Research Technical Report

Tidal Scour and its Relation to Erosion and Sediment Transport in Elkhorn Slough

Malzone, C.M. (1999)

M.S. Thesis, San Jose State University. 73p.

Elkhorn Slough is a shallow-water embayment that is part of a 585-km² watershed at the easternmost extent of the Monterey Bay in California. In 1947, the shoreline dunes along its western marsh were breached for the expansion of the Moss Landing Harbor. This action provided open access to coastal waters, which initiated a tidal scour process that has widened the main channel and eroded the banks of the slough. Field measurements of bathymetry, bank erosion, tidal and hydrologic characteristics, and sediment transport were undertaken from 1993 to 1996. These data were compared to results of previous studies to evaluate the erosive processes currently operating in Elkhorn Slough and their temporal evolution.

The results of this study show that a 55% increase in water volume has led to high current velocities (up to 1.47 m/s) and high average rates of sediment loss (8 x 10⁴m³yr). If the present conditions continue, Elkhorn Slough will evolve into a shallow-water tidal embayment with its primary habitats being an extensive lower-intertidal mudflat and subtidal main channel in 40 to 120 years.