An Update on Nearshore Berms in the Corps of Engineers: Recent Projects and Future Needs

Abstract

INTRODUCTION. Dredging of Corps navigation projects results in millions of cubic yards of sediment displaced each year. Many options for placement of the material exist, including Beneficial Use through creation of islands or wetlands, upland and offshore placement, direct beach placement, and nearshore placement. In recent years, the Corps’ project-centric focus has changed toward a more systematic approach that considers the sediment to be a valuable resource as part of the regional littoral system. The Corps’ Regional Sediment Management (RSM) Program supports active research on, and support for, modifying outdated project guidelines with new systematic approaches toward managing sediment as a resource. Nearshore berm placement is one RSM approach presently used by US Army Corps of Engineers (USACE) Districts that has the potential to provide an immediate benefit to beaches. As sediment is removed out of a littoral system through dredging, placement in the nearshore reintroduces the sediments to an adjacent littoral region that preserves valuable sediment resources that would have been lost otherwise to the nearshore system. The physical benefits of this practice to the adjacent beaches include wave attenuation and adding material to the nearshore beach profile that may be reworked by processes and migrate onshore. When in place, berms pose minimal impact to the environment if placed in what is typically an active littoral zone. Questions as to whether fines migrate onshore or disturb subaqueous habitat during the placement process and degrade water quality through suspension for some time following the placement must be addressed on a site specific basis. Here, we define the nearshore berm as dredged sediment that can be placed in deeper water as a mound to be stationary while attenuating waves as a “stable berm,” or can be placed in a shoreparallel form in shallower water as an active “feeder berm” (McLellan and Kraus 1991). To keep construction costs low and facilitate direct placement from dredges, berm placement has been limited generally to deeper water depths and the shortest travel distance to the placement location. Monitoring of shallower feeder berms has been limited. Many long-standing disposal sites such as Mobile Bay’s Stable Berm, AL, and the disposal site at Morehead City, NC, have been monitored and only recently have been categorized as “stable” placement sites. These monitoring data on stable placement sites provide insight on the behavior of stationary nearshore placements, but data for migrating nearshore berms in similar detail and quantity is limited. PRIOR STUDIES ON BERMS. Extensive studies on design considerations for nearshore berm placements were conducted in the late 1980s to mid-1990s, with several papers funded by