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reasons for under-delivery, or shortage, can include insufficient water rights (legal supply), <br />insufficient hydrology (physical supply) and inaccurate data (streamflows, diversions, efficiency, <br />return flows, etc.). In most instances, modeled shortages are a result of insufficient wet water, <br />although historical diversions under "free-river" conditions can also create modeled shortages. <br />The question of sufficient water rights can be addressed in StateMod through the addition of "free <br />water rights" -junior priorities which allow ditches to divert under very higher river flows. <br />Insufficient supply is addressed by re-examining hydrology input files, re-configuring the model <br />network, and/or adjusting operating rules to make additional supply available. Calibration of the <br />Rio Grande Surface Water Model was achieved primarily through hydrology, network, and <br />operating rule adjustments. <br />With respect to model calibration, a Phase la target was set to reduce basin-wide shortages to less <br />than 10 percent of total basin-wide diversions. Final Phase la modeled demand shortages over <br />the study period averaged approximately 20,000 of per year, or roughly 1.4% of the average <br />annual amount of water diverted. Shortages ranged from a high of 3.62% of total diversions to a <br />low of 0.57% (Attachment 2). <br />Shortages were also examined for each separate Water District and by river or stream to identify <br />any particular geographic areas with poorer calibration. Also shown in Attachment 2 are average <br />annual shortages for each of the eight water district. Although most modeled shortages were <br />experienced in District 20 (Rio Grande mainstem) it actually represents the smallest amount of <br />shortage as a percent of total District diversions. The greatest shortages as percent of diversions <br />was experienced in Water District 35 (Trinchera Creek) -this may be due to current <br />interpretation of historical diversion records and will be further examined in later stages of model <br />development. <br />Modeled Reservoir Operations <br />Results of comparisons between historical EOM contents and simulated EOM contents are shown <br />graphically for each of the reservoirs explicitly represented in the model (Attachment 3). These <br />comparisons are shown both for the entire study period (1950 - 1997) and for the most recent <br />years (1978 - 1997). The current status of the HydroBase database requires significant data <br />filling for early years of the study period for reservoir records, and therefore more recent <br />comparisons are more meaningful. <br />The Rio Grande Surface Water Model includes numerous operating rules which define how <br />reservoirs are operated. For example, these rules define when, how much, and to which <br />downstream user(s) water should be released. The rules are based on information developed <br />during Task 4 of the RGDSS Surface Water Component study (interviews with local water users). <br />As shown in the graphs of Attachment 3, modeled EOM contents are quite favorable in <br />comparison to historic observations. Seasonal trends (fill/release) are evident in both time-series <br />and match well in most cases. In some instances, the model clearly reports releases from storage <br />that apparently did not occur historically and vice-versa. Modeled operations at Platoro <br />Reservoir, for example, diverge from historic beginning in the mid-1980's and continuing until <br />the early 1990's -this is due to more significant modeled releases over this period which may <br />result from assumptions about reservoir access by downstream ditches or basic hydrologic input <br />data (proration factors, return locations, etc.). EOM contents at Platoro, as well as other <br />reservoirs will continue to be a focus of calibration efforts in later stages of model development. <br />C:Acdss\Task6-14.doc Phase la Model (Flistoric Monthly) February 22, 2000 -Page 8 of 10 <br />