Lagrangian Modeling and TMDL Development in Low-Gradient Streams

Michael G. Waldon, Paul A. Richards, and E. deEtte Smythe

Abstract: Low gradient streams present special challenges for water quality modeling and total maximum daily load (TMDL) estimation. Dye tracer techniques provide a practical source of information on flow and dispersion in these streams, but steady-state models can not directly simulate dynamic dye cloud development. The USGS branched Lagrangian transport model (BLTM) was applied in modeling three low-gradient Louisiana streams. This dynamic model simulates QUAL2E water quality kinetics using a parcel tracking algorithm which reduces numerical error and improves run time efficiency. It is concluded that although there are some difficulties in application of the BLTM, it is a practical and valuable tool for TMDL model development.

Waldon, M.G., P.A. Richards, and E. Smythe, 1999. Lagrangian Water Quality Modeling and TMDL Development in Low-Gradient Streams. 1999 Proceedings, “ASCE-CSCE Environmental Engineering Conference,” Norfolk, July 1999, pp. 563-569.