Effects of Incised Valley Topography on Grain Size of Coarse Bed Materials
Abstract
Channel bed materials are significant component of stream channel. In general, the grain size of channel bed materials changes systematically in downstream direction. However, topography variation may cause the hydraulic conditions such as width, depth and velocity to deviate from the general pattern which can influence grain size distribution of bed materials. The hillslope materials especially along incised valley entering channels through mass movement may also affect the grain size of channel bed materials. In order to explain the contribution of supplies from hillslope to channel to bed material coarsening, we investigated grain size and lithology of coarse bed materials in the upper and middle reaches of Gongneungcheon River in Korea. Then we analyzed the gradient of hillslopes and shear stress of stream channel using digital elevation models. The relationship between shear stress and the grain size of bed materials showed a significant positive correlation. In addition, we found a significant difference in grain size between incised valley and non-valley reaches. The mean grain size in valley reaches is coarser than that of non-valley reaches upstream and downstream. The results from the analysis of lithological composition of bed materials showed that the proportion of gneiss in bed materials increases rapidly as the river flows through the valley which the bedrock is also gneiss. Thus, we believe that there is a high probability that some of the bed materials come from the hillslopes. Our results demonstrate that a specific incised valley could reverse the pattern of grain size distribution. Additional research efforts should be required to explain what factors of the topography in incised valley affect the reversal.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP51E2131C
- Keywords:
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- 1824 Geomorphology: general;
- HYDROLOGY;
- 1825 Geomorphology: fluvial;
- HYDROLOGY;
- 1830 Groundwater/surface water interaction;
- HYDROLOGY;
- 1856 River channels;
- HYDROLOGY