The Suitability Evaluation Of Reconstructed Settlements After Earthquake In Beichuan

Beichuan Qiang Autonomous County was one of the most heavily destroyed areas of the Wenchuan earthquake in 2008.Urban and rural buildings in the county were seriously damaged.Since then,the county had been under reconstruction for three years.At the beginning,known geological disaster zones were not considered as new residential areas.However,reconstructed settlements were threatened by geological disasters and some became hallow due to the fast and large-scale reconstruction and extreme weather conditions in recent years.These undesirable phenomena show that reconstructed settlements with improper layouts still exist.Reconstruction is a long process,and reconstruction planning requires continually evaluations and corrections.Existing researches mainly focus on the reconstruction planning and construction of settlements and pay little attention to the situation and assessment of settlements in the post-earthquake period.This paper evaluates the suitability of the reconstructed settlements using an evaluation model generated by the weighted summation of multiple factors based on the analysis on some basic data collected after a flood occurring on July 9,2013,including geological disaster census data,DEM data,land use maps,road data and social service facility data.The evaluation results can provide reference for the Beichuan government to locally relocate the settlements in a scientific manner.Main research results of this paper are as follows:(1)Geological disasters impacting on the settlements are characterized by multiple types,wide distribution,large quantity,small scale,small-size disasters and dangers,and poor stability and trend.High-intensity geological disasters are located in Chenjiaba,Qushan,Leigu and Yuli,while low-intensity ones in Qingpian,Guanling,Xiangquan,Yong'an and An'chang.In view of spatial distribution,69.50%of the disaster zones are situated in areas with a slope ranging from 15° to 35°,53.49%in mountainous areas with a moderate elevation fluctuation,81.11%in areas with a distance less than 1 km from waters,and 37.48%in areas within 4000 m from faults.It is found that factors affecting the development of geological disasters vary from the fault-based endogenetic force in the east to the terrain-and water-based exogenetic force in the west.(2)Beichuan can be classified into five types of danger areas.Among them,high-and medium-high-danger areas,accounting for 28.48%of Beichuan's total area,are mainly distributed in fault development zones in the eastern part and the northeastern part featuring a steep terrain and fault development.Medium-danger areas,with an area of 939.31 km2,are situated in the central and western parts with a high elevation fluctuation.Medium-low-and low-danger areas,accounting for 41.01%,are mainly located in the flat southeastern part and the northwestern far away from faults and major water systems.(3)The spatial distribution of reconstructed settlements in Beichuan has two features:strip feature along the major water systems and central feature in areas with superior terrain conditions.71.12%of the settlements are located in areas with a slope less than 25° and good suitability,79.86%in areas with a distance less than 1 km from waters,51.15%in areas within 100m from road buffers,and 89%in areas less than 100 m from arable land.In site selection of reconstructed settlements,slope,water,transportation and arable land are considered.It is convenient to obtain medical and governmental services,but not educational resources,in most of the settlements.In reconstruction of settlements in Beichuan,three issues stand out:land area per capita is large and some settlements are seriously hollow;geological disasters and floods impose perilous threats on some settlements;and the layout of some settlements is improper.(4)According to the results of the evaluation on the suitability of reconstructed settlements in Beichuan,there are 7027 settlements with good suitability which are mainly distributed in Yongchang and An'chang in southeastern Beichuan as well as other township government centers and their surrounding areas,7871 settlements with moderate suitability which are far from government centers and along major water systems and roads,3136 settlements with poor suitability which are mainly in high-and medium-high-danger areas,and 1015 settlements which are threatened by geological disasters are mainly located in steep slopes and areas featuring complex structures and fault development.(5)Suggestions for optimization and relocation of the four settlements mentioned above are as follows:for settlements with good suitability,the governments should give priority to their urbanization over other areas;for settlements with moderate suitability,their layouts should be optimized,intensive degree of land use improved,and social service facility construction boosted;for settlements with poor suitability,the governments should limit their development and gradually reduce the scale to make them decline;for settlements threatened by geological disasters,the governments should guide people living in these areas to relocate and be free from geological disasters in long run except for those settlements where geological disasters are not severe and can be prevented.