Reservoirs

ReservoirsReservoirs

Various UsesVarious Uses Irrigation, electricity Irrigation, electricity

generation, flood generation, flood control, water control, water supply (urban), supply (urban), improved improved navigation, fish navigation, fish culture, recreation, culture, recreation, combinationcombination

Most are smallMost are small Built for irrigation Built for irrigation

by damming rivers by damming rivers in low rainfall (low in low rainfall (low runoff) areasrunoff) areas

Reservoirs vs. Natural LakesReservoirs vs. Natural Lakes Much in commonMuch in common Reservoirs usually Reservoirs usually

have larger drainage have larger drainage basins for their sizebasins for their size

Reservoirs usually Reservoirs usually youngeryounger

Reservoirs have Reservoirs have greatest depth at damgreatest depth at dam

Large ReservoirsLarge Reservoirs 3 types3 types Mainstream run-of-Mainstream run-of-

riverriver Tributary storageTributary storage Mainstream Mainstream

storagestorage

Mainstream run-of-riverMainstream run-of-river Used to generate Used to generate

electricityelectricity Rapid flushingRapid flushing Little or no Little or no

stratificationstratification No drawdownNo drawdown Water release from Water release from

deep outletdeep outlet Most river-likeMost river-like

Columbia RiverColumbia RiverGrand Coulee DamGrand Coulee Dam

Tributary storage reservoirsTributary storage reservoirs Built on smaller riversBuilt on smaller rivers Used for irrigation, flood Used for irrigation, flood

controlcontrol Slower flushingSlower flushing Stratified if deep enoughStratified if deep enough Periodic drawdownsPeriodic drawdowns Surface outletSurface outlet Most like natural lakes in Most like natural lakes in

areaarea

Acton Lake, OhioActon Lake, Ohio

Mainstream storage Mainstream storage reservoirsreservoirs

Intermediate in Intermediate in “position” between “position” between other typesother types

More lotic during More lotic during periods of high periods of high runoffrunoff

More lentic during More lentic during other timesother times

Mainstream storage Mainstream storage reservoirsreservoirs

Lie in well-defined Lie in well-defined river valleysriver valleys

Exhibit pronounced Exhibit pronounced longitudinal longitudinal zonationzonation

Mainstream storage Mainstream storage reservoirsreservoirs

Flushing ratesFlushing rates If flushing rate is If flushing rate is

greater than the greater than the doubling time doubling time of of planktonic planktonic organisms, organisms, washout will occurwashout will occur

Poor development Poor development environment for environment for planktonplankton

Impacts on riverImpacts on river Lentic system built Lentic system built

into a lotic into a lotic environmentenvironment

Interferes with Interferes with migrationmigration

Prickett Dam, MichiganPrickett Dam, Michigan

Impacts on riverImpacts on river Modified timing, Modified timing,

volume of dischargevolume of discharge Interferes with life Interferes with life

histories of biotahistories of biota Trapping materials Trapping materials

behind damsbehind dams Creates erosional Creates erosional

habitats downstreamhabitats downstream

Prickett Dam, MichiganPrickett Dam, Michigan

Impacts on riverImpacts on river Largest threat – large-Largest threat – large-

scale water diversion scale water diversion for agriculture, for agriculture, especially in dryland especially in dryland areasareas

Reduced or zero Reduced or zero discharge, loss of discharge, loss of downstream downstream wetlands, biotawetlands, biota

DrawdownsDrawdowns Necessary for dam Necessary for dam

maintenancemaintenance Increase flood Increase flood

capacitycapacity Remove accumulated Remove accumulated

sedimentssediments

DrawdownsDrawdowns Exposure, desiccation Exposure, desiccation

of littoral zoneof littoral zone Pronounced effects Pronounced effects

on biotaon biota

Benefits and CostsBenefits and Costs BenefitsBenefits

DevelopmentDevelopment AgricultureAgriculture FisheriesFisheries

CostsCosts FloodingFlooding Modified river reachesModified river reaches

• Above, belowAbove, below