强震区都江堰市白沙河流域松散物源时空演变趋势遥感分析

Remote sensing analysis of temporal and spatial evolution trend of loose material sources in meizoseismal area,Baisha River Basin,Dujiangyan,China

白沙河流域是成都市主城区主要饮用水源地,“5·12”汶川特大地震导致大量崩塌滑坡碎屑物质在陡峭的斜坡积累,在暴雨时造成严重的水土流失,对水源地供水产生严重影响。开展流域松散物源调查和变化趋势分析,对流域水土流失综合治理工作有重要的指导意义。选取地震前1年和地震后10年共4期高分辨率遥感影像,利用面向对象遥感自动解译结合人机交互提取松散物源,采用GIS空间分析方法分析物源空间分布及动态变化特征。结果表明:“5·12”汶川特大地震导致流域内产生总面积达86.26 km 2的新增松散物源,震后10年流域内植被恢复明显,物源总面积减少66.95 km 2,流域下游物源缩减趋势明显,呈逐步稳定的状态。虽然流域生态修复明显,但离震前还存在一定差距。上游西南偏西、西北偏西、西北偏北3个方向物源仍处于不稳定的状态,是下一步需重点治理的区域。

[Background]Baisha River Basin is the main drinking water source in the main urban area of Chengdu.The“5·12”Wenchuan earthquake led to the accumulation of a large number of collapse and landslide debris on the steep slopes,resulting in serious soil and water loss during rainstorm,which has a serious impact on the water supply of the water source.The investigation and change trend analysis of loose material sources in the basin have important guiding significance for the comprehensive control of soil and water loss in the basin.[Methods]Four periods of high-resolution remote sensing images one year before the earthquake and 10 years after the earthquake were selected.The loose material source was extracted by using object-oriented remote sensing automatic interpretation combined with human-computer interaction.The spatial distribution and dynamic change characteristics of material source were analyzed by GIS spatial analysis method.[Results]Before the“5·12”Wenchuan earthquake in 2008,the loose material sources area of the basin was only 20.05 km 2,accounting for 5.57%of the total area of the basin.The“5·12”Wenchuan earthquake caused a large number of new loose material sources in the basin,with a total area of 106.31 km 2,accounting for 29.52%of the total area of the basin.At 10 years after the earthquake,the total material source area decreased by 66.95 km 2.There are still a few new sources in the basin after the earthquake,and the new sources in the 5 years after the earthquake are mainly distributed in the lower reaches of the basin due to human activities such as post disaster recovery and reconstruction,river dredging and mining.At 5-10 years after the earthquake,the newly added sources decreased,which was mainly caused by the expansion of the source range of some slopes in the upper reaches of the basin or the newly added collapse and landslide sources.The earthquake caused the average source center of the basin to move about 6.7 km downstream as a whole,and the average source center gradually moved back at 10 years after the earthquake.[Conclusions]Although the ecological restoration of the basin is obvious,there is still a certain gap from that before the earthquake.The material sources in the three directions of southwest by west,northwest by west and northwest by north of the upstream are still in an unstable state,which is the area to be treated in the next step.