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<br />From: Rqn Blinne,. To: Shrr1ey Mondy <br /> <br />o <br />l."l <br />.... <br />~\ ., <br />1--' <br />t-' <br /> <br />Date: 01111/02 Time:: 2:56:42 PM <br /> <br />Pege6017 <br /> <br />daily percent time the monthly computed erR used in the natural flow analysis or <br />as identified for any proposed project. The result is a single time series of erR <br />data that is used directly in the daily model. If crop mix is an important variable to <br />retain in the model, the process could be computed on a crop-by-crop basis and <br />. then aggregated. <br /> <br />Disaggregation ofRetum. Flows and M&I Demands <br /> <br />In a few isolated cases return flows calculated in the monthly model will need to be fed <br />directly into the daily model (e.g. return flow from the Pine River basin entering the <br />Florida drainage). Since return flows are rather constant, we propose that the monthly <br />volume be divided by the number of days in the month. This produces a constant daily <br />flow for the month. There may be some flow discontinuities at month boundaries, but the <br />effect on the model results will be negligible. It is proposed that M&I demands be <br />similarly disaggregated. <br /> <br />Calculation of Daily Galns and Losses <br /> <br />In the development of natural flows, a set of gains and losses will be computed to force <br />balance to each gage. The gains and losses are the accumulation of unknown inflows, <br />phreatic water use, gage error and unknown diversions or other losses. Once calibrated in <br />the natural flow development, these gainslJosses are used in all future model runs. Since <br />these gains and losses will be computed on a monthly basis in the natural flow <br />development, they cannot be directly used in the daily time.step main stem model. <br /> <br />There are two possible approaches to developing daily gainlloss data. The first is to <br />develop a process to disaggregate the computed monthly values. The other is to operate a <br />daily time-step model to simulate historical conditions and directly compute gains and <br />losses. The first approach is problematic since there is no reliable key location that can <br />be used to develop a daily flow percentage as in the tributary flows. Utilizing daily gage <br />differences for each reach is not possible since they include non-natural activities that <br />must be accounted for. We propose the second approach as it is more straigh1forward <br />and will rely on the model configuration and assumptions in implementation, making it <br />consistent with future model operation. <br /> <br />We propose that the daily main stem model, configured to represent historical conditions, <br />be used to generate the gains and losses. This requires that all diversion, and tributary <br />daily data be in place and the daily main stem model be operational. This process <br />directly produces the daily gains and losses so there is no need to disaggregate a monthly <br />value. The process is envisioned as follows: <br /> <br />1. The daily main stem model. will be configured with the daily tributary gage flows <br />developed in the tributary disaggregation process. The Animas River at the <br />confluence will be set to the Animas at Fannington historical daily gage flow. <br /> <br />KeIler-Bliesner Engineering <br />Draft San Juan Model Input Data Generation <br /> <br />January 11, 2002 <br />Page 5 <br />