COPING WITH MODEL UNCERTAINTY: A CASE STUDY IN SEDIMENT TRANSPORT AND NUTRIENT LOAD ANALYSIS

We present the results of a case study on the significance of uncertainty in assessing the consequences of sediment and nutrient transport in a section of the Chattahoochee River south of Lake Lanier, as it passes through Atlanta, Georgia. Specifically, our computational analysis was aimed at identifying the key control and management actions, and the key scientific uncertainties about the fluvial system, that govern the attainment of a set of water quality objectives at the downstream end of the study area. To this end, we developed a computational framework that integrates a recently developed sediment-nutrient dynamics model with a novel sampling-based computational methodology for model evaluation based on the analysis of uncertainty. Our results suggest that, in general, efficient execution of controls and management actions is more crucial to meeting the target values for flow, sediment and phosphorus concentration, than the scientific uncertainties associated with the fluvial processes occurring within the river channel. We also discuss the various science- and policy-derived uncertainties in the TMDL process, and the potential for their integration within our computational framework.