compacted by notless than four overlapping passes bysheepsfoot or rubber tired rollers.Smooth steel rollers or passes bycaterpillar tracks are not consideredadequate for compaction of earth-filldams. The surface of the fill should bescarified or roughened if sufficient timeelapses between lifts for a crust todevelop.

Backfill adjacent to spillway structuresand anti-seep collars should be carefullyplaced and compacted by handequipment. Heavy equipment shall notpass over conduit structures until twofeet of compacted earth cover is in place.

H) Drains. Internal seepage control drainsare recommended for all dams and arenormally required on major structuresunless soils investigation finds they arenot needed. Drains should be capable ofpreventing saturation of the downstreamportion of the embankment byintercepting any seepage through the fillor the foundation and any seepage alongstructural spillways or conduits.

If springs are encountered during sitepreparation, drains should be provided toallow a controlled outlet.

I) Seeding. As soon as possible after earthfill for the embankment is completed, theembankment and any other exposedareas should be seeded. Mulch or othermeans of erosion control can be placedas part of seeding and maintained untilvegetation is established. Grass orvegetative species selected for useshould be appropriate for the soils andconditions expected at the site. Crownvetch is generally not acceptable for damembankments or emergency spillways.

J) Riprap. Riprap shall be designed for itsexpected use and anticipated watervelocities. All riprap should be placedon a properly designed bedding unlessthe gradation of the underlying basematerial is such that it will not infiltratethrough the riprap, or an acceptable filterfabric is used.

K) Groins. Where the embankmentforeslopes and backslopes intersectthe natural or modified abutmentslopes, appropriate groin design anderosion control recommendationsshould be provided.

Embankments composed of concrete, rock, or othermaterials, as associated with gravity, rockfill and archdams, designed in accordance with standards by theU.S. Army Corps of Engineers, U.S.D.A. SoilConservation Service, or the U.S. Bureau ofReclamation are generally acceptable. These types ofdams are not normally constructed in Iowa.

CHAPTER VISPECIAL REQUIREMENTS FOR MAJORDAM STRUCTURES

Because of the size, public importance, or potentialhazard of a major dam structure, a higher level ofinvestigation, design and assurance of properconstruction is needed. A major dam structure isdefined as a dam meeting any of the following criteria.

1. Any high hazard dam.

2. Any moderate hazard dam with apermanent storage exceeding onehundred (100) acre-feet or a total ofpermanent and temporary storageexceeding two hundred fifty (250)acre-feet at the top of the damelevation.

3. Any dam, including low hazarddams, where the height of theemergency spillway crest measuredabove the elevation of the channelbottom at the centerline of the dam(in feet) multiplied by the totalstorage volume (in acre-feet) to theemergency spillway crest elevationexceeds 30,000. For dams withoutemergency spillways, thesemeasurements shall be taken to thetop of dam elevation.

As a condition of permit approval, the following itemswill be required for major dam structures.

A) A soils and foundation investigationshall be made which includes theevaluation of slope stabilityrequirements, anticipated vertical


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settlement and horizontal elongation,seepage and under-seepage potential,whether cathodic protection is neededfor metal pipes, and proper constructionpractices for the soil types andconditions encountered. Stabilityevaluation shall include end ofconstruction, steady state seepage andsudden drawdown conditions.

B) Anticipated sedimentation rates and theirimpact on the life and usefulness of theimpoundment shall be investigated.Sediment storage shall be provided in thevolume necessary for continuation ofdesign uses of the impoundmentthroughout its design life.

C) A gated low level outlet shall beprovided which is capable of draining atleast 50 percent of the permanent storagebehind the dam within a reasonablelength of time. The pipe conduits shallbe designed so that negative pressureswill not occur at any point along thesystem.

D) In order to assess the degree of threat tolife and property located downstream ofthe dam, a dam breach analysis may berequired. The analysis will be made todetermine the most adverse failurecondition and the resulting peakoutflows and water surface elevationsdownstream of the dam following failureof the dam during the freeboard designstorm.

E) Construction shall be inspected by anengineer registered under Chapter 114 ofthe Code of Iowa or by a trainedinspector under the supervision of theengineer. The engineer shall prepare andcertify as-built plans after completionand a report detailing any unusualcircumstances encountered duringconstruction and submit them to theDepartment of Natural Resources,ATTN: Flood Plains.

F) The applicant, as a condition of thepermit, shall submit an annualmaintenance and inspection report. Thereport shall describe maintenance workdone since the previous annual report,describe any deficiencies observed in thedam or appurtenant structures, detail theremedial measures necessary and the

method and time the applicantproposes to correct the deficienciesfound. If there is a change in theland use downstream of the dam, thischange should be noted on the annualmaintenance and inspection report.The applicant may also be required toprovide additional inspections andreports by an engineer or otherqualified personnel.

CHAPTER VIISPECIFICATIONS

When detailed project specifications are prepared, theyshould include the following information.

A) The general provisions which specifythe rights, duties, and responsibilitiesof the owner, applicant, applicant’sengineer, and builder or contractor,and the prescribed order of the work.

B) The technical provisions whichdescribe approved work methods,equipment, materials and desired endresults.

C) Special provisions as may berequired which describe thosetechnical details that are not usuallycontained in standard technicalprovisions.

CHAPTER VIIIDAM BREACH ANALYSIS

A) In some cases, it will be necessary toevaluate the consequences of a damfailure to verify hazard classificationor adequacy of design. A specialcase of dam breach analysis willinvolve failure or improper operationof flood control gates or otherstructures.

B) Where such evaluations are made bythe department’s staff, the necessarydata will be obtained fromtopographic maps or other availableinformation. If that information isnot adequate, the applicant may berequired to obtain additionaldownstream survey data.


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C) Prediction of the downstreamconsequences of a hypothetical dambreach requires several component steps:development of the impoundment inflowhydrograph; routing the hydrographthrough the impoundment; selectingfailure conditions for the structure;calculating the outflow hydrograph fromthe failed structure; and modelingmovement of the flood wavedownstream to determine travel time,inundated areas, maximum water surfaceelevations, etc.

D) The criteria, methodology, and computerprograms developed by the U.S. Corpsof Engineers, the National WeatherService, the U.S.D.A. Soil ConservationService, and the U.S. Geological Surveyfor simulating a hypothetical dam failureare, in general, acceptable.

CHAPTER IXOPERATING PLAN

For any dam with gates or other moveable structures whichmust operate or be operated during times of flood or toprovide a minimum downstream release rate, a writtenoperating plan shall be prepared. Development of such aplan is considered part of the design process. Thefollowing shall be addressed in preparation of theoperating plan.

A) Responsibility

No operating plan can be expected towork properly unless it can be assuredthe necessary personnel will be presentto operate the equipment, or, in the caseof automatic equipment, to monitor itand insure it is functioning properly.

The plan shall identify who isresponsible for operating and monitoringthe equipment and provide means toassure the necessary personnel arepresent when needed.

B) Operating Circumstances

The circumstances under whichoperation must occur shall be clearlydefined, and a means provided to insurethat operating personnel are presentwhen necessary.

C) Method of Operation

The means and methods by whichoperation is to be conducted shall beclearly defined. Included shall besuch items as rates and sequences foropening or closure of gates, poollevel vs. gate setting tables, etc., asrequired.

The operating plan shall allow forsafe passage of all floods up to andincluding the freeboard design flood.Flood discharges through the damgreater than the design peak floodinflows into the impoundment shallnot be permitted. In design andanalysis, due consideration shall begiven to the potential impacts of theoperating procedure on bothdownstream and poolside lands.

The plan should also address lowflow situations and should specify aminimum release rate and how it willbe provided and maintained.

Consideration shall also be given toand allowance made for the possiblefailure of or malfunctioning of theequipment.

D) Discharge Measurement

A means shall be provided todetermine the discharge through thecontrol structures, especially whereoperation is to maintain a minimumdownstream flow. Control setting vs.discharge tables, streamflow gages orother means of obtaining dischargereadings shall be provided. Thesettings of control structures shall beeasily read.


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CHAPTER XLANDS, EASEMENTS, RIGHTS-OF-WAY*

The determination of lands, easements, and rights-of-wayrequired for the construction, operation and maintenanceof a dam project are considered part of the design process.An application for approval of a dam project shall includeinformation showing the nature and extent of lands,easements, and rights-of-way, which the applicant hasacquired or proposes to acquire for the project.Acquisition of lands, easements or rights-of-way forconstruction, operation, and maintenance of a dam projectshall be consistent with the following criteria.

A) Ownership or perpetual easements shallbe obtained for the area to be occupiedby the dam embankment, spillways andappurtenant structures, and thepermanent or maximum normal pool.

B) Ownership or easements shall beobtained for temporary flooding of areaswhich would be inundated by the floodpool up to the top of dam elevation andfor spillway discharge areas.

C) Easements covering areas affected bytemporary flooding or spillwaydischarges shall include provisionsprohibiting the erection and usage ofstructures for human habitation orcommercial purposes without priorapproval by the Department of NaturalResources.

D) In locating the site of a dam and inobtaining easements and rights-of-way,consideration should be given to theimpacts which changes in land usedownstream of a dam and adjacent to theimpoundment could have on the hazardclass of the dam, the operation of thedam, and the potential liability of thedam owner.

E) The applicant may be required to acquirecontrol over lands downstream from thedam as necessary to prevent downstreamdevelopment which would affect thehazard class of the dam.

*This chapter is substantively identical to 567—72.3(2)”b”, Iowa Administrative Code.

CHAPTER XIHYDROLOGIC AND HYDRAULIC DESIGNREFERENCES

General

Handbook of Applied Hydrology by Ven Te Chow,McGraw-Hill Book Company, 1964.

Handbook of Applied Hydraulics by David andSorensen, McGraw-Hill Book Company, 1969.

Handbook of Hydraulics by King and Brater, McGraw-Hill Book Company, 1963.

Water Resources Engineering by Linsley and Franzini,McGraw-Hill Book Company, 1963.

U.S. Department of Interior, Bureau of Reclamation

Design of Arch Dams , 1977.

Design of Gravity Dams , 1976.

Design of Small Canal Structures, 1974;Revised Reprint, 1978.

Design of Small Dams , 2nd Edition, 1973;Revised Reprint, 1977.

Discharge Coefficients for Irregular OverfallSpillways, Engineering Monograph No. 9,1952.

Hydraulic Design of Stilling Basins andEnergy Dissipators, Engineering MonographNo. 25, 1978.

Unitgraph Procedures, 1965.

Interim Guidelines for Preparing InundationMaps for Areas Downstream of Bureau ofReclamation Dams.

Corps of Engineers

Engineering Manuals (EM):

EM 1110-2-1411 Standard Project FloodDeterminations.

EM 1110-2-1602 Hydraulic Design ofReservoir Outlet Structures.

EM 1110-2-1603 Hydraulic Design ofSpillways.


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EM 1110-2-1908 Instrumentation of Earth andRockfill Dams.

EM 1110-2-2200 Gravity Dam Design.

EM 1110-2-2300 Earth and Rockfill DamsGeneral Design and Construction Considerations.

EM 1110-2-50 Low Level Discharge Facilitiesfor Drawdown of Impoundments.

EM 1110-2-1450 Hydrologic FrequencyEstimates.

ETL 1110-2-221 Wave Runup and Wind Setupon Reservoir Embankments.

Mining Enforcement and Safety Administration

Engineering and Design Manual, Coal RefuseDisposal Facilities, 1975.

Soil Conservation Service

National Engineering Handbook:

Section 4 – Hydrology

Section 5 – Hydraulics

Section 11 – Drop Spillways

TR-39 Hydraulics of Broad-Crested Spillway

TR-48 Computer Program for ProjectFormulation-Structure Site Analysis “DAMS-2”

TR-49 Criteria for the Hydraulic Design ofImpact Basins

TR-52 A Guide for Design and Layout of EarthEmergency Spillways

TR-55 Urban Hydrology for Small Watersheds

TR-59 Hydraulic Design of Riprap GradientControl Structures

TR-60 Earth Dams and Reservoirs

TR-61 Computer Program for Water SurfaceProfiles

TR-66 Simplified Dam Breach Routing Procedure

DN-8 Entrance Head Losses in Drop-InletSpillways

SMN-1 Tentative Guides for Determining theGradation of Filter Materials

National Weather Service

Technical Paper No. 40 – Rainfall FrequencyAtlas of the United States (for Duration from30 minutes to 24 hours and Return Periodsfrom 1 to 100 years), 1961.

Technical Paper No. 49 – Two to Ten DayPrecipitation for Return Periods of 2 to 100Years in the Contiguous United States, 1964.

Hydrometeorological Report No. 51 –Probable Maximum Precipitation Estimates,United States East of the 105th Meridian, June1978.

DAMBRK: NWS Dam-Break FloodForecasting Model, November 1979.

Illinois State Water Supply

Precipitation Relations for Use in Dam SafetyProject by Floyd Huff, 1980.

Time Distribution of Rainfall in Heavy Stormsby Floyd Huff, 1967.

Iowa Department of Agriculture and Land Stewardship

Climatology of Iowa Series #2, Revised, IowaRainfall Frequencies by Paul Waite, 1988.

Climatology of Iowa Series No. 3 – Iowa’sGreatest 24-Hour Precipitation and RelatedStorm Data by Paul Waite and Paul Jaeger,1981.

United States Geological Survey

Bulletin No. 7 – Drainage Areas of IowaStreams by O.J. Larimer, Reprinted, March1974.

Bulletin No. 12 – Floods in Iowa, AComparative Study of Regional FloodFrequency Methods by Oscar G. Lara, 1974.

Water Resources Investigation Report 87-4132 – Method for Estimating The Magnitudeand Frequency of Floods at Ungaged Sites onUnregulated Rural Stream In Iowa, by OscarG. Lara, 1987.


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Federal Highway Administration

Hydraulic Engineering Circulars:

HEC No. 10 – Capacity Charts for the HydraulicDesign of Highway Culverts, November 1972.

HEC No. 11 – Use of Riprap for Bank Protection,June 1967.

HEC No. 13 – Hydraulic Design of ImprovedInlets for Culverts, August 1972.

HEC No. 14 – Hydraulic Design of EnergyDissipator for Culverts and Channels , December1975.

HEC No. 15 – Design of Stable Channels withFlexible Linings, October 1975

Hydraulic Design Series No. 1 – Hydraulics ofBridge Waterways, 2nd Edition, 1970.

Hydraulic Design Series No. 3 – Design Chartsfor Open Channel Flow, 1973.

Hydraulic Design Series No. 4 – Design ofRoadside Drainage Channels , 1965.

Hydraulic Design Series No. 5 – Design ofHighway Culverts, September 1985.

Agricultural Research Service

The SAF Stilling Basin, 1959.Hydraulics of Closed Conduit Spillways, Parts I –XVII.

Dams Design

Documents

Transcript of Dams Design