Hydrograph-based approach to modeling bacterial fate and transport in rivers.

A new approach, called hydrograph-based approach, is proposed for predicting bacterial concentrations in rivers. The new approach is relatively simple and efficient in terms of data requirements. It uses widely available hydrographs as the main input data for estimating flow and sediment transport parameters responsible for bacterial transport under varying flow conditions. The major component of the hydrograph-based approach is a new model, called VARTBacT model which is an extension of the Variable Residence Time (VART) model by including effects of unsteady flow, sediment transport, and bacterial decay/growth processes on bacterial transport and fate in rivers. The applicability of the new hydrograph-based approach is demonstrated through three case studies, each with distinct sediment and flow conditions: (1) steady low flow without sediment transport, (2) flood events with significant sediment transport due to watershed inputs, and (3) sediment resuspension from the streambed. While the sediment resuspension from streambed may be an important process for bacterial transport during high flows, results from this study indicate that the most important mechanism responsible for bacterial transport in streams is watershed loading during flood events and hyporheic exchange during low flow periods.