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<br />;;~:{~ <br /> <br />(.l) <br />....' <br />a <br />c.:; <br /> <br />})~) <br /> <br />, <br />'"-".I <br /> <br />Water BudEet and Salt BudEet <br /> <br />Existing conditions pertinent to salinity, diverted flow, and return flow were <br /> <br />established using irrigation district records, salinity samples, and estimated <br /> <br /> <br />flow data from surface drains, and farm irrigation evaluations. Averaged data <br /> <br />from these sources were used to develop a water and salt budget (Table 4.) <br /> <br /> <br />Conditions that are forecast to exist in the future if no changes in operating <br /> <br /> <br />procedures or farming and irrigating practices occur are expected to be similar <br /> <br /> <br />to the existing circumstances. <br /> <br />To establish existing salinity conditions, 59 stations, including those for <br /> <br /> <br />return flow, were sampled during the study. Salinity data were collected from <br /> <br />July 1990 through October 1992. Twenty-two drains were selected as being <br /> <br /> <br />representative of drainage water from irrigated cropland. The data shown in <br /> <br /> <br />Table 3 are averages of the representative samples. Background EC for diverted <br /> <br />San Juan River water averaged 0.52 mmhos. Specific conductance values were <br /> <br />determined with a GLA M33.1 EC meter. <br /> <br />To arrive at an estimate of onfarm irrigation efficiencies and the amount of deep <br /> <br /> <br />percolation on the graded furrow systems in use, irrigation evaluations were <br /> <br /> <br />conducted in 1992 on 22 fields operated by 14 cooperating land users. <br /> <br />Eleven evaluations were conducted in the Hogback I.D., nine were conducted in the <br /> <br /> <br />Fruitland I.D., and two in the Cudei I.D. Fields were selected to include a <br /> <br /> <br />variety of soil textures ranging from clay loam to loamy fine sand. <br /> <br />The data were accumulated, averaged, and extrapolated. to the entire study area. <br /> <br />Table 4 gives an estimate of the balance between salt and water diverted for <br /> <br /> <br />irrigation and that returned to the river from the 5,800 acres (rounded) <br /> <br /> <br />currently irrigated. The amount of diversion was estimated from field data. <br /> <br />11 <br />