Editor's note
October 13 is the 34th International Day for Disaster Reduction, with the theme of "Building a Resilient Future Together", emphasizing the construction of a government-led, socially participatory, and multi-party collaborative disaster risk management model, protecting vulnerable groups in disasters, and strengthening resilience in disaster prevention and reduction.
There are many natural disasters on the mainland, and there are many types of disasters such as earthquakes, landslides, floods, and land subsidence, with wide distribution and high frequency. With the frequent occurrence of extreme weather events and the acceleration of urbanization, geological disasters have brought severe challenges to urban security and economic development. When geological disasters come, how to prevent and mitigate various pressures and impacts caused by disasters and ensure the safety of people's lives and property is one of the key issues that experts in the field of geological disaster prevention and control have pondered and explored in recent years. Making cities more resilient and making urban life better is the direction and goal of their efforts.
Do a good job in the "combined fist" of geological disaster prevention and control
Dry together
The continental topography and geomorphology, geological conditions and climate types are complex and diverse, with active fault development and strong seismic activity, coupled with the impact of climate change and increasing human engineering activities in recent years, geological disasters are easy, frequent and frequent. According to statistics, by the end of 2022, more than 281,000 hidden danger points of geological disasters had been identified and registered nationwide, threatening the safety of more than 12 million people and more than 600 billion yuan of property. According to statistics, in January ~ September this year, a total of 3453 geological disasters occurred in the country, including 839 landslides, 2080 collapses, 367 debris flows, and 167 ground collapses, resulting in 71 deaths, 3 missing and 36 injured. In particular, from July 29 ~ August 2 this year, due to the influence of the remnant circulation of Typhoon "Du Surui" carrying abundant water vapor to the north, coupled with the combined effect of the topographic uplift of the Taihang Mountain and Yanshan Mountain Ranges, a round of historically rare extreme rainstorm occurred in the Beijing-Tianjin-Hebei region. Most of Beijing, Tianjin, central and southern Hebei and other places experienced heavy to heavy rainfall. Among them, the rainfall in Beijing is the highest in 140 years of instrumental measurement records. According to survey statistics, this extreme heavy rainfall caused 1,085 new hidden danger points in the three provinces (cities) of Beijing-Tianjin-Hebei, an increase of 8.2% over the 13,209 previously identified, which shows the great impact of extreme weather and climate events on geological disasters. Since 2018, the Ministry of Natural Resources has resolutely implemented the spirit of General Secretary Xi Jinping's series of important instructions and instructions on disaster prevention, mitigation and relief, with "two persistences and three transformations" as the fundamental follow, improving geological disaster prevention and control capabilities and reducing geological disaster risks as the main line, taking the safety of people's lives and property as the starting point and foothold, relying on scientific and technological innovation and management innovation, and comprehensively promoting the identification, investigation and evaluation, monitoring and early warning, comprehensive management and grassroots disaster prevention capacity building of geological disasters. In recent years, the number of deaths and disappearances caused by disasters has remained at a low level for many years, and fell below 100 for the first time in 2021. However, we should be soberly aware that there are still many difficult problems and risk challenges in the prevention and control of geological disasters on the mainland, which are mainly manifested in: First, the risk of geological disasters caused by extreme weather and frequent earthquakes increases. Affected by climate change, the increase of abnormal weather in local areas of the mainland, the change of the range of the main rainfall belt, the extension of autumn rain and autumn flood time, the increase of typhoon intensity and path uncertainty and other factors have increased the difficulty of preventing land disasters. For example, in August 2019, affected by Super Typhoon Likima, Zhejiang added more than 400 geological hazard points; On July 20, 2021, more than 240 geological disasters occurred in Zhengzhou City due to heavy rainfall in many places in Henan Province. In addition, earthquake-stricken areas are prone to chain geological disasters under the conditions of aftershocks and heavy rainfall, which aggravates the risk of geological disasters. For example, on May 21, 2021, Yunnan Yangbi and Qinghai Maduo "overnight double earthquakes" (magnitude 6.4 and 7.4 magnitude respectively); In June ~ September 2022, the "March Three Earthquakes" in Sichuan Province caused consecutive earthquakes in Lushan, Malkang and Luding, with magnitudes of 6.1, 6.0 and 6.8 respectively, which not only caused many new hidden dangers, but also caused a large number of existing hidden dangers to intensify deformation. Second, human engineering construction activities have aggravated the difficulty of preventing geological disasters. In recent years, the scale, scope and intensity of engineering activities such as urbanization construction, major infrastructure construction and energy resource development in mountainous areas of the mainland have been increasing, and the risk events of geological disasters caused or aggravated by engineering activities have increased. Third, there are still weak links in the prevention and control work. Continental geological hazard points are multifaceted, concealed, complex, sudden, spatiotemporal uncertainty and dynamic change, with many stocks, large variables and fast increments. Although the mainland carried out multiple rounds of investigation in the early stage, the accuracy and coverage of geological disaster investigation and evaluation are still insufficient, the accuracy of regional geological disaster meteorological risk early warning is insufficient, the coverage of automated monitoring point network is insufficient, and the technical ability and information level of prevention and control still need to be further improved. In the future, we should start from the following aspects, actively respond to risks and challenges, comprehensively do a good job in disaster prevention and mitigation, and make every effort to prevent geological disasters. Management level: First, focus on "how to deal with and mitigate the risk of geological disasters", strengthen the overall planning and integration of geological disaster prevention and control with land and spatial planning, use control, ecological protection and restoration and major engineering construction, strengthen the source control, scientific control and legal control of geological disaster risks, formulate management regulations and technical standards for risk disposal and mitigation, coordinate and coordinate in an overall manner, adapt measures to local conditions, classify policies, and accurately dismantle bombs. Comprehensively improve the comprehensive management capacity of geological disasters and the capacity of disaster prevention and mitigation. The second is to focus on "where the rain falls", "where the water flows", "where the mountains slide" and "where people turn", cooperate with meteorological, water conservancy, emergency response and other departments, strengthen communication and coordination, departmental linkage, information sharing and technical support, strengthen early warning issuance, response and disposal, transfer and avoidance and return control, implement the main responsibility of local party committees and governments for disaster prevention, and ensure that everything should be turned, stopped, sealed and closed, and improve emergency response capabilities. Technical level: First, focus on "where are the hidden danger points + risk areas", improve the management system and technical standards, and improve the rapid identification ability of "hidden danger points + risk areas". The second is to focus on "what are the types and structures of hidden danger points + risk areas", improve the management system and technical standards for investigation and exploration, and improve the ability of geological disaster investigation and evaluation. The third is to focus on "who threatens geological disasters", formulate management regulations and relevant technical standards for disaster-bearing body investigation and vulnerability assessment, and improve the ability of dynamic assessment of geological disaster risks. The fourth is to focus on "what are the causes of geological disasters", formulate management regulations and related technical standards for geological disasters caused by rainfall, earthquakes, and human engineering activities, and improve the ability to control the source of geological disaster hidden risks. The fifth is to focus on "when geological disasters occur", improve the management regulations and technical standards for meteorological risk early warning, trend prediction, and "civil air defense + technical defense" monitoring and early warning of geological disasters, and improve the monitoring and early warning capabilities of geological disasters. [The author is the deputy director and professor-level senior engineer of the Geological Disaster Emergency Coordination Office of the Chinese Academy of Geological Environment Monitoring (Geological Hazard Technical Guidance Center of the Ministry of Natural Resources)]
Geological safety risk prevention and control from the source
Gweiya
Cities carry people's expectations for a better life. The urbanization rate of the mainland has increased year by year, reaching 65.22% in 2022. With the increase of the agglomeration effect of production factors such as population and resources, urban security risks are also increasing.
Cities have large populations and high degree of agglomeration, so geological disasters such as land subsidence, land subsidence, and landslides often cause greater losses than non-urban areas. For example, disasters such as the sudden land subsidence in the residential area of Balitai Town, Jinnan District, Tianjin on May 31, 2023, the road collapse on South Street in Xining, Qinghai Province on January 13, 2020, and the landslide in the muck field in Guangming New District, Shenzhen on December 20, 2015, all caused major losses of people's lives and property. Therefore, it is imperative to enhance the ability of urban residents to identify, identify and prevent disasters, do a good job in local disaster prevention and control, and help build resilient cities.
Many scholars believe that urban resilience refers to the city's own resilience, response and rapid recovery ability when it is hit by shocks, that is, the city's ability to respond to natural disasters such as earthquakes, floods, and land disasters. Therefore, to improve urban resilience, it is necessary to do a good job in urban safety risk assessment, establish a disaster risk database, carry out urban disaster risk and infrastructure vulnerability assessment, carry out prediction and analysis of different scenarios, and strengthen the prevention and control of high-risk disaster areas.
Geological disasters such as land subsidence, ground subsidence, and landslides that occur in cities are often caused by the combined action of urban geological conditions and urban human engineering activities, and are usually invisible and intangible before they occur. First, through geological survey, we should accurately discover hidden dangers of land disasters; Second, through instrument monitoring, timely warning and forecasting of local disasters; Third, it is necessary to effectively prevent and prevent local disasters through scientific decision-making. Therefore, to enhance urban resilience, we can carry out urban geological surveys, investigate the geological conditions and human activities under the city, and depict the hidden danger points of geological disasters through modeling technology, so as to make the urban underground "transparent"; Monitor the hidden danger points of geological disasters, grasp the activity status of geological disaster points, and perceive urban risks; The data obtained from the survey and the data obtained from monitoring are intelligently analyzed through the big data platform, and the urban disaster prevention and control are scientifically decided, so that urban management is smart.
At present, in the process of urban planning and operation in the mainland, there are still problems such as the uncountable hidden dangers of land disasters, the irregular development and utilization of underground space, and the urgent need to strengthen land space planning and use control. In this regard, the author suggests that the investigation and risk zoning of urban geological safety risks should be strengthened, combined with land and spatial planning and use control, the prevention and control of geological disaster safety risks should be carried out from the source, and the prevention and management of urban geological disasters should be coordinated in multiple aspects, a new concept of resilient city construction should be established, and the whole process management mode of risk assessment-prevention planning and emergency countermeasures should be changed from a passive disaster prevention management model focusing on disaster emergency response to a whole-process management model of "trinity" of risk assessment, prevention planning, and emergency countermeasures.
The first is to carry out in-depth investigation and zoning of urban geological safety risks. According to the responsibility for the prevention and control of geological disasters, the Ministry of Natural Resources may take the lead in organizing and implementing geological security risk investigation and zoning in major cities across the country, carry out investigations on geological conditions and the development and utilization of underground space around key cities where disasters such as land subsidence, land subsidence, and landslides develop, identify hidden dangers and prone sections of geological disasters, and carry out risk zoning. The second is to comprehensively strengthen urban land spatial planning and land disaster safety risk management and control. Scientifically carry out urban construction land planning and engineering construction planning, include areas prone to high land disasters and high-risk areas into special areas for urban land space planning and use control, strictly control major engineering construction, strengthen the examination and approval of construction land and project access permits, limit the intensity of engineering construction, and reduce the risk of land disasters from the source. The third is to carry out overall planning and management of urban geological disaster prevention and control. In view of the fact that geological disasters occurring in cities are often the result of the comprehensive effect of human activities and complex geological environmental conditions, natural resources departments should strengthen information sharing and technology integration with municipal, housing and construction, civil air defense, transportation, water conservancy and other relevant departments, and promote the establishment of a joint prevention and control mechanism for urban geological disasters. The fourth is to improve the legal system for preventing urban geological safety risks. Carry out legislative work on urban geological safety risk assessment, raise awareness of the importance of land disaster prevention and control in the construction of resilient cities, strengthen the geological safety risk assessment management system for major planning and construction, and strengthen the geological environmental impact assessment system for the development and utilization of urban underground space.
(The author is the director of the Engineering Technology Innovation Center for Urban Underground Space Exploration and Evaluation of the Ministry of Natural Resources and the director of the Urban Geology Department of the Nanjing Geological Survey Center of China Geological Survey)
Continuously improve the urban geological perception system
Nanyun
At the end of July, Typhoon Du Surui brought "once-in-a-century" heavy rainfall to the Beijing-Tianjin-Hebei region, causing flooding and geological disasters. During this heavy rainfall, more than 29,000 people in Beijing were evacuated to safety, and no one died due to geological disasters.
After the "7.21" heavy rainstorm disaster in Beijing in 2012, the Beijing Municipal Commission of Planning and Natural Resources focused on building a disaster prevention and mitigation system of "civil air defense + technical defense", coupled with the Beijing Municipal Institute of Geology and Mineral Resources Exploration (hereinafter referred to as the Beijing Institute of Geological Exploration) to build the Beijing sudden geological disaster monitoring and early warning system, Beijing's "disaster prevention network" has become more and more dense, and the ability to "pocket" lives is getting stronger and stronger.
In the face of record-breaking rainstorms, how can cities become more "resilient" when geological disasters strike? Through the "once-in-a-century test" that Beijing encountered in July this year, the author believes that the following five aspects can be started.
The first is to strengthen emergency response and optimize the emergency work system.
To improve emergency response capabilities during heavy rainfall, efforts should be made in normal times. Take precautions and improve the peacetime prevention and wartime emergency response work system. Tighten the responsibility for the prevention and control of physical disasters, effectively strengthen the reserve of technology, equipment and personnel, strengthen emergency drills under extreme conditions, and do a solid job in peacetime protection and wartime emergency response.
The second is to strengthen the investigation of hidden dangers and broaden the depth and breadth of investigation.
From July 29th ~ August 16th, Beijing Institute of Geological Exploration investigated more than 3,900 hidden danger points of geological disasters in 10 mountainous areas, and completed emergency investigation reports at the district and municipal levels. Due to the concealment and complexity of sudden geological disasters, the fineness of the investigation in the investigation stage is difficult to support the needs of accurate early warning and judgment, so it is necessary to carry out special investigation and evaluation of geological disasters in a timely manner after heavy rainfall to further clarify the disaster risk base and provide a basis for economic construction, environmental governance, disaster prevention and mitigation.
The third is to strengthen risk research and judgment and improve the accuracy of monitoring and early warning.
In the emergency response to land disaster prevention and control, before the typhoon, the hospital identified 144 key debris flow prevention ditches, cooperated with the Beijing Meteorological Bureau to produce 9 geological disaster meteorological risk warning products and 6 phases of meteorological risk warning products for collapse disasters along mountainous roads during heavy rainfall, and issued more than 360 early warning reminders for debris flow ditches, providing scientific and technological support for government leaders' decision-making and early warning response. It can be seen that by improving the urban geological perception system and improving the monitoring and early warning ability of geological disasters, the emergency investigation work has truly achieved timely and efficient.
The fourth is to strengthen scientific and technological empowerment to help emergency rescue and post-disaster reconstruction.
In this emergency response, using the emergency satellite images provided by the Beijing Municipal Institute of Surveying and Mapping, the Beijing Geological Survey Institute interpreted the collapse and landslides in the 1400 square kilometers image coverage area in the west of Fangshan and the west of Mentougou, and compiled the emergency map of the safety and elimination of the rescue channel, which played an important role in opening up the rescue channel. The aerial photogrammetry data of six key disaster-stricken villages in Liucun Town, Changping District, and the satellite data of 1,600 square kilometers in Fangshan and eastern Mentougou were continuously interpreted, and the results were provided to all emergency investigation detachments and relevant units in the field in a timely manner.
The rapid processing, interpretation and distribution of remote sensing data can ensure that the results of emergency monitoring reach the front line of disaster relief as soon as possible. However, in the face of massive remote sensing data processing and analysis, as well as the relatively small scale of disasters in Beijing, low metamorphological variables, but greater harm and social impact, the remote sensing identification of hidden dangers of geological disasters needs to be further promoted in the direction of industrialization, precision and intelligence.
Fifth, strengthen collaborative linkage, and discuss resources, jointly build and share.
During the flood control period, the Beijing Institute of Geological Survey, Beijing Urban Planning and Design Research Institute and Beijing Institute of Surveying, Mapping and Design cooperated to provide rainfall monitoring data at rainfall stations, geological disaster risk assessment maps, and debris flow distribution maps, which strongly supported geological disaster investigation and post-disaster reconstruction. Coordinate with the competent departments of natural resources, meteorology, water affairs, transportation and other departments of each district to strengthen data integration and sharing, and provide important support for the formulation of decisions such as disaster early warning, disaster transfer, and opening up life channels. This practice proves that strengthening the work connection between relevant units, promoting the integration of disaster prevention and mitigation, fully integrating existing data resources, network resources and information systems, optimizing and improving information application systems and business processes, establishing and improving data governance mechanisms and unified data standard systems, realizing the interconnection of key geological information with the management platform of the municipal party committee and municipal government, can effectively improve the effectiveness of geological disaster prevention and control.
(The author is the director of the Department of Geological Disaster Prevention and Control of Beijing Institute of Geology and Mineral Exploration)
Be wary of small ditches and catastrophe – narrow and steep mudslides
Cui Huali
A typical cross-section of a narrow steep debris flow
In areas that have experienced strong earthquakes, the conditions for geological disasters have changed dramatically, and debris flows will be active for a long time. Due to the low degree of development before the earthquake, the narrow and steep debris flow has not attracted enough attention, and the characteristics of post-earthquake activity have changed significantly, and its concealment and destructive are extremely strong, which cannot be ignored in disaster prevention and mitigation.
Disaster characteristics: large longitudinal drop, deep lateral cutting, rich loose material sources
The narrow and steep debris flow was formally proposed in 2013 by summarizing and studying the pregnancy and disaster characteristics of more than 100 special debris flow trenches in the Wenchuan MS8.0 earthquake area. It is defined as the debris flow on the slope of the development period with narrow adjacent ridges, steep longitudinal slopes of the trench bed and abundant surface material sources, and the main characteristics are that the watershed area is less than or equal to 5 square kilometers, the average longitudinal slope of the trench bed is greater than or equal to 300‰, the integrity coefficient of the watershed is less than or equal to 0.4, the plane form is narrow and long, and the cross-sectional morphology of the channel is mainly "V" shape. This type of debris flow mainly develops in middle and high mountainous areas with a height difference of 1000 meters or more in the basin, with fault development, frequent new tectonic movements, humid regional climate, concentrated heavy rainfall in the rainy season, high frequency of outbreaks, and large dredging.
Disaster process: high potential energy is converted into high kinetic energy
Narrow and steep debris flows are mostly developed in alpine valley areas, distributed along the banks of rivers and their tributaries, steep slopes and deep cutting trench terrain, and adverse geological disasters such as collapse and landslides in the ditch provide rich sources for the occurrence of debris flows. After heavy rainfall, the river basin quickly converges in a narrow and steep channel, debris flow materials pour down, high potential energy is converted into high kinetic energy during the downward flow process, the flow rate increases sharply, and the water catchment is continuously absorbed along the way like a snowball, and erodes, washes, and shovels new solid substances, the number of solid substances carried is increasing, the particle size and impact force of the block increase rapidly, and the flow rate and flow rate change sharply. At this time, the ditch resembles a "fire hose". The debris flow material in the narrow channel in a short period of time is easy to stagnate or quickly collapse and wash, the sharp change of fluid flow leads to a large pressure fluctuation in the channel, and its instantaneous pressure can greatly exceed the normal pressure and have a destructive effect. This mudslide with great inertial force is like a water hammer in a fire pipe, and the hammer hits and wraps loose materials along the way all the way to the mouth of the ditch, eventually blocking the main river, silting up and washing away infrastructure such as roads, electricity, communications and residential areas, causing fatal harm to the disaster-bearing body.
Prevention and control ideas: make full use of natural conditions, optimize the configuration of engineering systems, and develop new applicable structures
After fully recognizing the hazards of narrow and steep debris flows, it is best to avoid hidden danger points or risk areas in road planning and infrastructure construction in relevant areas, and if they cannot be avoided, they should respect natural laws when selecting sites. Compared with ordinary conventional debris flows, narrow and steep debris flows have a large frequency of outbreaks and small critical rainfall, and the prevention and control design parameters calculated by the existing specifications are difficult to meet the actual needs. The construction of a barrier dam in a narrow and steep channel stabilizes the material source, and its silt recovery length is short and the width to depth ratio of the dam body is small, resulting in limited silt storage capacity and backpressure stability. Moreover, the narrow and steep debris flow has fast flow speed and strong impact, and the erosion and erosion of the foundation of the treatment project are serious, resulting in the structure of the treatment project being easily damaged. In addition, the construction site does not have space for equipment transfer and layout, and the construction safety risk is greater.
Therefore, in the investigation of hidden danger points in the early stage, relevant departments should carefully identify the source of materials, considering not only the source of landslides in the upstream basin, but also the distribution, type and quantity of Quaternary deposits near the mouth of the gully.
In the stage of prevention and control planning, it is necessary to appropriately and evenly allocate the prevention and control engineering system, make full use of the transmission capacity of the main river, rationally allocate the materials of the debris flow along the process, and select corresponding treatment measures according to the comparison of the amount of debris flow outflow and the scale of the main river transport capacity.
In the treatment stage, it is necessary to reasonably select the layout location of the project, optimize the structure of the treatment project, and use new structures and technical processes such as flexible sand barrier dam, permeable grid dam, micro steel pipe pile dam foundation and bottom dissipation drainage channel; Preferably stable and wear-resistant engineering materials, it is recommended to use lightweight and easy assembly and transfer construction machinery, and choose a construction method that is simple and fast and has a small amount of excavation and filling.
(Author's affiliation: Institute of Prospecting Technology, China Geological Survey)
Text editor: Zhao Lingling
New Media Editor: Qu Bingjie (Trainee)
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