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<br />001972 <br /> <br />The flow balances for 1929 to 1969 were found by segregating the monthly natural flow <br />balance betWeen Archuleta and Bluff (the difference in the CRSS monthly natural flows) into <br />the 4 reaches using reach flow ratios determined from the 1970-1993 USBR natural flows. <br /> <br />(BluffMNF - ArchuletaMNF) * (S-FC reach ratio) = S-FC MNF Balance <br />MNF = Monthly Natural Flow <br /> <br />The natural flow balances for 1970 to 1993 were found by subtracting the USBR monthly <br />natural flows at the gauge locations appropriate in each of the 4 reaches. <br /> <br />2. Daily gauged flow balance 1929 to 1993. Daily records were extended for gauges with <br />missing or incomplete daily data flow data. For each gauging location a complete daily <br />flow record was completed for the period October 1928 to September 1993. The daily <br />gauged records were lagged relative to the Bluff downstream station. The lagging ranged <br />from three days at Archuleta to one half day at McElmo Creek. The daily gauged flow <br />balance was then computed for each reach by subtracting the upstream daily flows from <br />the downstream daily flows. After the daily gauged flow balance was calculated, the <br />balance for each reach was smoothed using a centered five-day running mean. <br /> <br />3. Daily natural flow balance 1929 to 1993. For each river reach, its lagged and smoothed <br />daily gauged flow balance was used to disaggregate its monthly natural flow balance into <br />a natural daily flow balance. Please refer to section 6.42 for details. <br /> <br />This process results in the daily natural flow balances for each of the four reaches. The flow data are <br />a series of positive and negative numbers which are reformatted for spreadsheet use in the post- <br />processing. The daily natural flow balance is a static data set and does not change based on the <br />modeled development scenario. However, these flow balances have been subsequently modified to <br />account for lagged return flows, offstream depletions and phreatophyte depletions. These issues are <br />discussed in the Natural Flow Balance Adjustments section. <br /> <br />Dailv Disaaareaation of Tributaries <br /> <br />Any change in the modeled development scenario may change the tributary inflow of the Animas <br />River, La Plata River, Mancos River and McElmo Creek. The San Juan Model estimates monthly <br />tributary inflows to the San Juan for each of these four streams. These must be disaggregated into <br />daily values to complete the spreadsheet daily balance. Unlike the calculation of the daily natural <br />balance which is static, the tributary disaggregation must be done after each model run. To fully <br />understand the disaggregation process, the implementation of the Animas-La Plata project within the <br />San Juan Model and the resulting effect on the tributaries must be explained. <br /> <br />The San Juan Model does not explicitly operate ALP. The project is added as gains/losses along any <br />river reach it would affect. The USBR (Durango) supplied gain/loss data for both the llLitell and <br />llFu1lll versions of ALP. As configured in the San Juan Model llUtell ALP and llFullll ALP have <br />average annual depletions of 55,610 ac-ft and 143,514 ac-ft, respectively. The river reaches affected <br />with object names containing the gain/loss data (shown in parenthesis) are: <br /> <br />DRAFT - SJRIP Hydrology Model Documentation <br />June 18, 1999 <br /> <br />33 <br />