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<br />OOi971 <br /> <br />Daily Disaggregation of Simulated Monthly Gauged Flows <br /> <br />General <br /> <br />The San Juan Model currently runs on a monthly time step with flows in ac-ftImonth or the monthly <br />equivalent cfs as output. In order to assess the effect of the various flow conditions on habitat, daily <br />flows are necessary. Conversion of the monthly flows to daily flows takes place outside of <br />RiverWare. <br /> <br />After the completion of each model run, two files are exported from the ModeL The first is a user <br />configurable output file that consists of depletion, flow, reservoir evaporation and storage, basin <br />import/export and other miscellaneous data. The other file consists of the daily releases from Navajo. <br />This is the only daily data set produced by the ModeL All pertinent flow balance data is post- <br />processed in spreadsheets or BASIC programs from monthly data into daily data. A daily flow <br />balance is completed within a set of linked spreadsheets and then summed back to monthly data. If <br />this computed monthly data matches the Model estimated flow at appropriate locations (within <br />rounding error) then the process is complete. <br /> <br />Most of the monthly model output data required for the daily flow balance is disaggregated into daily <br />data in Excel spreadsheets. The monthly data is first split into bi-monthly data and then split again in <br />quarter-month data. The monthly data is not simply divided by 4 to yield quarter-month data. <br />Formulas in the spreadsheet look at pre- and post-time steps to see if the hydrograph is in an <br />ascending or descending phase and then attempts to distribute the monthly values so there are no <br />abnormal reversals. Each quarter-month data point is uniformly distributed over the appropriate <br />number of days (7,7.25,7.5, 7.75) depending on the number of days in the month, Data points are <br />interpolated between weeks as needed. <br /> <br />The monthly flows along the river mainstem between Archuleta and Bluff and the tributary inflows <br />of the Animas, La Plata, Mancos and McElmo were disaggregrated differently than described in the <br />preceding paragraph. These disaggregation methods are developed in the following sections. <br /> <br />Daily Natural Flow Balance on the San Juan Main Stem <br /> <br />As described in the previous section, the daily disaggregation of monthly flow balances in the river <br />reaches from Archuleta to Bluff was performed differently than other model output. The term Dflow <br />balancell will be used throughout this document. It is simply the difference between a downstream <br />and upstream gauge. The natural flow balance between the main stem gauge locations is the gains <br />and losses in natural flows along the San Juan River and the tributaries in each reach. The monthly <br />natural flow balances between reaches were disaggregated into daily flow balances using the daily <br />gauged flows at these stations. While conceptually simplistic, implementation is rather complicated. <br />The procedures are outlined below. Additional details may be found in Section 6.4. <br /> <br />1. Monthly natural flow balance 1929 to 1993. Monthly natural flow balances were <br />calculated for four reaches: Archuleta to Farmington (A-F), Farmington to Shiprock (F- <br />S), Shiprock to Four Comers (S-FC) and Four Comers to Bluff (FC-B). <br /> <br />DRAFT - SJRIP Hydrology Model Documentation <br />June 18, 1999 <br /> <br />32 <br />