Coastal Inlet Bank Erosion

Much focus is placed on beach erosion on the open coast. However, coastal processes often occur on sandy shorelines interior to inlets that can lead to severe erosion. These shorelines lie adjacent to coastal inlets and extend around the inlet from the ocean to bay. In particular, an examination of coastal inlets with jetties or terminal groins that are connected to a sandy shoreline develop inner-bank erosion in the absence of preventive measures. Many mature projects show eroded regions that required extensive revetment. Typically, if the erosion is permitted to proceed unabated, a crenulate-shaped shoreline region will develop from the terminus of the jetty, extending both bayward and laterally into the adjacent beach. This expansion of erosion leads to loss of property and difficulties in reclamation as a shallow water environment develops. The eroded sediment moves into the channel creating shoaling problems. Many times the eroded region may flank the jetty structure, leaving it isolated from the shore. Isolation of the jetty may lead to potential problems of tidal current scour near the structure, opening the already eroded embayment to increased wave activity and additional erosion, and permitting increased wave attack on the jetty itself. As part of the Coastal Inlets Research Program (U.S. Army Corps of Engineers), this type of erosion was studied in a movable bed physical model of an inlet. After the governing processes were understood, several preventive techniques were investigated. A case study is included.