Advancing Watershed Modeling for Total Maximum Daily Load and Holistic Watershed Management Including Climate Change Impacts

Fourteen leading watershed models simulating hydrology, erosion, and transport/fate of sediment and pollutants were critically reviewed by the EWRI Total Maximum Daily Load (TMDL) Analysis and Modeling Task Committee. The review was published in Chapter 2 of the ASCE Manual of Practice (MOP) 150: TMDL Development and Implementation – Models, Methods, and Resources, to provide guidance in selecting models. The mathematical formulations of the procedures used by the 14 models to simulate the physical processes were compiled and compared in tabular forms and ranked graphically.
Spatial discretization such as lumped, semi-distributed, or fully distributed, are key steps or considerations in conceptualizing a watershed model. Similarly, temporal resolution is key to the success of a model in preserving the most dynamics of the physical processes. Other important considerations in advancing watershed modeling are simulating best management practices, computing probability and confidence level of model outputs, enhancing hydrologic and water quality process descriptions and algorithms, incorporating computational efficient numerical solutions, adopting standard file formats for model inputs and outputs, and simulating emerge contaminants such as mercury, selenium, and other metals such as lead and copper. The applicability of the models beyond TMDL, such as holistic watershed management including the consideration of climate change impacts is also relevant to successful modeling.
The Task Committee is currently looking into the above aspects of the existing watershed models (the 14 previously reviewed and other models) to provide future directions in achieving those goals to advance watershed modeling. A progress on the work will be presented and feedback from audience will be specifically encouraged.