Effect of increasing antecedent flows on equilibrium bed load transport rates in a laboratory channel with a sand and gravel bed channel

Authors: Kuhnle, Roger; Wren, Daniel; Langendoen, Eddy

Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2021
Publication Date: 10/15/2021
Citation: Kuhnle, R.A., Wren, D.G., Langendoen, E.J. 2021. Effect of increasing antecedent flows on equilibrium bed load transport rates in a laboratory channel with a sand and gravel bed channel. Journal of Hydraulic Engineering. 147(10).040210838.

Interpretive Summary: Accurate knowledge of the rate of movement of the sediment on the bottom of a stream or river is important for several reasons. Whether the rate of movement balances the supply from upstream and the movement of sediment downstream is an important indication as to the stability of the channel bed and banks. Stability of the channel boundary is also an important indicator as to the health of the biota that live in the stream. Channel erosion has been shown to be a the major source of soil loss in unstable channels of agricultural watersheds in several regions of the United States. Therefore accurate knowledge of the rates of transport of the bed material are critical knowledge for watershed managers to attain stable channels and maintain the integrity of the the soil and to preserve the aquatic biology of the channels. A series of experiments were conducted in a laboratory channel at the National Sedimentation Laboratory to investigate the effect of immediately prior flows on the rate of bed load in a sand and gravel bed channel. It was found that the magnitude of the antecedent flow affected the long term average transport rate in the channel for four experiments with the same rate of flow of the water. Knowledge of the flow history of a channel is necessary to improve predictions of sediment movement for subsequent flows. This information will potentially allow watershed managers to benefit from improved tools for effective and environmentally responsible management of watersheds.

Technical Abstract: A series of experiments were conducted in a laboratory flume in which gravel and total bed load rates were measured continuously using independent methods which allowed the effect of four different antecedent conditions on the transport of bed load during a standard flow condition to be evaluated. It was found that both mean total bed load rate and rates of gravel transport were related to the magnitude of the antecedent flow. These changes in mean bed load rate were attributed to changes in the stability of the coarsest fractions of the bed material, caused by the previous high flow event. This work indicates that long-term mean bed load transport rates for a sand and gravel bed are not just a function of grain size and flow rate, but they also vary with the magnitude of antecedent flows.