High Salinity Increases the Fluidity and Erodibility of Sand-Clay Mixtures

Mud, consisting of clay and sand, is commonly found in freshwater and saltwater ecosystems including wetlands, coastal regions, and estuaries. However, our understanding of how mud behaves under various salinity levels is still limited. In this research, we investigated the impact of salinity on the rheological properties and erosion resistance of sand-clay mixtures through flume experiments. To simulate natural mud under various salinity conditions, we mixed sand and clay in ratios representative of natural mud and added pore water with salinities ranging from 0 to 35 ppt. We used a rheometer to measure the viscosity and yield stress of the mixtures and determined the critical bed shear stress needed to erode them in a water-recirculating flume. Our results indicate that as salinity increases, the critical bed shear stress and yield stress decrease by one order magnitude and two order magnitude, respectively. This dependency on salinity reflects a transition of the sand-clay mixture from a cohesive gel-like state at lower salinity levels (10 ppt) to a liquid state as salinity increases to a higher level (≥ 10 ppt). Our research underscores the important role of salt in controlling the erosion threshold of mud. The results will help design erosion prevention structures and forecast sediment movement in coastal areas.