Soil erosion and sediments in the Lancang-Mekong River Basin as a result of climate change and changes in land use pose a threat to the existence of the riparian people,biodiversity and ecosystems.This study seeks to assess the annual soil erosion in terms of spatial distribution and the trends of sediment yield with the climate and land changes in future scenarios in 2030 and 2040 through the modified RUSLE model.Future lands were simulated by using the MLP artificial neural network and the Markov chain analysis.The future climate was examined by using the Max Planck Institute model,which showed a corrected bias and downscaled grid size under the Representative Concentration Pathways(RCPs).The simulated land use indicated that the forest areas were converted mostly to agricultural lands and urban areas.In the future,the average rainfall under all RCP scenarios is higher than that from the historical period.The R and C factors changed constantly,thereby affecting the soil erosion rate and sediment yield.The maximum erosion was estimated at approximately 21,000 and 21,725 t/km2/y under RCP8.5 in both years.Meanwhile,the results of sediment yield in 2030 and 2040 under RCP scenarios were much higher when compared to historical sediment data around 66.3%and 71.2%,respectively.Thailand's plateau,some parts of Cambodia and Laos PDR and the Mekong Delta are vulnerable to increase soil erosion and sediment yield.Measures to address these issues need to be planned to prepare and mitigate the possible effects,especially the loss of storage capacity in dams.
Engineering geological and hydro-geological characteristics of foundation rock and surrounding rock mass are the main factors that affect the stability of underground engineering. This paper presents the concept of multiscale hierarchical digital rock mass models to describe the rock mass, including its structures in different scales and corresponding scale dependence. Four scales including regional scale,engineering scale, laboratory scale and microscale are determined, and the corresponding scaledependent geological structures and their characterization methods are provided. Image analysis and processing method, geostatistics and Monte Carlo simulation technique are used to establish the multiscale hierarchical digital rock mass models, in which the main micro-and macro-structures of rock mass in different geological units and scales are reflected and connected. A computer code is developed for numerically analyzing the strength, fracture behavior and hydraulic conductivity of rock mass using the multiscale hierarchical digital models. Using the models and methods provided in this paper, the geological information of rock mass in different geological units and scales can be considered sufficiently,and the influence of downscale characteristics(such as meso-scale) on the upscale characteristics(such as engineering scale) can be calculated by considering the discrete geological structures in the downscale model as equivalent continuous media in the upscale model. Thus the mechanical and hydraulic properties of rock mass may be evaluated rationally and precisely. The multiscale hierarchical digital rock mass models and the corresponding methods proposed in this paper provide a unified and simple solution for determining the mechanical and hydraulic properties of rock mass in different scales.
