This data package is a key deliverable for the Research to Understand Impacts of Bay Sand Mining on Sand Supply and Transport in San Francisco Bay and the Outer Coast project.

A sediment budget for the Bay was completed that accounted for the sediment entering (inflowing, sources) and leaving (outflowing, losses) while taking into account the change in storage in the system. If the time period chosen is long enough to average out the variability of the larger contributing terms, the basic concept of a sediment budget, conservation of mass should hold. The inflows minus the change in storage will balance the outflows. If all terms but one are known, the unknown term can be computed by difference but will incorporate the cumulative uncertainties of all the other terms. Given Subtasks 1.2, 1.3, 1.4, and 1.5 qualified sediment inflows from the Central Valley larger rivers, the smaller local tributaries flowing from the nine counties that surround the Bay, the sediment stored and removed from the flood control channels around the Bay, and bathymetric change respectively, the remaining terms that needed to be determined were:

       1. wetland deposition due to rising sea levels,

       2. dredging removal,

       3. mining removal, and

       4. exchange through the Golden Gate Bridge cross-section. 

This subtask focused on the first three of these items; exchange of sediment between the Bay and Pacific Ocean via the Golden Gate Bridge cross-section (and indeed between each subembayment) was the term that was left for quantification by difference. 

Subtask Contact: Lester McKee, Senior Environmental Scientist ([email protected]).

File Contents

The data package includes the following input files:

1. Subtask 1.6 Wetland deposition computation.xlsx
This simple MS Excel file contains the data and computation used to estimate the volume of sediment associated with passive wetland deposition associated with rising sea level. Since the units of SLR are in mm/y, the resulting volume estimates are in m3/year. 

2. Subtask 1.6 DMMO Grainsize and Disposal Summary Database.xlsx
This file contains data on volume of removal and grain size (mud: <0.0625 mm; sand: 0.0625-2mm; gravel >2 mm), %moisture, and %solids of that sediment (when lab measured) for 803 dredging events that occurred from 2001 to 2020 classified by subembayment and fate (disposal or reuse location). Removal events ranged in size from 18 cubic yards (CY) to 4.5 million CY. %sand ranged from 0-87%. The data were also collated in this file for subembayment, and fate. By volume, 32% of the material dredged was sand or gravel sized and 40% of it was used for upland and reuse restoration projects.

3. Subtask 1.6 GIS data of dredging locations and footprints 05-07-22
This folder of GIS files provides the 124 locations where sediment dredging occurred. 

4. Subtask 1.6 SFLMTS map 1-18-23.pdf
This PDF map provides the locations where sediment dredging materials were either disposed of or reused, as part of the San Francisco Bay Long Term Management Strategic Planning Area. The notation for each site was used as the basis for the “DMMO Grainsize and Disposal Summary Database.xlsx” file.

5. Subtask 1.6 Sand mining volume and grainsize database.xlsx
The file provides the volumes of material mined for each lease area from 2001-2020. The database of sand mining data provided here was mostly compiled by BCSC staff over the past decade from information submitted by the mining companies as a condition of their permits. BCDC (Brenda Goeden) emailed the BCDC database to SFEI (Lester McKee) in October, 2021 and then McKee and Goeden discussed it in detail in February 2022 as small glitches were identified and reconciled. The BCDC database contained twice annual data for calendar year 2015 and quarterly data thereafter. Data for calendar years 2017, 2018, 2019, and 2020 were separately submitted to SFEI under an independent data request for grain size data by the mining companies. This provided a quality assurance opportunity. The data on volumes for these four years were found to match almost (<0.01% difference) exactly with the data in the BCDC database. In general, data for the recent 20 years is considered to be of high quality (Brenda Goeden, personal communication, February 2022), but data for earlier periods (1975 to the mid to late 1990s) may be incomplete. Overall, there may still be minor discrepancies in the data for 2001-2020 due to transcribing errors but (if) these exist, they would have <<1% impact the 20-year total volume or average volume mined. The file also contains pictures of the lease locations.

The data on the grain size of material mined from San Francisco Bay were obtained via email in MS Excel spreadsheet format from Lind Marine and Lehigh Hanson in September 2021. Data for calendar years 2017, 2018, 2019, and 2020 were complete. The data were compared to that provided in a MS PowerPoint presentation given to the STAC in May of 2021 and found to reconcile very well. There appears to be no grain size trends both within years and between years which seems logical. Overall, there is no reason to question the quality of this grain size data - the data appear to be of very high quality. Overall, 96% of the volume of material mined from the Bay was sand-sized (0.7-2.4 mm), about 1% was mud, and the remainder was gravel.