River Valley Settlement In Upper Reaches Of Minjiang River Under The Influence Of Debris Flow Disaster Preparedness Research

The upper reaches of Minjiang River are the areas affected by the superposition of various unfavorable conditions and difficult factors in the social and economic development of China,the uplift area and the economic trough area on the terrain,and the frequent geological disasters such as collapse,landslide and debris flow.Because the upper reaches of the Minjiang River are mainly located at the gully mouth,the Wenchuan earthquake has formed a large number of landslide and collapse loose deposits accumulated in the channel.The debris flow formed by rainfall in the rainy season causes serious casualties and property losses.It has become an important factor affecting and restricting the social and economic development of settlements.Because of the weak ability of debris flow management and the lack of debris flow evaluation ability,the traditional ideas of pre-disaster experience prevention and post-disaster recovery and management can no longer meet the needs and objectives of disaster prevention and mitigation.The emergence of disaster preparedness concept to a large extent makes up for the lack of urban and rural planning disciplines in mountain settlements disaster prevention and mitigation,and provides a new way of thinking and direction for the combination of urban and rural planning and disaster prevention and mitigation.In this paper,typical town and village settlements in the debris flow disaster-prone areas in the upper reaches of Minjiang River are selected as the research objects.The risk of individual buildings and schemes is quantified by evaluating the risk of individual buildings and schemes.The following conclusions are drawn:(1)According to the statistical analysis of the damage of Cutou vally(village settlement)and Qipan vally(town settlement)buildings under the action of debris flow,the closer the distance from the main ditch line of the channel,the more serious the damage the angle between the main axis of the building and the main debris flow line,the greater the damage;the order of damage degree from low to high building structure is frame,brick,masonry,brick and steel frame structure.According to the law of building damage under the influence of debris flow,combined with land use planning,building quantity,building type and living custom,the construction layout plan for 2009 and 2013(Cutou vally only the first phase of land use planning in 2009),the residential custom building layout plan,the disaster prevention and mitigation building layout plan,and the current building layout plan were formulated to compare and analyze the risk and disaster adaptability of different schemes.(2)The risks of Qipan vally settlement under different debris flow scale are as follows:current situation plan >2009 plan >2013 plan > residence custom plan > disaster prevention and mitigation plan.The risk of Cutou vally settlement under different debris flow scale is:current situation plan > residence custom plan >2009 plan,disaster prevention and mitigation plan.The risk of disaster prevention and mitigation schemes in Qipan vally settlement and Cutou vally settlement is the lowest,which indicates that the disaster prevention and mitigation scheme can effectively reduce the loss caused by debris flow,but the disaster prevention and mitigation scheme of Cutou vally settlement reduces the risk more greatly.(3)According to the statistics of disaster-adaptive ability of single building,the location of building space,building direction and building structure are the main control factors that affect the disaster-adaptive ability of single building.The space position of the building is within 50 m from the main gully line of debris flow,the angle between the building direction and the flow direction of debris flow is 60?90,and the disaster adaptability of the single building with lower building structure than that of brick and concrete structure is generally low.With the increase of debris flow scale,the influence of these main control factors decreases gradually.The disaster adaptability of Qipan vally settlement under different debris flow scale is as follows: disaster prevention and mitigation program > residential custom program >2013 program > status plan >2009 program;Cutou vally is: disaster prevention and mitigation program >2009 program,residential custom program > status plan.Under the same building layout scheme,with the increase of debris flow scale,the disaster tolerance ability of settlement decreases,and the disaster preparedness ability of disaster prevention and mitigation scheme is least affected by the change of debris flow scale,which only reduces 13%.It shows that disaster prevention and mitigation scheme can adapt to different debris flow.(4)According to the influence range of debris flow and the influence degree of debris flow velocity and mud depth on buildings in different space locations,the strategies and suggestions for settlement planning in mountainous areas affected by debris flow are put forward from three aspects: scope disaster,intensity disaster and location disaster.Scope of disaster preparedness : according to the disaster response capacity from large to down to divide the appropriate area,can be built area,careful construction area,no construction area.Due to the shortage of land,urban settlements should arrange buildings as much as possible,give priority to residential construction land,give priority to public service construction land,followed by industrial and commercial buildings,and build industrial and commercial buildings as little as possible.The village settlement is mainly residential building.Under the condition of abundant land use,the building layout is mainly suitable for construction area.When the land is insufficient,it can be arranged in the construction area.Strength of disaster preparedness: because the debris flow velocity and mud depth of the main channel line are the largest,the damage and influence to the building are also the greatest,50 m on both sides of the main channel line should not be arranged.The minimum should not be lower than brick-concrete structure.In buildings outside the suitable construction area,buildings located on both sides of the channel should be arranged parallel to the channel as far as possible,and the angle between the building direction and the channel direction from the gully mouth should be controlled within 30 as far as possible.Disaster preparedness for site selection: the important buildings of urban settlements are placed on the higher side of the channel(the north side of Qipan vally is 4 m higher than the south side),and the necessary emergency shelter for debris flow disaster should be reserved on the higher side of the suitable area.