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<br />001995 <br /> <br />scaling the 1929-1969 baseline monthly return flows by the ratio of the average annual historic to <br />average annual baseline values during their concurrent record. The resulting estimated historic return <br />flows for the early period were combined with historic values from the model run to give 1929-1993 <br />records for both baseline and historic conditions. The historic values were adjusted for operation of <br />the irrigation projects included in the three nodes. The period of operation is shown in Table 4-1. <br /> <br />The difference in monthly return flows for the baseline and historic conditions ( RF. - RFH ) were <br />calculated for all the return flow nodes for the three reaches described above. The historic return <br />flows at each site were only included in the difference calculation if the monthly values fell within the <br />period of operation shown in Table 4-1. Otherwise, the difference was solely the baseline return flow <br />for that month. These monthly values were summed into annual values which were then redistributed <br />( [RF. - FH].........) throughout the year. The redistribution was calculated using a unit hydrograph <br />denoted as Other Return Flow in the 1991 version of the USBR Fish Model. The hydrograph shape <br />is shown in the appendix. The lag correction file is the difference between the monthly return flows <br />for the baseline and historic conditions and the redistributed monthly values. This is described by the <br />foHowing equation: <br /> <br />[RFe - RFH ] - [RFa - RFH ]""""ri' = Lag Correction; <br /> <br />Where RF. = Baseline Return Flow <br />RFH = Historic Return Flow <br /> <br />Table 4-1. Project Operation <br /> <br />Sites Assumed Historic Period of Operation <br /> Node 1 - San Juan Above Fanninoton <br />Citizens Ditch 1929-current (whole period) <br />Hammond Proiect 1963 - current <br /> Node 2 - Animas above Fanninoton <br />Fanners Mutual Ditch 1929 - current (whole period) <br />Fannington Return Flow 1929 - current (whole period) <br />Minor Retum flows below Cedar Hill 1929 - current (whole Deriod) <br /> Node 3 - San Juan below Fanninoton <br />Cherry Creek 1929 - current (whole period) <br />Below CO-NM Stateline on La Plata 1929 - current (whole period) <br />Jewitt Valley 1929 - current (whole period) <br />Hogback 1903 - current. <br />Cudei 1900 - current. <br />Fruitland 1937 - current. <br /> <br />*Reference: Inventory of Navajo Indian Irrigation Projects, August 1986 <br /> <br />DRAFT - SJRIP Hydrology Model Documentation <br />June 18, 1999 <br /> <br />56 <br />