Water Well Journal

November 2015

Water Well Journal

Issue link: http://read.dmtmag.com/i/592194

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Page 63 of 90

A lthough I will not be able to travel to the 2015 NGWA Groundwater Expo and Annual Meeting this December in Las Vegas, Nevada, I want to encourage the atten- dees who wish to take a break from the important functions of the Expo or escape the glitter and excitement of Sin City for a short period to witness and view one of the true engineering wonders of the 20th century: Hoover Dam. I have been able to tour this marvel twice, including an ex- tended tour of the entire dam and powerhouse before security restrictions were placed into effect after the September 11, 2001 tragedy. I will always cherish that visit. For those of you who may be contemplating the 25 to 30- mile jaunt to see the dam (as well as the recently constructed new bridge I have yet to see), I want to provide you with a few salient facts and figures regarding the dam as well as dispel a few myths to assist your visit. The River The Colorado River runs north to south within the Col- orado River Basin. The river runs through parts of Wyoming, Utah, Colorado, New Mexico, and northeastern Arizona (the Upper Basin) and continues through Nevada, California, the remaining part of Arizona, and ultimately drains into the Gulf of California in northern Mexico (the Lower Basin). The two basins are roughly equal in physical size and are separated by a region known as the "canyon region." This region is a 300-mile-long geological bottleneck where the Black Canyon and Boulder Canyon—and Hoover Dam—are located. The Colorado River is 1700 miles long and drains an area of 244,000 square miles. Roughly 99% of the total drainage basin is located within the United States and the remaining 1% within Mexico. All told, about 8% of the continental area of the United States lies within the Colorado River Basin. Through untold generations, the Colorado River has been an important source of water for human consumption and agricultural use, along with acting as a conveyance route for huge volumes of runoff to numerous agricultural areas— particularly the Imperial Valley in California. Along with these events, the river often transported large quantities of silt and other material. The combination of these two uncontrollable and unpredictable happenings often de- stroyed agricultural crops and land. Extreme flooding occur- ring in the Lower Basin was offset by periods of drought due to periodic lower precipitation and runoff in the Upper Basin, which also threatened thousands of acres of agricultural prod- ucts and farmers' livelihoods. The Colorado River begins its journey in the Upper Basin with a typical gradient of 8 feet per mile in the Grand Canyon and collects a considerable portion of precipitation from the Rocky Mountains. It meanders and travels downgradient through the Lower Basin, where the average gradient falls to approximately 3.2 feet per mile and then eventually down to 1.2 feet per mile. This large difference of grade creates conditions where rapid runoff results in severe erosion throughout the Upper Basin, with the resulting silt deposited in several regions of the Lower Basin. Although some measure of flood intensity could be forecasted for the Colorado River each and every year, the primary impediment to a reliable prediction was due to the unknown and varying conditions of the flood conditions each year. The Problem Due to the variable contribution of runoff from the Upper Basin, the number and accumulated volume of tributaries joining into the Colorado River along its path, the relatively large drainage area as opposed to the river's carrying capac- ity—particularly through the narrower canyon region—the velocity of water in the river would vary greatly throughout the year. During these uncontrolled conditions, along with natural changes in the average grade, the variability of these two situ- ations could create a wide disparity of flow in the river. It could be everything from a reported low flow of 2500 cubic feet per second to a peak flow upwards of 250,000 cubic feet per second—or 100 times as much. At best, the river became an uncertain and unpredictable source of irrigation and potable water supplies. At worse, it became a raging and uncontrollable river with the ability to wipe out thousands of acres of productive farmland and po- tentially cause the deaths of hundreds of people and livestock. Alternate periods of enduring perhaps a severe flood one year only to be followed by a drought the next underscored the need for some method of controlling the Colorado River. The Attempted Solutions Most of the efforts to use the waters from the Colorado River were directed toward diverting the water to irrigate much of the fertile ground that lies in the southwestern United States. In particular was the Imperial Valley of California, a rich and fertile area of potentially irrigable farmland exceed- ing several hundred thousand acres. ED BUTTS, PE, CPI ENGINEERING YOUR BUSINESS THE WONDER OF HOOVER DAM If you get a chance while at the Groundwater Expo, head over and visit an engineering marvel. 60 November 2015 WWJ waterwelljournal.com

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