Submitted to: Sedimentology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2005
Publication Date: 6/20/2006
Citation: Kuhnle, R.A., Horton, J.K., Bennett, S.J., Best, J.L. 2006. Bed forms in bimodal sand-gravel sediments: Laboratory and field analysis. Sedimentology, 53: 631-654. Interpretive Summary: Accurate determinations of the rate of sediment being moved in streams and rivers are necessary because the sediment may fill reservoirs and reduce their capacity, may fill channels and cause flooding, may degrade water quality, and may cause instability of the channel banks which can cause the destruction of valuable agricultural and other lands. Accurate knowledge about the processes which cause sediment to be moved on the bottom of sand and gravel bed streams in watershed is rare. This information is needed to improve our understanding and predictive capability of sediment movement rates by streams and rivers. During water flow the sediment bed of many streams becomes molded into a series of high and low features (dunes) which vary dramatically in size and shape across and down the channel. These dunes greatly affect the amount of sediment carried in the water column and on the bottom of the stream. They also affect the depth of flow in the channels during runoff events. A series of experiments were conducted in a model stream channel in the laboratory to measure and characterize the features on the channel bottom. Data on channel bottom features was also collected from a stream in an agricultural watershed. This study has led to a more complete understanding of the mechanisms of formation of bed features and how they affect the transport of sediments in streams and rivers.. The information from this study is critical for improving sediment prediction and sampling techniques and will lead to advances which will allow agricultural and other watersheds to be managed in a more informed and environmentally sensitive manner.
Technical Abstract: Bed forms were studied in Goodwin Creek and a laboratory flume channel. The bed sediment had median diameters of 8.3 and 1.82 mm, respectively and both had bimodal size distributions. Cluster analysis was used to identify three groupings of bed forms from the laboratory flume experiments. For the range of flow depths and discharges investigated in the flume, bed forms became higher and longer with increasing bed shear stress (ripples, bed load sheets, low relief bed waves). Bed forms from Goodwin Creek were similar to those from the flume with comparable ratios between bed form length, height, and flow depth. Fluctuations in total bed load transport have been linked to the migration of the bed forms. A conceptual model of bed form migration in bimodal sediment mixtures is presented.