Evaluation of Benthic Resources in Upper Savannah Harbor Estuary, Chatham County, Georgia

The contractor will perform a bathymetric survey, map the river depths, identify substrate types, and quantify the extent of each type of bottom substrate.  The contractor would perform a field survey, consisting of transects of the area of interest on the Savannah River (River Miles 19.7 to 27.8) and Middle River (Station 0 to 3+000).   The survey would cover the river bottom from mean high water on one bank to mean high water on the opposite river bank.  The rivers are roughly 500-800 feet wide and 10-20 feet deep in this reach, and experience diurnal tides.  Sufficient transects would be conducted to ensure overlap of their coverage.  Information on the bottom substrate will be obtained using a side-scan sonar with a dual frequency sensor.  One frequency will be in the 100 to 150 kH range and the second frequency in the 450 to 600 kH range.  The side-scan sonar survey will be geo-referenced using a GPS.  Following completion of the side-scan survey, at least 23 sediment samples will be collected in areas of differing acoustic signatures to "ground truth" the various signatures and allow the contractor to delineate the distribution of substrate types through the project area.  Diving will not be conducted as part of the ground truthing effort.  Consolidated maps would be prepared that jointly display the water depth and bottom substrates.  The aerial extent of the different bottom substrates would be calculated.  At a minimum, the following types of bottom substrate would be identified:  silt, sand, gravel, and bedrock/clay.