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<br />~ <br /> <br />e <br /> <br />e <br /> <br />~ <br /> <br />Table 2 (run in the Yuma Projects Office), and a spreadsheet program with the <br />title "Colorado River Monthly Operation, Imperial Dam to Northerly <br />International Boundary" operated by the Regional office in Boulder City, <br />Nevada. Both tools perform a mass balance (budget) of flow and salt on the <br />Colorado River (river) between Imperial Dam and NIB. The FORTRAN program <br />performs a detailed flow and salt budget using measured and projected values. <br />The spreadsheet performs a similar but simplified flow and salt budget, using <br />monthly data, in an interactive environment. Input to the program and/or <br />spreadsheet is based on judgement, experience, and studied expectations. <br /> <br />To use these tools, known and/or estimated data values are entered for the <br />calendar year. Estimates are based on previous years values for corresponding <br />flow conditions plus any updated or new information that is pertinent. Actual <br />monthly values are usually from one to two months in arrears. This delay is <br />due to the time required for processing and reporting of the daily flow data by <br />the USGS, and the processing of this flow data, daily EC data, and salinity <br />data from the laboratory analysis into .monthly values of flow and salinity by <br />Reclamation. <br /> <br />If our analysis shows the projected flow weighted average annual salinity <br />differential to be greater than 145 ppm, actions or mitigation measures are <br />modeled with these tools to test their effectiveness. These actions or <br />mitigation measures include: (1) discharging the South Gila Valley drainage <br />pumping into the Main Outlet Drain (MOD) or Main Outlet Drain Extension (MODE) <br />instead of the river, (this action bypasses these flows to the Santa Clara <br />Slough); (2) reducing the pumping from the South Gila Valley drainage pumping <br />and/or the flows in the Yuma Mesa Conduit; (3) reducing Southerly International <br />Boundary (SIB) deliveries and increasing NIB del~veries within the limits of <br />the requirements at SIB and the Mexican water order; fu1d (4) dilution by <br />delivering more water at NIB than scheduled by Mexico. <br /> <br />Some construction is still necessary to allow the Sou~h Gila Valley drainage <br />pumping to be discharged into the MOD or MODE. This construction is scheduled <br />to begin by mid-June 1989, and be completed by the end of July 1989. <br /> <br />Enclosed is an output report from Table 2 and the spreadsheet. These reports <br />show the projected salinity differential to be about 140 ppm as of the <br />beginning of April 1989. Therefore, no action or mitigation is planned at this <br />time. <br /> <br />Due to the comparatively large projected value for the differential, the <br />projections will be closely watched as they are updated with actual data. <br />Also, possible actions or mitigation measures are being postulated and tested, <br />using the tools mentioned above, by Reclamation persor~el. <br /> <br />The choice of action or mitigation is based on the effectiveness of the <br />measure, and the impact to water users in the United States. The objective of <br />studies, using the tools mentioned above, is to identify the measure that meets <br />the requirements of Minute 242, and requires the least amount of water at <br />Imperial Dam to meet the delivery requirements of:he Republic of Mexico <br />without impairment to water users in the United States. <br /> <br />2 <br />