Expert Report of D. Randolph Seahom and Exhibits

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Consumptive Uses and Losses 5 0 There is further provision that the measurement method can be changed by unanimous action of the Commission. Nearly all the water exported from the Upper Colorado River Basin is measured; however, the remaining beneficial consumptive use, for the most part, must be estimated using theoretical methods and techniques. Reservoir evaporation loss is a consumptive use associated with the beneficial use of water for other purposes. For the purpose of this report, main stem reservoir evaporation is carried as a separate item for the Upper Basin. Channel losses within the basin are normally construed to be the consumptive use by riparian vegetation along the stream channel (or conveyance route) and the evaporation from the stream's water surface and wetted materials. Seepage from the stream normally appears again downstream or reaches a ground -water aquifer where it may be usable again. A decided lack of data and acceptable methodology, along with the intermittent flow characteristics of many Southwest streams, combine to make a reasonable determination of channel loss difficult. Channel losses have not been estimated for this report within the Upper and Basin. METHODOLOGY AND DATA ADEQUACY This report is based almost entirely on data obtained from ongoing programs and current reports. Quantitative measurements of water use were used wherever available, but the majority of the basin water use was 'theoretically calculated. The following sections describe these calculations for both the Lower Colorado River Main Stem and the Upper and Lower Colorado River Basin tributaries. Upper Colorado River Basin Tributaries In the tributary areas of the basin, records of diversions and return flows are not complete enough to allow direct calculation of consumptive water use. Theoretical and indirect methods of estimating consumptive use must then be relied upon. In the New Mexico portion of the Colorado River Basin, the annual consumptive use of water is reported by the New Mexico Interstate Stream Commission. For the Arizona, Colorado, Utah and Wyoming portions of the Colorado River Basin, the annual consumptive use of water was estimated using the following methodologies. Agriculture The percentages of irrigation consumptive use range between 55 and 87 percent for the Upper Basin tributaries. The percent range excludes main stem evaporation. The annual irrigated acreage of most crops grown within each reporting area was estimated from information published in the yearly State Agriculture Statistics, 2002 National Census of Agriculture (since the State statistics do not include pasture land), and from Geographic Information System (GIS) irrigated acreage data available for Colorado, Utah, and Wyoming.