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TABLE 2 <br />RETURN FLOW FACTORS <br />(FRACTIONAL PORTION OF FIELD INFILTRATION <br />RETURNING EACH MONTH) <br />Year Month No. <br />123456789101112 <br />Return Pattern No. 1 <br />10.89 0.08 0.01 <br />9 9 2 <br />Return Pattern No. 2 <br />1.205.088.065.053.046.045.040.036.033.029.027.027 <br />2.026.022.021.018.017.016.015.014.012.012.011.010 <br />3.010.008.008.008.006.006.006.005.005.005.004.004 <br />4.004.003.003.003.003.002.002.002.002.002.002.002 <br />5.001.001.001.001.001.001.001 <br />Return Pattern No. 3 <br />1.115.048.037.031.028.026.024.022.020.019.018.017 <br />2.016.015.015.014.014.013.013.013.013.013.012.012 <br />3.011.011.011.011.010.010.010.010.010.009.009.009 <br />4.008.008.008.008.008.008.008.008.008.008.008.007 <br />5.007.007.006.006.006.006.006.006.006.006.005.005 <br />6.005.005.005.005.005.005.005.004.004.004.004.004 <br />7.004.004.004.004.004.004.004.004.004.004.004.004 <br />8.004.003.003.003.003.003.003.003.003.003.003.003 <br />9.002.002 <br />Return flow pattern No. 1 represents general field conditions in which the irrigated lands are relatively <br />close to the stream and/or the hydraulic conductivity of the alluvial material is relatively high. On the <br />other end of the spectrum, Return pattern No. 3 represents field conditions in which the irrigated lands <br />are relatively far from the stream and/or the hydraulic conductivity of the alluvial material is relatively <br />low. Return flow pattern No. 2 represents an average field condition generally in the mid-range of the <br />hydrogeologic parameters. <br />The timing pattern for irrigation return flows can be calculated directly by MODSIM, which incorporates <br />a subroutine for the Glover methodology. As an alternative, MODSIM will allow the user to specify <br />monthly return flow factors from one of the recommended patterns shown above. Additionally, <br />MODSIM will allow the user to specify factors that are different from the three patterns. If the user <br />elects to have MODSIM calculate the return flow factors, the user must input all the required Glover <br />parameters (hydraulic conductivity, saturated depth, void ratio, and distance from stream). <br />Irrigation Streamflow Depletion <br />The timing of irrigation return flows is also an essential element in the estimation of historic stream <br />depletion, which is defined as diversions from the stream system minus concurrent return flows from <br />irrigation for the current and prior months. For purposes of estimating natural (virgin) streamflow at key <br />USGS gaging stations, the stream depletions attributable to the activities of man will be estimated by <br />corenatfl <br />using the data management interface (DMI) Utility (see Task Memorandum 1.15-15). Four <br />3 <br />A275 01.09.95 1.15-17 Hyre, Fosha <br />