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Research Project: Managing Water and Sediment Movement in Agricultural Watersheds

Location: Watershed Physical Processes Research

Title: Using detailed surface topography to classify dune beds in a laboratory flume

item Wren, Daniel
item Kuhnle, Roger
item Langendoen, Eddy
item Rigby Jr, James

Submitted to: American Society of Civil Engineers Hydraulic Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/9/2017
Publication Date: 7/12/2019
Citation: Wren, D.G., Kuhnle, R.A., Langendoen, E.J., Rigby Jr, J.R. 2019. Using detailed surface topography to classify dune beds in a laboratory flume. American Society of Civil Engineers Hydraulic Conference Proceedings. University of New Hampshire, Durham, New Hampshire, July 9-12, 2017. 7 p.

Interpretive Summary: Models that are used for the prediction of sediment transport in streams assume that stream conditions do not change in time and that the bed of the stream contains bed forms that are appropriate for the existing flow conditions. This is often not the case, since large rain storms can generate high flows that create larger bed forms. Smaller flows that occur after the large event will inherit bed topography caused by the large event. The work described here is focused on using mathematical tools to quantify complex sand bed shapes so that changes caused by different flow conditions can be detected. This work is relevant to streams that are near areas of agricultural production, since these small streams often only have flow when rainfall events generate runoff that enters the stream. It was found that a clear progression in mathematical indicators could be found to describe bed conditions for a flow that was stepped down in power and then stepped back up.

Technical Abstract: Dune beds are common in streams and rivers, but linking complex three-dimensional sand bed topography to flow conditions remains challenging. It has been shown that bed topography created by a set of steady flow parameters produces unique elevation fields in time. Several techniques have been used to quantify dune bed topography, including elevation statistics, semivariograms, and two-dimensional structure function analyses. Improved methodology for quantifying bed topography and relating it to flow conditions and sediment transport is needed for more accurate sediment transport modeling. A combination of approaches is needed to account for both vertical and horizontal structure and create a set of useful indices to describe complex morphology. The goal of the work described here is to use a range of analysis techniques to identify aspects of bed topography that can be used to identify morphological characteristics that are unique to sets of flow conditions. Results from analyses of dune topography for a sand bed in a laboratory flume will be presented, including a range of flow conditions resulting from rapid increases and decreases in flow rate.