Subaqueous Sediment Characterization Near Oyster Colonies By Means Of Side-Scan Sonar Imaging And Portable Free-Fall Penetrometer

Bivalve colonies are being explored regarding their potential contribution to erosion and scour mitigation. As a first step toward this goal, the in situ conditions of a tidal riverbed around an oyster reef in the Piankatank River in Virginia were investigated using a rotary side-scan sonar (SSS) and a portable free-fall penetrometer (PFFP), among other methods. The field survey was performed on October 4 and 5, 2018, in an area with a radius of approximately 300 meters in the direct vicinity of an oyster reef. The SSS results showed a significant increase (>20%) in the standard deviation of the backscatter intensity where the oyster reef was located, indicating an increased surface roughness. The PFFP results suggested somewhat of an increase of in situ peak friction angles with increasing proximity to the oyster reef. This correlation can be explained by an expected increase in sharp oyster shell fragments near the oyster reef. Thus, the SSS offered clear imaging and a measure of increased surface roughness of the oyster reef, while the PFFP provided insights into changes in sediment behavior in the riverbed surrounding the reef.