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Assessment of long-term impacts due to sediment supply changes towards San Francisco Bay-Delta

Assessment of long-term impacts due to sediment supply changes towards San Francisco Bay-Delta. 15%. Fernanda M. Achete - UNESCO-IHE - f.achete@unesco-ihe.org Mick van der Wegen - UNESCO-IHE - m.vanderwegen@unesco-ihe.org

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Assessment of long-term impacts due to sediment supply changes towards San Francisco Bay-Delta

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  1. Assessment of long-term impacts due to sediment supply changes towards San Francisco Bay-Delta 15% Fernanda M. Achete - UNESCO-IHE - f.achete@unesco-ihe.org Mick van der Wegen - UNESCO-IHE - m.vanderwegen@unesco-ihe.org Bruce E. Jaffe - U.S.G.S, Pacific Coastal and Marine Science Center, Santa Cruz - bjaffe@usgs.gov 50% 35% Results INTRODUCTION The main source of sediment to San Francisco Bay is the Sacramento San-Joaquin Delta. The objective of this poster is to assess sediment trapping in the Delta and the influences of river discharge and pumping on trapping. • The decrease in Sacramento River sediment flux at the inland and bay sides of the Delta is greater than 1 order of magnitude. • Lower discharge results in a larger trapping efficiency • Sacramento River contribution to the bottom sediment composition varies spatially due to discharge. Higher Sacramento River flows result in sediment depositing further south. • Q black < Qgreen< Qred Numerical Model Dflow-FM • D-Flow FM • Flexible mesh • Process-based model • 2D • Hydrodynamics • Delft WAQ (Water Quality) • Offline Coupling • Sediment Suspension Concentration (SSC) • Deposition • Two mud fractions Inflow Total Sediment in S1 Outflow Inflow • The highest sedimentation observed in the Delta is located in the breached island • Varying discharge results in the same sedimentation pattern but different layer thicknesses Anomaly map of total Sediment in S1 [g] Boundary Conditions Sacramento River andPumping 12.7x106g 12.7x106g • The Delta works as a trap for sediment coming from the Sacramento and San Joaquin Rivers • ~70% of the sediment stays in the Delta (no pumping), increasing to ~ 80% with pumping • This trend correlates with pumping vs. non-pumping changes in Delta in/outflow Kimmerer, 2004 4.2x106g 2.8x106g Discussion Points No Pumping Pumping 4.6x106g 4.6x106g • How much does the grain size influence dynamics? • How applicable are these results to other estuaries?

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