East Orleans Landbridge Shoreline Protection
GeoEngineers helped the Louisiana Department of Natural Resources combat coastal erosion with a protective landbridge.
Over the past 50 years, Louisiana has lost more than 1,300 square miles of land to coastal erosion. The causes of this loss are varied and are due to both natural processes, such as hurricanes, and human activities, such as levee and canal construction. In 2005, Hurricanes Katrina and Rita dramatically accelerated land loss in Louisiana’s coastal areas, transforming an estimated 217 square miles of marsh into open water.
In an effort to slow these losses, the Louisiana Department of Natural Resources (LDNR) initiated a series of shoreline protection projects, including a major project on the East Orleans Landbridge. This thin strip of land separates Lake Pontchartrain and Lake Borgne east of New Orleans and provides an important storm surge barrier, marsh habitat and recreation area.
The project called for a nine-mile rock wall—extending two to three feet above the waterline—to protect the coast and marsh from erosion. LDNR engaged GeoEngineers’ Principal Charlie Eustis to determine whether the soft, compressible soils in this coastal area could support the weight of the rock barrier and predict the extent to which the wall might settle over time.
- GeoEngineers conducted a series of soil borings in the project area, using a specialized buggy in the marsh zone and a barge-mounted drill rig for in-water testing and performed lab tests to determine whether the soft coastal soil could support the weight of the rock wall.
- Based on lab results and previous experience in the region, GeoEngineers estimated the rate at which the wall would settle. Possible settlement is an important issue because the rock structure could lower over time, undermining its effectiveness against wave action.
- Settlement information approximates if and when the wall will need to be replenished with additional rock to maintain effectiveness.
- GeoEngineers determined that the soft soils in the project area could sustain rock structures up to three feet above the waterline, demonstrating that the project was feasible.
- Estimated that the rock wall would settle 2 to 3 feet over 25 years, providing LDNR with important information to guide long-term planning