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<br />Chapter II <br /> <br />Development of a Physically Based Distributed <br />Parameter Rainfall Runoff Model <br /> <br />municipal and industrial use depletions, and transbasin diversions, adding such water back to the <br />measured volume at the station. Natural flow studies to detennine these virgin flows were <br />conducted by Reclamation's Denver Technical Center. Virgin flow data were developed for water <br />years ] 952-90. Observed, unregulated, and virgin flow data sets were all used in the calibration of <br />the Gunnison Model. <br /> <br />Figure] 2 shows climate and SNOTEL stations used in the Gunnison Model. Daily maximum and <br />minimum temperature, daily precipitation, and daily snow water equivalent (SNOTEL sites only) <br />were collected for these sites and stored in the relational database. The temperature and <br />precipitation data were used as input data to the Gunnison Model. Snow water equivalent data <br />were used in model calibration. <br /> <br />An algorithm for the generation of missing input data (temperature and precipitation) was <br />developed and consistently used in the synthesis of data to fill in gaps in the historic record. For <br />each climate station, the five closest stations were identified. The distances between the climate <br />station and each of the five nearest stations were determined using a spatial processing program <br />(AML) in the GIS. Using HDB and utilities of the Ingres relational database software, monthly <br />averages for precipitation, maximum temperature, and minimum temperature for all climate sites <br />were then calculated and stored in the database for continued use. <br /> <br />The methodology for calculating missing precipitation data in the Gunnison Model is shown in the <br />following equation: <br /> <br />5 <br />P, = Il: <br />j=1 <br /> <br />5 <br />P, * (A VE,IA VEj) * (lID;j)] I (l: ]ID, j)] <br />j=] <br /> <br />where: <br /> <br />P, <br />P, <br />AVE, <br />AVE, <br />D <br />'J <br /> <br />= Station of interest, but missing precipitation <br />= Array of five values of precipitation at the five nearest sites to the site of interest <br />= Monthly average for site of interest for current month <br />= Monthly average for five closest sites for current month <br />= Array of five distances between site of interest and each of its five nearest sites <br /> <br />18 <br />