Laserfiche WebLink
<br /> <br />,> <br /> <br />were taken from the total farm supply and the remainder compared <br />with the crop irrigation requirement to determine the crop irri- <br />gation shortage. Estimates were made to determine the additional <br />diversion necessary at the river to satisfY the computed crop <br />shortage. Line 4 in the lower section of Table' 1 lists the river <br />diversion shortages by reach. The losses, computed from our <br />studies, return to the river either as surface runoff or as sub- <br />surface return flow. The lag time of surface water poses no <br />problem. However, percolating waters travel slowly through the <br />previous stratum underlying the irrigated lands in the South Platte <br />Valley. A return flow study was made to check upon the adequacy <br />and accuracy of our historic water utilization study, and to <br />determine the effect of changing conditions in the South Platte <br />Valley. <br /> <br /> <br />Return Flow <br /> <br />A theoretical return flow analysis was made which relates <br />the time that irrigation losses return to the river, to aquifer <br />permeability, depth and volume of voids as well as the distance <br />traveled underground to reach the river. From the analysis we <br />computed the amount of irrigation losses which would return to <br />the river by the end of the month of application and at monthly <br />intervals thereafter during the study period. Line 12 of Table .J. <br />shows our computed average annual return flow, 620,000 acre-feet. <br /> <br />Reach Gain Study <br /> <br />A reach gain study was made for each month during the 1952 <br />through 1957 period for each of the six reaches of the river <br />coinciding with main stem gaging stations. The results were <br />compared with the computed return flows to determine their adequacy <br />and accuracy. For the purpose of this study the definition of gain <br />includes only the subsurface flows and unmeasured surface inflows <br />accruing to the South Platte River in a given time period. Line 13 <br />of Table 1 shows the average annual river gain during the study <br />period to have been 640,000 acre-feet. This compares favorably with, <br />620,000 acre-feet of computed irrigation loss return flow. A reach <br />breakdown is not given because the canal and farm loss estimates <br />shown on lines 6 and 10 of the lower section of Table 1 are for <br />ditches diverting within a reach and do not directly pertain to the <br />flows returning in the same reach. <br /> <br />Our studies show that there were significant river diversion <br />shortages existing during the study period. The total river shortage <br />was 391f,000 acre-feet, 153,000 of which is located above the Weld <br />County site, 49,000 between the two sites and 192,000 acre-feet below <br /> <br />19 <br /> <br />