Hydro- and morphodynamics of riffle-pool sequences in the middle Elwha River, Washington, USA

摘要

Riffle-pool sequences are ecologically important features of mild-sloped gravel-bed rivers. They are composed of alternating vertical bed undulations and are often forced by variations in width. The natural formation and maintenance of riffles and pools remains poorly understood, as does their response to certain disturbances such as changes in sediment supply. The Elwha River restoration project and associated removal of Glines Canyon Dam provides a natural setting to explore how large increases in sediment supply affect downstream riffles and pools. Here we present results from bathymetric/topographic surveys conducted in fall 2014 and spring 2015 and two-dimensional hydrodynamic modeling associated with each of the surveyed surfaces. Riffle and pool units for each survey were classified using the hydrodynamic model results, and riffle areas increased by 33% while pool areas decreased by 50% over the winter 2014/2015 season.