Combining 18 years of bathymetric surveys with terrestrial and aerial LiDAR surveys to monitor subtidal and intertidal morphology in Elkhorn Slough, California

Estuaries are impacted and threatened by human activity, climate change and sea level rise. As a result, many highly altered estuarine systems are the focus of extensive habitat restoration and preservation projects. The success of management actions such as the addition or removal of sediment and tidal control structures hinges on the ability to accurately measure and predict rates of environmental change before and after implementation. In 2012 a subtidal sill was completed to reduce tidal scour and erosion in the second largest tidal salt marsh in California, the Elkhorn Slough. We analyzed the results of singlebeam and multibeam sonar surveys conducted in 1993, 2001, 2005, 2009, 2011, and 2012 to reveal changes in annual rates of erosion and accretion throughout the 12 km long main channel. We then combined bathymetic data with terrestrial and aerial LiDAR data to quantify volumetric changes in the tidal prism between 2005 and 2011. Our results show spatial and temporal patterns of erosion throughout the Slough prior to the construction of the sill as well as in the year after the sill was completed. This work is an example of how high-resolution sonar and LiDAR data can be combined to create comprehensive subtidal and intertidal estuarine digital elevation models and enable fine scale geomorphological monitoring.;