Turbulent flow in bedrock canyons

• Applicant: Dr. Eva Kwoll
• Subject Area: Palaeontology
• Term: from 2015 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 279698502

The rate at which Earth rivers erode and discharge bedrock material is one of the key processes that dictate the pace of landscape evolution. Rivers erode and transport sediment from upland sources to the ocean and cause the formation of deep valleys and canyons. In tectonically active regions, the removal of mass by fluvial erosion further enhances the isostatic uplift of majestic mountain peaks. Hence, in order to predict how landscapes respond to tectonic activity or climate change with the help of large-scale landscape models, the rate of river incision needs to be adequately represented in the model framework. River incision rate is determined by the shear stress exerted by flow on the river bed. Yet, flow in bedrock canyons remains understudied. This is mostly due to the difficulties and dangers inherent to accessing and measuring flow in the steep-walled canyons. Current model approaches therefore assume steady uniform flow and infer shear stresses from this assumption. A recent survey however, has indicated that flow in narrow bedrock canyons deviates significantly from steady uniform flow and shear stresses may be biased in current model approaches. The aim of this project is to attain a deterministic understanding of the turbulent flow field in bedrock canyons. It is aimed to develop the scientific groundwork to improve implementation of river incision in current landscape models. Specifically, this project is designed to study the effect of canyon aspect-ratio (width/depth) and flow stage on the redistribution of flow and the associated spatial distribution of shear stress exerted on the canyon floor and walls. The 2-year project builds on the combination of two research methodologies. The first project component consists of detailed natural observations. Ship-based measurements are made in two bedrock canyons of the Canadian Fraser River with different aspect ratios and under high and low flow stages. Data collection will make use of well-established, originally oceanographic instrumentation and produce novel, high-resolution measurements of flow and topography in bedrock canyons. The second component consists of a series of laboratory investigations using fixed canyon geometries. Downscaling field conditions in the flume allows the study of the flow field for a comprehensive range of canyon aspect ratios and flow stages. Laboratory investigations allow further the detailed investigation of the entire turbulent spectrum. This complementary approach will allow a systematic expansion of findings from natural observations and a deterministic understanding of turbulent flow in bedrock canyons. Findings will improve our current ability to predict river incision into rock and aid substantially in overcoming current shortcomings of landscape models.

• DFG Programme: Research Fellowships
• International Connection: Canada
• Host: Professor Dr. Jeremy Venditti