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<br />002269 <br /> <br />Chapter II <br /> <br />Development of a Physically Based Distributed <br />Parameter Rainfall Runoff Model <br /> <br />For Some Gunnison Model parameters, physical data of sufficient detail were not available for <br />development of initial parameter values (panicularly model parameters dealing with ground-water <br />and subsurface systems). For these parameters, educated guesses were made for initial values. <br />Ouring the calibration phase of model development, parameters were judiciously adjusted to <br />generate a good fit between the observed and the modeled streamflows in the Upper Gunnison <br />River Basin. <br /> <br />MODEL INPUT - DATA MANAGEMENT <br /> <br />Significant effon went into the management of time series data used in the Gunnison Model. <br />Historic time series data were collected for all streamflow gages, reservoirs. climate stations, and <br />snow telemetry (SNOTEL) stations in the Gunnison River Basin. All these data were stored in the <br />Upper Colorado Regional OffIce's HOB. HOB is a database which runs on a Oata General work- <br />station and uses Ingres relational database software. A description of HOB can be found in <br />attachment A of this document. <br /> <br />As stated earlier, 16 subbasins were defined for the Upper Gunnison River Basin. At the outflow <br />point of each of these subbasin.s, a USGS gage or Reclamation reservoir provides the historic data <br />necessary for model calibration. These outnow points can be considered the nodes in the <br />Gunnison Model. Figure 11 displays the 16 nodes. Table 4 lists (he USGS gages or Reclamation <br />reservoirs at each of these nodes. <br /> <br />For each node, three time series data sets were collected and stored in HOB. These time series <br /> <br />data sets included: (lj observed daily now, (2) unregulated daily now, and (3) monthly virgin <br />flow. Unregulated daily flow data were generated by adjusting the observed flow for the effects of <br />upstream reservoir storage and evaporation.' Virgin flows were developed by adjusting observed <br />data for effects of upstream reservoir storage, upstream reservoir evaporation. irrigation depletions, <br /> <br />~ For sites withom upstream storage, the unregulated time series data are lhe same as the observed data. <br /> <br />17 <br />