Opportunity
The Port of Corpus Christi on the Texas coast in the western Gulf of Mexico is the third largest port in the US by tonnage, handling more than 6000 vessels each year. To accommodate the new generation of megaships at the port’s La Quinta terminal, the sea channel on the north side of Corpus Christi Bay had to be made deeper, longer and wider. As part of agreeing a permit, the US Army Corps of Engineers, the federal agency that oversees shipping channels, requires compensatory mitigation to offset the effects of port expansions. In this case, the Port of Corpus Christi Authority was required to create a new estuarine habitat using dredged material, making best use of large quantities of valuable sediment deposits.
Solution
Our design for beneficial-use site 6 or BUS-6 created a seagrass and wetland habitat that exceeds regulatory requirements. The berm covers 81ha and is planted with more than 5ha of smooth cordgrass and over 10ha of shoal grass. Both species help stabilise habitats, reduce water turbidity and are a source of food for fish and invertebrates. Large fields of cordgrass are common near the heads of tidal creeks in the area and our design of the mitigation berm was optimised to enable similar extension growth. Forecast sea-level rise and wave conditions were evaluated as part of the design process. Dredged material is valuable and has vast potential for beneficial use, including beach restoration, shore protection and habitat enhancement. More than 10.4M tonnes was used to create the 81ha seagrass and wetland habitat at La Quinta.
Outcome
BUS-6 was completed in 2016 and was the first phase of the mitigation project. An additional 457m long section, made from material previously recovered during routine maintenance dredging, was completed in 2017, adding 8ha of shoal grass. The vegetation acts an incubator for young fish by providing protection from predators. Common near-shore fish include spotted sea trout, red drum, southern flounder, striped mullet, shrimp and blue crab, while the berm is a nesting area for seabirds. The project also reduces basin siltation, cutting the frequency of maintenance dredging. The berm also protects the port and surrounding area from storm surges and erosion. Its protective power was demonstrated in August 2017 when Hurricane Harvey, a category 4 hurricane, hit the Texas coast, bringing dramatically increased water and tide levels. Wind speeds topped 161km/hr and storm surges were in excess of 1.5m. The berm dissipated storm waves and there was little damage to the aquatic habitat.