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Show PART VIII TECHNOLOGICAL ADVANCEMENTS Weather Modification Weather modification as an operational tool represents a source of new or additional water for a basin by producing runoff from precipi- tation that normally would not have fallen on the basin. Research into precipitation management is being actively pursued in the Western United States to develop methods for beneficially modifying weather elements important to the area's water resources. Current techniques involve adding proper quantities of minute particles to selected clouds to change cloud composition and help form more raindrops or snowflakes. Commonly called "cloud seeding," it is usually done by burning silver iodide mixtures. The relatively large increases in runoff that may be expected combined with probable low operational costs, program flexibility, and the high quality of water produced make precipitation management a unique method for increasing the water supply. More research is needed to develop a better understanding of the physical mechanisms of precipitation and the statistical effects of cloud seeding operations, and to improving existing techniques. Of great importance are the legal, environmental, and economic aspects that must be considered before large-scale modification of precipitation may be relied upon as an additional water source. Watershed Treatment Research conducted in the United States over the last 60 years has amply demonstrated that various land management activities and water- shed treatment measures can affect rates of soil loss, debris-sediment content in streams, total water yields, timing of waterflows, and water quality. The type and degree of change following a specific activity or treatment on any given area is a function of climate, geology, soils, topography , vegetation, and other factors of the environment. Manipulation of vegetative cover and other water yield improvement techniques can result in increased streamflow without damage to the watershed or to areas downstream if the activity is carefully planned and executed as a part of a coordinated land and resource management program. The danger lies in proceeding too fast with too little knowledge of the intricate plant-soil-water and other environmental relationships involved. Ill-conceived, poorly executed programs are likely to cause considerable damage to watershed soils and water quality and add to flood problems. Close coordination between weather modification programs and watershed treatment programs will be essential to minimize any adverse effects of anticipated increases in precipitation. 36 |