Search

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]

Computer-based coupled soilscape-landform evolution models provide an avenue for estimating the erosion potential of a landform over geological timescales. They also provide tools to understand soil-landform relationships in the context of both field and modelled pedogenesis processes. In this study, we used the State Space Soil Production and Assessment Model (SSSPAM) and CAESAR-Lisflood landform evolution model to simulate the evolution of a natural catchment where soil erosion rates have been closely monitored over the last 20 years. Both models predict comparable erosion rates to that of field measurements and produce similar catchment scale geomorphological patterns. Rock content data measured in the field along two transects were compared with SSSPAM simulations at the same representative points. The results showed that SSSPAM produced similar rock content variation along the respective transects. The findings demonstrate 'SSSPAM's ability to predict catchment scale erosion and surface soil distribution. The insights demonstrated here provide confidence in the SSSPAM model for Soilscape predictions for natural, agricultural and post-mining landform assessment. [Display omitted] • SSSPAM and CAESAR-Lisflood models were used to simulate the evolution of a natural catchment. • Both models produced catchment erosion rates comparable with field observations. • SSSPAM reproduced surface rock content variation on 2 transects observed in the field. • SSSPAM also revealed a possible relationship between area, slope and soil grading. • This study demonstrates SSSPAM's ability to predict erosion and surface soil distribution. [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]