Interactions among gravel and sand fractions during transport as measured by impact plates and sedflux monitor in a laboratory channel

Authors: Kuhnle, Roger; Wren, Daniel; HILLDALE, ROBERT - Us Bureau Of Reclamation

Submitted to: Joint Federal Interagency Sedimentation and Hydrologic Modeling
Publication Type: Proceedings
Publication Acceptance Date: 4/24/2019
Publication Date: 6/24/2019
Citation: Kuhnle, R.A., Wren, D.G., Hilldale, R.C. 2019. Interactions among gravel and sand fractions during transport as measured by impact plates and sedflux monitor in a laboratory channel. Joint Federal Interagency Sedimentation and Hydrologic Modeling. June 24-28, 2019, Reno, Nevada. 1-3.

Interpretive Summary: Knowledge of the rate of gravel movement in streams is important for a number of reasons. The rate of movement and the erosion and deposition of coarse sediment are major determinants as to whether a channel and its banks are stable or actively eroding. In agricultural watersheds, several studies have shown that channel erosion is often the main process by which soil is eroded and removed from the watershed. Thus accurate knowledge of rates of gravel transport in streams are important pieces of information needed by watershed managers to attain stable channels in agricultural watersheds to preserve the soil and the productivity of crop lands. Experiments were conducted in a laboratory flume at the National Sedimentation Laboratory to understand the processes controlling the transport of sand and gravel in model river channels. The same standard flow was repeated four times after a range of higher flows were imposed on the channel to determine the effect of past history on the rate of transport in the channel. It was found that the immediate past flow to the channel was an important indicator of the rate of sediment movement in the channel during the standard flow. This information will allow watershed managers to calculate improved estimates of gravel sediment erosion and transport and therefore allow more sustainable use of agricultural lands.

Technical Abstract: Accurate measurements or predictions of bed load transport are difficult to make for alluvial channels especially when the bed material consists of a mixture of sand and gravel. A series of experiments were conducted in a laboratory flume in which gravel and total bed load rates were measured continuously using independent methods. The effect of four different antecedent conditions on the transport of bed load during a standard low flow condition was evaluated in a series of experiments. It was found that the different antecedent flow strengths yielded different mean rates of bed load transport for the standard lower flow. This work indicates that a portion of the uncertainty of accurately predicting transport rates for gravel bed streams is likely caused by structural changes in the surface of the gravel bed that result from antecedent flows and the rate of transport for other flows is therefore affected.