Multi-beam sonar data was collected in December 2009 for the main channel of Groves Creek from the mouth at the intersection of the Wilmington River to the area referred to as “the forks”, where the channel dissects into three more shallow channels. The multi-beam data was collected and processed by Coastal Carolina University resulting in a 0.25m grid of the survey area. Single-beam sonar data was focused on shallow creeks and channels of the study area as well as large areas of un-vegetated tidal flats. Single-beam data was collected during 23 survey missions between 2010 and 2011 from a small shallow draft electric boat around high tide using an Ohmex Sonarmite echosounder with RTK-GPS positioning. Pedestrian RTK-GPS survey data was collected across the low gradient marsh platforms, creek levees, and throughout creeks found to be too small or shallow for the survey boat. Pedestrian data was acquired during times around low tide using Trimble R6 GPS receivers with RTK correction data obtained through a Virtual Reference System. This dataset includes positions from 241 individual survey missions over 169 field days in 2010 and 2011.

The Groves Creek modeling domain in Chatham County, GA exhibits a broad range of salt marsh geomorphic features typical of those found in southeastern salt marsh habitats. The domain includes large vegetated marsh platforms, creeks ranging from 1m to 75 m wide, creek levees, and dissected un-vegetated intertidal flats. Vegetation throughout the study area is dominated by Spartina alterniflora grasses in short, medium and tall forms up to approximately 2m tall in creek and levee regions. Previous modeling studies in the Groves Creek domain using a Light Detection and Ranging (LiDAR) derived coarse resolution digtal elevation model (DEM) (approximately 4.5 m2 cell resolution) identified the necessity for a DEM with both higher spatial resolution and accuracy (Blanton et al., 2010). The coarse resolution elevation model failed to identify many of the small (1-3m wide) creeks that dissect through creek levees and enable a conductive path for water flow between marsh platforms and larger creeks. Because saltmarshes are generally composed of very low relief topography, small vertical errors may have large affects on surface hydrology, tidal inundation and sediment distribution (Blanton et al., 2006; Chasserau et al., 2011; Hladik and Alber, 2012; Rosso et al., 2006).

In order to generate a high-accuracy topographic/bathymetric elevation dataset for use in hydrodynamic modeling studies and for comparison with other remote sensing techniques three survey styles were developed to acquire data from the various habitat zones found throughout the domain: multi-beam sonar, single-beam sonar, and pedestrian RTK-GPS. Multi-beam sonar data was collected in December 2009 for the main channel of Groves Creek from the mouth at the intersection of the Wilmington River to the area referred to as “the forks”, where the channel dissects into three more shallow channels. The multi-beam data was collected and processed by Coastal Carolina University resulting in a 0.25m grid of the survey area. Single-beam sonar data was focused on shallow creeks and channels of the study area as well as large areas of un-vegetated tidal flats. Single-beam data was collected during 23 survey missions between 2010 and 2011 from a small shallow draft electric boat around high tide using an Ohmex Sonarmite echosounder with RTK-GPS positioning. Pedestrian RTK-GPS survey data was collected across the low gradient marsh platforms, creek levees, and throughout creeks found to be too small or shallow for the survey boat. Pedestrian data was acquired during times around low tide using Trimble R6 GPS receivers with RTK correction data obtained through a Virtual Reference System. This dataset includes positions from 241 individual survey missions over 169 field days in 2010 and 2011. Areas of the marsh with low topographic complexity were delineated from aerial photographs guided by detailed knowledge of the field site. These areas were classified as platform habitat. Platforms were surveyed using targeted 5 m grid spacing. Non-platform zones surrounding creeks and levees were surveyed with point spacing from 0.5m to 3m depending on topographic complexity. The 0.25m gridded multi-beam data generated 2,361,154 survey positions, the single-beam data generated 201,310 survey positions, and the pedestrian surveys generated 159,589 positions for digital elevation model creation. The multi-beam and single-beam sonar data was merged with Pedestrian RTK-GPS data using ESRI ArcGIS software and interpolated into a 0.5m cell resolution DEM for use with hydrodynamic modeling efforts. Elevation models were generated with the ArcGIS extension 3D Analyst using the Topo to Raster function.

Results were published in:
Alexander, C.R., Hodgson, J.Y.S. and J.A. Brandes. 2017. Sedimentary Processes and Products in a Mesotidal Salt Marsh Environment: Insights from Groves Creek, Georgia. Geo-Marine Letters. https://doi.org/10.1007/s00367-017-0499-1

This project was funded by DOI, Agency Project No.: 86176-002-10.