The Nature Conservancy and National Wildlife Federation

Development and application of a hydrological model in the Anahuac National Wildlife Refuge

Analyzing freshwater inflow addition scenarios

Four months

The Challenge

In 2011, an extended drought in southeastern Texas led to elevated salinity levels in a number of locations throughout the Anahuac National Wildlife Refuge. The Nature Conservancy, the National Wildlife Federation, and other partners wanted to find out what impact the addition of freshwater into the system could have on making the area more resilient during drought conditions.

The Approach

Using the Integrated Compartment Model, the Institute set out to test three different potential freshwater additions to certain marsh tracks on the wildlife refuge. This Integrated Compartment Model can account for a number of different components from plant impacts to daily water surface elevations and allows each part to communicate in order to form a more complete picture. In this case, the objective of the study was to determine how certain marsh areas would react over time depending on several scenarios that varied in water volume, where this additional water was added, and how long additional water was added. The modeling also looked at differing impacts if all of the water was added to the Jackson Ditch Tract or if it was split between this tract and the East Bay Bayou Tract.

In the second phase of the project, funded by the National Wildlife Federation, additional information was gathered to refine the model and added a vegetation modeling component based on current field surveys.

The modeling results indicated that delivering more freshwater to both the Jackson Ditch and the East Bay Bayou tracts over a shorter period of time resulted in larger reductions in salinity than a single flow to just the Jackson Ditch portion of the refuge, at least while the freshwater is flowing. In all the scenarios, the modeling indicated that adding freshwater to the system resulted in salinity reductions across the entire area, although to varying degrees.

In the second phase of the project, modeling results indicated that how long the fresh water flowed into the refuge was the most important factor in minimizing drought impacts on wetland vegetation. This allows managers to better plan how much additional fresh water needs to be secured and when that fresh water can be best utilized.