Research On Distribution Characteristics Of Seismic Soil And Water Loss Based On The GIS Platform After The Wenchuan Earthquake

Changes in the spatial distribution of soil erosion caused by the Wenchuan earthquake, is the area change of land use/land cover and soil erosion. Using changes of variation range of area, the soil erosion intensity indexes and the land use structrue indexes,spatial distribution of the freshmen soil erosion within the study area was investigated. Based on remote sensing images before earthquake (2007) and after earthquake (2008) of three counties (Pingwu, Qingchuan and Beichuan County) in the study area, and GIS, land use/land cover, vegetation cover and the degree of soil erosion and other data were extracted, and combined with the three counties1:50000DEM data, land use/land cover, slope, vegetation cover, soil erosion area variation and area variation range were analyzed. Through the analysis of the natural ecosystem, farmland ecosystem, different segments of slope, different vegetation cover segment, and different soil erosion to the extent changes in the amount of area under the variation range in amplitude, spatial variation of soil erosion characteristics of three counties after the earthquake inthe study area were studied.The results showed that:(1) The main land use types of the study area are paddy field, dry land, woodland, grassland. A relatively large proportion of≤5°and8°slope area are paddy fields and dry land. Major types of8～15°,15～25°,25～35°,>35°slope area are dry land, woodland and grassland. The major land use structure in the different slopes of the three counties of the study area before the earthquake and after the earthquake changed little. Main land use types in the area of paddy fields net change in the biggest, followed by dry land; The net change is the smallest. The major type of Pingwu and Qingchuan County area is woodland, andit is grass on Beichuan. Influenced by the earthquake, the net change in area of Qingchuan County is the biggeset; The net change in area of Beichuan County is the smallest, and affeted by the earthquake little.(2) Natural ecosystems in the three counties after the earthquake, woodland, grassland area tended to decrease. The natural ecological system on the Pingwu and Qingchuan County,is affected by the earthquake of the largest grassland. It is forest land on Beichuan County. The woodland area to reduce the amplitude on Pingwu is the largest, followed by Beichuan and Qingchuan County.The grassland area to reduce the amplitude on Qingchuan is the largest, followed by Pingwu again Beichuan. The grassland ecosystem by the Wenchuan earthquake in Qingchuan and Pingwu is relatively large.Its woodland ecosystem is relatively small.The woodland ecosystem by the Wenchuan earthquake on Beichuan County is relatively large. The impact of its grassland ecosystem is relatively small.The farmland ecosystem dryland area reduction on Qingchuan and Pingwu is relatively large. The paddy field is relatively small. The dryland and paddy area reduction on Beichuan County is relatively small. The dryland ecosystems and the impact of its paddy fields by the Wenchuan earthquake on Qingchuan and Pingwu is relatively small. The farmland ecosystem to class the total area of change in amplitude on Qingchuan and the Pingwu is relatively large.The magnitude of the arable land ecosystems on Beichuan County. The total area of land type change is relatively small. The farmland ecosystems by the Wenchuan earthquake on Qingchuan and Pingwu is larger. The farmland ecosystem effects on Beichuan County is relatively small.(3) The change of the paddy field and dry in amplitude of8～15°slope area on Pingwu is the largest,and it is relatively small in the≤5°and>35°slope segment. The change rate of the Woodland and grassland in the area of5to8°slope is the largest and it is relatively small in the>35°slope segment. The changes of the paddy fields, dry land, woodland and grassland in amplitude in8～15°slope area on Qingchuan County is the largest. The changes of the paddy field in amplitude in the area of25～35°slope is the smallest. The change rate of the dry land is minimal in the area of≤5°slope. The change of the Woodland and grassland in the area is the smallest in amplitude of>35°slope segment. The changes of the paddy fields, forest and grassland in amplitude in the area of8～15°slope on Beichuan County is the largest. The change of the dry land in the>35°slope segment is the largest. The changes of the paddy field in amplitude in the area of≤5°slope is the smallest. The change of the dry land is a segment of15to25°slope. It is25～35°slope segment of the woodland and it is15to25°slope segment of the grass. It is the largest that the impact after the earthquake of8～15°slope segment of land use/land cover on Pingwu. Tt is the smallest that the>35°slope of the segment.It is the largest that the impact of5～8°slope segment of land use/land cover on Qingchuan and PingWu. It is relatively small of25～35°and>35°slope.(4) The focus of the study in the area is60to75%and>75%coverage segment. Coverage segment area of the three counties with the increase in vegetation coverage degree increases. The area after the earthquake in>75%increase in coverage segment on Pingwu is the largest.The area covering of60to75%reduction of the degree segment is the largest.The area of the study From60to75percent,45to60%,15～30%to>75%≤15%,30～45%of transfer. The area increase after the earthquake in the45～60%coverage section on Qingchuan County is the largest. The area reduction in the>75%coverage section is the largest.The area of the study by>75%,60to75percent to45～60%,15～30%,≤15%,30～45%of the transfer trend. The area of coverage paragraph after the earthquake in>75%increase on Beichuan County is the largest. The area is reduced, only60～75%coverage section on Beichuan County. The Area of the study from60～75%to>75%,30～45%,15～30%,≤15%,45～60%of the shift. The rate of increase after the earthquake in>75%area coverage section on Pingwu is the largest. The area reducted is the largest of60～75%of the coverage section on Qingchuan County. The area increase after the earthquake in the15～30%of the coverage section is the largest. The amplitude reducted of>75%coverage section of the area is the largest. In30to45percent of the coverage section of the area after the earthquake on Beichuan County, the rate of increase is the largest. The area only60～75%coverage section on Beichuan County is reduced.(5) Different vegetation cover type area comparison shows that in60～75%and>75%coverage segment the greatest impact on Pingwu. It is the largest in>75%,60～75%and45～60%coverage segment on Qingchuan County. It is the largest in>75%and60～75%coverage segment on Beichuan County. Different vegetation cover type area change with the vegetation coverage increases. The study area of≤15%,15～30%,30～45%of vegetation cover section in the net amplitude is relatively large.The most obvious is the magnitude on the area of the net change on Beichuan County. On Beichuan County, in30～45%vegetation cover degree segment of the area increase. It is310.52%in the area of the net amplitude. The area of coverage of different vegetation types change with the vegetation coverage increases, the degree of positive correlation with vegetation cover. Different vegetation cover type area of the net amplitude with the vegetation cover decreases, and area change in a negative correlation with vegetation cover.(6) Different soil erosion to the degree type, three counties before the earthquake and after the earthquake slightly eroded area is larger. Slightly eroded area after the earthquake to be reduced. The micro-degrees and slight erosion after the earthquake on Pingwu is reduced. It is increased On the moderate intensity, strength and intense erosion area. The slight erosion, mild erosion and intensity of erosion area on Qingchuan County is reduced. The moderate erosion, erosion and severe erosion area of the pole strength is increased. The slightly eroded, mild erosion, the erosion area of the intensity of erosion and the very strength on Beichuan County is reduced. The moderate erosion and severe erosion area was increased. The soil erosion area in the three counties after the earthquake of slight erosion, mild erosion and severe erosion to moderate erosion, the very intensity of erosion and severe erosion of the transfer. On the impact of the Wenchuan earthquake, severe soil erosion is significant. It is obvious that erosion of soil in the three counties after the earthquake of slight erosion, slight erosion, moderate erosion and intensity of erosion to the very intensity of erosion, severe erosion of the transfer, the increase of mild soil erosion area.(7) Pingwu earthquake before the soil erosion intensity index (SEI) is11741.84.After the earthquake, the SEI is39550.22. It is337times before the earthquake. On Qingchuan County, before the earthquake, the SEI is8197.68. After the earthquake, it is22933.02. It is2.8times before the earthquake. Before the earthquake in Beichuan County, the SEI is9847.59. After the earthquake, the SEI is16649.53. After the earthquake is169times before the earthquake. Soil Erosion in the three counties after the earthquake intensity increases is obvious. On Pingwu,the seismic impact of soil erosion is the largest, followed in Qingchuan County. The impact of Beichuan County is relatively small. On Pingwu, the land use structure index (LUI) before the earthquake is467.00. After the earthquake,it is447.81.The LUI reduce the19.19, is0.96times before the earthquake.On Qingchuan County, before the earthquake, the LUI is330.51.LUI after the earthquake is306.17.LUI reduce24.34, which is0.93times before the earthquake. Before the earthquake in Beichuan County, LUI is243.60. LUI after the earthquake is242.68. LUI is reduced by0.92. LUI is almost no change. Changes in the study area after the earthquake LUI is very slim. On Beichuan County, the LUI is almost no change. The results show that the Wenchuan earthquake Pingwu and Qingchuan County, and the land use structure is very small. On Beichuan County, the land use structure has almost no effect.