Thoughts on expanding Louisiana’s official coastal footprint
Editor’s note: Regular readers of LaCoastPost know that I’m an ardent advocate of shrinking Louisiana’s carbon footprint and expanding its coastal footprint. The latter goal is addressed in this guest post by an anonymous but highly qualified author who is currently active in quantifying landscape area and elevation in south Louisiana in great detail.
Expanding the coastal boundary for Louisiana is currently under consideration. I strongly support this effort and offer the following specific recommendation to those involved in carrying out this vital exercise.
A watershed-based system is necessary for credible predictive modeling of water flow and geographically-based coastal planning. Thus, I propose that the new Watershed Boundary Dataset (WBD) completed by the Natural Resources Conservation Service (NRCS) be used as a fundamental criterion for the expansion of the functional coastal boundary for Louisiana.
The WBD is tied to the National Hydrology Dataset (NHD), the national standard database for mapping and water quality modeling used by the US Geological Survey (USGS) and the Environmental Protection Agency (EPA). This dataset was recently “certified” for Louisiana and the surrounding states.
Louisiana’s official coastal boundary, created in the late 70′s and approved in the early 80′s, was clearly drawn without regard to the geological and ecological processes that influence the dynamic deltaic landscape. In other words, the current boundary is more political than science-based. Successful restoration and management of the Louisiana coast is obviously contingent on acknowledging and working within the scientific context and limits of the real world.
Despite a popular misconception, erosion is a significant but not primary cause of coastal land loss in the Mississippi River delta (or in the other major deltas around the world). Watershed level thinking is essential to understanding the complex interactions of hydrology (water flow), water quality and all the environmental processes that cascade through each basin and down toward the coast.
A strategy to restore the Louisiana deltaic coast using ecological engineering, hydrologic modification and wetland nourishment must comport with the laws of nature. Watershed processes are the arbiters and enforcers of those laws.
Much is made of the fact that over 40% or the continental US drains via the Mississippi River and into the Gulf of Mexico through Louisiana. This great “riverine machine” directly or indirectly created most of south Louisiana during the past seven millennia but we should not forget that coastal Louisiana is also influenced by rivers and in state headwaters not connected to the Mississippi system.
So how should the proposed expansion of the official coastal boundary of Louisiana toward a functional boundary be approached, in order to accommodate real world geophysical and ecological processes?
The US Department of Agriculture (USDA) Natural Resource Conservation Service (NRCS) recently completed watershed mapping for the entire state of Louisiana.* The watershed boundary dataset (WBD) is comprised of polygons representing relatively small, local watersheds. Each polygon defines an area that drains the immediate area and all lands upstream of the “pour-point” (the location where the water exits the polygon and flows downstream).
These polygons make perfect management units, as they are tied to many NRCS activities and data collection programs. In addition to the USDA, other federal agencies (e.g., USGS, EPA) and state and local government agencies also recognize these boundaries. USGS maintains the nation’s streamflow gauging network and EPA is responsible for water quality and other environmental monitoring programs. The Louisiana Department of Environmental Quality (LDEQ) manages the state non-point source water pollution (319) program, using these watershed boundaries.
The hydrology dataset (NHD) is being tied to the watershed boundary dataset (WBD) units. This combined dataset provides watershed management tools that link land use, agriculture, industrial, and other activities in the watershed to the flow of water through the entire system.* Some of these tools address issues such as sediment runoff, toxic and hazardous spills, industrial point source pollution, municipal sewage treatment outfalls and many other environmental impacts (including agricultural nutrient runoff, the primary cause of gulf hypoxia).
The combined hydrology dataset should be used to provide the modeling framework to evaluate planning alternatives and impacts from proposed coastal protection/restoration projects. An arbitrarily narrow designation of the new coastal boundary will not alter the influence of upstream hydrologic effects. Using the combined watershed and hydrology datasets could bring a new level of scientific objectivity to coastal planning.
Here are some objective questions to help distinguish coastal from non-coastal watersheds:
Is streamflow subject to tidal influences?
Is the watershed above or below the freshwater/saltwater interface?
What is the elevation of the main-stem water body within the watershed?
Does the watershed have a history of being influenced by storm surge?
What flora and fauna are present in the watershed (e.g., freshwater, brackish, saline species)?
What soil types are present in the watershed?
Editor’s addition: What is the mean elevation of the watershed with respect to mean sea level?
All of these questions have answers that can contribute to the development of a more realistic and comprehensive coastal area. Furthermore, by using a watershed approach, a more coherent management program can be developed that involves objective data and more complete planning alternatives.
We are attempting to manage processes that are independent of political boundaries. Management is simply the wise application of science. Determination of the specific boundary of an expanded coastal area will require deciding whether to honor Mother Nature or the more traditional agenda of the good ol’ boys (and girls).
Edited by Len Bahr
*The Cabin-Teele sub-watershed project in northeast Louisiana, described in an October 5 post, is a perfect example of how the use of the watershed boundary dataset could quantify the impacts on gulf hypoxia of hydrological and ecological processes far removed from south Louisiana.