Salton Sea Atlas: Hydrology

salton sea hydrology 38 39 limnology

Great Basin Precipitation One of the largest rivers in North America, the Colorado River drains 17 percent of the United States. Spring rains and winter snow fill the river each year, sustaining a complex ecology of temper- salton sea hydrology ate forests, arid deserts, and riparian areas. Much of this water is stored in immense reservoirs behind massive dams constructed in the early twentieth Evaporation century, and is used to quench the thirst of millions The large surface area of the Sea and the hot, arid of people and agriculture throughout the western desert environment cause a large amount of water to states and Mexico. he Salton Sea has evaporate. Each year, 1.36 million acre-feet evapo- rate. Evaporation concentrates various chemicals in no outflow. The the Salton Sea, including salts. TSea lies at the bottom of a 7,851 sq. mi. Salton Basin (20,333 km2) watershed col- lecting all drainage within salton sea atlas the redlands institute this closed Basin. Over 90 per- Colorado River Water Closed Basin cent of all water entering the Like any river, the natural runoff feed- All water bodies have a watershed, ing the Colorado accumulates various Sea results from agricultural the catchment area where natural sediments and minerals. As the River runoff, with the remaining precipitation falls before flowing to churns its way southward, it picks up the lake or river. Unlike many water- more sediment—sometimes turning it coming from natural precipita- sheds, the Salton Basin has no outlet, chocolate brown. Before damming the tion, ground water, or urban use. since no streams or rivers flow from Colorado, the River carried sediments the Sea. This geography influences Inflow Sources Irrigation water, diverted from the along its entire course. Some natu- the chemical, physical, and biological Ground water rally occurring elements, like salts Colorado River to a complex system processes of the Sea. Usually, an outlet Rainfall Other Sources (1%) and selenium, become concentrated can serve to stabilize water quality by Whitewater as the River progresses. of canals and drains, flows through constantly flushing the system. River the agriculture fields of the Imperial and Coachella valleys before draining to the Sea. Agriculture Runoff

The Colorado River drains 17 percent Just as evaporation at the Sea of the land in the United States on its Agricultural Alamo River concentrates things in the water, Drains New River evaporation of irrigation water similarly 1000-mile journey to Mexico and can concentrate these same substances. the Gulf of California. On the Irrigation water collects salts and other minerals way, the natural runoff feed- naturally occurring in soils. Fertilizers and pesticides can also accumulate in drain water. Most of the nutrients ing the river accumulates feeding the Sea originate as fertilizers on agri- various sediments and min- cultural fields. Pesticide levels in the Sea however are currently lower than federal erals. Before the construc- drinking water standards. tion of dams in the twentieth century, these sediments, including various soluble minerals and salts, were car- ried the entire course of the river—all the way to the Gulf. In-Basin Precipitation The large sediment loads often Like many deserts in the American turned the River chocolate Southwest, periodic downpours brown as it churned south- characterize the Basin, including thunderstorms and flash floods. ward, picking up more sedi- This brief rainfall can turn the ment and minerals. Desert into a colorful scene of blooming wildflowers. Anza Borrego State Park, just west of Once diverted to the Salton the Sea, is renowned for spectac- ular spring wildflowers. Slightly Basin, urban and agricultural more than 3 percent of the water practices concentrate salts and entering the Sea comes from nat- minerals already in the water. ural precipitation. Agriculture and urban uses in the watershed further add more nutrients, salts, and chemicals. Several million tons of salt are added to Ground Water the Salton Sea every year. Water enter- Fresh-water aquifers under the Salton Basin ing the Sea can be as much as five are the smallest contributors of water Urban Runoff times saltier than the Colorado River. entering the Sea. Less than 100,000 acre- feet enter the Sea from ground water each A relatively small portion of water entering the Sea year. Historically a lifeline for Native results from urban uses. Wastewater from urban An enormous amount of water— Americans during dry periods, plants and areas, primarily the city of Mexicali, Mexico, but also 50 animals rely on natural springs fed by these from smaller communities in Imperial Valley, carries 1.36 million acre-feet, over 15 per- Lake nutrients and urban pollutants. Much of these urban 40 Mead aquifers. Increased pumping of ground water resources has lowered the ground pollutants are sequestered in riparian vegetation cent of the total volume of the Sea— 30 water level in some areas. and sediments before they reach the Sea. evaporates each year, leaving 20 behind millions of tons of salts, 10 5 minerals, and nutrients. Over its Salton Sea 100-year history, salinity has increased from the very low levels found in the Colorado 50 Lake Havasu 40 River to 25 percent more than 30 Lake Powell ocean water—more than a 40- 20 Salinity Levels 50 5 ppt A l Water entering the Sea is about five times fold increase. 10 l A 5 m 40 e saltier than the Colorado River. Salt, ri 50 ca 30 New River and n naturally occurring in the River, concen- Can 50 Alamo River al 20 40 trates as it progresses. Evaporation at the 40 1 ppt C o l 30 Sea further concentrates salts. Over the 10 o r a 30 5 d o 20 100-year history of the Sea, salinity has R 20 0 ppt increased from low levels found in the i v 10 e 5 Colorado River to 25 percent more than 10 r Salt ocean water—more than a 40-fold increase. 5 (parts per thousand) Fresh water Ocean water Gulf of California © 2002 University of Redlands