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<br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />0i678 <br />Table 4 shows that 2,206 acres were irrigated during February <br />or March each year. These irrigations built up the available <br />soil moisture and recharged the groundwater reservoir. water <br />was evaporated from both water and saturated soil surfaces <br />during these irrigations, and this evaporation is an additional <br />consumptive use. It was estimated to be 263 acre-feet annually <br />by computing lake evaporation4 during February and March and <br />applying it for a two week period. <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Actual consumptive use was estimated from crop irrigation re- <br />quirements using a monthly water budget (Appendix C). It was <br />assumed that water applied in excess of crop irrigation require- <br />ments was retained in the crop root zone as soil moisture, up <br />to the field capacity, and that this water was available to <br />satisfy later water shortages. Water applications in excess of <br />crop irrigation requirements and field capacity were recharged <br />to the groundwater aquifer through deep percolation. water <br />applications were estimated by reducing historic headgate <br />diversions from Table 2 by 20 percent to allow for losses and <br />prorating according to the number of State-owned shares. After <br />consulting with representatives of the SCS, field capacity was <br />estimated using the following data: <br /> <br />Crop Root Depth Moisture @ Field Capacity <br />Corn 4.5 feet 9 inches <br />Grain sorghums 5.0 feet 10 inches <br />Alfalfa 6.0 feet 12 inches <br />Sugar beets 4.0 feet 8 inches <br />winter wheat 3.0 feet 6 inches <br /> <br />In the water budget computations, it was assumed that soil <br />moisture would be evaporated from the top foot of soil during <br />the winter season. These computations allow a check of the <br />previous estimate of winter consumptive use. The top one foot <br />of the soil is 80.47 percent of the root zone; therefore, winter <br />evaporation is 19.53 percent of the soil moisture available at <br />the end of October. This produces an average of 252 acre-feet <br />annually which agrees very well with the original estimate of <br />263 acre-feet. <br /> <br />Thus, actual consumptive use (Table 6) is the smaller of the <br />crop irrigation requirement or the total available water. Total <br /> <br />-18- <br />