Sediment

Suspended sediment concentration (SSC) is of critical importance to the management of San Francisco Bay (SFB), yet has not been a focus of sustained high frequency monitoring efforts in shallow shoal and slough habitats that make up a majority of the area of the South Bay (SB) and Lower South Bay (LSB). In this report, we provide a status update for year one of a three year collaboration between the San Francisco Bay Nutrient Management Strategy (NMS) and Regional Monitoring Program (RMP) with the South Bay Salt Pond Restoration Project (SBSPRP) to estimate high frequency SSC throughout the SB and LSB. As a part of this effort, 15-minute turbidity data from seven locations, collected as part of the NMS Moored Sensor Program (MSP), was paired with monthly discrete SSC sampling, with the goal of creating a robust turbidity-SSC calibration. An additional turbidity-specific sensor was also deployed and paired with discrete SSC sampling on the shoal near the Eden Landing Whale’s Tail. Here we present preliminary results from turbidity-SSC calibrations at these eight sites, which together span a range of environments (deep channel, shoal, slough) representative of SFB. Following completion of this calibration, resource managers will be able to convert continuous high-frequency turbidity data to SSC at locations throughout SB and LSB, greatly aiding future sediment-focused efforts

This report provides a project update for year two of a three-year collaboration between the San Francisco Bay Nutrient Management Strategy (NMS), San Francisco Bay Regional Monitoring Program, and South Bay Salt Pond Restoration Project, to estimate high frequency suspended sediment concentration (SSC) in San Francisco Bay (SFB). Through its role in monitoring water quality in SFB, the NMS maintains an array of autonomous sondes that record high frequency (15-minute) water column turbidity, amongst a suite of other environmental parameters. Turbidity data from these monitoring sites was combined with discrete SSC samples to create a bay-wide turbidity-SSC calibration, allowing for estimates of high frequency SSC.

This report outlines details from the annual Regional Monitoring Program for Water Quality in the San Francisco Estuary (RMP) sediment cruise, conducted July 24 – 27, 2023. The Regional Monitoring Program conducts routine monitoring of water, sediment and biological tissue. For 2023, sampling operations entailed dry season collections at 16 RMP sediment sampling sites.

This data release provides bathymetric change grids of four geographic areas of San Francisco Bay, California, comparing digital elevation models (DEMs) created from bathymetric data collected in the 1970s and 1980s with DEMs created from bathymetric data collected in the 2010s and 2020. These types of change analyses can provide information on the quantities and patterns of erosion and deposition in San Francisco Bay over the 9 to 47 years between surveys, and they reveals that the bay floor lost about 34 million cubic meters of sediment between the intervening time period. Results from this study can be used to assess how San Francisco Bay has responded to changes in the system such as sea-level rise and variation in sediment supply from the Sacramento-San Joaquin Delta and local tributaries, and supports the creation of a new, system-wide sediment budget. These bathymetric change grids can also provide data to ecosystem managers about the quantities and patterns of sediment volume change in San Francisco Bay to assist in decision-making for a variety of sediment-related issues, including restoration of tidal marshes, exposure of legacy contaminated sediment, and strategies for the beneficial use of dredged sediment.

Bathymetric change analyses document historical patterns of sediment deposition and erosion, providing valuable insight into the sediment dynamics of coastal systems, including pathways of sediment and sediment-bound contaminants. In 2014 and 2015, the Office for Coastal Management, in partnership with the National Oceanic and Atmospheric Administration (NOAA) Office of Coastal Management, provided funding for new bathymetric surveys of large portions of San Francisco Bay. A total of 93 bathymetric surveys were conducted during this 2-year period, using a combination of interferometric sidescan and multibeam sonar systems. These data, along with recent NOAA, U.S. Geological Survey (USGS), U.S. Army Corps of Engineers, and private contractor surveys collected from 1999 to 2020 (hereinafter referred to as 2010s), were used to create the most comprehensive bathymetric digital elevation models (DEMs) of San Francisco Bay since the 1980s. Comparing DEMs created from these 2010s surveys with USGS DEMs created from NOAA’s 1971–1990 (hereinafter referred to as 1980s) surveys provides information on the quantities and patterns of erosion and deposition in San Francisco Bay during the 9 to 47 years between surveys. This analysis reveals that in the areas surveyed in both the 1980s and 2010s, the bay floor lost about 34 million cubic meters of sediment since the 1980s. Results from this study can be used to assess how San Francisco Bay has responded to changes in the system, such as sea-level rise and variation in sediment supply from the Sacramento-San Joaquin Delta and local tributaries, and supports the creation of a new, system-wide sediment budget. This report provides data on the quantities and patterns of sediment volume change in San Francisco Bay for ecosystem managers that are pertinent to various sediment-related issues, including restoration of tidal marshes, exposure of legacy contaminated sediment, and strategies for the beneficial use of dredged sediment.

The U.S. Geological Survey, Western Ecological Research Center collected sediment and accretion data at a wave-exposed tidal salt marsh in South San Francisco Bay, California. Sediment traps and feldspar marker horizons (MH) were deployed along transects of increasing distance from the sediment source, at primary, secondary and tertiary marsh channels/bay. Data were collected bi-monthly over two month periods in summer 2021 and winter 2021/2022. Included here are trap and MH plot locations, calculated sediment fluxes at each station by deployment period, annual accretion rates, and covariates associated with sediment deposition and accretion including vegetation structure and elevation. This project aimed to assess the temporal and spatial patterns in sediment deposition in order to better understand sediment delivery and marsh resilience to sea-level rise.

Sediment samples were collected on and adjacent to the Whale’s Tail South marsh. Short push-cores of bed sediment were collected in South San Francisco Bay adjacent to Whales Tail South marsh on five days from June through August 2021 and 3 days from November 2021 to January 2022. Additional samples were taken from ceramic tiles placed on the marsh to measure sediment deposition and from rip-up clasts deposited on the marsh edge. Samples were analyzed for sediment properties including bulk density, particle size distribution, and percent carbon. These data were collected as part of a collaborative study with the USGS Western Ecological Research Center to quantify sediment fluxes, deposition on the marsh, and changes in marsh morphology at Whale's Tail marsh in southern San Francisco Bay.

The U.S. Geological Survey (USGS) Pacific Coastal and Marine Science Center collected hydrodynamic and suspended sediment flocculation data at channel and shallow water sites in south San Francisco Bay in July 2020. The data were used to determine water column stratification, turbulence profiles, and floc size evolution. The goal of this project was to bound the controls on floc size and floc settling velocity to improve estimates of sediment fluxes and consider error in numerical models of sediment transport in San Francisco Bay. This data release includes hydrodynamic, sediment concentration, and particle size timeseries during July 2020, as well as sediment bed properties, water column particle size distributions, and CTD profiles collected on four days in July 2020 at both sites. Details on station location, instrumentation, and measured variables are included on pages for each data type. These data were collected as part of a collaborative project with the USGS California Water Science Center. Funding was provided by the San Francisco Estuary Institute.