WSP03614 - Laserfiche WebLink

Home Browse Search

. ~ ~ ~ ~ . . PART V. EFFECTS OF SALINITY ON WATER USE Water quality can be a factor in limiting the use of a water supply. Different water uses require waters of different qualities, and a supply may be acceptable for some uses but unsuitable for others. Most water uses have a range of Quality within which a supply may be acceptable for that use. Use of water at the low quality end of this range may impose an economic, social, and/or a political penalty on the water user in com- parison to use of the water at a higher quality. The suitahility of the quality of a water supply for use is thus a relative matter and must he evaluated with regard to specific uses and the social and economic aspects of such use. An important objective of salinity investigations is to assess the suitability of Colorado River water for various beneficial uses. The following sections discuss the physical and economic effects of salinity on water uses in the Colorado River Basin. A. In-stream Use The major in-stream uses (u~es where water is not depleted) of water in tIle Colorado River Basin include 11ydroelectric power production, propa- gation of fish and aquatic life, recreation (inclurlin~water contact sports), and ae~thetics. Within the range of salinity concentrations expected in the foreseeable future, salinity should have no significant effects on these uses. B. Irrigation Use The major portion of the basin water supply is consumptively used for irrigation. Any effects of water quality on this use are thus of major importance. Crops. grown in the basin differ in sensitivity to a salt concentration in the soil root zone, with some crops tolerating signifi- cantly higher concentrations in the root zone than the more sensitive crops. Also, most crops require a lower salinity concentration in the root zone during the germinating and seedling stage than they do later in the growing cycle. Salinity concentrations in the root zone are affected by the salinity concentration of the irrigation water, method of irrigation, irrigation efficiency, depth and concentration of ground water, draina- bility and texture of the soil, weather patterns, and other factors. If, however, all other factors remain unchanged, the salinity concentration of the root zone will vary with the salinity concentration of the irrigation water. Thus an increase in the salinity concentration of the irrigation water will decrease the productivity of the salt-sensitive crops if its tolerance limit of salinity concentration in the root zone is exceeded. Because of the many factors affecting the salinity concentration in the ~oot zone, an exact irrigation water concentration that will damage a crop cannot be determined. For economic studies to determine Lower Basin damages, a salinity level of 750 mg/L was assumed as the level at which losses begin to occur. 34