In an interview with Metropolis’ POV blog, Jan H. De Jager, a Dutch civil engineer and dike and dam expert, finds fault in New Orleans’ new coastal and storm management system and discusses how “soft coastal engineering” is more effective than vertical walls in combatting sea level rise.
De Jager says the current reconstruction work in New Orleans, which involves rebuilding solid vertical walls, is the wrong way to go. “One of the projects I’ve seen is the storm-surge barrier being built across the New Orleans Inner Harbor Navigation Canal. In my opinion, this is a completely wrong structure. It’s a vertical wall to stop the waves. That thing will collapse when you have another category-five hurricane.” Instead, soft coastal engineering, featuring natural marsh systems, would be more effective: “I would restore the marine marshes, the growth of trees, the barrier islands. That’s where your protection should be, not in these massive storm-surge barriers.”
Os Schmitz, Professor of Population and Ecology at Yale University, made a similar argument for restoring natural barrier systems in New Orleans in a recent interview. “The mangroves that used to grow there were excellent buffers for hurricanes before there was much settlement. These mangroves were a highly cost-effective way of controlling hurricane damage. When those were removed and the wetlands were removed and the dikes were put in their place, the human built environment became less resilient. The mini-experiment that sort of proved this was a year after Hurricane Katrina hit New Orleans, there was another hurricane of I believe close to or equal in magnitude to Katrina that hit the Yucatan in a tourist area. The people in the Yucatan were really worried that the hurricane was going to destroy a lot of the hotels. But, they still have their mangroves in place. They still had those marshlands in place. These features acted as terrific buffers against that hurricane. The resort areas were spared a lot of damage because nature helped buffer the winds and the tidal surge. Here’s an example of where nature provides an important service to humankind. It isn’t about fighting nature and getting rid of nature in favor of built environments. It’s the idea that nature can be beneficial to us.”
Holland is a country well versed in climate change adaptation, and the Dutch are now tapping their long history of carefully managing water levels to prepare for ongoing sea level rise. “It’s a country built on sediments, which were brought in by the Rhine River. A couple hundred thousand years ago we didn’t even exist. Our ancestors have dealt with sea level rises in the past. And they had only modest means, so what they did was build little platforms, plateaus, where they built up their farms and houses. So when sea water would rise, they would run to their earth plateau and sit out the high water.”
In addition to maintaining its complex system of dikes and dams, Holland will also preserve the role of sandbars in coastal sea level maintenance. “Our coast is all sand dunes, like you have in certain parts of the Carolinas and some parts of Texas. Big waves form in deeper water. So when you lower the water depths just in front of the coastline, even if the sea level rises and the waves come in, the sandbar breaks the waves into smaller ones. Depending on the type of storm and the way the water is flowing, the sandbars will last one to ten years. If the sandbar has eroded too much, you pump sand again.”
However, De Jager thinks its inevitable that some land will have to be given back to the sea. In some cases, ceding back the land doesn’t need to be negative: it can be an opportunity for restoring coastal ecosystems. “In Holland, we have been doing that, making cuts in the dunes and letting seawater enter in a safe way. But that was largely an environmental move, because we wanted to bring back certain plant species that had been lost for one hundred years. It’s not so much a safety concern as a matter of creating new brackish habitats.”
Read the interview and check out an earlier post on Metropolis Magazine’s vision for the future of landscape architecture.
Image credit: Dutch Sandbar. Climate Adaptation Lab, Netherlands