Sediment flux through the Golden Gate during the high flows of 2016 and 2017

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1 NOTE: This information is preliminary and is subject to revision. It is being provided to meet the need for timely best science. The information is provided on the condition that neither the U.S. Geological Survey nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information. Sediment flux through the Golden Gate during the high flows of 2016 and 2017 U.S. Department of the Interior U.S. Geological Survey Maureen Downing-Kunz David Schoellhamer, Paul Work California Water Science Center, Sacramento Presented to attendees of the RMP Annual Meeting, October 11, 2018

2 Background Watershed and sediment discharge enter SF Bay from Sacramento and San Joaquin Rivers, and smaller local tributaries Sediment supply to SF Bay has changed over time Quantifying the SF Bay sediment budget aids in management of: Navigation dredging Contaminant transport Shoreline resilience Wetland restoration Beach erosion Aggregate mining Sediment outflow at Golden Gate Yolo Bypass Sacramento Image date: 3/16/16; worldview.earthdata.nasa.gov

3 Sediment fluxes and budgets Flux: rate of transport at a cross-section Flux = discharge * concentration van Rijn 2006 Inflow Deposition Erosion Outflow Budget: a way to account for sediment gains and losses within a region of interest Change in storage = inflow - outflow

4 Example of sediment budget for SF Bay Schoellhamer et al RMP Pulse of the Estuary, sediment budget Outflow = inflow - change in storage

5 Suspended-sediment flux at Golden Gate Sediment budgets show that suspended-sediment flux at the Golden Gate is the largest and most uncertain term Objective: Collect sediment flux measurements during high runoff, build upon existing work documented in Erikson et al. (2013)

6 Golden Gate is extreme great depths, fast currents 6 ft (1.8 m) tidal range ~25% of SF Bay volume exchanged per tide Depth m ft Cochrane, G. R. et al Cooler colors = greater depths

7 Water Year 2015: The height of the drought Source: NOAA Regional Climate Centers

8 Water Year 2016: Great expectations Source: CA Dept of Water Resources

9 Water Year 2017: Extreme defined Wettest WY 2017 WY 1983 WY 2016 Average ( ) WY 2015 Driest WY 1924 Source: CA Dept of Water Resources

10 2016 and 2017 storms in context Month/Year Peak Delta Outflow (m 3 /s) February ,800 January ,000 January ,400 January ,450 March ,100 March ,100 February ,700 Source: CA Dept of Water Resources Erikson et al. (2013) This study

11 Dartnell et al Flux = discharge * concentration

12 ADCP: The sediment flux whisperer Simpson 2001 Acoustic Doppler current profiler (ADCP) basics: Transmit acoustic energy at known frequency f 0 Receive acoustic energy at a Doppler-shifted frequency f D Compute water velocity (u) as f(f 0, f D, speed of sound c) Range gate return signal to get velocity profile Use 3 transducers to calculate 3-D velocity Compute acoustic backscatter (ABS) from return signal Use water samples to relate ABS to SSC uu = ccff DD 2ff 0

13 Dartnell et al Mueller et al. 2013

14 Underway aboard R/V Questuary

15 Velocity Magnitude (ft/s) Dartnell 60 et al Depth (feet) Distance along transect (miles)

16 Acoustic Backscatter (db) Depth (m) Distance along transect (m) Velocity Magnitude (ft/s) Depth (feet) Distance along transect (miles)

17 Calibration of backscatter to SSC Wall et al. 2006

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19 Calibration of backscatter to SSC Suspended-sediment concentration (mg/l) Sediment-corrected backscatter (db) Preliminary Information Subject to Revision

20 ADCP-derived fluxes Ebb tide, out of SF Bay Flood tide, into SF Bay Qw (m 3 /s), Qs (kg/min), ebb positive Time Since 00:00 2/27/17, hours PST Qw, cms Qs Stage, MSL, m Measured Tidal Stage, m (MSL) Water Sediment Preliminary Information Subject to Revision

21 Water Flux Q * 1,000,000 (cfs) Ebb tide, out of SF Bay Flood tide, into SF Bay Parameter/Date Mar 2016 Jun 2016 Feb 2017 Max Q 4.6e6 cfs 1.3e5 m3/s 4.2e6 cfs 1.2e5 m3/s 4.4e6 cfs 1.2e5 m3/s Max Qs 2100 kg/s 2100 kg/s 5800 kg/s Max SSC 27 mg/l 35 mg/l 64 mg/l Preliminary Information Subject to Revision

22 Looking upstream Preliminary Information Subject to Revision 2017 Tidally filtered data from near-bed sensor except Alcatraz (mid-depth)

23 Comparison of 3 wettest months of 2016 and Preliminary Information Subject to Revision

24 Strong vertical gradients at Richmond Bridge in 2017 Richmond sensors: Mid-depth: 4.5 m MLLW Near-bottom: 12 m MLLW Water depth: 13.7 m MLLW Salinity, near-bottom mid-depth (-)

25 Strong vertical gradients at Richmond Bridge in 2017 Richmond sensors: Mid-depth: 4.5 m MLLW Near-bottom: 12 m MLLW Water depth: 13.7 m MLLW Date: 2/24/17 Upper water column: fresher water, flow toward Golden Gate Lower water column: salty water, flow into San Pablo Bay

26 Very exciting physics in San Pablo Bay in 2017! Simpson 1990 Velocity Direction (degrees) Velocity Magnitude (m/s) Snapshot of flow during early phase of ebb on 2/24/17

27 Trapping mechanism: Estuarine Turbidity Maximum (ETM) (SSC) Burchard et al ETM: a region along an estuary with a localized maximum in SSC

28 Typical location of SFB ETM (Schoellhamer 2001) Hypothesized location of SFB ETM during Feb 2017 caused by longitudinal density gradient ETM is a mechanism to retain sediment in SFB during high watershed runoff

29 Challenges Getting the timing right Physical factors are complex and not well understood Scheduling an appropriate vessel requires lead time Labor intensive ADCP frequency

30 Next step: Modeling suspended-sediment flux (SSF) Measured SSF Modeled SSF Alcatraz Island 1) Run a well-calibrated numerical suspended-sediment model to estimate SSF 2) Compare modeled and measured fluxes, determine regression model 3) Inspect residuals to identify causes of scatter, improve numerical model 4) Correct modeled SSF with regression model 5) Develop relation between SSF and available parameters such as Alcatraz SSC, Delta Q 6) Augment field observation data during high flow events to improve model

31 Acknowledgements San Francisco Bay Regional Monitoring Program San Francisco Bay Regional Water Quality Control Board San Francisco Estuary Institute San Francisco Estuary Partnership US Environmental Protection Agency, Region 9 US Army Corps of Engineers, San Francisco District US Bureau of Reclamation National Water Quality Monitoring Network for U.S. Coastal Waters and their Tributaries Rachel Allen, David Bell, Paul Buchanan, Gwen Davies, Brian Downing, Darin Einhell, Li Erikson, Larry Freeman, Daniel Livsey, Scott Nagel, Mark Stacey, David Stevens, Kurt Weidich, and Scott Wright