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I I I I I I I I I I 7 Benefi ts The benefits tbat will be derived from the proposed Rock Creek Channelization Project are twofold. Firat, water loat to nonbeneficial use by evapotranapira- tion will be salvaged to a large extent and can be applied to deliveries stipulated in the Rio Grande Compact. Second, a portion of the water logged land can be adequately drained as tbe channelization will furnish a conveyance cbannel to the Rio Grande. A recent study carried on by U. S. Geological Survey indicates pan evaporation to be 52.25 inches for the six month period April to September. Measurable losses in phreatopbytic areas by evapotranspiration occur when the water table is as low as 12 feet below tbe surface of the land. It is interesting to note thst at a deptb to water of six feet, an annual loss of one foot is sbown in such areae. With such significant losses of water the value of water table control is readily apparent. While Lower Rock Creek cannot be considered a true pbreatophytic area, loeses by transpiration to grasses of low nutritional value are significant as are losses by evaporation from water wbich is ponded in many places in the area from the Hio Grande west for approximately five miles and from Alamosa south to the Norton Drain. The area in which this ponding occurs is vary flat and would require pumping to lower tbe water tahle, however, even tbough a shallow drain would not control the water table adequately it would reduce the area of ponds significantly. It is felt that a conservative evaluation of salvaged water sbould be presented in tbis report. Using information obtained from reports prepared by and work done by U. S. Geological Survey, Soil Conservation Service, Colorado Water Conservation Board and Water Administrators of the San Luis Valley togetber with field information obtained for this study, an estimate of salvaged water is presented below. a . Area affected by channelization b . Area affected by water table control c Q Surface area of exposed water . 60,000 acres = "0,000 acree = 1,280 acres Considering the evapotranspiration 108s of "b" as one foot (loss at six foot depth to water) and assuming two-thirds of the land area "a" eventually will have controlled irrigation and not contribute to water developedl 1 x "0,000 x 0.33 = 13,200 acre feet Assuming salvage of water from half the estimated exposed water surface "c": ".35 x 1280 x 0.5 .. 2,78" acre feet Total estimated annual salvaged water .. 15,98" acre feet. 0578