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EFFECTS OF WATER QUALITY ON WATER USERS 13 headcutting and gullying occur. Most of the salts have been leached from the alluvial deposits, thus erosion of their landform type yields less salts per unit volume of sediment than the other two landform types. However, channels incised into alluvium incorporate both sediment and salt from sloughed channel backs and salts from efflorescence at the alluvium- bedrock contacts[12]. The soluble mineral content of saline formations is variable and can be significantly different within one stratigraphic unit. The determination of the soluble mineral content of surficial soils is highly dependent upon the sampling and analytical methods used. The effects of contact time and sediment to water ratios on rate and extent of dissolution are extremely important. Since much of the salt is dependent upon sediment load, contact time and sediment to water ratio must be considered. Laronne[15] recommends a sediment to water ratio of 1 percent. This ratio allows for greater dissolution of salts and a better estimate of salinity contributed from erosion. EFFECTS OF WATER QUALITY ON WATER USERS Economic Estimating Economic Impacts of Salinity of the Colorado River[16] updated the economic impacts of salinity in the Colorado River Basin and developed a method of forecasting economic impacts as salinity levels rise and water use changes in the future. The first objective ofthe study was to update, revise, clarify, and refine the estimates of economic damages from salinity that had been described in earlier studies [17,18] . Figure 4 shows the relative impact of salinity on water users in the Lower Colorado River Basin. The study estimated damages were $311 million per year based on existing water quality levels and water uses in the Lower Basin. The second objective of the study was to provide a better means of estimating present and future salinity damages through the development of a comprehensive computer program. Present damages were estimated by the study to be $311 million per year, but as salinity levels Crop (36%) Management (11%) Household (50%) Figure 4.-Salinity damages and costs. increase to more normal levels, damages (figure 5) will also increase. Sensitivity analysis[19] using the damage model showed that damages (or the value of salinity control) increases with salinity. At the salinity standards (879 mg/L at Imperial Dam), damages are projected to exceed $1 billion per year. Using a relatively conservative analysis, the benefit of salinity control was estimated to be $257 per ton (1986 dollar value). In comparison, the cost of salinity control generally ranges from $20 to $100 per ton. $2,000 $1,500 Numeric Crheria of the SaHnIty Standard 879 mgll. Ul Q) C> OS E OS o ~ :~ OJ CIl '" c: ~ :E $1,000 $500 $0 400 500 600 700 800 900 1000 1100 Salinity at Imperial Dam (mglL) Figure 5.-Salinity damage curve.