Shoreline Seasonality of California's Beaches

American Geophysical Union (AGU) | January 30th, 2025

We report on remote sensing techniques developed to characterize seasonal shoreline cycles from satellite-derived shoreline measurements. These techniques are applied to

We report on remote sensing techniques developed to characterize seasonal shoreline cycles from satellite-derived shoreline measurements. These techniques are applied to 22-yr of shoreline measurements for over 777 km of beach along California's 1,700-km coast, for which the general understanding is that shorelines exhibit winter-narrow and summer-recovery seasonality. We find that approximately 90% of beach transects exhibit significant and recurring seasonal cycles in the shoreline position. Seasonal shoreline excursions are twice as large in northern and central California (17.5–32.2 m) than southern California (7.3–15.9 m; interquartile ranges). Clustering analyses were effective at characterizing the temporal patterns of the seasonality, revealing that ∼459 km of beach (59%) exhibit winter-narrow conditions, whereas ∼189 km (24%) and ∼50 km (6.4%) exhibit spring-narrow and summer-narrow conditions, respectively. These spring- and summer-narrow conditions are most common in southern California, where they represent over half of the total length of beach shoreline. Multivariate analyses reveal that wave climate and geomorphic setting are significantly related to the magnitude and timing of shoreline seasonal cycles. Combinations of these variables explain 44% of the seasonality variance of the complete data set and 85% of the variance for a subset of 93 long (>1 km) continuous beaches. We conclude that diversity in waves and geomorphic setting along California cause a broad range of seasonal patterns in the shoreline. Combined, this indicates that the overly generalized “winter-narrow/summer-recovery” conventions for California beaches are not expressed universally and that shoreline seasonality is far more diverse than these simple canonical rules.

Storage Capacity and Sedimentation Characteristics of the San Antonio Reservoir, California, 2018

U.S. Geological Survey (USGS) | January 15th, 2020

Strategy for In-Bay Fate Modeling to Support Contaminant and Sediment Management in San Francisco Bay

San Francisco Estuary Institute (SFEI) | August 15th, 2022

This report presents a strategy and multi-year workplan for modeling polychlorinated biphenyls (PCBs), contaminants of emerging concern (CECs), and sediment in San Franci

This report presents a strategy and multi-year workplan for modeling polychlorinated biphenyls (PCBs), contaminants of emerging concern (CECs), and sediment in San Francisco Bay (the Bay). Robust in-Bay fate modeling is needed to address priority management questions that have been identified for these constituents.

Stratigraphic Analysis of Corte Madera Creek Flood Control Channel Deposits

U.S. Geological Survey (USGS) | September 3rd, 2019

Sedimentation in a channel can reduce flood conveyance capability and potentially place nearby property and life at risk from flooding. In 1998, Marin County Public Works

Sedimentation in a channel can reduce flood conveyance capability and potentially place nearby property and life at risk from flooding. In 1998, Marin County Public Works dredged the concrete-lined segment of Corte Madera Creek, which drains a hilly and largely urbanized watershed that terminates in San Francisco Bay, California. From then through 2015, approximately 4,100 cubic meters of sand and gravel infilled the concrete-lined segment. Determining when and under what conditions this material was deposited informs dredging operations for the Corte Madera Creek Flood Control Project and increases understanding of sediment delivery timing and mechanisms from this and other San Francisco Bay tributaries. Two hypothesized scenarios were investigated: (1) complete flushing during high flows and re-deposition of channel fill afterward and (2) more steady, gradual channel infilling. Stratigraphic analysis of eight sediment cores collected from the flood-control channel deposits in August 2017 was used to identify the most likely scenario. In addition, sediment elevation profiles, grain-size data, and a one-dimensional hydrodynamic model were used to assess the potential for longitudinal-channel scour and deposition following the wet winter of water year 2017 in the intertidal reach of the concrete channel in Corte Madera Creek. Results indicated the channel is undergoing gradual infilling. Storm flows of water year 2017 did not completely scour the concrete channel fill. Sediment cores, stratigraphic analysis, and sediment elevation profiles indicated 0.23 meter of scour at the downstream end of the concrete-lined section and that roughly 0.5 meter of channel fill remained in the channel. The hydrodynamic model demonstrated that sediment deposition in the concrete channel is expected to start downstream from the point where the channel bed reaches mean lower low-water level. High flows can carry most of the sediment through this segment of channel, depositing the bed-material load downstream from the transition to a wide channel, where velocity and bed shear stress decrease abruptly. Although the storm flows of 2017 did not completely scour the channel fill, subsequent material deposited in the channel could be transported downstream from the concrete channel if the sediment elevation profile is in equilibrium with present (2019) mean sea level. A calibrated, coupled hydrodynamic-sediment transport model could be used to test the present equilibrium between sediment elevation profiles and mean sea level, such that additional sediment build-up in the concrete channel is remobilized during subsequent wet-season flows and deposited downstream from the concrete-lined segment.

Summary of Suspended-Sediment Concentration Data, San Francisco Bay, California, Water Year 2010

U.S. Geological Survey (USGS) | June 6th, 2014

Suspended-sediment concentration data were collected by the U.S. Geological Survey in San Francisco Bay during water year 2010 (October 1, 2009–September 30, 2010). Tur

Suspended-sediment concentration data were collected by the U.S. Geological Survey in San Francisco Bay during water year 2010 (October 1, 2009–September 30, 2010). Turbidity sensors and water samples were used to monitor suspended-sediment concentration at two sites in Suisun Bay, one site in San Pablo Bay, three sites in Central San Francisco Bay, and one site in South San Francisco Bay. Sensors were positioned at two depths at most sites to help define the vertical variability of suspended sediments. Water samples were collected periodically and analyzed for concentrations of suspended sediment. The results of the analyses were used to calibrate the output of the turbidity sensors so that a record of suspended-sediment concentrations could be computed. This report presents the data-collection methods used and summarizes, in graphs, the suspended-sediment concentration data collected from October 2009 through September 2010. Calibration curves and plots of the processed data for each sensor also are presented.

Support for Sediment Bioaccumulation Evaluation: Toxicity Reference Values for San Francisco Bay

San Francisco Estuary Institute (SFEI) | December 3rd, 2018

This special study of the Regional Monitoring Program for Water Quality in San Francisco Bay was conducted to support the Dredged Material Management Office (DMMO) proces

This special study of the Regional Monitoring Program for Water Quality in San Francisco Bay was conducted to support the Dredged Material Management Office (DMMO) process of evaluating results from bioaccumulation testing performed for routine dredging projects. The goal was to use the current DMMO methodology for selecting Toxicity Reference Values (TRVs) from the US Army Corps of Engineers Environmental Residue-Effects Database (ERED), in order to develop a standard list of TRVs for San Francisco Bay. TRVs are used as a conservative screening tool to efficiently evaluate whether observed invertebrate test organism body burdens could indicate adverse ecological effects on benthic organisms in situ. Currently, there are no published standard TRVs for the Bay, and TRV selection is presently performed on a case-by-case basis during the evaluation of bioaccumulation testing results submitted by individual dredgers. A standard list would promote consistent application of the methodology and improve the efficiency of dredging project evaluations. 

Suspended Sediment Flux in the San Francisco Estuary: Part I—Changes in the Vertical Distribution of Suspended Sediment and Bias in Estuarine Sediment Flux Measurements

Estuaries and Coasts (Springer) | April 22nd, 2020

In this study, we investigate how changes in the vertical distribution of suspended sediment affect continuous suspended sediment flux measurements at a location in the S

In this study, we investigate how changes in the vertical distribution of suspended sediment affect continuous suspended sediment flux measurements at a location in the San Francisco Estuary. Current methods for measuring continuous suspended sediment flux estimates relate continuous estimates of suspended-sediment concentration (SSC) measured at-a-point (SSCpt) to discrete cross-section measurements of depth-averaged, velocity-weighted SSC (SSCxs). Regressions that compute SSCxs from continuous estimates of SSCpt require that the slope between SSCpt and SSCxs, controlled by the vertical distribution of SSC, is fixed. However, in tidal systems with suspended cohesive sediment, factors that control the vertical SSC profile—vertical turbulent mixing and downward settling of suspended sediment mediated by flocculation of cohesive sediment—constantly vary through each tide and may exhibit systematic differences between flood and ebb tides (tidal asymmetries in water velocity or particle size). We account for changes in the vertical SSC profile on estimates of SSCxs using time series of the Rouse number of the Rouse-Vanoni-Ippen equation combined with optical turbidity measurements, a surrogate for SSCpt, to predict SSCxs from 2009 to 2011 and 2013. Time series of the Rouse number were estimated by fitting the Rouse-Vanoni-Ippen equation to SSC estimated from optical-turbidity measurements taken at two elevations in the water column. When accounting for changes in the vertical SSC profile, changes in not only the magnitude but also the direction of cumulative sediment-flux measurements were observed. For example, at a mid-depth sensor, sediment flux estimates changed from − 319 kt (± 65 kt, negative indicating net seaward transport) to 482 kt (± 140 kt, positive indicating net landward transport) for 2009–2011 and from − 388 kt (± 140 kt) to 1869 kt (± 406 kt) for 2013–2016. At the study location, estimation of SSCxs solely from SSCpt resulted in sediment flux values that were underestimates on flood tides and overestimates on ebb tides. This asymmetry is driven by covariance between water velocity and particle settling velocity (Ws) with larger Ws on flood compared to ebb tides. Results of this study indicate that suspended-sediment-flux measurements estimated from point estimates of SSC may be biased if systematic changes in the vertical distribution of SSC are unaccounted for.

The effects of kaolin clay on the amphipod Eohaustorius estuarius: Part Two

San Francisco Estuary Institute (SFEI) | April 3rd, 2017

A number of lines-of-evidence suggest that the amphipod Eohaustorius estuarius has variable tolerance to clay in sediments. In Phase 1 of the current RMP special study, l

A number of lines-of-evidence suggest that the amphipod Eohaustorius estuarius has variable tolerance to clay in sediments. In Phase 1 of the current RMP special study, laboratory dose-response experiments were conducted in 2014 with kaolin clay to evaluate whether clay effects varied with amphipod size. The results indicated that smaller amphipods were more tolerant of clay than larger individuals. Average survival was 81%, 79%, and 65% for small, medium and large amphipods, respectively, in concentrations > 50% clay. As part of Phase 2 confirmation studies conducted in 2015-2016, the original kaolin dose-response experiments were repeated. Results of this experiment showed that average amphipod survival was 88%, 63%, and 41% for small, medium and large amphipods, respectively, in concentrations > 50% clay. Standard 96-hour reference toxicant tests with cadmium chloride (CdCl2) were conducted to determine whether there were size-specific differences in response to this metal reference toxicant. The CdCl2 median lethal concentrations (LC50s) for small, medium and large amphipods were 6.78, 5.13, and 4.63 mg/L, respectively. Responses of all three size classes to cadmium were within historic confidence intervals for this reference metal, and were not significantly different from one another based on overlapping confidence intervals. Additional experiments with high clay reference site sediments from San Francisco Bay were conducted to confirm the size related response with field sediments. The results confirm that use of smaller amphipods in routine monitoring of high clay sediments will reduce the influence of this factor on test results. 

The evolution of dam induced river fragmentation in the United States

Nature Portfolio (Springer Nature) | June 28th, 2023

The Historical Ecology of the Tijuana Estuary & River Valley (Restore America's Estuaries 2018 Conference Presentation)

San Francisco Estuary Institute (SFEI) | December 12th, 2018

This talk was given at the 2018 Restore America's Estuary Conference in Long Beach, CA as part of a special session titled "Restoration Perspectives from the Tijuana Rive

This talk was given at the 2018 Restore America's Estuary Conference in Long Beach, CA as part of a special session titled "Restoration Perspectives from the Tijuana River National Estuarine Research Reserve." It is based on information from the Tijuana River Valley Historical Ecology Investigation, a report published in 2017. Though many areas of the binational Tijuana River watershed remain relatively undeveloped, land and water use changes over the past 200 years have resulted in significant ecological impacts, particularly in the more urbanized areas of the lower watershed. Drawing upon a diverse set of historical data, we reconstructed the ecological and hydrogeomorphic conditions of the lower Tijuana River valley prior to major Euro-American modification (ca. 1850) and documented major changes in habitat distribution and physical processes over this time. The river corridor, which was historically dominated by riparian scrub, today instead supports dense stands of riparian forest. The valley bottom surrounding the river corridor, which historically supported extensive seasonal wetlands, has largely been converted to drier habitat types and agricultural uses. The estuary, which historically supported large expanses of salt marsh and mudflat as well as seasonally dry salt flats, has retained much of its former extent and character, but has been altered by increased sediment input and other factors. The new information about the historical landscape presented here is relevant to a number of issues scientists and managers are dealing with today, including the conservation of endangered species, the fate of the valley’s riparian habitats after the recent invasion of invasive shot-hole borer beetles, and the effects on groundwater levels on native plant communities. We will also draw from other historical ecology studies conducted in Southern California to illustrate how the information about the past has been utilized to improve the functioning and resilience of nearby coastal ecosystems.