Modeling for TMDL Implementation

Abstract

The Clean Water Act and USEPA’s total maximum daily load (TMDL) program established requirements to determine the amount of a pollutant that a waterbody can assimilate and still attain water-quality standards. A variety of methods have been used in order to determine the TMDL, from complex hydrodynamic and water-quality modeling to simpler analytical techniques. This paper explores TMDL modeling from the perspective of the agencies tasked with implementation to reduce pollutant loads from within their jurisdictions. The paper discusses the difference in emphasis between modeling for TMDL development and implementation. The discussion includes the need for modeling by stakeholders and agencies implementing TMDLs, criteria for selecting models, and a short summary of several that have proven useful. Finally, recommendations are offered for TMDL developers and implementers to improve the modeling effort that leads to successful attainment of water quality.