Support for this project was provided in part by a Miller Foundation grant to the Institute of Sustainability and Systems at Portland State University and a Portland State Research enhancement grant. D.A. Jay and S.A. Talke were supported in part by the National Science Foundation grant: Secular Changes in Pacific Tides, OCE-0929055. S.A. Talke was supported in part by National Science Foundation grant: 19th Century US West Coast Sea Level and Tidal Properties, OCE-1155610, and the US Army Corps of Engineers, award number W1927N-14-2-0015. D.H. Schoellhamer was supported by the Delta Science Program and USGS Priority Ecosystem Science Program
Journal of Hydrology
San Francisco Bay Watershed (Calif.) -- Sediment transport -- History, San Francisco Bay Watershed (Calif.) -- Sediment transport -- Analysis, Estuarine hydrology
River flow and sediment transport in estuaries influence morphological development over decadal and century time scales, but hydrological and sedimentological records are typically too short to adequately characterize long-term trends. In this study, we recover archival records and apply a rating curve approach to develop the first instrumental estimates of daily delta inflow and sediment loads to San Francisco Bay (1849 – 1929). The total sediment load is constrained using sedimentation/erosion estimated from bathymetric survey data to produce continuous daily sediment transport estimates from 1849 to 1955, the time period prior to sediment load measurements. We estimate that ~55% (45 – 75%) of the ~1500±400 million tons (Mt) of sediment delivered to the estuary between 1849 and 2011 was the result of anthropogenic alteration in the watershed that increased sediment supply. Also, the seasonal timing of sediment flux events has shifted because significant spring-melt floods have decreased, causing estimated springtime transport (April 1st to June 30th) to decrease from ~25% to ~15% of the annual total. By contrast, wintertime sediment loads (December 1st to March 31st) have increased from ~70% to ~80%. A ~35% reduction of annual flow since the 19th century along with decreased sediment supply has resulted in a ~50% reduction in annual sediment delivery. The methods developed in this study can be applied to other systems for which unanalyzed historic data exist.
Moftakhari, H. R., Jay, D. A., Talke, S., Schoellhamer, D. H., (2015). Estimation of historic flows and sediment loads to San Francisco Bay, 1849–2011. Journal of Hydrology. Volume 529, Part 3, Pages 1247–1261.