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<br />ALTERNATIVE PLANS <br /> <br />Most of the irrigated land needs improved systems and management. <br />One-half of the water withdrawn for irrigation goes to deep percolation. <br />This percolating water dissolves salts from the underlying strata, result- <br />ing in increased salt loading of subsurface flows. Major irrigation <br />system improvements would increase efficiency and reduce deep percolation. <br /> <br />Formulation of irrigation alternatives considered: (1) water control <br />and measuring devices; (2) using the irrigation system and method best <br />adapted to the soils, crops and level of management desired; and (3) applying <br />the proper amount of water at the proper time to meet consumptive use plus <br />cultural practice (leaching, sluicing, prewetting, etc.) requirements. <br />Orainage is inadequate in some areas and aggravated by inefficient water <br />scheduling that results in over irrigation. Improved irrigation efficiency <br />would alleviate some drainage problems. Land leveling and planing on a <br />regular basis are important conservation practices for better distribution <br />of water on the field. Land planing will continue as a part of the ongoing <br />program regardless of which alternative is implemented. <br /> <br />The SCS computer program for Irrigation Methods Analysis (IRMA) was <br />used to estimate irrigation efficiencies for the alternative water manage- <br />ment plans (see Table 8). Water and salt budgets (Table 9) were prepared <br />for alternative plans using IRMA output information for crop consumptive use, <br />and deep percolation to ground water. The predominant irrigation methods <br />are graded border and level border systems. The alternatives minimize <br />changes in these irrigation methods. Only minor changes in crops and <br />field size are suggested. Changes in irrigation methods, crops, field <br />size and land use are dictated by physical geography and institutional <br />constraints of road location, land ownership and water rights. The sample <br />of fields processed in the computer analysis is representative of crop, <br />soil type and location in the valley. Twenty eight percent or 1,388 acres <br />of the total irrigated land in the valley was used in the computer analysis. <br /> <br />Gully and channel erosion of saline soils contributes both salt and <br />sediment to Muddy River. Water erosion results in salts being removed <br />through solution and the sediment detached and moved by surface waters. <br />Erosion control alternatives are limited by climate. Vegetative measures are <br />difficult to establish because of low rainfall. Structural treatment which <br />traps sediment is not recommended because of the high expense relative to <br />salinity benefits. Control of erosion is limited to channel bank shaping <br />and seeding and protecting drain outlets and road crossings. These erosion <br />measures have the highest salinity benefit relative to cost and would be <br />limited to areas where implementation is practical. <br /> <br />Change in land use was considered for the program area. Only a small <br />portion of the Subeva1uation Unit is in private or Indian ownership. <br />Purchase of a~ricu1tura1 lands by the government for conversion to nonirrigated <br />land was consldered. Opposition to government land ownership is high in the <br />study area, and future State and local acceptance of such an alternative is <br />unlikely. <br /> <br />34 <br /> <br />002714 . <br />