Author(s): Stefan Haun; Assem Mayar; Markus Noack; Silke Wieprecht

Linked Author(s): Stefan Haun, Markus Noack, Silke Wieprecht

Keywords: Gamma-ray attenuation method; Gravel-bed rivers; River bed clogging; Sediment infiltration

Abstract: The infiltration and accumulation of fine sediments in gravel bed rivers leads to a reduction of the existing pore space and may lead in worst case to a complete clogging of the river bed. To understand the highly dynamic process of sediment infiltration, measurements with high temporal and spatial resolution are required. Within this study, the development of sediment accumulations in an artificial river bed is investigated to gain further understanding on the process of colmation. The artificial river bed, implemented in a research flume, is made of 0.040 m and 0.026 m spheres in different packing arrangements. Three sediment mixtures, with different grain size distributions, are supplied to observe the dynamic infiltration process, and to get information on the distribution over depth. In addition, supply rates (1.4kg/min and 3.7kg/min) and supplied masses (10kg and 20kg) are varied. To observe the dynamic development of sediment accumulation, the gamma ray attenuation method is used, which provides the opportunity of non-intrusive and undisturbed continuous measurements during the experiments at a certain position (1-point measurements). Additionally, the accumulated sediment masses are obtained right after the supply of sediments and 28 minutes later, with a high vertical resolution to detect changes as results of consolidation within the pores. From the measured amount of infiltrated sediments can be seen that the accumulated sediment mass is strongly particle size dependent. The measurements of the fine sediment mixture show that the filling started from the bottom until the accumulation reach the surface of the artificial river bed. The experiments with the coarse sediment mixture resulted in a clogging layer in the upper section of the river bed and subsequently less sediments reached the flume bed. The 1-point dynamic measurements show that a higher supply rate leads to an earlier start of the infiltration and a rapid filling, while lower supply rate resulted in a later infiltration and slow filling process. The feeding mass itself has no considerable effect on the infiltration behavior of the current setup, as once the pores are filled no additional particles penetrate the bed. Measurements right after the sediment supply period and 28 minutes later show that dynamic changes happen mainly in the upper layers due to washing of surface sediments by the flow, and only to a smaller extent by further settlements due to solidification within the pores. Especially higher supply rates result in higher depositions in the upper layer and even on the surface. The within this paper presented method proved to be suitable to investigate the dynamic development of sediment accumulations in an artificial river bed. Due to the use of different sediment mixtures, and different supply conditions, future insight on the process of fine sediment infiltration could be gained.

DOI: https://doi.org/10.3850/IAHR-39WC25217119202247

Year: 2022