Enhanced Estimation of Terrestrial Loadings for TMDLs: Normalization Approach

Abstract

The effective implementation of total maximum daily loads (TMDLs) usually requires that relationships between terrestrial contaminant loadings and instream concentrations be estimated using deterministic fate and transport (DFT) models. The limitations of using conventional DFT models are that model predictions do not converge to observations as source loadings approach their calibrated values, and model-prediction errors are not explicitly included in the model output. A normalization approach is proposed that yields an accurate convergence to observations and can explicitly account for prediction errors. The proposed approach is demonstrated using field data collected at the Little River Experimental Watershed in Georgia, where source-load reductions are related to the confidence of compliance with a water-quality standard.