Gravity erosion in small watershed after earthquake is one of the research hotspots and difficulties in the field of debris flow and soil erosion,for its process and mechanism are complicated with significant sediment yield and transportation effect,thus causing strong soil erosion and threatening post-disaster reconstruction and major engineering safety. In this paper,Lianhuaxin gully in the epicenter of Wenchuan Earthquake is taken as a typical study area and three debris flow occurring between 2008 and 2010 are selected. By means of multi-source remote sensing and GIS technologies,the system of digital slope-channel-watershed is established. Combined D-InSAR with offset tracking technology,three-dimensional surface deformation fields are created before and after different scence of debris flows. Correspondingly,multi-scale erosion and sediment characteristics and the material migration process of debris flows after earthquake in different types of slope,channel and watershed is analyzed. The results show that:a. considering three scenes of debris flows between 2008 and 2010,the total amount of slope erosion is respectively 6. 44 × 105 m3 ,3. 36 × 105 m3 and 3. 02 × 105 m3 ,the total amount of sediment from slope to channel respectively 3. 54 × 105 m3 ,1. 56 × 105 m3 and 5. 16 × 105 m3 ,and the total amount of sediment transportation in watershed 3. 84 × 105 m3 ,2. 24 × 105 m3 and 2. 96 × 105 m3 . b. the yield amount of slope sediment accounts for more than 50 percentage of the total incoming sediment amount of channels at all levels. So the gravity erosion and sediment from slopes is the main sediment source of channels at all levels;among them,most of yield sediment amount comes from convex-concave,convex and mixed slopes,which accounts for more than 85 percentage of the total slope yield sediment amount and presents a decreasing trend with channel level increasing. The secondary channel has the largest contribution rate of sediment transport in all levels of channels and is the main sediment source of the main channel. c. There are exponential function relationships between the ratio of slope erosion amount and corresponding erosion area as well as that of slope accumulation amount and accumulation area;there is a linear positive correlation between the ratio of slope sediment yield and slope unit area;slope erosion, accumulation and sediment yield amount increases with its corresponding area increasing. d. After the earthquake, the slope erosion rate decreases firstly and then increases,and the maximum erosion rate appears in convex-concave slopes,up to 0. 24 m each time;the watershed erosion rate also shows the same trend,additionally,it takes on an increasing trend from low to high levels and the largest erosion rate is in the main watershed,up to 0. 39 m each time. e. The sediment transport ratio at all levels of watersheds decreases with increasing watershed level,which is the lowest in the main watershed with 0 . 28 while the highest in the third level watershed with 0 . 93 . The research results have great significance to safeguard public safety in mountain areas,and can provide basis and reference for sediment control in small watersheds in earthquake-stricken area, site selection for major projects, river rehabilitation,risk assessment for secondary mountain disasters and prevention and control engineering design%震后小流域重力侵蚀过程与机制复杂,具有显著的产沙输沙效应,造成强烈的水土流失,严重威胁灾后重建和重大工程安全,是泥石流和土壤侵蚀领域研究的热点与难点之一.本文以震中莲花芯沟为典型研究区,选取2008—2010年的三场泥石流,采用多源遥感和GIS等手段,建立数字坡沟系统,融合D-InSAR和偏移量跟踪技术,生成不同场次泥石流前后的三维地表形变场,研究震后泥石流在不同类型"坡体-沟道-流域"上的多尺度侵蚀产沙特征与物质迁移过程.结果表明:1)2008—2010年三场泥石流,坡体侵蚀总量分别为6.44×105 m3、3.36×105 m3和3.02×105 m3,输入沟道的泥沙总量分别为3.54×105 m3、1.56×105 m3和5.16×105 m3,流域侵蚀总量分别为6.736×105 m3、5.217×105 m3、5.540×105 m3,流域输沙总量分别为3.84×105 m3、2.24×105 m3、2.96×105 m3;2)坡体重力侵蚀产沙量占各级沟道总来沙量的50%以上,是各级沟道泥沙的主要来源,其中以凸凹型坡、凸型坡和混合型坡三类坡体产沙最多,占坡体总产沙量的85%以上,且随沟道级别升高(三级→二级→一级)而呈递减趋势,二级沟道在各级沟道中输沙贡献率最大、达45%,是主沟泥沙重要来源;3)坡体侵蚀量与侵蚀面积及堆积量与堆积面积的比值均存在指数函数关系,坡体产沙量与坡体单元面积的比值呈线性正相关关系,坡体侵蚀量、堆积量、产沙量均随其对应面积的增大而增大;4)震后坡体侵蚀速率呈先减小后增大趋势,最大侵蚀速率在凸凹型坡体单元、达0.24m/次;流域侵蚀速率也呈先减小后增大趋势,同时,存在由低到高逐级递增趋势,其中主流域侵蚀速率最大、达0.39m/次;5)各级流域泥沙输移比随流域级别增高而减小,其中主流域泥沙输移比最低、为0.28,三级流域最高、达0.93.研究结果可以为灾区小流域泥沙调控、重大工程选址选线、河流整治和次生山地灾害风险评估及防治工程设计提供依据和参考,对保障山区公共安全具有重要意义.
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