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<br />ENCLOSURE A <br />- National Forest Water Yield Augmentation - <br />Limited Opportunities Due to Operational Realities <br />1. What are the opportunities for augmenting water yield on National <br />Forests? <br />• Opportunities are limited by current legal constraints, land allocations, technological <br />realities and societal values; environmental, ecological and biological realities; Forest Plans <br />and Forest Service mandates to manage for a wide range of values. <br />• Opportunities are generally limited to areas with precipitation greater than 16 in. (400 mm) <br />and less than 48 in. (1200 mm) (Adams and Coppock, 1986). <br />-- While this range applies to California, it has broader application elsewhere. <br />-- Augmentation has a strong potential on public lands in the Eastern US due to high rainf <br />yet it is limited by the actual extent of National Forest lands. Demand is greatest during <br />drought periods when opportunities for yield increases are least effective. Timber harvest <br />and other cultural treatments require roads and therefore may have a water quality cost <br />associated with a yield increase. <br />-- Hardwood and pine forests offer the best opportunity for water yield when coupled witr <br />over 40 inches (1000 mm) of annual precipitation (Douglass, 1983). <br />• Opportunities are greater in forests associated with higher precipitation. <br />-- For example, the mixed conifer type in Arizona is the highest per unit <br />producer in the southwest. <br />-- Higher precipitation is associated with higher elevation in the western <br />US. <br />• Many high precipitation areas include wilderness and, therefore, opportunities are limited. <br />-- Sagebrush, Pinyon-Juniper, and low Chaparral have no practical opportunities to <br />contribute to water yield (see Beaver Creek Studies by Aldon and Skau, Wyoming <br />studies by Sturges, and Mingus Watershed studies by Hibbert). <br />• Removal of riparian phreatophytes has the greatest predicted per unit area effect but with <br />large consequences to riparian and aquatic habitats and, with the exception of tamarisk, the <br />yield increase values are questionable. <br />• Research studies on very small basins (less than 3 mi2) indicate measurable increase when <br />more than 20% of the cover is removed (Stednick, 1996). <br />-- For forests, this is primarily from reduced evapotranspiration and interception.