Water Quality Model: Flow Input Needs and Low Flow Selection December 14, 2011 Laura Weintraub

TROM Flow Disaggregation for Input to Water Quality Modeling TROM Output: –Oct – Apr: monthly –May – Sep: bi/tri-monthly Three types of data linked to WQ models: –Reservoir releases –Diversions –TMWRF effluent discharge What spatial / temporal disaggregation of TROM flows is needed? 2

Application of TROM Flows: Time Scale Reservoir Releases, TMWRF, diversions: WARMF hydrologic calculation of tributary flow will include daily variation Check streamflows with TROM Output 3 Apply monthly / bi-monthly TROM flow directly; use step function to fill daily values

Application of TROM Flows: Spatial Scale Truckee Meadows Diversions have individual output –TROM output used directly Lower River Diversions lumped into 2 parts –Vista Gage to Derby Dam –Derby Dam to Pyramid Lake –TROM output will be “split” to correspond with correct river segments in model based on current diversion records and/or water rights 4

Use of TROM Model Output to Select Low Flow Year 100 years of predicted flows: TROM Scenarios: –Future No Action: Estimated “Buildout” Level of Development (2033) Truckee River Agreement Operations (TRA) –Future TROA: Estimated Buildout Level of Development Truckee River Operating Agreement Operations (TROA)

TROM Flow Ranking Analysis Tool for assessing flow ranking based on a variety of methods Two Scenarios: Future No Action, Future TROA Considered Six Locations –Farad, Sparks, Vista, Above Derby Dam, Below Derby Dam, Inflow to Pyramid Lake Applied Seven Ranking Methods –Minimum annual (lowest flow during the year) –Annual average –Minimum monthly (lowest average monthly flow) –Minimum Irrigation Season (Apr - Sep) (lowest flow during these months) –Average Irrigation Season Apr - Sep) –Minimum Summer (May-Sep) (lowest flow during these months) –Average Summer (May-Sept)

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Climate Data Ranking Analysis Considered five locations from three sources of data –Truckee, CA ; (NCDC) –Tahoe City, CA (NCDC) –Independence Lake, CA (SNOTEL) –Sacramento Valley (California DWR) –San Joaquin Valley (California DWR) Three Ranking Metrics –Water Year Precipitation Sum (Truckee, Tahoe City, and Independence Lake) –Water Year River Runoff Sum (Sacramento and San Joaquin) –Water Year River Runoff Index (Sacramento and San Joaquin) Tool Assessment Methods –Percent rank and absolute rank –Compare with 10 th, 25 th, 50 th, and 75 th percentile of the data

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Proposed Approach For Low Flow Year Selection Identify 5 – 10 candidate years based on TROM flow and climate ranking Review resulting hydrographs for each year Consider availability of supporting data –e.g., climate, solar radiation Coordinate with NDEP to select best choice for representative year Consider most appropriate TROM scenario and characterization of Truckee Canal capacity limits 10

Questions? 11