D AMS Holding their water for time immemorial.

W HY DO WE BUILD DAMS ? Irrigation of cropland. This has been done for thousands of years. Think Aswan Dam. Municipal water use. As people moved west into the Great Plains, demand for water in arid regions required construction of reservoirs. Hydroelectricity generation. As a energy source, the kinetic energy of moving water is a renewable, dependable, and clean source. Flood management. This has also been done for years. Floods can be managed and destruction minimized.

E ARTHEN D AMS Constructed of rocks, stones, sand, silt, and soil. Have been built for millenia. If carefully constructed, are quite durable.

C ONCRETE D AMS Were first developed to span narrow, deep canyons. Structural integrity comes from that basic engineering marvel – the “arch”.

C ONCRETE D AMS ( CONTINUED ) Perhaps the most famous and recognizable dam in the US is the Hoover dam. Constructed between 1931 and 1936, Hoover Dam created Lake Mead (covers 247 mi 2 ), which is used for irrigation, municipal water, and recreation.

C ONCRETE D AMS ( CONTINUED ) As a result of damming the Colorado River, the water that previously reached the Gulf of California is no longer doing so. We tend not to concern ourselves with this, as it primarily impacts Mexico.

C ONCRETE D AMS ( CONTINUED ) Recent construction and engineering advances have permitted the spanning of broad, flat valleys. The best example of this would be the Three Gorges Dam in China.

S HOULD WE BUILD D AMS ? We need to balance our need for energy, and water with a need to maintain a sustainable environment for other organisms. Let’s identify some harmful effects of Dam construction and use. Are dams ecologically safe and “carbon neutral”?

N EGATIVES OF D AMS Limited advection of nutrients. Farmland downstream is being deprived of replenishment of needed fertilizer. Destruction of habitat both above and below the dam. The reservoir floods land and alters the temperature and DO levels of the river. Downstream, the river velocity and volume are reduced intermittently. Anadromous fish breeding practices are inhibited. Silting occurs upstream and the reservoir must be dredged. Dams are very expensive to build and maintain. The materials and fuel needed to build them often far outweigh the carbon savings.

S OLUTIONS FOR FISH Fish Ladders – Fish Elevators –