Control of territorial space in mountainous urban areas based on risk assessment of geological disasters:A case study of the"9·02"debris flow disaster in Malipo county

ZHANG Weifeng; TONG Bin; DING Zhongkai; ZHOU Cuiqiong; YANG Yingdong; TAN Weijia; YANG Wenli

doi:10.11932/karst20250412

Abstract：Mountainous areas in West China are most severely threatened by geological disasters.With the rapid development of mountainous cities and towns,there is an increased demand for more accurate risk assessments of geological disasters.Especially in recent years,extreme weather events have occurred frequently,accompanied by a sharp rise in local rainfall intensity.Consequently,the risk,damage degree,and losses associated with geological disasters in mountainous cities and towns have escalated.These intense rainfall events and major geological disasters have become more pronounced,making disaster prevention and mitigation more difficult.This study focuses on the territorial space control of group-occurring rainfall-induced geological disasters as its research objective.Based on the ground investigation of geological disasters,the fuzzy comprehensive evaluation method was used to conduct a quantitative risk assessment.The evolutionary characteristics,distribution patterns,and impact intensity of group-occurring rainfall-induced geological disasters were analyzed.Governance measures were scientifically implemented,and suitable,restricted,and prohibited construction zones were accurately proposed according to territorial space zoning of mountainous cities and towns.Macro-control measures,such as source control,active avoidance,proactive prevention and control,as well as localized and intensity-based control of geological disasters,will be refined and implemented.Emphasis will be placed on integrating urban disaster prevention,mitigation resilience,emergency planning,and strategic layout to effectively enhance the capacity of mountainous cities and towns to respond to disasters. Taking the"9·02"debris flow disaster in Malipo county of Yunnan Province as an example,this study examines the disaster triggering mechanisms,risk assessment,and territorial space control of debris flow disasters.Between 3 a.m.and 4 a.m.on September 2,2018,a catastrophic mountain torrent and debris flow disaster occurred in Mengdong town,Malipo county.The urban area where the township government is located was severely affected.This debris flow is characterized as a low-frequency,viscous debris flow gully.The primary sources of debris flow materials were from group-occurring rainfall-induced landslides,gully bank collapses,and gully bed materials from the middle and upper reaches.The volume of debris flow deposits in the urban area was 100×104 m3.The formation conditions of debris flow disasters are closely related to topography,provenance,and hydrodynamic effect.According to the investigation,the total volume of solid movable materials for the"9·02"debris flow is 3 84.4× 104 m3,including 180.4× 104 m3 from the Mengdonghe River,165.2× 104 m3 from Shuichongxiang Gully,and 38.8× 104 m3 from Xiangcaopeng Gully.The provenance type is mainly landslide,accounting for about 98％of the total.There are 614 landslides induced by rainfall,with the landslide masses primarily being small in size.Landslide materials and trees provide abundant loose material sources that contribute to the formation of debris flow disasters.Tall trees on the landslide obstruct the drainage and diversion of the gully,which increases gully erosion and exacerbates the consequences of debris flow disasters.The debris flow discharge is calculated and compared by the morphological investigation method and rain flood method,respectively.The calculation result from the morphological investigation method is slightly higher than that from rain-flood method for a 100-year return period,and the calculation result from the morphological investigation method aligns more closely with the actual disaster. Through a refined investigation process,this study provides a foundation for the territorial space control in Mengdong town.It examines the distribution,characteristics,stability,and susceptibility of unstable disaster-prone bodies.The fuzzy comprehensive evaluation method is used to quantitatively assess the risk of debris flow.It is necessary to fully consider the risk level,degree of harm,and recurrence frequency of geological disasters,while allocating sufficient space for debris flood channels and ultra-high sidewall protections in curves to ensure the safety of cities and towns.This approach integrates various measures of geological disaster risk management and control into territorial space planning,aiming to eliminate or mitigate geological disaster risks at their source.Future studies can focus on the coupling relationship between geological environment carrying capacity and urban development,ecological protection,resource security,and related factors.In the management and control of territorial space,it is essential to coordinate economic and social development,urban construction intensity,restoration and utilization for territorial space,emergency response,and other activities to achieve comprehensive management and control and harmonious development between people and land.The impact area of debris flow can be scientifically and quantitatively defined into three zones:the forbidden area,the restricted area within the affected zone,and the safe area after treatment.Key aspects of territorial space management and control in mountainous cities and towns include disaster source management and control,reasonable avoidance,early prevention and control,and ensuring sufficient space.Additionally,the resilience of cities and towns to disasters must be strengthened.