Section 3.3: Levees and Flood Walls
Another large-scale engineering solution that is more specific to the problem of coastal flooding is the installation of structural barriers along coastal waterways. These barriers include levees, floodwalls, and floodgates, all of which are supported by pumping systems that reclaim the land behind them.
Structural protection projects are currently planned to receive more than $19 billion in funding according to the 2017 Louisiana Coastal Master Plan. One such project that has been proposed is Lake Pontchartrain Barrier. This would install various structural barriers, especially floodgates and levees, that would prevent storm surge water from entering Lake Pontchartrain during tropical storms. The goal of this plan would be to prevent flood of the kind that occurred on the North Shore during Hurricane Isaac in 2012 and in New Orleans during Hurricane Katrina in 2005. The Lake Pontchartrain Barrier is expected to cost $2.4 billion, but it could save lives and many billions of dollars in property damage over the next 50 years.
It is clear these structural barriers are key tools in protecting human populations from the effects of storm surges and other sources of coastal flooding. Urban areas like New Orleans and Houma could not continue to exist without these sorts of structural protections. Plans for the construction of further structural barriers are designed to protect other at-risk communities and economic resources. They also have the effect of limiting land loss by protecting inland land surfaces.
Yet, structural barriers come with problems and dangers, many of which have already been exposed in past flooding events, such as those resulting from Hurricane Katrina. As discussed previously, the installation of flood barriers and the reclamation of land using pumping systems dramatically alters wetland ecosystems and landscapes, which have been instrumental in buffering the impacts of erosive forces in the past. This approach also accelerates subsidence within the boundaries of flooding barriers through the dewatering of clay sediments.
Furthermore, it is very depressing to envision a future for Louisiana in which all of the coastal land surfaces are protected by a system of flood barriers and there are no land surfaces beyond them. In this scenario, land surfaces inside the flood barrier system would continue to sink through subsidence, enhancing the potential consequences of levee failures during hurricanes—and generally making life more difficult for the engineers that maintain the flood control system. While it may seem like we are already approaching this situation, we still have a lot to lose in terms of land beyond the coastal flood protection system.