A mechanistic and predictive understanding of temporal variations in the onset of sediment motion

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The movement of rocks along river beds, called sediment transport, is essential for estimating river channel stability and therefore risks to infrastructure and human lives during floods. Sediment transport predictions are also used to help restore rivers for numerous aquatic species. Despite its importance, sediment transport is notoriously difficult to predict, and this project will investigate how changes in river bed structure (e.g. rock arrangement) influences sediment transport. Such information will then be used to improve sediment transport predictions. Through a collaboration with artists, sculptures will be temporarily placed in rivers to serve as 1) flow obstructions (e.g. boulders and wood) that provide habitat for a range of fish species, and 2) public outreach installations through signs posted near the sculptures with links to websites containing information and videos about the science of this project. Errors in sediment transport predictions can be partly explained by the common assumption that the onset of sediment motion always occurs at the same flow magnitude in a given river. Large temporal changes in the onset of sediment motion can occur because of variations in the channel bed structure. The goals of this proposal are to better understand these temporal changes in bed structure and to use this understanding to accurately predict the onset of sediment motion. Laboratory experiments and a mechanistic theory are used to identify and quantify the channel bed parameters that control variations in the onset of sediment motion. This theory will be tested using field measurements in a well instrumented channel and could replace the often arbitrary choice of a single flow magnitude that causes the start of sediment movement.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.