The Response of Pool-Riffle Bedforms to Variations in Stream Discharge: A Modelling Approach.

Pool-riffle sequences (PRS's) provide habitat for aquatic life in many natural streams. They are maintained by scour of pools and deposition on riffles during high flow. Reversals in the position of maximum velocity and shear stress between low and high flow have been used as explanations for this process. The reversals have previously been found to not occur ubiquitously in all PRS's, leading to conjecture as to their importance in PRS maintenance. An alternative mechanism is developed, which uses sediment continuity to link scour and deposition with gradients of shear stress along the channel. This mechanism is tested in a HEC-RAS numerical model of a prototype PRS in south-eastern Australia. The shear stress profiles from the model are used as an input to the mechanism to develop a prediction for the bed deformation occurring. Pool scour and riffle deposition are predicted at high flow, concurring with previous observations. This work improves understanding of the sediment dynamics of PRS's and has application in the design of environmental flow regimes.