By Luke Carothers
When it comes to planning for climate change and protecting our communities, there are a few regions that are more vulnerable than the rest. As evidenced by several massive hurricanes in recent decades, the Gulf Region of the United States is paramount within these vulnerable regions. Over the course of geologic history, the Mississippi River has served an important purpose for the region, transporting sediment and debris from up-river and depositing it downstream to form new marsh lands. It is this process that formed what we know as the Mississippi Delta. Now, with the river unable to move in a natural course due to human infrastructure such as levees, floodwalls, and guidewalls, this process is being interrupted and no new marshland is being created. In addition, these processes are causing what land is created to settle, which is then pushed under water by rising sea levels, which is known as subsidence.
Several projects are currently underway to help curb these issues including an interesting project in Plaquemines Parish, Louisiana where WSP is designing a massive intake structure for the Mid-Barataria Sediment Diversion Project; the goal of this project is to divert sediment-laden water from the Mississippi River during high flow times. The sediment-laden water from the Mississippi River will travel miles through a series of gates and channels before being deposited in the Delta marsh to create new land. By re-establishing this crucial link between the Mississippi River and the Mid-Barataria Basin, the team at WSP is hoping to solve the chronic loss of Mississippi Delta land stemming from hydrologic alteration, sediment deprivation, subsidence, sea-level rise, and saltwater intrusion.
According to Ian Chaney, Project Manager for WSP, there have been discussions about the Mid-Barataria Project for nearly a decade; he notes that one of the driving factors behind this project was the formation of a government agency called the Louisiana Coastal Preservation and Restoration Authority (Louisiana CPRA). This agency was crucial in securing funding for the project, which remained a looming question in the early days of planning. However, funding was procured as a result of a man-made natural catastrophe when BP oil rig Deepwater Horizon spilled over 5 million barrels of oil into the Gulf of Mexico. The resulting fines from BP are being put to good use and are funding the Mid-Barataria Sediment Diversion Project. The resulting cash-in-hand means there is at least enough funding to support two similar sediment diversion facilities along the Mississippi River.
For the Mid-Barataria Sediment Diversion Project, WSP is working alongside AECOM and the FTA as well as CPRA and contractor Archer Western. According to Cheney, the project is currently in a value-engineering phase, meaning the team is working to lower the budget constraint while also being mindful of the hydrologic goals of the project.
When it comes to protecting the coastline in the Gulf Region, the teams at WSP are also getting creative in using what they call “nature-based solutions”. According to Jennifer Brunton, National Practice Lead for Ecosystem Restoration at WSP, these solutions not only serve some sort of structural purpose within a project, but also have a secondary function through environmental or ecological impact. Brunton also manages a team of engineers who focus on areas such as coastal marsh restoration, improving national park visitor centers, dam rehabilitation, and coastal protection. This team is currently working to employ some of these nature-based solutions on a project in the Florida Panhandle’s Apalachicola Bay where 12 miles of living shoreline support a road that serves as a crucial hurricane evacuation route. According to Brunton, up until now, millions of dollars have been spent applying “band-aids” to the shoreline through traditional methods such as adding rock.
WSP’s solution was innovative, developing reef balls to solve the problem of an eroding shoreline. From an engineering perspective, these reef balls are essential in that they attenuate wave energy, reducing the impact of their force on the coastline. From an ecological perspective, these reef balls also provide a habitat for the local oyster population. Additionally, these structures also provide protection to the marshland between them and the shoreline. In order to determine the optimal shape for the reef balls, the team at WSP used a model called Computational Flow Dynamic (CFD) to develop 31 different versions, testing how the energy dissipates on each structure.
While many of these nature-based solutions are innovative and are generally beneficial, Brunton believes that the only way to increase their adoption is to continue to educate clients on their benefits. With the success of these projects, however, more attention can be given to developing solutions that not only benefit the human population of a given environment, but also benefit the area environmentally.
Luke Carothers is the Editor for Civil + Structural Engineer Media. If you want us to cover your project or want to feature your own article, he can be reached at firstname.lastname@example.org.