Dams

Enhanced economic prosperity Public health Agriculture Altered natural environments Reduced streamflows Water quality degradation Fish and wildlife Dams

Ancient Cultures Earth, rocks, logs Flood control and irrigation

Dams Flood control Irrigation Redistribution Recreation Navigation Electricity

Dam Basics

Components Face – exposed surface of the structure Abutments – sides of the dam Crest – top of the dam Toe – natural ground surface Outlet – opening to discharge water Spillway – chute to allow excess water flow

Components Face Abutments Crest Toe Outlet spillway upriver

Types of Dams Gravity Concrete Concrete Arch Earthen Embankment

Gravity Concrete Concrete Arch Earthen Embankment Types of Dams

More than 50% Compacted earth Gravity Concrete Concrete Arch Earthen Embankment (mass)

Dam Storage Dead Storage Active Storage Flood Pool Storage Surcharge (temp. flood pool) Total capacity

Capacity Total Capacity – all storage space Live Capacity – total that can be released by gravity (total – dead) Freeboard – difference in elevation between the dam crest and the maximum water surface

Major U.S. Dams

Examples Hoover Dam Grand Cooley Dam Kingsley Dam

Hoover Dam One of 11 major dams Completed 1935 $165 million Concrete Gravity Arch Black Creek Canyon (Boulder Canyon Dam)

Hoover Dam 726 feet high 1244 ft length 660 feet thick at base 45 feet thick at crest Lake Mead Base Crest

Lake Mead Irrigation Hydroelectric power Municipal use Recreation Fish and wildlife Lake Mead Elwood Mead 10.5 trillion gallons 581 feet deep 110 miles long 2000 megawatts

Grand Cooley Dam Concrete Gravity Dam Columbia River in Central Washington Constructed

Grand Cooley Dam Largest concrete Structure in the U.S. 550 feet high 5223 feet long 500 feet wide at base 30 feet wide at crest 1244 ft length 660 feet thick at base 45 feet thick at crest Hoover

Kingsley Dam Earthen Dam Ogallala Nebraska North Platte River Constructed Steel and Clay core Sand, gravel, soil

Kingsley Dam Width = 3.5 miles Height = 162 feet Base width = 1100 feet Crest width = 28 feet 5223 feet long 500 feet wide at base 30 feet wide at crest 1244 ft length 660 feet thick at base 45 feet thick at crest Hoover Grand Cooley

Dates Hoover Dam Grand Cooley Dam Kingsley Dam

The Great Depression  Over 25% unemployment  Manufacturing down 50%

Impacts of Dams Change in river character Temperature Stress Rigid barriers to migratory fish Water release changes – sediments, O 2

Sedimentation Still water behind the dam deposits sediments Clear water released, scouring the riverbed downstream Further downstream, new sediment load deposited creating sandbars and islands slowing the river. Reservoir capacity reduced

The Three Gorges Dam

Yangtze River Concrete Gravity Length = 1.2 miles Height = 608 ft

Yangtze River Watershed Houses 1/3 China’s population Supplies ½ China’s food

The Reservoir 574 feet deep 373 miles long Filled by 2009 Equal in length to Lake Superior

Benefits Hydroelectric Power 85 billion kilowatts per year 10% of future energy needs Clean energy alternative Flood Protection 300,000 deaths by flooding Navigation Commercial shipping to central China

Costs Water stagnation in Reservoir Increased temperatures Increased salinity Human wastes Sedimentation and nutrients Cultural Consequences Relocation of up to 2 million people Breakup of traditional rural social system Adaptation to urban lifestyles, industry Farmlands and burial grounds flooded Importation of food

Rodman Dam

7,200-foot-long Earthen Dam completed in 1968

Cross-Florida Barge Canal Philip II of Spain in 1567 Funded first in 1935 Stopped in 1936 Reauthorized in 1942 Construction resumed 1964 Stopped in 1971 Cancelled in 1991 Nuclear power

Ocklawaha River

Rodman Reservoir 9,600 acres 15 miles long 2 miles wide

Migratory fish blocked from the river The floodplain and adjacent woodlands are a rare land-use classification of sub-tropical hardwood forest nutrient enriched impoundment, seasonally choked by exotic weeds, lined with stumps of the remnant bottomland hardwood forest Between 1985 and 2000, at least three major fish kills have occurred. River Restoration 20 natural springs submerged by the reservoir

River Restoration Rodman Reservoir is a viable and complex ecosystem that supports a wide variety of native plants and wildlife, including many endangered species. The water quality of Rodman Reservoir is good and is one of the few major sources of uncontaminated water entering the St. Johns River. Rodman Reservoir is consistently listed by major fishing magazines as one of the ten best bass lakes in the United States.