Geotechnical Characterization of an Eroding Wetland

The Louisiana coastline experiences drastic levels of deterioration due to marsh edge erosion, pipeline and navigation channel construction, saltwater intrusion, and restricted sediment supply. The role of geotechnical properties as a driver of wetland behavior is underscored by the many studies on wetland loss, e.g., marsh edge erosion, shallow subsidence, wetland collapse, and uprooting. A modified piezocone penetrometer was implemented alongside soil cores to evaluate shear strength and hydraulic properties of the vegetated mats at two marshes in Terrebonne Bay, Louisiana. Based on the field measurements, the test method was found to be repeatable and consistent with the ASTM D5778 standard guideline. This study provides a geotechnical assessment of the two locations to better understand the implications of the root-soil matrix on wetland stability. The results show these marshes are supported primarily by an offshore sediment supply and a progression inland from the shore is accompanied by a reduction in soil strength.