Comparison of sediment transport and bedforms from steady and unsteady flow hydrographs of a similar flow rate

Authors: Wren, Daniel; MCALPIN, TATE - Us Army Corp Of Engineers (USACE); Ozeren, Yavuz; Langendoen, Eddy

Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2026
Publication Date: 5/9/2026
Citation: Wren, D.G., Mcalpin, T.O., Ozeren, Y., Langendoen, E.J. (2026). Comparison of sediment transport and bedforms from steady and unsteady flow hydrographs of a similar flow rate. Journal of Hydraulic Engineering. 152(4). 04026016. https://doi.org/10.1061/JHEND8.HYENG-14697.
DOI: https://doi.org/10.1061/JHEND8.HYENG-14697

Interpretive Summary: Measurement and prediction of sediment transport are needed for management decisions that concern rivers and streams. Sand bedforms on the bottom of channels affect flood depths and channel navigation. Measurements of transport rates and bedforms are particularly difficult in streams with flow rates that change rapidly in response to runoff from storm events. We used laboratory flume experiments to compare transport rates and bedforms in changing flow rates to those during unchanging flows. Bedforms during rising flow rates were smaller than bedforms from the same unchanging flow rate. Bedforms were larger during falling flow rates than they were for unchanging flows of the same rate. The amount of difference depended on the length and magnitude of the flows. Longer flows hade smaller differences, while higher flow rates had greater differences. This information will be used to improve the prediction of sand transport and the timing of bedform adjustment to changing flow rates, which will help improve sediment transport modeling. The work can also aid in flood forecasting for streams, since bedform characteristics also affect water depths. The results will be used by river managers, model developers, and other researchers studying river engineering and sediment transport.

Technical Abstract: Flow rates and depths in natural rivers and streams can change rapidly with time due to runoff from rainfall and snowmelt. These changing conditions complicate the prediction of sediment transport, bed topography, and flow depth. Due to the difficulty in collecting field data during unsteady flow events, it is necessary to use laboratory flume experiments to study sediment transport and bedform properties during unsteady flows. The goal of the this work described here was to isolate the effects of hydrograph flows on bedform dimensions, water surface slope, and sediment transport relative to the same flow rates in equilibrium conditions for steady flows while also comparing results across the various flowrates. For three repeated hydrographs of 1-, 3-, and 6-hour periods, quantities measured at four different flow rates during the hydrographs were compared to equilibrium conditions for each respective flow rate. The development of bedforms during rising and peak flow rates competed with the decay of bedforms during falling flow rates. When bedform growth was greater than decay, bedform sizes, water surface slopes, and transport rates during falling flow rates were typically greater than for equilibrium steady conditions at the same flow rate, while they were typically smaller than equilibrium bedforms for rising flow rates.