Fluvial erosion, transport and deposition
Coarse-Bedded transport-limited channels
- Models do not fully treat coarse bed channels at present. Some issues that need to be addressed:
- Transport of mixed grain sizes. Appropriate transport formulas
- Size range of sediment influx from slope erosion
- Comminution
- Sorting during deposition and thickness of exchange layer
Notes:
Most landscape evolution models do not at present treat alluvial channels that transport a wide range of sediment sizes (primarily gravel bed channels). When multiple grain sizes are present a number of issues make their inclusion in landform models problematic. Firstly, there is much less agreement on appropriate bed sediment transport formulas for mixed grain size beds than for single-size channels. Some researchers assume that the previous transport formula can be used if corrected for the proportion of each grain size present on the bed. There are a number of hysteretic effects on transport rate as a function of changes in discharge when mixed sediment sizes are present. Furthermore, the landscape model must specify the size range and flux of sediment of all size ranges from slope erosion. Little data exists to calibrate the input flux for natural drainage basins. Finally, both reduction of size during transport due to abrasion and breakage (comminution) and differential transport and deposition (sorting) occur in mixed size channels. This remains as an area for future improvement of landscape evolution models.