Death of a Delta: The Colorado - Part I

Beginning in the early 1930s the United States began building mega-dams, including the Hoover and Grand Coulee Dams. There is no doubt that these dams have “watered” the desert West and resulted in numerous benefits to the people of the Southwest. They have made the desert bloom, providing irrigation water to the most arid portions of the nation . . . They have tamed mighty rivers shielding communities from rushing floodwaters and storing spring torrents to provide a dependable year-round supply of water . . . [and] they have generated inexpensive electricity, bringing warmth and light to impoverished, rural areas.

These benefits have nevertheless come at a substantial cost to the Southwest’s natural resources. Dams completely transformed the Colorado’s ecosystems, especially those that that lie downstream of the dams, in the Colorado River Delta. Nevertheless, one should not be surprised. These environmental facts of life are such that dams block fish runs, and irrigation return flows are notoriously high in silt, fertilizers, pesticides, and salts and metals leached from the soil.

The Colorado River Delta comprises three thousand square miles of extensive riparian, freshwater, brackish, and tidal wetlands in the midst of the Sonoran or Gila Desert, which straddles the U.S.-Mexico border, in Arizona, California and the Mexican state of Sonora. Verdant in the 1920s, today the delta has lost more than 400 species of plants and numerous animal species, including the desert pupfish, coyotes, and jaguars, who called the delta their home. Gone too are the Cucupa Indians, who settled the delta over one thousand years ago, drawn by the bounty of fish and wildlife.

The upstream dams have shut-off the normally ample supply of water and stopped the annual floods. Additionally, development upstream in the Lower Basin States and in Mexico, during the twentieth century, diverted, distorted and polluted the water sourcing the Delta’s fertile land. As a consequence, the River’s sediments and water required to maintain life in the delta are gone. So are the natural flow patterns of the Colorado River that “maintained the delta habitats that supported both animals and humans.” Without these flows and the annual floods that flushed out the salt from the tidal influxes the land surrounding the Delta is now barren and sterile.
The dams also reduce or hold-back the River’s sediment load, affect its temperature as well as its rate of flow. Additionally, the mega-reservoirs associated with dams like Hoover and Glen Canyon Dams, reworked the River’s flow forming deep pools, which like oceans have broad thermal swings, from sun heated surface water to frigid depths. With their ecosystems destroyed, fish populations and the food they rely upon die out. The result: the Colorado River Delta’s biological productivity is only 5 percent of what it was before the mighty Colorado’s waters were diverted for human uses.