Laserfiche WebLink
<br />G001S7 <br /> <br />. <br /> <br />factors. In order to arrive at a rational method of determining efficiency <br /> <br />variations, the SCS recommendations for attainable field irrigation effi- <br /> <br /> <br />ciencies under border irrigation were used as a base point (USDA, 1974). <br /> <br /> <br />Recognizing that farmers to not reach attainable efficiencies, and that <br /> <br /> <br />there are conveyance losses from the irrigation company canal to the farm, <br /> <br /> <br />the SCS values were reduced by a constant value, 0.1. The SCS does not <br /> <br /> <br />recommend irrigation for some combinations of slope, requirement and intake, <br /> <br /> <br />and therefore give no values of field irrigation efficiency. These places <br /> <br /> <br />in the table were filled with a valup. of 0.3, which is 0.1 lower than any <br /> <br /> <br />value in the original table, In order to reduce the size of the table, <br /> <br /> <br />and because the slope values determined from the soil association infor- <br /> <br /> <br />mation were on a coarser scale than in the SCS original table, efficiencies <br /> <br /> <br />were averaged over some ranges of slopes. The resulting table is given <br /> <br />as Table 6. <br /> <br />. <br /> <br />Table 6 was used as follows. From the tabulation for each irrigation <br /> <br /> <br />area, the expected value of farm irrigation system efficiency was deter- <br /> <br /> <br />mined and a composite efficiency was found as a weighted average. The <br /> <br />initial values are given in Table 7. <br /> <br />Adjustment of Initial Values of <br />Farm IrriRation System Efficiencies <br /> <br />Essentially, all water delivered by the ditch company in excess of <br /> <br />that which is not necessary to meet the requirement is wasted through deep <br /> <br /> <br />seepage or runoff, unless it is required for leaching in salinity control. <br /> <br /> <br />This, in effect, decreases the efficiency. On the other hand, as water <br /> <br /> <br />becomes in short supply, irrigation efficiencies increase because the <br /> <br /> <br />farmer will take more care to use his water wisely. However, even with <br /> <br /> <br />the most restricted water supply it is probable that there are some losses. <br /> <br /> <br />Therefore, the following algorithm was developed. <br /> <br />. <br /> <br />-30- <br />