Exploring the links between sediment character, bed material erosion and landscape: implications from a laboratory study of gravels and sand-gravel mixtures
Lynne Frostick, Brendan Murphy, Richard Middleton, 2008. "Exploring the links between sediment character, bed material erosion and landscape: implications from a laboratory study of gravels and sand-gravel mixtures", Landscape Evolution: Denudation, Climate and Tectonics over Different Time and Space Scales, K. Gallagher, S. J. Jones, J. Wainwright
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Rates of landscape evolution and landform development depend on the capacity of the main transporting medium, predominantly water and the river system, to move material away from the site of production in the upland slopes. In upland areas the main river bed material is coarse gravels, with various admixtures of finer sand and silt. This paper reports a series of flume experiments to investigate the impact of admixtures of finer material on the entrainment of coarse particles. In all experiments the main framework of the bed was made up of quartz-density gravels with a mean particle size of 8 mm. In some of the experiments unimodal, 0.09 mm mean particle size, quartz sands were introduced upstream of the experimental section and transported into place in order to simulate a common condition in natural river beds, of sand migrating over a static gravel bed. New image analysis techniques were developed to extract data from video recordings of the experimental runs. These revealed important differences in entrainment processes among the experiments with a distinctive contrast between the clean gravel and sand–gravel runs. Observations suggest that the presence of sand increases the rates of gravel entrainment and leads to a distinctive patchiness in bed break-up which will encourage bed form development. In the mixtures, sand removal prior to gravel entrainment destabilizes the bed and allows large areas to become entrained. This contrasts with clean gravels where grains tend to entrain individually. These observations show the importance of bed material character in controlling river form and process and point to its role in controlling sediment flux through the landscape.
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Landscape Evolution: Denudation, Climate and Tectonics over Different Time and Space Scales
The morphology of Earth’s surface reflects the interaction of climate, tectonics and denudational processes operating over a wide range of spatial and temporal scales. These processes can be considered catastrophic or continuous; depending on the timescale of observation or interest. Recent research had required integration of historically distinct subjects such as geomorphology, sedimentology, climatology and tectonics. Together, these have provided new insights into absolute and relative rates of denudation, and the factors that control the many dynamic processes involved. Specific subject areas covered are sediment transport processes and the timescales of competing processes, the role of the geological record and landscapes in constraining different processes, the nature of landscape evolution at different spatial scales and in contrasting geological environments.