The Colorado River and Dam

1. The Colorado River and Dam Case Study

2. Back ground information • With a drainage basin covering 630000 km, the Colorado is the third largest river in North America, after the Mississippi and the Columbia. Its source is the snowfields of the Rocky Mountains in Colorado and Wyoming; Its mouth is the Gulf of Columbia in Mexico, 2300km to the southwest. (see picture 1 on picture page) • Apart from the Rocky Mountains, most of the Colorado drainage basin is desert. The climate at Moab on the Colorado Plateau is typical. • Mean annual rainfall is low and evaportransiration in summer, when temperatures routinely rise above 40c, is high. • On the Colorado Plateau, the combination of erosion by the Colorado River, tectonic uplift and desert climate have produced some of the worlds most spectacular landforms. They include the Grand canyon’s horse shoe bend ( picture 3), The grand canyon (picture 2) and the entrenched meanders or goosenecks on the San Juan River (picture 4) . 1 2 3 4

3. Managing water resources in the Colorado basin • The Colorado River flows across the arid Colorado Plateau and Great Basin. There water is scarce: significant amounts are only available from the Colorado River and its tributaries. This explains why the Colorado is the most dammed river in the USA. • In its lower course in Nevada, Arizona and California, the Colorado is little more than a series of reservoir is created by the Hoover, Davis, Parker and Imperial Dams. • The Colorado River is used between 8 states. It is all tied up in a legal agreement (CRC- The 1992 Colorado River Compact) Ninety % of the water is used for irrigation and agriculture. The rest is used by authorities from: L.A, San Diageo, Phoenix, Denver, Salt lake city and Las Vegas. • Since the states have all had surges in their population and economic growth, they have all started to exceed their legal share. This is mainly in California. Now, Arizona, Nirvana and Colorado have put a squeeze California and called upon its sustainability of the current waters supplies. • The four dams I mentioned earlier: Hoover, Davis, Parker, Imperial Dams control the water resources in the lower basin. Nevada already uses its full allocation of water under the CRC and is urgently searching for new ground water supplies in the Mojave Desert north of the city. • 50% of southern California's water comes from the Colorado River. Series of aqueducts of the Hoover Dam provide water for irrigated agriculture in the imperial Valley and the Paulo Verde and Yuma irrigation areas. Also water is supplied to the metropolitan areas of L.A and San Diego. • Like Nevada's demand for more water, Arizonans need for water has increased immensely over the last 30 years. • What is left of the Colorado's flow when it finally reaches Mexico is diverted mainly to irrigation. There have been major issues concerning the quality of this water. Much of it is run off from irrigated land in southern California, and has high levels of salinity that make it unfit for agriculture.

4. Glen Canyon dam • The Glen Canyon was the last major dam built on the Colorado. Completed in 1963, it was sited at the narrowest point in the canyon close to the Utah-Arizona border. Its location was so remote that a small town, page, was built tom accommodate the workers. • The primary purpose of the glen canyon dam was to improve water management in the lower basin. • The dam created a huge reservoir-Lake Powell – over 300km long and with a surface area of nearly 1650km. This is very useful lake in times of flooding and securing water supplies for drought periods. • The other purposes of the dam include|: Generating power (1300MW OF HYDRO) This power goes to the 7500 inhabitants of Page and to the near by power station. Also the lake offers a wide variety of water based sports and leisure activities such as: Sailing, rowing, fishing, walking. • What ever the dam has achieved has come at the cost of the environment. The impact is greatest down stream of the dam. Creating the dam has degraded the rivers ecosystem between Glen Canyon and Lake Mead. • The lake has changed The Colorado River. Before construction its channels flooded every spring and the water was warm and muddy. Because the Dam acts as a sediment trap, the water leaving lake Powell is clear and because of how deep it is the water temp is now a constant 8c. • Effects of these changes are: Deprived of sediment and flood waters, sand banks that previously formed within the river channel have been eroded. The loss of Important habitats for fish, amphibians and birds have been lost. Also the fish migration was unable to occur with the dam. Because of all this 3 fish species have been extinct and 5 more are now endangered. With out the floods to clear out bank side vegetation, alien plant species like Tamarisk have been able to colonize the canyons, which now dominate large tracts of the river bank. These create new habitats for animals. • Up stream the effects have been just damaging; Beautiful scenery has been flooded dew to lake Powell. • There have been attempts to drain lake Powell by conservationist groups. They want to restore Colorado to it wild state, rehabilitate its unique ecosystems and reclaim hundreds of square km of desert canyons. People have obviously been fighting for the lake to stay where it is. No more then the people of Page whose lively hood depends on its existence. Especially the tourism it brings and the money that comes with it. • Losing the dam would also mean losing all the power that is generated from its dam. And the counties supplied would be effected in terrible ways, and it would be a monster of a task finding other sources that could satisfy.