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Memorandum To: Ray Alvarado M~1~ch 10, 2003 <br />Page 4 <br />Thanks to StateMod's efficiency in creating binary output files, the output from a daily mod 1 simulation <br />is generally of a manageable size. Printable, ASCII output, by comparison, can be quite ext ~sive. <br />StateMod allows the user to specify the structures for which printable output should be gen ated, and <br />this feature must be used judiciously with a daily time step model. <br />4.0 Using a monthly model to develop a daily model <br />StateMod and the CDSS DMI's contain features that allow the user to develop daily data se ~ from an <br />existing monthly model's input files, using a variety of approaches to the disaggregation p Cess. In this <br />section, it is assumed that the CDSS user has a monthly model available to him and wants t ,create a <br />daily time step model. The user can direct StateMod to apply any combination of these six )pproaches to <br />daily baseflows, demands, and reservoir targets: <br />1. read in daily data <br />2. divide a monthly estimate by the number of days in a month <br />3. set daily data to the average value for the month <br />4. pattern the daily disaggregation of a monthly value after another daily time series s ..plied by the <br />user <br />5. interpolate between monthly values assigned at the middle of the month. <br />6. interpolate between monthly values assigned at the end-of--month <br />In addition to these daily data approaches, which can be applied to any time series type, the `"daily <br />decrementing" approach is available for demands. The daily decrementing approach allows a user to <br />estimate daily demands by providing a monthly total that is decreased each day that a diver ~on occurs. <br />This capability, which is assigned globally to all diversions, can be important when simulat mg a ditch <br />with a significant flood right that typically diverts water for only a few days a month. Whe this option <br />is used for ditches without a significant flood right, water rights or canal capacity typically Xrnit the <br />amount diverted in a day. <br />The remainder of this section provides general guidance on daily estimation techniques of s me <br />parameters, based on general modeling experience and the daily model pilot study that was done in the <br />Yampa basin. <br />4.1 Daily Baseflows <br />Baseflow exhibits the greatest daily variability of any model input parameters, and is th efore the <br />parameter to which the model is most sensitive. The Yampa basin pilot study conclude (that the best <br />approach to baseflow estimation was to pattern the daily disaggregation after an existin 'gage <br />(Approach 4 above). Conversely, when daily flows were set to monthly averages, the d lly model <br />essentially provided the user with the same information as a monthly model. <br />Developing daily baseflows from basic daily data (Approach 1) required much more e rt, without <br />significantly better results relative to the "daily pattern" approach. However it is reco 'zed this <br />result maybe limited to a basin with a relative abundance of water such as the Yampa. deed <br />CS-B99-190-00/B /TASKMEM03FINAL.DOC <br />