Evaluating a Prefabricated Submerged Breakwater and Double-T Sill for Beach Erosion Prevention, Cape May Point, NJ

摘要

As part of the US Army Corps of Engineers National Shoreline Erosion Control Development and Demonstration Program, a demonstration project has been installed at Cape May Point, NJ to evaluate prototype-scale 'innovative' or 'non-traditional' methods of shoreline erosion control. The project consists of placing a linear prefabricated concrete submerged breakwater called the Beachsaver Reef(TradeMark) and a linear prefabricated concrete sill called the Double-T across the seaward end of two adjacent groin compartments, in order to assess the effectiveness of these structures in retaining sand within the groin compartments and to reduce shoreline erosion. The beach site, at the mouth of Delaware Bay on the extreme southern tip of New Jersey, is subject to both wave and tidal current interactions and has experienced historic erosion and shoreline retreat. Nine existing stone groins have created eight groin cells around a curved shoreline from the Atlantic Ocean into Delaware Bay. The Beachsaver Reef(TradeMark) in cell 5 is the second such structure at this site and new improvements include shallow placement with a crest elevation of 0 MLW and a geotextile fabric base to minimize settlement and scour. Placement was in August and September 2002, by barge-mounted crane and divers, in -2.7 m of water. Some excavation and fill of the bed was required to maintain the desired depth of placement. The Double-T sill in cell 6 is the first installation of such a device for erosion control. These units were placed at the same -2.7 m depth in four days in October 2002 with the same barge-mounted crane and divers. No bed cut/fill was required and no filter cloth was used. Stone was placed between the side of the groins and both structures to fully enclose each cell as a perched beach compartment.