PWA - Project Detail - South Bay Salt Pond Restoration Project Geomorphic Assessment

Tidal wetland restoration in the breached ponds of the South Bay Salt Pond (SBSP) Restoration Project relies on capturing recirculated estuarine sediments to build subsided former marshes up to mature marsh plain elevations. This large new sediment demand, combined with significant increases in tidal prism caused by tidal inundation of the ponds, will affect the South bay sediment dynamics, extent of offshore mudflats and shoreline erosion rates at the estuary scale.

PWA documented a sediment budget model for the South Bay, which was combined with a set of empirical geomorphic tools, to predict how intertidal mudflats would respond over the next 50 years under no action and maximum tidal restoration scenarios for the ponds. Our methodology was based on a projection of the sediment budget of the South Bay taking into account physical constraints on erosion, sedimentation and sediment transport pathways within the estuary. We did this by analyzing the response of the major geomorphic units that comprise the estuary to waves, tidal currents, and relative sea-level rise. Our analysis drew upon historical bathymetric change data and analysis carried out by the U.S. Geological Survey.

The analysis showed that most of the restoration sediment demand is located in the upper reaches of the estuary where sediment naturally accretes. Here, under a no action scenario a gain in mudflat area is predicted whereas under full tidal restoration, a significant loss of mudflats due to increased sediment demand in the restored ponds is anticipated. A sensitivity analysis showed that variability in the magnitude of suspended sediment inflow from Central Bay induces the greatest uncertainty in predicted mudflat area.

Our analysis can be used to assess ecologic implications of physical habitat change, such as the impact of mudflat area change on shorebird feeding. It also informs an adaptive management process that is an integral part of the Restoration Project.

Report is available for download on the South Bay Restoration site as Appendix I to the Final EIS/R.

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Title		South Bay Salt Pond Restoration Project Geomorphic Assessment (pdf) 79KB
Project Summary		PWA completed a sediment budget model for the South Bay, which was combined with a set of empirical geomorphic tools, to predict how intertidal and shallow water habitats (tidal marsh, mudflats, and open water) would respond to large-scale restoration over the next 50 years.
Location		South San Francisco Bay, CA
Client		California State Coastal Conservancy

Project Detail		Tidal wetland restoration in the breached ponds of the South Bay Salt Pond (SBSP) Restoration Project relies on capturing recirculated estuarine sediments to build subsided former marshes up to mature marsh plain elevations. This large new sediment demand, combined with significant increases in tidal prism caused by tidal inundation of the ponds, will affect the South bay sediment dynamics, extent of offshore mudflats and shoreline erosion rates at the estuary scale. PWA documented a sediment budget model for the South Bay, which was combined with a set of empirical geomorphic tools, to predict how intertidal mudflats would respond over the next 50 years under no action and maximum tidal restoration scenarios for the ponds. Our methodology was based on a projection of the sediment budget of the South Bay taking into account physical constraints on erosion, sedimentation and sediment transport pathways within the estuary. We did this by analyzing the response of the major geomorphic units that comprise the estuary to waves, tidal currents, and relative sea-level rise. Our analysis drew upon historical bathymetric change data and analysis carried out by the U.S. Geological Survey. The analysis showed that most of the restoration sediment demand is located in the upper reaches of the estuary where sediment naturally accretes. Here, under a no action scenario a gain in mudflat area is predicted whereas under full tidal restoration, a significant loss of mudflats due to increased sediment demand in the restored ponds is anticipated. A sensitivity analysis showed that variability in the magnitude of suspended sediment inflow from Central Bay induces the greatest uncertainty in predicted mudflat area. Our analysis can be used to assess ecologic implications of physical habitat change, such as the impact of mudflat area change on shorebird feeding. It also informs an adaptive management process that is an integral part of the Restoration Project. Report is available for download on the South Bay Restoration site as Appendix I to the Final EIS/R.