Monitoring The Water Quality of the Nation's Large Rivers Colorado River NASQAN Program

Since 1995, the National Stream Quality Accounting Network (NASQAN) of the U. S. Geological Survey (USGS) has focused on monitoring the water quality of the Nation's largest rivers including the Colorado, Columbia, Mississippi, and Rio Grande. The NASQAN program in the Colorado River Basin consists of eight stations that span seven basin States including Colorado, Wyoming, Utah, New Mexico, Arizona, Nevada, and California. Data collected from these stations are used to quantify the transport of chemical constituents and evaluate trends in water quality of the river. Currently, the NASQAN program in the Colorado River Basin is providing necessary data and information required by resource managers of the river who are responsible for meeting longstanding legal agreements that regulate the flow and quality of the river water. The Colorado River often is described as the most controversial and regulated river in the United States. The river currently provides 25 million people with drinking water and also provides enough water to keep 3.5 million acres of farmland in production. Other uses include industrial, recreation, and electric-power generation. The river is highly regulated with 83 reservoirs in the upper basin and 10 reservoirs in the lower basin that are capable of storing 4 years of flow. Twelve legal agreements, compacts, contracts, and State and Federal legislation apportion and regulate the use, management, and quality of water for the Colorado River water among the seven States in the basin and Mexico (Newcom, 1998). The Colorado River drains about 250,000 square miles. Annual flows in the river fluctuated greatly before the big dams were built on the river because of winter snowmelt and summer thunderstorms. Water, sediment, and chemical transport from the upper basin are greatest in June. Daily fluctuations in the lower basin are caused by irrigation and water-supply diversions, power generation, losses to evaporation and transpiration from riparian vegetation, and irrigation return flows.