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Memorandum To: Ray Alvarado Much 10, 2003 <br />Page 6 <br />On the other hand, according to State personnel familiar with daily modeling in the wat~r short Rio <br />Grande basin, this approach resulted in better calibration in that basin. <br />4.3 Daily Delayed Return Flows <br />Depletion and return flow analyses are typically done on a monthly, not daily, basis in Ater <br />resources applications. Estimating daily return flow fractions that result in a monthly re flow <br />pattern that has been estimated previously, or which seems reasonable, may not be strai tforward. <br />This is because the monthly return fraction is the result of superimposing 30 or 31 non ' 'ear daily <br />patterns on top of one another. In the Yampa basin, daily return fractions were develop .using the <br />Glover solution method with a single one-day pulse of recharge to the alluvial groundw ter system. <br />(See the memo CRDSS Daily Yampa Model Subtask 1 -Equivalent daily return flo factors.) <br />The same technique and aquifer parameters had been used to estimate the monthly mod 1, so the <br />summed effect of daily returns over a month was the same as the effect of the monthly turn <br />fraction. <br />In general, daily return flow fractions should be generated using whatever analytical ap xoach was <br />taken for monthly return fractions, with 0t set to one day. If monthly return fractions w re estimates <br />using a less rigorous approach, the user may have to resort to trial-and-error to achieve .series of <br />daily factors with an equivalent monthly effect. <br />5.0 Summary <br />StateMod has the capability to operate on a daily time step by allowing the user to select m a variety <br />of approaches to provide or estimate daily data. These capabilities overcome the biggest back to <br />daily modeling, namely, the development and management of daily data. However, selectin an <br />appropriate approach to provide or estimate daily data is not trivial. The selection may be d $ferent for <br />different types of data (streamflows, demands and reservoir targets), the type of system be' g modeled <br />(water-short vs. water-abundant) and the nature of an application (reconnaissance vs. fmal). Options <br />available in StateMod and their application to the Yampa and Rio Grande basin indicate th e different <br />approaches can result in a calibrated daily model in a very cost effective manner. The expe 'ences <br />described herein should assist future applications of calibrating and applying a daily water source- <br />planning model. <br />6.0 Comments and Concerns <br />Development of quality daily data cannot, in general, be replaced by an estimation techniq .The <br />approaches available to estimate daily data from monthly estimates that are available in Sta Mod and <br />described herein should be considered only when basic data and/or development resources e limiting. <br />Future enhancement to StateMod might reevaluate the treatment of negative baseflows part ¢ularly on a <br />daily basis. If aggressive development of quality data and engineering estimates cannot eli mate <br />negative baseflows, a more sophisticated treatment should be considered. For example acs ting <br />CS-B99-190-00/S /TASKM&b103FINAL.DOC ~~~1"~LE <br />