WSP04506 - Laserfiche WebLink

Home Browse Search

W Coil -..J Q) In 1987, the plan of implementation was reviewed and modified to reflect changes that have occurred since 1984. The plan is described in Chapters IV and V. Temporary Increases The plan of implementation as set forth in this Review is designed to meet the objective of maintaining the salinity concentrations in the lower mainstem at or below those found in 1972 (numeric criteria) while the Basin states continue to develop their compact apportioned waters. The plan of implementation is based on the assumption of a long term mean water supply of 15 maf/yr. However, many natural and manmade factors affect the river's salinity. Consequently, salinity will vary from year to year and may exceed the adopted numeric criteria on qccassions and fall below them on others. In recognition of this, the approved standards permit temporary increases above the cr(teria levels if appropriate salinity control measures are, included in the plan. The salini ty control plan is designed to meet the criteria and to miminize the magnitude and duration of temporary increases. In Figure 2, Chapter 2, the annual average flow weighted salinity concentrations can fluctuate greatly. Recent analyses have shown that impact of natural variations in the hydrologic cycle can have a significant impact on salinity. The above normal runoff of 1983-86 has resulted in a: temporar..y decrease insalini ty concentra ti on of about 300 mg/l TDS at Imperial Dam. By contrast, the plan of implementation, as set forth in this Review, will reduce salinity concentration by approximately 85 mg/l at Imperial by 2010. Efforts to determine the time and magnitude of temporary increases are not practicable because of the uncertainty of accurately projecting the complex and natural variations in river conditions. To date the numeric criteria have not been exceeded nor are they expected to be exceeded in the near future. Uses and Associated Impacts of Salinitv The Colorado River, from its headwaters in the Rocky Mountains to its mouth in the Gulf of California,is utilized for a wide variety of purposes. A portion of the fJow is transported out of the Co.lorado Basin for use in adjacent river basins. In the Colorado River Basin irrigation,municipal and industrial, powerplant cooling, fish ~nd wildlife, and recre~tion are the major uses of river water. Many uses of the waters of the Colorado River are adversely affected by increasing salinity concentrations. Colorado River water users in the lower Basin have suffered significant economic impacts due to. elevated salinity levels. These damages have been estimated to have reached over $100 million per year. If the proposed plan of implementation for salinity Qontrol. as set forth in this review, is not implemented these damages could double early in the twenty-first century. -20-