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Water rights associated with explicitly modeled reservoirs were then deleted from this list. The <br />listing was then sorted by both Water District and by source stream in order to geographically <br />group. In discussions with the State it was then decided to aggregate storage rights by Water <br />District - in most instances, storage decrees in each of the Districts were located within a fairly <br />small geographic area, typically at higher elevations and above most direct flow diversion <br />structures. In two instances (District 20 and District 22), source streams supplying storage decrees <br />were sufficiently spread out geographically to require more than one aggregation point. This <br />resulted in a total of 10 aggregated reservoirs to incorporate into the model network. <br />Aggregated reservoirs were generally located in the model network below the lowest source <br />stream serving a storage decree in each group. In most instances, the aggregated reservoirs were <br />located on the primary stream within each Water District. For example, storage decrees on many <br />of the upper tributaries of the Rio Grande were grouped into a single aggregated reservoir and <br />represented in the model at a single point on the mainstem. This simplifying procedure is <br />consistent with previous StateMod applications in other river basins. <br />Aggregate Reservoir Operation <br />Each aggregated reservoir and stock pond was assigned one account and an initial storage equal to <br />their capacities. Each of the aggregated reservoirs were estimated to remain full during each <br />month of the study period. Furthermore, the aggregated reservoirs were assumed to be 10 foot <br />deep in order to estimate open water surface area and allow calculation of evaporative losses. <br />Total surface area of the aggregated reservoirs in the basin was estimated to be 3695 acres. <br />Aggregated reservoirs located at higher elevations in the basin were assigned net evaporation <br />losses associated with mountain areas, as discussed in a memorandum documenting Task 6.8 <br />("Prepare Reservoir Files"). Aggregated reservoirs located at lower elevations were assigned net <br />evaporative losses associated with areas within the San Luis Valley Floor. The net evaporation <br />values (inches) used in the model are shown in Table 1 (note a negative value indicates more <br />precipitation than evaporation: <br />Table 1 <br />Net Monthly Evaporation Values <br />Used in the Rio Grande SurFace Water Model (inches) <br />Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Total <br />SAN LUIS VALLEY FLOOR 4.14 -0.34 -0.21 -0.22 -0.17 -0.30 7.08 7.31 8.37 7.42 6.48 6.08 45.63 <br />MOUNTAIN AREAS 2.88 -1.03 -0.61 -0.44 -0.39 -0.59 -0.76 5.49 7.61 6.12 3.74 4.34 26.35 <br />Aggregated Reservoir Structures <br />Based on water right information extracted from HydroBase using watright there are 244 absolute <br />storage water rights in Division 3 excluding those rights associated with explicitly modeled <br />reservoirs. These rights are associated with 219 different smaller reservoirs and stock ponds <br />(Table 2). Using Water District boundaries, these reservoirs and stock ponds were grouped as <br />shown in Table 3. More detailed information concerning specific reservoirs aggregated under <br />each group may be found in Attachment 1. <br />C:Acdss\Task7-2.doc Reservoir Aggregation March 13, 2000 -Page 2 of 5 <br />