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<br />2379 <br /> <br />. <br /> <br />programs, so that inefficiency will not contribute to the salinity <br />problem of the river. <br />It is recognized that this preliminary analysis is based on limited <br />information in relation to the complexity of the situation, and that the <br />estimated salt retention of the recent past and the future portrayed <br />on Figure 5 is an approximation. The fact that the estimated current <br />salt retention of 80,000 tons is only about 14 percent of the amount of <br />salt currently diverted is a matter of concern, since hydrologic <br />measurements are generally regarded as having a preCISIOn of no <br />better than 10 percent. However, the regular pattern of salt reten- <br />tion shown by ISSP data in spite of variations in diversion and drain- <br />age seems to indicate that the data are reasonably reliable. <br />It is also recognized that higher onfarm efficiencies than needed <br />for ultimate acreage development could cause an increase in net salt <br />retention for probably a number of decades. However, the chances <br />of achieving them are regarded as low because of probable lack of <br />incentive to irrigate more efficiently than needed to irrigate the <br />ultimate acreage. <br />The salt inflow and outflow of the Reservation should continue to <br />be monitored in the future by means of the ISSP program. That will <br />be helpful in determining trends of salt retention. In addition, a <br />program to monitor subsurface flow between the river and the upper <br />part of the Reservation has recently been initiated by the U. S. <br />Geological Survey, and this information will permit further refinement <br />of the water and salt budget for the Reservation. The Soil <br />Conservation Service study will deal with the question of whether a <br />significantly higher efficiency, 80 percent for example, is attainable, <br />and the nature and cost of onfarm improvements required to attain it. <br />If conditions become more adverse than presently projected, or if <br />the attainment of significantly higher onfarm efficiency appears feasi- <br />ble, the prospects for a salinity control project can be reevaluated in <br />the future. As the irrigation system is improved in the future, <br />measurement of water supplied to various parts of the system can be <br />estimated more precisely, and greater precision will be possible in <br />estimating the salt and water budgets. <br /> <br />. <br /> <br />30 <br />