Barnard, Patrick L; Erikson, Li H; Elias, Edwin; Dartnell, Peter (2012): Bedform measurements from the San Francisco Bay Coastal System. PANGAEA, https://doi.org/10.1594/PANGAEA.802345, Supplement to: Barnard, PL et al. (2012): Sediment transport patterns in the San Francisco Bay Coastal System from cross-validation of bedform asymmetry and modeled residual flux. Marine Geology, 345, 72-95, https://doi.org/10.1016/j.margeo.2012.10.011
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The morphology of ~45,000 bedforms from 13 multibeam bathymetry surveys was used as a proxy for identifying net bedload sediment transport directions and pathways throughout the San Francisco Bay estuary and adjacent outer coast. The spatially-averaged shape asymmetry of the bedforms reveals distinct pathways of ebb and flood transport. Additionally, the region-wide, ebb-oriented asymmetry of 5% suggests net seaward-directed transport within the estuarine-coastal system, with significant seaward asymmetry at the mouth of San Francisco Bay (11%), through the northern reaches of the Bay (7-8%), and among the largest bedforms (21% for lambda > 50 m). This general indication for the net transport of sand to the open coast strongly suggests that anthropogenic removal of sediment from the estuary, particularly along clearly defined seaward transport pathways, will limit the supply of sand to chronically eroding, open-coast beaches. The bedform asymmetry measurements significantly agree (up to ~ 76%) with modeled annual residual transport directions derived from a hydrodynamically-calibrated numerical model, and the orientation of adjacent, flow-sculpted seafloor features such as mega-flute structures, providing a comprehensive validation of the technique. The methods described in this paper to determine well-defined, cross-validated sediment transport pathways can be applied to estuarine-coastal systems globally where bedforms are present. The results can inform and improve regional sediment management practices to more efficiently utilize often limited sediment resources and mitigate current and future sediment supply-related impacts.
Latitude: 37.826200 * Longitude: -122.453800
From the 1-m gridded bathymetry, two sets of transects were hand-drawn orthogonal to the bedform crests, one set for large bedforms (lambda ~> 20 m, n= 398), where occasional smaller superimposed bedforms were filtered out, and the second for smaller bedforms (lambda ~< 20 m, n= 1545). The geo-referenced depth along each transect was extracted at one meter distance intervals (to match the grid resolution) for the automated bedform analysis. Bedform parameters were obtained with an automated procedure based on previously established robust methods (e.g., Knaapen, 2005, doi:10.1029/2004JF000195). Bedform parameters were calculated from trough to trough with transects generally oriented from west to east so that As (asymmetry) < 0 indicates net ebb-directed transport, As > 0 indicates net flood-directed transport, and As = 0 indicates the presence of symmetric bedforms with no inferred net transport direction.
Prior to determination of crests and troughs, transects of large bedforms were placed through a low-pass filter to eliminate noise caused by superimposed smaller bedforms. Crests and troughs were then defined by local maxima and minima calculated from neighboring points along each transect. For each bedform analyzed, the wavelength, height, depth, steepness and asymmetry measurements were assigned to the crest, and spatially gridded to 50-m cell sizes and trimmed by a bedform mask.