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<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 />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Soil Moisture'Storage <br /> <br />Since the timing of ditch diversions does not always coincide with crop <br />irrigation water requirements, the carryover effects of soil moisture storage can <br />have a significant impact on consumptive use and river depletions. The amount <br />of water which can be stored as soil moisture, and which is subsequently available <br />for use by crops, is referred to as the available soil moisture storage. <br /> <br />A vailable soil moisture is defined as the volume of water retained in the <br />soil between the field capacity (or the moisture content above which water drains <br />freely from the soil), and the wilting point (or the moisture content below which <br />plants can no longer remove water). The available soil moisture storage capacity <br />of a particular soil is a function of soil texture and the moisture extraction or <br />rooting depth of the crop irrigated. <br /> <br />The types of soils irrigated by the Keesee Ditch were identified from the <br />Bent County Soil Survey (U. S. Soil Conservation Service, 1971) and included mostly <br />clay loam soils with minor areas of sandy soils. Available moisture capacities <br />for each soil type were obtained from the Colorado Irrigation Guide (U. S. Soil <br />Conservation Service, 1979), and weighted according to the irrigated area. In <br />general, the mixture of soils encountered have a moderate to high available soil <br />moisture capacity. <br /> <br />The moi~ture extraction depths for the four crops irrigated under the Keesee <br />Ditch as detrrmined from the Colorado Irrigation Guide ranged from three feet <br />for wheat and barley, to six feet for alfalfa. Accounting for the distribution of <br />crops and the time needed for crop roots to develop to maximum depths, a moisture <br />extraction depth of four feet is representative of average conditions for the Keesee <br />Di tch. <br /> <br />t;l . , <br />a..JJ ,,~-4'_ <br />W6'< ','+ <br />Je..rlT' 1 <br />h <,=J <br />.-e_<~.' <br />l'-'c I ,,~ <br />. J.~,~...Jl'~\ Cl <br />T\~GY c,~~:..,-s e-, ~ <br />0'\- t-"'-.lC-- r.;e'::ISdl <br />. , <br />>.' <br />(.~' -~ <br /> <br />Using this moisture extraction depth and the proportional areas for the <br />different soil types, the weighted average available soil moisture capacity was <br />estimated to be 0.62 acre-feet per acre. For the 1400 acres irrigated by the ditch, <br />this amounts to a maximum of up to 868 acre-feet of available soil moisture storage. <br />This storage capacity was used as a maximum storage amount in the water budget <br />analysis for the ditch. <br /> <br />-13- <br /> <br />~ - <br />