Abstract

Many streams and rivers in agricultural areas have been straightened in order to enhance the drainage of cultivated land and facilitate crop management. This practice is now viewed as unsustainable as periodic re-straightening is often necessary to address the problems associated with bank erosion, compromising the ecological integrity of lotic and riparian ecosystems. This research aims to assess the current sediment dynamics, as well as directions of current and future channel morphology change, of a straightened upland gravel-bed river in order to provide guidelines for sustainable management schemes. The case study is the Sunday River (Quebec), located in the foothills of the Appalachian Mountains and regarded to contain prime trout habitat. The lowest reach has proved the most problematic as a mid-channel bar repeatedly establishes itself, resulting in considerable erosion of adjacent agricultural land. In response, stakeholders have sought to regularly intervene by extracting gravel and re-straightening the channel. The study methodology combines a GIS analysis of historical aerial photos, field data collection and hydraulic and sediment transport modeling. Topographic channel geometry, sediment grain size and discharge data were acquired over the span of 2 field seasons. Additionally, repeated terrestrial lidar scans of eroding banks were acquired to aid in sediment budget evaluation. The 1D model HEC-RAS was employed to simulate current hydraulics and sediment transport, and to recreate pre-disturbance hydraulics by increasing cross-section spacing to mimic a longer, more sinuous channel.