SPDSS_Task3_KeyDiversionSTructures_Summary

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used to estimate agricultural consumptive use in the Phase 3 Historical Crop Consumptive Use Analysis (Task 74). The key structure lists also includes municipal diversions, reservoir carriers, and "demand" structures representing demands that receive water from more than one source. For consistency, the surface water and ground water modeling effort are expected to use these same structures. Approach Consumptive use modeling (StateCU), water budget modeling (StateWB), and surface water modeling (StateMod) for the 1950 to present study period will represent 100 percent of the consumptive uses within the SPDSS study area. Key diversion structures that make up approximately the top 85 percent of net absolute decreed surface water rights and diversions within specific Water Districts will be modeled explicitly. The remaining diversions will be modeled in an aggregate fashion. The final percentages of explicit (key) and aggregate structures to be modeled within each District are based on specific characteristics of the Water Districts. Key diversion structures in the SPDSS study area were identified in each Water District based on the following approach: • Identify and accumulate net absolute water rights per structure • Identify recorded diversions per structure for 1950 to present period • Rank structures according to net total absolute surface water rights • Highlight the top 85 percent of net absolute water rights • Identify preliminary average annual diversion threshold amounts associated with top 85 percent of water rights. This resulted in a threshold annual amount of 1,000 ac-ft for most Water Districts. • Recognize and add structures with absolute water rights not included in the initial list that divert greater than the threshold amount. • Remove structures with absolute water rights that will not be explicitly modeled, including: - Reservoir outlet structures - Duplicate structures used in coding for one Water District as FROM structures (CIU code = `F') from another Water District - Structures identified as non-existent (CIU code = `N'), historical (GILT code = `H'), or inactive (GILT code = `I') by the Water Commissionner - Structures receiving water from anon-river source (spring, seep, drainage, runoff, waste, salvaged water) • Add structures integral to Water District operations, as recommended during the Task 3 Water District meetings. Generally these included: - Reservoir supply ditches and important carrier diversion structures - Smaller, very senior absolute direct flow water rights and calling ditches - Ditches integral to municipal operations • Review percentage of total water rights and, if necessary, revise threshold amount to meet goal of explicitly modeling approximately 85 percent of diversions in the study area • Review irrigated acreage assigned to structures in the SPDSS Irrigated Acreage Assessment and remove previously identified key irrigation structures that have not been assigned acreage. Remove key structures without consistently available diversion records.