Southern California’s Imperial Valley is home to California’s earliest agricultural drainage success story, one that converted a desert landscape to an agricultural one, but at the same time created far reaching consequences.
Located in the southeast corner of the state on the Mexican and Arizona borders, the Imperial Valley region was once largely arid (parts of it are still desert). But in the early 20th century, canals and aqueducts helped transform part of the landscape into a rich agricultural area. The accidental rupture of some of this irrigation infrastructure also led to the forming of the Salton Sea in 1905.
By the 1920s, however, it was apparent a drainage problem existed when accumulating salts and a rising water table forced some lands out of production and threatened the productivity of thousands of acres.
A $2.5 million bond issue passed in 1922 allowed the Imperial Irrigation District to construct a drainage system to collect water from farms and transport it to the Salton Sea. Subsurface drainage systems were also introduced in 1929. To date, 38,000 miles of subsurface drains have been installed on more than 95 percent of Imperial Valley farmland. About 1 million acre-feet of agricultural drainage water flows to the Salton Sea annually from IID.
Two northward-flowing river channels, the New and the Alamo, became the system’s main drainage conveyance channels, as well. Other inflow is received from the Coachella Valley Water District, Mexico and stormwater runoff.
Imperial Valley and the Salton Sea
Over time, nutrients and salt from agricultural runoff built up in the Salton Sea, helping nurture a vibrant ecosystem of fish and birds, but creating problems as well. As part of this, the Salton Sea has no natural outlet, concentrating the salt content.
Most recently, questions have been raised about the presence of toxic concentrations of elements such as selenium in the waters and waterfowl of the Salton Sea.
As a result, officials are exploring alternatives to decrease the sea’s salinity level (currently more salty than the Pacific Ocean) by at least 5 million tons per year. Studies on the impact of selenium on the Salton Sea are now underway.
Meanwhile, a comprehensive agricultural drainage water quality improvement program for IID is on hold while regulatory issues such as total maximum daily loads and habitat conservation plans are resolved. Increased conservation of irrigation water drawn from the Colorado River [see also 4.4 Plan] could exacerbate the Sea’s salinity problems by allowing existing salt to buildup in high concentrations.
A transfer of water between the IID and the San Diego County Water Authority could result in a reduced flow of 200,000 acre-feet into the sea further reducing its water levels and increasing the concentration of salinity.