Protecting the Sponge: Community meetings on Floodplain Resilience in the Pontchartrain Basin
The last of three Floodplain Resilience presentations was given in Madisonville, La. to engage citizens and decision makers about the 2014-2018 wetland loss trends in the Parishes in the Lake Pontchartrain drainage basin.
Healthy Gulf presented the third of its Floodplain Resilience in the Lake Pontchartrain Basin community meetings in Madisonville, La. Thursday November 14th at the public library. In this presentation and in Hammond and Abita Springs, we showed maps and graphics made with Army Corps of Engineers data on the location and size of wetland fill permit applications in St. Tammany, Tangipahoa, Livingston, East Baton Rouge, Ascension, St. James and St. John Parishes.
Scott Eustis and Naomi Yoder are two of our staff members who examine and comment on Army Corps Section 404 Clean Water Act wetland fill permit public notices. Their maps and the presentation created with them are intended to let people see the wetland loss problem through their eyes. Overall, they’ve been witnesses to a growing number of wetland fill permits over the last 5 years; this raises the following concerns as they continually monitor the Army Corps public notice website. Where does all the water go when the wetlands are filled in areas that already have significant urban development? Are people aware of the magnitude of wetland filling that is happening near them? Are Parish and state planners tracking this moving target of wetland loss? What does this do to the floodplain’s ability to absorb this volume of water without putting people at worse risk of flooding, and what does all of this do to flood insurance maps?
What we hope to do with the Army Corps’ data is hold up a mirror to the residents and Parish governments on the Northshore and around Lake Pontchartrain to let them see how their “sponge is shrinking” and motivate them to do more to protect their remaining wetlands.
In the presentation, tables show the year-by-year acreage of wetlands affected by the permit applications. Accompanying maps have red circles of varying sizes showing where the wetland filling permit applications have been located 2014-2018. There are three hotspots, moving counter-clockwise around the Pontchartrain Basin starting at the Pearl River, going west. The first is western St. Tammany Parish, southwest of Covington, right along Interstate 12. There’s a second hotspot along both sides of the Amite River in Livingston and E. Baton Rouge Parishes, and a third below Baton Rouge along I-10 near Prairieville in Ascension Parish.
A major point the presentation makes is that the State of Louisiana has acknowledged that there are certain places where the flood risk is already high, making them good candidates for elevating existing homes and businesses, flood-proofing them or buying out repetitive loss properties. For example in St. Tammany Parish, a Coastal Protection and Restoration Authority (CPRA) non-structural project to do those three things has been outlined along I-12, mostly in the coastal zone south of that interstate all across the Parish. The cost reported to do such non-structural risk reduction is $1.61 billion. This is money the state doesn’t have yet, but this cost is included within the 2017 Coastal Master Plan so that when the money comes, these elevation, flood-proofing and floodplain buy-outs of at-risk properties can happen. Putting the funding question aside, the CPRA report highlights the need to elevate structures.
Another main point is that within the Coastal Zone, the La. Department of Natural Resources has the authority to require elevation for new construction through that agency’s coastal use permit jurisdiction. We show one such example in St. Tammany Parish, but overall, the data we present showing trends of wetland loss demonstrates a need for elevation of new structures on piers rather than filling wetlands with mounds of clay and placing new slab foundation homes and businesses on them. Mounds of compacted clay fill in the floodplain and displace water much the same way as putting bricks in a toilet tank. In this simple example a “vessel” holds a smaller volume of water if space within it is taken up by something solid.
Pier construction was the state of the art for building in all of these wet, relatively flat locations for over 100 years. From Ponchatoula to Mandeville, anyone can see old homes that have persisted because piers, not mounds of clay raised them out of the floodplain. Pier construction methods, to a greater degree, leave spongy wetland soils alone to do their job of retaining water. One acre of wetlands can hold and store a million gallons of water, according to easily available EPA websites. A wetland permit allowing a subdivision to fill 25 wetland acres on a 50 acre subdivision project will unleash 25,000,000 gallons of water to the surface drainage system. Off-site mitigation (like a mitigation bank) for the wetland loss often does little to deal with this water that will no longer be sequestered in wetland soils or taken up by growing wetland vegetation at the developed parcel of land. Municipal public works departments then must deal with this volume whether that means gravity drainage to ditches and canals or engineered solutions like storm drains and detention basins.
Meanwhile, even in this high flood risk area identified as a place for the St. Tammany CPRA non-structural project, the wetland fill permit applications continue being filed with the Army Corps of Engineers (and usually granted). The cost, identified as $1.61 billion in 2017 for elevations and flood-proofing of structures, rises with each acre of additional wetland filled. It’s up to the Parishes and to the State itself to look at the big picture of what’s happening with wetlands in rapidly developing regions of Louisiana. We’ve demonstrated in our presentation that it’s relatively easy to do this using publicly available data from the Army Corps of Engineers.
Convincing state and local decision makers that now is the time to bend to the task of “protecting the sponge” will be the challenging part.
Andrew Whitehurst is Healthy Gulf's water program director and covers water pollution and wetland issues in Mississippi and Louisiana.