Studies Completed on Sediment and Water Quality in Cotton Bayou & Terry Cove in Orange Beach, Alabama

Map of the study area in Cotton Bayou and Terry Cove near the Perdido Bay inlet of Alabama Point.

A project funded by the Gulf Coast Ecosystem Restoration Council (RESTORE Council) and implemented by Auburn University has completed data collection and modeling in two popular coastal water bodies in Orange Beach, Alabama. Terry Cove and Cotton Bayou, near the Perdido Bay inlet at Alabama Point, have undergone extensive shoreline development over the years. As seawalls have replaced natural shorelines, sediment accumulation has disrupted natural hydrodynamic mixing. This can result in degradation of water and sediment quality resulting in low water column oxygen levels that lead to seasonal menhaden fish kills as well as impacts to other marine life.

To begin to address this issue, scientists from Auburn University utilized a $550,000 grant provided by the Alabama Department of Conservation and Natural Resources (ADCNR) and the RESTORE Council to develop a 3-dimensional hydrodynamic model (Environmental Fluid Dynamics Code+) to evaluate potential restoration options for improving low oxygen in these embayments.

To build the model, Auburn University began by collecting water quality data for 1 year to calibrate and test the model. After the model was built and tested, scientists tested restoration scenarios and the effects on oxygen levels in the Cotton Bayou/Terry Cove System. The four restoration scenarios tested were:

1) Installing large bottom mounted aerators/bubblers throughout the areas with low oxygen,

2) Pumping water directly from the Gulf of Mexico to the western end of Cotton Bayou,

3) Dredging the shallow channel between Cotton Bayou and the channel that leads to Perdido Pass and the open Gulf of Mexico and,

4) A combination of aerators and dredging.

Researchers were able to predict the effect of each scenario using the model and which of the four scenarios would result in successfully increasing oxygen in the water column. By evaluating the four different scenarios, scientists determined that a combination of targeted dredging and installation of bottom aerators placed throughout these areas of the bay would have the highest probability of success. Based on the simulations, the optimum scenario would maintain water oxygen levels high enough to prevent menhaden fish kills and other detrimental impacts by eliminating seasonal low oxygen.

ADCNR Commissioner Chris Blankenship expressed his appreciation for the completion of the study, "the goal of this project was to develop a science-based comprehensive understanding of the factors governing the environmental and ecological health of the Cotton Bayou/Terry Cove system. These modeling efforts have accomplished that and given us information to guide future restoration activities to improve water quality and avoid fish kills."

Orange Beach Mayor Tony Kennon also commented on the value of the work, "Water quality is integral to our way of life in Orange Beach. This work provides practical suggestions on maintaining that water quality for our citizens to continue to enjoy."

For further details on this project including model simulation results and observational data please visit the Project Website (https://www.eng.auburn.edu/users/jsh0024/cb-tc/cb-tc.html) or the Alabama State Expenditure Plan.

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State Expenditure Plan

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Keala J. Hughes

Director of External Affairs & Tribal Relations

(504) 717-7235

[email protected]