Nature Versus Nurture: Evaluating Man-Made Sediment Diversions in Coastal Louisiana

By Christine Wendling

Matthew Hiatt, assistant professor in Oceanography and Coastal Sciences at LSU’s College of the Coast & Environment, is an expert in coastal hydrology and hydrodynamics who is working on measuring the efficacy of sediment diversions. In particular, he is studying diversions that are part of Louisiana’s Comprehensive Master Plan for a Sustainable Coast and will be critical in alleviating flooding and storm surge concerns, and protecting human lives and infrastructure, all while returning the Mississippi Delta plain to a more natural, more hydrologically- connected environment. The Coastal Master Plan is a multi-agency collaboration and a driving force behind wetland restoration in coastal Louisiana.

Hiatt's area of expertise, hydrology, is concerned with where water flows, how much of it flows there, and how long it remains. And, hydrodynamics is concerned with the physics of the water flow, for example: how patches of vegetation along a river influence the flow structure and velocity, or even the deposition and erosion of material at the bottom of the river.

Since part of the Coastal Master Plan includes building river diversions that deliver water and sediment to restore coastal wetlands, Hiatt is looking at Wax Lake Delta to serve as a proxy for these engineered sediment diversions and developing metrics with which to evaluate their effectiveness.

Photo of matt hiate with his catamaran

Matt Hiatt poses with catamaran and ADCP. Photo Credit: LSU
 

 

Research on the Wax Lake Delta

The Wax Lake Delta is an excellent, natural example of river and sediment diversion because not only is it retaining sediment, but it is growing. This delta formed downstream of the Wax Lake Outlet, which diverts water from the Atchafalaya River. And, the Atchafalaya River delivers a large amount of water and sediment into the delta where it can expand freely into a shallow area and build land.

“Understanding how a natural system that is building land behaves, in terms of its hydrology, is a really nice benchmark for evaluating the efficacy of these river and sediment diversions. If we know how a healthy, natural system behaves, we know how to monitor a sediment diversion after it's been built,” Hiatt said.

Part of his work includes modeling the growth of river deltas over hundreds of years and evaluating the changes to the delta’s hydrology. Additionally, Hiatt and his graduate student are also monitoring the effects of atmospheric events on water level fluctuation throughout the Louisiana coast. While much of his work involves using freely-available data, such as raw data published by the United States Geological Survey or Coastal Protection and Restoration Authority, he does take measurements out in the field.

 

The Doppler Effect

Hiatt uses several devices that measure water velocity, including Acoustic Doppler Current Profilers (ADCPs). ADCPs rely on the Doppler effect by sending out acoustic beams which the particles in the water reflect back to the sensor enabling it to measure water velocity. Hiatt has mounted an ADCP onto a small remote-operated catamaran, or a fast, stable, twin-hulled boat that’s about the size of an inflatable pool float.

“What's nice about this boat is that it can be used in pretty shallow water. One of the limitations of using these [ADCPs] is that you usually have to be in kind of a deep channel because you have it attached to your big, 20-foot boat. So, with this thing, I'm hoping that we can get into the wetland environment, where usually there's not these types of measurements. This allows us to gather detailed information to learn about how water flows through coastal wetlands,” Hiatt said.

This fall, he looks forward to piloting the catamaran with his students on its first excursion to the Wax Lake Delta.

CC&E’s world-class faculty explores environmental, social, and economic sustainability from the Mississippi River to deltaic zones around the world. And, hydrology and hydrodynamics are important factors that influence almost all deltaic processes, including sediment transport and deposition. Increasing understanding of these processes will give scientists like Hiatt more accurate modeling and predictive power and enable stakeholders to better manage and restore the Louisiana coast.

Contact Christine Wendling christinew@lsu.edu LSU College of the Coast & Environment   225-578-4984