Featured Projects — Modeling ACF and ACT River-Reservoir Water Quality Modeling

The Apalachicola-Chattahoochee-Flint (ACF) and Alabama-Coosa-Tallapoosa (ACT) River systems have a combined watershed of approximately 42,000 square miles. Within the watershed, more than 30 multipurpose reservoirs regulate flows to meet recreational, power generation, flood control, water supply, and navigation requirements. The watershed also contains Atlanta, Georgia and Montgomery and Birmingham, Alabama metropolitan areas. These cities and numerous smaller communities discharge reclaimed water to the rivers, where it combines with agricultural runoff and natural inflows to deliver nutrients and oxygen-consuming materials to the river system. The combined loads and high summertime water temperatures (i.e., temperatures greater than 30 degrees Celsius) result in low dissolved-oxygen concentrations and associated problems.

We developed an HEC-5Q model of the system to provide an analytic tool for analyzing the water quality response of the ACF/ACT system and to evaluate water quality effects of waste-load reduction and alternative operations options.

HEC-5 and HEC-5Q model schematic of ACT basin showing rivers.

The HEC-5Q model was generalized and improved to meet the requirements of the ACT/ACF river system. Longitudinally segmented reservoirs were layered so that the vertical distribution of phytoplankton, dissolved oxygen and other parameters could be represented. In addition, we created a graphical user interface (GUI) to facilitate display and interpretation of model results and made numerous model input refinements to expedite model input preparation, including expanded capabilities for DSS formatted input and output.

We initially calibrated the model and performed HEC-5Q model simulations to evaluate the water quality impacts of the many proposed water-allocation formulas for various levels of development. An interface with the BASINS model and specialized HEC-5Q model output was developed to expedite the evaluation process.

We recently developed a model interface with HEC-ResSim to provide temperature and water quality capabilities within ResSim, which included the option to compute reservoir releases to meet downstream temperature objectives. The ACT/ACF models were verified to more recent temperature and water quality data and used in evaluating impacts of reservoir operation to support the Reservoir Operations Manual Update Environmental Impact Statement.

Results and benefits

We provided an analytic tool for analyzing the water quality response of the ACF/ACT system and to evaluate water quality effects of waste-load reduction and alternative operation options in support of the Reservoir Operations Manual Update Environmental Impact Statement.