The Death Of A River, Part 2

  A few miles upstream from Yuma are two dams that lie athwart the Colorado River. There are many, many dams along this overused, abused and overallocated river, but these two dams are significant because the Colorado ceases to be a big river at this point. Heck it ceases to be a river at all because below these two dams, the Colorado is more of an irrigation canal than it is a river. The first dam is Imperial Dam. This dam impounds Martinez Lake. This lake is an oasis in the bone dry desert of Arizona and California. There is a settlement called Martinez Lake on the Arizona shore of the man made reservoir.
  Five miles further downstream is Laguna Dam. There is no reservoir behind Laguna Dam. It was built as a diversion dam, not an impoundment dam, between 1903 and 1905, and was the first dam on the Colorado River. When maps or atlases show both of these dams, they usually show a reservoir stretching all the way from Laguna Dam to Imperial Dam, but this is not the case. Laguna Dam is no longer needed  because of the presence of Imperial Dam nearby. Imperial Dam serves as both an impoundment dam and a diversion dam. At Imperial Dam, 80% of the river's flow gets siphoned off through the All American Canal to water California's famous farming region, the Imperial Valley. On the east side of Imperial Dam, another 16% of the river's flow gets siphoned off to the east to water Arizona's Mohawk Valley, east of Yuma. This is the area I mentioned previously that is a rich agricultural area  that is bisected by Interstate 8 and contains the towns of Wellton and Tacna, among others. This leaves only 4% of the river's water to flow downstream to Yuma to water a a region with 200,000 people on the United States side and  an even greater number on the Mexican side! Why does the Mohawk Valley, with approximately 5,000 people, get so  much more water than the much more populated Yuma Valley? Why does the Imperial Valley get such a disproportionate share? Under normal circumstances the Imperial Valley would not support agriculture at all with a paltry 2 inches of rain per year.
  When the Colorado emanates from Laguna Dam, the natural river channel is dry, just a wide, sandy bed. Instead, the river comes out in two narrow, man made channels on each side of the natural channel. After about a mile, these narrow channels merge and flow as a united stream to Yuma and beyond. A paltry amount of water in a wide river channel. At this point, the middle of the river is not necessarily the border between Arizona and California. The border lies in the middle of the natural channel and the narrow channel we see today meanders from side to side in the ancient riverbed. There is an exception to the river being the state border. It involves a loop of the old river channel that lies on the California side. Here the river cut itself a new channel in the past and the two states divided the land in half, putting a brief stretch of the Colorado entirely in Arizona.