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The grain size of sediment delivered to a river by hillslope processes is an important factor which could impact fluvial erosion, sediment transport, and associated geomorphic changes. Grain size distribution (GSD) is increasingly recognised as an important factor for the impact of landslides on sediment pulses and long-term erosion rates. Therefore a better comprehension of grain size control on landslide-generated sediment transport and dynamics will help with understanding post-seismic fluvial processes and landscape evolution. In this study, we modelled the recovery of the Hongxi River basin affected by the Wenchuan earthquake under different landslide GSD scenarios. The CAESAR-Lisflood (CL) model was first modified to enable the spatial input of sediment GSD, which allows the model to distinguish the grain size composition of landslide sediment and the background sediment sourced from other areas. Using the modified CL model, we simulated three different landslide GSD scenarios (Original, Coarser, Finer) by altering the original landslide sediment GSD observed from a post-earthquake basin. In particular, we analysed the fate of landslide-generated sediment using a new sediment tracing function embedded in CL. This enabled us to evaluate the role of landslide GSD variation on the spatio-temporal heterogeneity of sediment transport. Our results show that the GSD of landslide material exerts a clear control on both sediment yield and channel deposition, the sediment transport of landslides disconnected to the fluvial system is more sensitive to grain size variation, while the GSD of landslides connected to the fluvial system has less impact on sediment dynamics. The duration of landslide disturbances on basin sediment dynamics can largely be dependent on the period of time (e.g., 20 years in this study basin) taken for grain coarsening (the grain size is increasing upward), which is dominated by the evacuation of fine sediments. The modelling results and findings highlight the importance of grain size distribution of landslide material and provide information to support basin sediment management and environmental risk mitigation. [ABSTRACT FROM AUTHOR]

An important part of planning for the rehabilitation of a mine site is the design of stable final landforms for waste rock dumps or spoil piles. Whilst able to be assessed over the short-term (years to decades), the longer term behaviour (centuries to millennia) of such landscapes is not within any meaningful human time frame of observation. Predictive numerical models, therefore, form an important tool with which current landscape behaviour and longer term trajectory can be assessed. However, an important issue associated with the use of models is the ability to assess the reliability and accuracy of the model. Here the SIBERIA and CAESAR-Lisflood Landscape Evolution Models (LEMs) are used to simulate and assess the geomorphic stability of a conceptual rehabilitated landform of the Ranger uranium mine in the Northern Territory, Australia, for a simulated period of up to 1000 years. Utilising both models in this study enabled an independent assessment of likely landscape processes and evolution as well as each model. Results show that SIBERIA and CAESAR-Lisflood produce erosion rates and patterns that are broadly similar. At millennial time scales, short-term processes such as gullying appear to be the dominant erosion features in the proposed landforms and may produce substantial erosion in terms of size and amount of hillslope material eroded and transported downslope. Vegetation was found to have a major effect on the erosion potential of the landform surface. Overall both models produce very similar results. [ABSTRACT FROM AUTHOR]

As evidenced by recent earthquakes in Chi-Chi, Wenchuan and Gorkha, seismic triggered landslides can have a major impact on river basins and landscape evolution. The location of landslides with respect to river channels plays an important role in post-earthquake sediment dynamics. As well as direct impacts such as damming rivers, the connectivity of landslides to the fluvial network can alter how quickly sediment is moved and stored within river basins. Such "landslide-landscape relationships" are dominated by factors including geology, hydrological and geomorphic characteristics of the landscape, the location of landslides, and the geometric properties (e.g., size and runout length) of landslides. These factors will therefore control the magnitude and retention of associated sediment transportation. But key characteristics of this relationship and how it controls sediment dynamics are poorly understood. In this research, we probed the impact of landslide location on sediment dynamics and the response of sediment yields through numerical modelling. We modified the landscape evolution model, CAESAR-Lisflood (CL) to enable sediment from landslides to be tracked throughout the basin, and to include spatial changes in landslide failure angle. The model was then used to investigate impact of the different landslide location scenarios on basin morphology and sediment yields. Using a study area in the Hongxi river basin, four different regions (upstream-high, upstream-low, downstream-high, and downstream-low) were determined in terms of the distance to main stream for an upstream and downstream basin - and in each region landslides were generated for twenty times at random locations. The model results indicate that the location of landslides could alter the fluvial sediment yields and spatial pattern of the sediment dynamics, with low location landslides being more likely to link or connect to the drainage system (higher connectivity) thus leading to greater sediment yields at basin outlet. Whereas material generated by high location landslides tended to accumulate on hillslopes, which could lead to a lag sediment evacuation from the basin. Simulations also show a big latency of sediment yield between upstream and downstream scenarios, which is largely due to the differences of the flow length from landslides source to the basin outlet. These findings are of great importance to understand the characteristics especially the location of landslides and measures for landslide risk prevention and mitigation. • Using a novel tracing technique embedded in CAESAR-Lisflood model. • Landslide location impact on sediment transport and dynamics was investigated. • Relationship between the connectivity of landslide and sediment yields was analyzed. [ABSTRACT FROM AUTHOR]