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<br />of twelve hours conform to existing general practice throughout the valley <br /> <br />for manual control of irrigation water; (3) determining the time of set to <br /> <br />the closest multiple of three hours and determining the flow rate per furrow <br /> <br />to the closest one gallon per minute to establish values that more precisely <br /> <br />apply the desired amount of water during each irrigation. Semi-automatic <br /> <br />controls in the irrigation system will enhance the opportunity for achieving <br /> <br />these refinements. <br /> <br />The two options for irrigation management are managing for maximum <br /> <br />irrigation efficiency or managIng for mInImum deep percolation. The com- <br /> <br />puter derives one combination of time of set and flow rate that tends to <br /> <br />maximize irrigation efficiency and another combination that tends to <br /> <br />minimize deep percolation. <br /> <br />The IRMA program computes irrigation application and efficiency, <br /> <br />summarizes and displays inventory data that describes the existing system, <br /> <br />and computes and displays the cost of improvements needed for each field <br /> <br />identified during the inventory. The program has the capability to summar- <br /> <br />ize and display the results of each field analysis for any of several types <br /> <br />of summaries, and was used to summarize the 26 watersheds delineated for <br /> <br />this study. <br /> <br />From the summaries generated for this study, lengths of lined and <br /> <br />unlined ditches were summarized for the present condition and each level of <br /> <br />structural improvement, and the respective volumes of ditch seepages were <br /> <br />calculated. Volumes of seasonal application, runoff, and deep percolation <br /> <br />also were totaled. From these totals the Water Budget shown in Table IV-3 <br /> <br />was developed. Finally, the water budget was converted into the annual salt <br /> <br />yields shown in Table IV-I. <br /> <br />In all levels of improvement the intent is to make better use of water <br /> <br />while reducing subsurface return flow to the river with its salt load. It <br /> <br />\.;01212 <br /> <br />11-9 <br />