Living With Dams: Know Your Risk April 2012 I
Living with Dams: Know Your Risk April 2012 I
“Fact or Fiction” – Common Beliefs about DamsFictionFact“The Army Corps of Engineers isresponsible for most of the damsin the U.S.”State dam safety programs have oversight of most dams in the U.S.“Dams are like roads and bridges.The government takes care of them.”Most dams are privately owned. Dam owners are responsible formaintenance and upgrades.State agencies regulate more than 80% of the nation’s dams.Private dam owners are responsible for more than 65% of the nation’sdams. Many lack the financial resources necessary for adequate dammaintenance.“There are only a few dams in mystate.”There are more than 85,000 dams in the U.S. Most states are hometo hundreds – or thousands – of dams of regulatory criteria.Texas has the most dams – more than 7,000 – followed by Kansas(6,087), Missouri (5,099), Oklahoma (4,755), and Georgia (4,606).[2010 data]Mississippi, North Carolina, and Iowa each have more than 3,000dams.Five states – Alabama, Montana, Nebraska, South Carolina, andSouth Dakota – each have more than 2,000 dams.More than 1,000 dams are in each of 15 additional states.Of all states, Delaware has the fewest number of dams, with 86.“That dam has been here for years –it’s not going anywhere.”Advancing age can make dams more susceptible to failure.The average age of dams in the U.S. is more than 53 years old.As dams get older, deterioration increases and repair costs rise. Somecommon problems of older dams are:Deteriorating metal pipes and structural components—after 50years, metal rusts and fails.Sediment-filled reservoirs. Some sediment may have contaminantsfrom chemicals in runoff from upstream areas.Subdivisions and businesses built upstream—roofs and concretestreets and sidewalks increase the volume of runoff to thereservoir.II Living with Dams: Know Your Risk April 2012
Could my life and property be affectedby a nearby dam?Dams provide drinking water, hydroelectric or waterpower, flood control, recreation and many other benefitsto people or local economies. But dams can posesignificant risks to people living downstream should theyfail.There are dams in every U.S. state. It is important to knowif you and your loved ones live, work or recreate in areasthat may be affected by the presence of a dam and whatto do if this is the case.This booklet was created to help answer questions aboutdams: what purposes they serve, what risks are associatedwith dams and where you can get information abouthow to react if you are affected by a dam.This booklet was prepared by the Association of State Dam Safety Officials inconjunction with and through a grant from the Federal Emergency ManagementAgency.Living with Dams: Know Your Risk April 2012 1
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What Dams ProvideDams are often hidden assets but theycan also be hidden liabilities.Although dam failures areinfrequent, the impacts canbe catastrophic, often farexceeding typical stream/riverflood events.Dams provide vital benefits includingflood protection, water supply,hydropower, irrigation and recreation.Imagine the impact of losing a majorreservoir or flood control dam:Would there be catastrophicflooding? How many homes andbusinesses might be flooded? Howmany people displaced?Would there be adequate water fordomestic use? Irrigating crops? Caringfor livestock? Fighting fires?Are local utilities dependent onhydropower? How many lives andjobs could be affected by temporaryshutdown or closure of an industrydependent on hydropower?How would transportationsystems—roads, railroads, navigablewaterways—be affected?How would economies, jobs andareas dependent on recreation beaffected should the reservoir be lost?Dams can pose risks to those livingdownstream if they are not maintainedand operated correctly. Some damsincrease safety risks to an often unawarepublic when they age, deteriorate ormalfunction, releasing sudden, dangerousflood flows.There are over 85,000 dams in theU.S. Most every state has at least severalhundred dams.More than half of these dams are olderthan 50 years and many are in need ofextensive rehabilitation.4 Living with Dams: Know Your Risk April 2012Many communities in the United Statesare impacted by at least one dam. Inmany cases large populations, vitalelements of our infrastructure, jobs, andbusinesses are located downstream ofdams.When dams fail or malfunction, they canadversely affect people, their livelihoodand property.Dam failure floods are almost alwaysmore sudden and violent than normalstream, river or coastal floods. They oftenproduce damage that looks like tornadodamage.Dams are owned and operated by manydifferent types of owners. Sometimesthey only serve the interest of theowner—for instance in the case of aneighborhood association that wantsits homes built around a lake—andsometimes they serve the interest ofcommunities—for instance in the case ofa water supply utility.Downstream development affects a dam’srisk. Dams that used to be out in therural areas, affecting nothing but openfields, are now affecting neighborhoodsand industrial areas. Due to increaseddevelopment, dam failure consequenceshave become much higher. The numberof dams that pose a risk to human life issteadily increasing. In the last decade, thenumber has increased by over 1,000 to atotal of about almost 14,000. The causeof this increase is a combination of newdam construction and/or downstreamdevelopment.The point is twofold: any dam hasthe potential to adversely affectdownstream areas and lives; Manydams, should they fail, can also affectthe delivery of essential utilities or floodcontrol.
Embankment damPurposesRegulationThe purpose of a dam is to impound (store)water, or other liquid borne materials forany of several reasons, such as humanwater supply, irrigation, livestock watersupply, energy generation, containment ofmine tailings, recreation, pollution or floodcontrol. Many dams fulfill a combinationof the above functions.The vast majority of dams are regulated forsafety by state and Federal governments,much the same way as are bridges, food,drugs, factories, etc. States regulate thevast majority of dams in the U.S. (about80%). The Federal government regulatesthe remaining number.OwnershipDams are unique components of theU.S. infrastructure in that most dams areprivately owned.Dam owners are solely responsible forkeeping their dams safe and financingmaintenance, repairs and upgrades. Dammaintenance, repairs and upgrades can beexpensive. Price tags for non-Federal damrehabilitation projects commonly rangefrom 100,000 to millions of dollars perdam. Such high price tags place a hugeburden on dam owners, many of whomcannot afford to maintain their dams.Dams by Owner TypeMain Typesof DamsManmade dams may be classifiedaccording to the type of constructionmaterial used, the methods used inconstruction, the slope or cross-sectionof the dam, the way the dam resists theforces of the water pressure behind it,the means used for controlling seepage,storage characteristics (on a watercourse,off-stream, above or below ground level),and, occasionally, according to the purposeof the dam.The materials used for construction of damsinclude earth, rock, tailings from mining ormilling, concrete, masonry, steel, timber,miscellaneous materials (such as plasticPrimaryOwner Typeor rubber) and combinations of thesematerials.Embankment dams—Embankmentdams are the most common type ofdam in use today. They have the generalshape shown above. Materials usedfor embankment dams include naturalsoil or rock or waste materials obtainedfrom mining or milling operations. Anembankment dam is termed an “earthfill”or “rockfill” dam depending on whether it iscomprised of compacted earth or mostlycompacted or dumped rock. The ability ofan embankment dam to resist the reservoirwater pressure is primarily a result of themass weight, type and strength of thematerials from which the dam is made.Concrete dams—Concrete dams maybe categorized into gravity and arch damsaccording to the designs used to resistthe stress due to reservoir water pressure.The most common type of concrete damis a concrete gravity dam, shown below.The mass weight of concrete and frictionresist the reservoir water pressure. Abuttress dam is a specific type of gravitydam in which the large mass of concretePercentagePrivate69.0%Local Govt19.7%State5.1%Federal3.8%Public Utility2.0%Not Listed0.6%Concrete damLiving with Dams: Know Your Risk April 2012 5
is reduced, and the forces are diverted tothe dam foundation through vertical orsloping buttresses. Gravity and buttressdams are constructed of vertical blocks ofconcrete with flexible seals in the jointsbetween the blocks.Concrete arch dams are typically thinnerin cross-section. The reservoir water forcesacting on an arch dam are carried laterallyinto the abutments. The shape of the archmay resemble a segment of a circle oran ellipse, and the arch may be curved inthe vertical plane as well. Such dams areusually constructed of a series of verticalblocks that are keyed together; barriersto stop water from flowing are providedbetween blocks. Variations of arch damsinclude multi-arch dams in which morethan one curved section is used andarch-gravity dams which combine somefeatures of the two types of dams.Recreation – 34%Dams by PrimaryPurposeFlood Control – 16%Fire Protection, Stock or Small Fish - 15%Irrigation – 9%Water Supply – 8%Spillway Discharge andSeepageBecause the purpose of a dam is to retainwater effectively and safely, the waterretention ability of a dam is of primeimportance. Water may pass from thereservoir to the downstream side of a damby:Passing through the main spillway oroutlet worksPassing over an auxiliary spillwayOvertopping the damSeepage through dams, throughabutments or under dams.Tailings - 1%Debris Control – 1%Navigation – 1%Living with Dams: Know Your Risk April 2012Ash impoundments, or ponds, are usedto store or dispose of ash primarilyfrom the combustion of coal. Theseimpoundments are a type of wastemanagement facility consisting of anexcavated, dammed or diked reservoirin which coal ashes are stored for futureremoval or disposed of as a slurry orsludge. The coal ash solids settle outand leave water at the surface that isdischarged through a designed andmanaged outlet structure to a nearbystream, surface water or plant processwater system.Unknown – 4%Fish and Wildlife Pond – 2% Tailings dams are industrial waste damsthat impound waste materials frommining operations or mineral processing.Other – 6%Hydroelectric – 3%6Other Types of DamsOvertopping of an embankmentdam is very undesirable because theembankment materials may be erodedaway. A number of concrete dams havebeen designed to be overtopped.
Water normally passes through the mainspillway or outlet works; it should pass overan auxiliary spillway only during periods ofhigh reservoir levels and high water inflow.All embankment and most concretedams have some seepage. However, itis important to control the seepage toprevent internal erosion and instability.Proper dam construction and maintenanceand monitoring of seepage provide thiscontrol.inspectionRelease of WaterIntentional releases of water from dams areconfined to outlet works and spillways. Adam typically has a principal or mechanicalspillway and a drawdown facility.Additionally, some dams are equippedwith auxiliary spillways to safely passextreme floods.Even when operated as designed, manydams will pass huge volumes of floodwater into downstream areas.Outlet Works—In addition tospillways designed to prevent overtoppingof dams, dams contain outlet works thatallow water to be drawn continuously, oras needed, from the reservoir, and providea way to draw down the reservoir for repairor safety concerns. Water withdrawn maybe discharged into the river below thedam, run through generators to providehydroelectric power, or used for irrigation.Dam outlets usually consist of pipes, boxculverts or tunnels with intake inverts nearminimum reservoir level. Such outlets areprovided with gates or valves to regulatethe flow rate.Spillways—The most common type ofspillway is the free overflow spillway. Thisspillway may be located over or throughthe dam or an abutment. To permitmaximum use of storage volume, movablegates are sometimes installed above thespillway crest to control discharge. Manysmaller dams have a pipe and riser spillway,used to carry most flows, and a vegetatedearth or rockcut spillway through anabutment to carry infrequent high floodflows. In dams such as those on theMississippi River, flood discharges are ofsuch magnitude that the spillway occupiesthe entire width of the dam and theoverall structure appears as a successionof vertical piers supporting movable gates.High arch-type dams in rock canyonsusually have downstream faces too steepfor an overflow spillway. In Hoover Damon the Colorado River, for example, a shaftspillway is used. In shaft spillways, a verticalshaft upstream from the dam drains waterfrom the reservoir when the water levelbecomes high enough to enter the shaftor riser; the vertical shaft connects to ahorizontal conduit through the dam orabutment into the river below.Outlet WorksGroin areaSource: ODNR Division of WaterCrestEmbankmentFreeboardTrashrackDrain ermToe of damBlanket drainFoundationSheet pilingcutoffSeepagePipe conduitAnti-Seepage collerToe drainOutletStilling basinLiving with Dams: Know Your Risk April 2012 7
Dam failures or partial failures are notalways caused by storm events. Mostfall into one or more of the followingcategories:Dam failures are low probabilitybut high consequence. But, theytypically happen somewhere in theU.S. every year.While thousands of lives havebeen lost and substantial propertydamage has occurred due todam failure, good planning andimproved dam safety programs, asadvocated in this brochure, havereduced loss of life dramatically inrecent years.8 Living with Dams: Know Your Risk April 2012Near failures include:malfunction of dam components;partial dam breach;1 Structural failures - Foundationdefects, including settlement andslope instability or damage caused byearthquakes, have caused about 30%of all U.S. dam failures.auxiliary spillway flow;2 Mechanical failures –Malfunctioning gates, conduits,or valves can cause dam failureor flooding both upstream anddownstream.embankment damage or signsof distress (erosion, cracks, slides,sinkholes, settlements, or bulges).3 Hydraulic failures - Overtoppingof a dam is often a precursor of damfailure. National statistics show thatovertopping due to inadequatespillway design, debris blockage ofspillways, or settlement of the damcrest account for approximately 34%of all U.S. dam failures.principal spillway damage ormalfunction;seepage problems; andThere are thousands of dams nationwidethat are considered deficient andsusceptible to failure because of reasonscited here.Planned releasesOperation of spillways, both plannedand in emergency situations, can createflooding and public safety hazards, evenin absence of a dam failure. Duringperiods of extreme flow, dams may fillto capacity, necessitating emergencyreleases that can flood downstreamareas. People swimming and fishingdownstream of dams have been caughtin planned spillway releases, at times withtragic results. Many dams incorporatesirens to warn the public of an impendingrelease.
Recent Dam FailuresJuly 25, 2010 – Lake Delhi Dam,Delaware County, IowaThe failure drained a nine-mile recreationallake and damaged or destroyed up to 300homes.January 6, 2009 – Dam in EtowahCounty, AlabamaFloodwaters washed away a culvert and aprivate dam broke producing up to 12 ft.of flooding in the area causing residencesto be evacuated. A dozen roads werealso closed due to the floodwaters andproperty damage was reported to be 100,000*.December 22, 2008 – Kingston CoalWaste Dam, Roane County, Tennessee5.4 million cubic yards ( 1 billion gal) ofsludge damaged 12 homes and coveredhundreds of acres. Cleanup costing 1million* per day. The Kingston Dam was a40-acre pond used by the Tennessee ValleyAuthority to hold slurry of ash generatedby the coal-burning Kingston Steam Plant.The dam gave way just before 1 a.m.,burying a road and railroad tracks leadingto the plant. No one was seriously injuredor hospitalized.Historically Significant DamFailuresMarch 14, 2006 – Ka Loko Dam, Kauai,HawaiiThe failure of an embankment damin a relatively undeveloped area killedseven people and caused extensiveenvironmental damages.February 26, 1972 - Buffalo CreekValley, West VirginiaDecember 14, 2005 – Taum Sauk Dam,Lesterville, MissouriThe failure of this off-stream hydropowerfacility, located high above Johnson’s ShutIns State Park, destroyed the home of thepark superintendent and swept his familydownstream. Miraculously, all survived.The flood washed out part of a state roadand caused extensive environmentaldamages to the East Fork of the Black Riverand to the park, which in warm weathermonths is typically populated withhundreds of campers and hikers.The failure of a coal-waste impoundmentat the valley’s head took 125 lives, andcaused more than 400 million* indamages, including destruction of over500 homes. This disaster wiped out 16communities.June 9, 1972 – Rapid City, South DakotaThe Canyon Lake Dam failure took anundetermined number of lives (estimatesrange from 33 to 237). Damages, includingdestruction of 1,335 homes, totaled morethan 60 million*.June 5, 1976 – Eastern IdahoEleven people perished when TetonDam failed. The failure caused anunprecedented amount of propertydamage totaling more than 1 billion*. Thefailure flooded at least six communitiesand tens of thousands of acres.July 19-20, 1977 – Laurel Run,PennsylvaniaLaurel Run Dam failed, killing over 40people and causing 5.3 million* indamages.November 5, 1977 – Toccoa Falls, GeorgiaKelly Barnes Dam failed, killing 39 studentsand college staff and causing about 2.5million* in damages.May 31, 1889 - Johnstown,Pennsylvania*Dollar amounts have not been calculated to account for current monetary inflation.The deadliest dam failure in U.S. historytook the lives of more than 2,200 people.Living with Dams: Know Your Risk April 2012 9
The “inundation zone” is the area thatwould be impacted downstream ofthe dam in the event of a failure oruncontrolled release of water generallymuch larger than the normal river orstream flood event.The “dam failure inundation zone” isbroader than the FEMA “100-year flood”insurance mapped zone.How do I find out if I live in a damfailure inundation zone:Contact your local emergencymanagement agency (a simpleinternet search will most likelylocate the appropriate office).Contact the state dam safetyprogram (see the U.S. map atwww.damsafety.org).Before Buying: Do Some Research,Know the FactsBefore buying a home or business,determine whether it is in a dam failureinundation zone. This determination isthe buyer’s responsibility. Prospectivebuyers should know if there is anupstream existing dam or the potentialfor an upstream dam to be built. This issometimes very difficult to determinewhile standing on the property since theupstream dam may not be in sight. Insome cases, the dam site may be severalmiles upstream of the property and theview may be obscured. Listed beloware some resources that will assist yourresearch:7.5 minute U.S. Geological Surveytopographic maps:topomaps.usgs.govGoogle EarthMany people who live indam failure inundationzones are completelyunaware of the potentialhazard lurking upstream.Number of high- and significant-hazard potential dams;those that have the potential to cause loss of life (high) orextreme property damage (significant) should they fail.Note: Since Alabama is the only state that does nothave a state regulatory program the data on numbers ofdams may
“Fact or Fiction” – Common Beliefs about Dams FaCt State dam safety programs have oversight of most dams in the U.S. State agencies regulate more than 80% of the nation’s dams. Most dams are privately owned. Dam owners are responsible for maintenance and upgrades. Private dam owner
Dams in Oregon More than 1,100 dams in state dam inventory . 48 dams more than 100ft tall . 10 dams more than 300 ft tall . Cougar Dam is tallest – 519 ft
3.2 Types of Concrete Gravity Dams 3.2.1 Conventional Concrete Dams (CC Dams) These are dams constructed with Mass concrete Mass Concrete is any volume of concrete with dimensions large enough to require that measures be taken to cope with generation of heat from hydration of the cement and attendant volume change to minimizing cracking.
water for domestic needs, small earth dams otherwise also referred to as water pans are good water sources for livestock. Water from Small Dams is a handbook that is expected to serve as a guide for technicians and water users who are contemplating to design and construct small earth dams.
Design of Small Dams, USBR Technical Manual: Conduits through Embankment Dams, FEMA Technical Manual: Plastic Pipe Used in Embankment Dams, FEMA Filters for Embankment Dams, FEMA NOAA Atlas 14 Precipitation Frequency Atlas of the United States Selected and Accommodating Inflow Des
25 Tallest Dams In The World. Throughout history man has been building dams for various reasons, whether it was to prevent floods, generate electricity, or create a water supply. Starting thousands of years ago in the middle east as small walls, today dams are immense
poses. Historically, Bureau of Reclamation dams primarily served water storage and delivery requirements, while U.S. Army Corps of Engineers dams supported QDYLJDWLRQ DQG ÀRRG FRQWURO )RU ERWK DJHQFLHV K\GURSRZHU SURGXFWLRQ KDV EH-come an important secondary function. This history explores the story of federal contributions to dam planning,
Unit 2A 1.3 Living and growing 1Bp1 Know animals or plants are living things. pages 33–36 pages 34–38 pages 21–25 3.1 Living and non-living 3.2 Living and non-living 3.5 Living things around me 6.2 Parts of a plant 6.7 What plants need 6.4 Where do plants come from? 1Bp2 Know that there are living things
Although adventure tourism is recognized as an important, growing tourism segment, primary research to quantify the size and scope of this market in the U.S. or internationally (Schneider 2006) has been lacking. For this reason, George Washington University, along with its partners, the Adventure Travel Trade Associ-ation (ATTA) and Xola Consulting, sought to better understand the adventure .
