The monitoring of bedload transport processes in rivers is a still challenging task in research and the parameter effective transport width (ETW) allows, for the first time, a process description of the local variability of the bedload transport. In this paper, the distribution of bedload transport over a river cross-section was studied by statistically analyzing long-term monitoring data. Using an innovative integrated measurement system, combining geophones distributed over the river width with bedload traps and basket sampling, allows for continuous, high-resolution, long-term monitoring data of bedload transport characteristics to be generated. Geophone data can be used to record and describe bedload transport processes such as intensity, temporal variability, and local variability. One parameter observed was the ETW, which describes the width where bedload transport is taking place for different discharge classes in gravel bed rivers. With the help of a data series recorded over more than a decade, it is now possible, for the first time, to statistically describe the continuously and directly measured ETW. Hence, it became evident that the effective bedload transport width depends on the discharge rate and local transport capacity, and that bedload transport over the entire river width only occurs at high flows that prevail a few days a year.

Conclusion

Through the parameter ETW, the local distribution of bedload transport in a cross-section of a river can be described for the first time. Due to the long-term, high-resolution, and continuous observations of the bedload transport on the Drau River, the discharge-dependent bedload-carrying width can be described with the help of the ETW. This parameter is a statistical description of the spatial distribution of bedload transport, and, thus, allows a better understanding of the local variability of bedload transport. The ETW shows, for example, that at mean flow, bedload transport prevails statistically for just 1.2 m of the entire river cross-section of 50 m. Bedload transport occurs over the entire river width only at discharges exceeding a one-year flood event. This again proves that an extrapolation of bedload transport (kg/m s) over the entire river width is only justified during a few days of the year, when flood conditions prevail. While the ETW does not directly represent the intensity of bedload transport, the changes in bedload transport width that occur due to supply fluctuations are accounted for by the performed curve fitting of ETW with discharge or shear stress. The concept of the ETW contributes to a better process description of the spatial distribution of bedload transport in river systems and can simplify the estimation of bedload transport rates.

More information: 

Rolf Rindler, Sabrina Schwarz, Marcel Liedermann, Dorian Shire-Peterlechner, Andrea Kreisler, Johann Aigner, Michael Tritthart, Helmut Habersack. Effective transport width—A methodology to describe the spatial variability of bedload transport, International Journal of Sediment Research (2023). DOI: 10.1016/j.ijsrc.2022.09.007