Mallard Island cross-sectional variability: low-flow, moderate-flow, and high-flow events SF Bay Sediment Project U.S. Geological Survey Sacramento, CA Item #2b

Mallard Island Cross-sectional Variability Validation of sediment load calculation methodology by McKee et al. (2005) Low-flow measurement on August 31, 2004 Freshwater outflow at a minimum (~ 113 cms = 4,000 cfs) Peak spring tide Large wind-waves (>1 m) Moderate-flow measurement on January 4, 2005 Freshwater outflow moderate (~ 1830 cms = 64,000 cfs) 2 days after neap tide No wind-waves High-flow measurement on January 5, 2006 Freshwater outflow highest since 1997 (~ 9700 cms = 340,000 cfs) 3 days after peak spring tide No wind-waves Item #2b

Protocol ADCP: Perform discharge measurement, identify five discharge centroids CTDO profiling: After ADCP measurement, return to five centroids, lower and raise CTDO package through water column at each centroid Water sampling: Periodically collect water samples for optical sensor calibration, at multiple depths Compare discharge-weighted SSC with SSC at gagehouse (used for McKee calculation) Item #2b

Suspended-sediment record at Mallard Island Low-flow, spring tide sampling: 8/31/2004, Q = 3,892 cfs Item #2b

Suspended-sediment record at Mallard Island Moderate-flow, first-flush sampling: 1/4/05, Q = 64,000 cfs Item #2b

Suspended-sediment record at Mallard Island High-flow, first-flush sampling: 1/5/06, Q = 340,000 cfs Item #2b

Comparison of cross-sectional, velocity-weighted SSC and Mallard Island upper SSC Bias due to high SSC on north side of channel Item #2b

Reasons to reserve judgment: NASA Satellite image taken over SF Bay Pulse at Mallard Island Item #2b

NASA-ASTER image March 3, 2000, Q=150,000 cfs Centroid of sediment pulse seaward of Suisun Bay 17 days after peak Dayflow, 12 days after peak SSC at Mallard Island Sediment storage in Honker Bay affecting SSC in Mallard Island X-S Reasons to reserve judgment: NASA Item #2b

Reasons to reserve judgment: models Modeled cross-sectional SSC vs. modeled upper sensor SSC Item #2b

Mean error = 25% McKee (2005) estimate = 30% Reasons to reserve judgment: models Daily averages: modeled cross-sectional SSC vs. modeled upper sensor SSC Item #2b

Next steps Not enough information to definitively modify McKees flux estimates Are extremes bracketed? I think so… Need quasi-continuous velocity and SSC data over the duration of a multi-day flood event, across the channel Two possible approaches - Deploy multiple instrument packages in channel - Perform a few cross-sectional surveys everyday for the duration of a 3-5 day flood pulse Item #2b