IMPROVING BEST MANAGEMENT PRACTICES FOR SENSITIVE KARST FEATURES ON THE EDWARDS AQUIFER RECHARGE ZONE

Rapid development on the Recharge and Contributing Zones has led to increased risk of non-point source contamination of the Edwards Aquifer. Nutrients, as well as metals and other stormwater contaminants can build up during antecedent dry periods and runoff in relatively higher concentrations with first flush waters. The objective of this research is to define contaminant loading changes seasonally and during single events to design best management practices (BMPs) and offer improvements to existing designs to better protect karst features. High resolution turbidity, flow, stage and water chemistry data for multiple storm events were collected from an ephemeral tributary to Leon Creek. The subject watershed is a heavily developed approximately 670-acre drainage area located on the Edwards Aquifer Recharge Zone. Results from the water quality analysis show a strong first-flush effect for total suspended solids and a weak first flush effect for nitrates. Results indicate seasonal loading trends for both nitrates and TSS are far more significant than concentration changes during single events. Conceptual BMP designs were developed using Solid Works software to blind swallow holes from first flush contaminants. Manual, pressure transducer, turbidity, and conductivity sensor controlled BMPs were used to trigger recharge. All designs would effectively reduce elevated concentrations of nitrate and TSS from entering potential recharge features, while continuing to allow recharge during periods of relatively cleaner streamflow. The conceptual BMP designs are shown to out-perform existing BMP designs by reducing TSS by 70% to 80% and nitrates by 6% to 20%.