Development of Web-based Load Duration Curve System for TMDL Analysis

ABSTRACT: Development of TMDLs requires quantification of flow duration and load duration data for the waterbody of concern. Flow and load duration curves help identify specific flow regimes for which water quality standards are violated. Similarly, load reduction strategies for point and nonpoint source pollutants to meet TMDLs can be identified using the flow and load duration curves. Traditionally, development of these curves has been a time consuming process involving downloading and processing of flow and water quality data, and plotting of the data in a format suggested by EPA. We have developed an online tool to automate this process. The on-line tool provides options to upload a user’s flow and water quality data. Alternatively, a user can select stream flow data from an existing USGS gauging station using a Google MapsTM interface for the tool. The Google Maps interface has allowed us to scale the applicability of this tool to any watershed within the continental US. We have provided training for the use of this tool to various stakeholder groups involved in TMDL development. The use of this tool has resulted in significant time savings for the groups involved in TMDL development. In addition, it provides a consistent approach of quantifying and interpreting flow and load duration curves for different watersheds.