Division of debris flow susceptibility in China

4.4. 1 Discriminating characteristics of debris flow susceptibility zoning

The distribution of debris flow in China is roughly bounded by Daxinganling-Yanshan Mountains-Taihang Mountains-Wushan Mountains-Xuefeng Mountain. To the east of the line, that is, the low hills and plains in China, debris flows are relatively scattered (only the southern mountainous areas of Liaodong are relatively dense). To the west of this line, that is, the first and second steps of China's landform, including the vast plateau, the extremely high mountain, the high mountain and the Zhongshan area, are the most developed and concentrated areas of debris flow, and the debris flow valleys are often distributed in strips or sheets. Among them, the patches are concentrated in the mountainous areas on the southeast edge of the Qinghai-Tibet Plateau, around the Sichuan Basin, and in areas such as Longdong-southern Shaanxi, western Shanxi, northern Hebei, etc., which are dominated by the eastern edge of the Loess Plateau.

The distribution pattern of debris flow is the same as that of landslide and collapse, which is obviously controlled by natural factors such as geological structure, stratum lithology, topography, hydrometeorology and so on. The influence of human engineering activities can also play a leading role in many times and local areas.

(1) Control of Geological Structure on Debris Flow Disaster

Because landslide and collapse disasters are closely related to debris flow disasters in mountainous areas, the control effect of geological structure on the susceptibility of landslide and collapse disasters is basically the same as that of geological structure on the susceptibility of debris flow disasters. The relationship between large-scale and extra-large debris flow concentrated distribution areas and regional geological structures and fault structures is basically consistent with landslides and collapses. I won't go into details.

(2) The controlling effect of topography on debris flow disaster.

Because landslides and collapses in mountainous areas are closely related to debris flow disasters, the landform pattern basically controls the susceptibility of landslides and collapses. Large-scale and extra-large debris flows in China are mostly distributed in the transition zone between the first and second steps and the second and third steps. The landform features of steep mountains, deep valleys, multi-level leveling and highly developed rivers also laid the foundation for the formation of large-scale and extra-large debris flows. Its specific characteristics can be seen in the above discussion on the influence of landslide and collapse disasters on geomorphic pattern.

(3) The controlling effect of stratum lithology on debris flow disaster.

The lithology of strata prone to collapse and landslide is also prone to debris flow.

The stratum composed of Quaternary residual clay and loam is easy to cause the concentrated distribution of small and medium-sized debris flows. These Quaternary loose deposits and soft rocks have low mechanical strength index, soften when meeting water, and are easy to collapse and landslide, which in turn leads to debris flow or debris flow. The exposed areas of schist, phyllite, shale, carbonaceous shale, coal seam, salt rock, gypsum and other soft rocks from pre-Paleozoic to Mesozoic, as well as the exposed areas of strata composed of upper hard quartzite, limestone, sandstone, conglomerate, basalt, granite and lower soft rocks, are also areas where large and medium-sized debris flows are concentrated. These lithology are beneficial to the development of debris flow, which is consistent with the mechanism of landslide and collapse.

(4) The control effect of rainstorm and long rain weather and melting of snow and ice on debris flow disaster.

Atmospheric precipitation is not only an exciting factor of debris flow activity, but also an integral part of debris flow. Therefore, debris flows mostly occur in wet years, especially in heavy rain years. China is a world-famous monsoon climate zone with abundant precipitation, but the regional and seasonal distribution is uneven and changes greatly, which provides basic conditions for debris flow activities. Therefore, it can be considered that monsoon climate influences and controls the distribution pattern of debris flow in China. The eastern and southeastern parts of China are affected by the Pacific monsoon; The southwest corner is affected by the southwest monsoon of the Indian Ocean. The general trend of precipitation distribution in China is gradually decreasing from southeast to northwest, and local rainstorms are mostly concentrated in western mountainous areas. For example, 198 1 year, the debris flow activities in the vast mountainous areas of Sichuan, Shaanxi and Liaoning are caused by such weather processes. In the mountainous areas with modern glaciers in western China, especially in the mountainous areas with maritime climate, marine glaciers develop, and glaciers advance and retreat to form glacial mudslides and glacial lake bursts.

(5) Unreasonable human engineering activities and mudslides.

Unreasonable human engineering activities are closely related to the development and distribution of debris flow. For a long time, with the economic development and population growth in mountainous areas of China, people's economic activities in mountainous areas are increasing day by day, and the demand for natural resources is excessive, which destroys the ecological balance in mountainous areas, worsens the natural environment in mountainous areas and promotes the development of mudslides. However, the debris flow caused by human factors is mostly punctate.

To sum up, China's unique geological, geomorphological, hydrological and meteorological conditions are the main controlling factors for the development and distribution of debris flows in mountainous areas, and human engineering activities only play a leading role in local areas and in some cases. The classification of debris flow disaster susceptibility should be based on the relevant indicators of the main control factors (Table 4.4).

Table 4.4 Discrimination Characteristics of Debris Flow Susceptibility Zoning

4.4.2 Brief description of debris flow susceptibility zoning and characteristics of each zoning.

According to the remarkable characteristics of the above classification of debris flow susceptibility, the debris flow susceptibility in China is classified, and the results are shown in Figure 4.2 and Table 4.5.

Table 4.5 List of debris flow susceptibility zones

sequential

4.4.2. 1 debris flow prone area

(1) Liaodong-Beijing Beishan high debris flow prone area (H 1)

Including the mountainous areas in Liaodong and the piedmont areas around the plain, Miyun, Huairou and Yanqing areas in the north of Beijing.

The mountains in this area are steep, the valleys are deep and narrow, and metamorphic rocks and magmatic rocks are widely distributed. Because the east and south slopes face the sea, there is abundant rainfall, heavy rain and strong earthquake activity.

Debris flow occurs frequently in this area, with a wide range, large scale and serious disasters. Debris flow in gully is mainly large and medium-sized debris flow. There are124,000 debris flow hazards, and the debris flow density is 7.9/100km2. From 1960 to 200 1 year, 17 13 people died, and the direct economic loss reached1200 million yuan. There were many group mudslides in 1950, 1969, 1972, 1976 and 1977 in Beishan, Beijing, resulting in 2 13 deaths.

(2) High-risk area of debris flow in hilly region of southern Hunan and northern Guangxi (H2)

Including Hunan Passage, Shibu from Xupu to Taoyuan, and the border area between northern Guangxi and Hunan.

This area belongs to the landform of middle and low mountains, with severe cutting and large slope. The highest altitude is 1890m, generally 400-900 m, and the local terrain is high hills. Formation lithology ranges from magmatic rocks to metamorphic rocks and clastic rocks, and then to carbonate rocks, clastic rocks and metamorphic rocks. It is obviously affected by typhoon, and the annual precipitation is1600 mm.

There are more than 20 large and medium-sized debris flows in this area, and there are thousands of debris flows on the slope, and slag debris flows are widely distributed.

(3) Xining-Lanzhou debris flow prone area (H3)

Including Xining in eastern Qinghai, the upper reaches of the Yellow River, and Yanguoxia-Lintao in Gansu.

The elevation of this area is between1500 ~ 2,500m ~ 2,500m, with broken terrain and criss-crossing gullies, mainly loess hills and hilly areas. Rock mass types are mainly clastic rocks and carbonate rocks, followed by metamorphic rocks. The soil is mainly loess, with a thickness ranging from 30 to 400 m, and the loess structure is loose and collapsible. The annual precipitation is 400 ~ 600 mm.

The density of debris flow in this area is 6 ~ 10 /20km, especially in Baodian and Tianlan lines.

(4) High risk area of debris flow in West Qinling (H4)

Including Gansu Cisse-Minxian, Zhouqu-Wenxian, Lixian-Liangdang, Zhang Xian-Tianshui and Huanxian-Chongxin.

North and South Qinling Mountains, the Loess Plateau in central Gansu, including Xili Basin, Huicheng Basin and Tianshui Basin. The altitude is between 2500 and 4500 m, and the cutting depth is greater than 1000m, which belongs to the middle and high mountain terrain. The main types of rock and soil are metamorphic rocks, clastic rocks, carbonate rocks and loess. The annual precipitation is generally 600mm, the neotectonic movement is strong, and the earthquake intensity is above seven degrees.

The landslide density in this area is 10/10km2, and the landslide area accounts for 20% ~ 30% of the total area. Debris flow is mainly viscous, with more than 5,000 debris flow gullies.

(5) East Qinling-Dabashan high debris flow prone area (H5)

Including north of Weihe River in Baoji, Shaanxi, Baoji-Chang 'an, Lintong-Huayin, Fengxian-Taibai, Foping-Ningshan, Lueyang-Yangxian, Zhen 'an-Yang Shan, Ankang-Ziyang, Pingli-zhenping county, etc.

The altitude of this area is 1000 ~ 3000 m, with complex landform types, high mountains and deep valleys, and large relative height difference. This mountain is mainly composed of magmatic rocks, metamorphic rocks and carbonate rocks. Strong fault tectonic activity, rock fragmentation, residual slope deposits and loose structures are widely distributed, and the slope stability is poor.

There are many landslides and collapses in this area. Debris flow disasters are more prominent in Micang Mountain and Daba Mountain in the south, Ziyang-Baihe section of the Han River in the east, and the north slope of Huashan Mountain in the northeast.

(6) The high-risk area in the east of Hengduan Mountain (H6)

The area is dominated by mountains and Zhongshan, and Jialing River, Minjiang River, Dadu River, Yalong River and Jinsha River are deeply located in it, with a general north-south trend. Metamorphic rocks and magmatic rocks are widely distributed, mainly clastic rocks and carbonate rocks. The structure is complex, with latitudinal, Cathaysian, meridional, zigzag, Xinhua Gorge and other structural systems from north to south, and the active faults are dense, which belongs to the distribution range of the famous north-south seismic belt in China. The annual precipitation is 600 ~ 1400 mm.

There are many landslides in this area, mainly giant and large landslides, with the maximum density exceeding 20/100km2, with an average of 10 ~ 20/100km2. The distribution density of debris flow reaches 5.34/100km2.

(7) High debris flow prone area (H7) west of Hengduan Mountain-Ailao Mountain.

Nujiang, Lancang, Jinsha, Daying, Longchuan, Yuanjiang, Jiang Lixian, etc. Among the mountains, the terrain is high in the north and low in the south, from the mountains to Zhongshan, and the terrain is highly cutting. The lithology is complex, and a large area of clastic rocks, carbonate rocks, metamorphic rocks and magmatic rocks are exposed and staggered. Zigzag structure is reconnected and compounded by meridional structure, and active faults are dense, which belongs to the distribution range of western Yunnan seismic belt. The annual precipitation is 400 ~ 2000 mm, which increases rapidly from north to south, and the vertical zoning of climate is also obvious.

Debris flow is the main geological disaster, most of which are distributed along the Nujiang River and Lancang River basins and their tributaries. Its density is 14.08 strips/100km2.

(8) Debris flow prone area in the east of Nyainqentanglha Mountain (H8)

This area belongs to the lower reaches of Yarlung Zangbo River, with tributaries such as Nianqu and Palong Zangbo River, and is a concentrated distribution area of marine glaciers in China. Due to abundant precipitation, high temperature, rapid glacier movement and strong melting, and heavy rainfall in summer and autumn, most river valleys develop along active fault zones, with steep terrain and broken rock formations on both sides, especially rich glacial deposits, and strong seismic activity in the adjacent areas.

Strong debris flow development zones (regions) are often formed along highways and valleys. The Sichuan-Tibet highway section is the most serious area of debris flow disaster. There are more than 140 large debris flow gullies along the 280km highway from Ranwu to Lulang, and debris flow breaks out every year, which often leads to serious disasters.

Debris flow prone areas in 4.4.2.2

(1) The debris flow prone area from Changbai Mountain to Taihang Mountain (M 1)

Including the Baishan area in Heilongjiang, Qianshan-Fushun in Liaoning, western Liaoning, northern Hebei, the border area between western Hebei and Shanxi, and the middle and low mountain areas in eastern Shandong.

The mountains in this area are steep, the valleys are deep and narrow, and metamorphic rocks and magmatic rocks are widely distributed. Because the east and south slopes of the mountain face the sea, there is abundant rainfall, heavy rain and strong earthquake activity.

There have been many mudslides in this area in history, and the distribution density of mudslides is 1.57/100km2.

(2) Debris flow prone areas in hilly areas of Hunan, Jiangxi, Guangdong and Guangxi (M2)

Including the border areas of southeastern Hunan, southwestern Jiangxi, northern Guangdong and western Guangxi.

From the coast to the inland, the formation lithology ranges from magmatic rocks to metamorphic rocks and clastic rocks, and then to carbonate rocks, clastic rocks and metamorphic rocks. Affected by typhoon, the annual precipitation is 1600 ~ 2000 mm.

Landslides and collapses develop in this area, and the scale of debris flow is mainly small and medium. Large and medium debris flow 13.

Figure 4.2 National Debris Flow Vulnerability Map

Figure 4.2 National Debris Flow Vulnerability Map

(3) Debris flow prone area in middle and low mountains of Zhejiang Province (M3)

Including northwest Zhejiang and middle and low mountainous areas in Zhejiang.

The landform is mainly middle and low mountains, with high mountains and steep slopes and complex landforms. The average annual precipitation is between1800 and 2200mm. Pyroclastic rock series and granitoids are widely distributed.

Landslides and collapses develop, and the scale of debris flow is mainly small and medium-sized, and the distribution density of debris flow is about 2.24/100km2.

(4) Debris flow prone area in the Loess Plateau (M4)

Including western Shanxi, northern Shaanxi and central Gansu.

There are extremely dense valleys in the loess ridges, mounds and plateau margins in this area, and landslides at the foot of the mountain are well developed, which provide topographic conditions and rich sources of solid materials for the formation of debris flows. The precipitation in this area is mostly concentrated from July to September, and it is easy to form debris flow in the form of heavy rain.

Both slope debris flow and gully debris flow are developed, widely distributed and frequently active in this area. The distribution density of debris flow is about 1.9/100km2.

(5) The debris flow prone areas in Qilian Mountain and the upper reaches of the Yellow River (M5)

Including Huangshui River basin and its tributaries and the upper reaches of the Yellow River.

The northeastern slope of Qilian Mountain and the mountainous areas along Hexi Corridor are dominated by metamorphic rocks and igneous rocks, and loess is also widely distributed, with dense faults, and both rainstorm-type and glacier-type mudslides are developed. The distribution density of debris flow is about 1.6/100km2.

(6) Debris flow prone area in Qinba Mountain area (M6)

Southern Shaanxi. The landforms in this area are hills, low mountains and Zhongshan in turn from the coast of the Han River to the banks. The middle part of Qinling Mountain is a high mountain area, which belongs to a folded mountain area with strong uplift. The lithology of strata is mainly metamorphic rocks and magmatic rocks, with a small area of loess and developed faults. The annual rainfall is 800 ~1200mm.

Landslides and collapses continue to occur. The distribution density of debris flow is about 3.43/100km2.

(7) Wushan-Daloushan debris flow prone area (M7)

The area spans the mountainous areas of Chongqing, western Hubei and western Guizhou, with medium and low mountains as the mainstay and strong terrain cutting. The strata are mainly Mesozoic red clastic rocks or carbonate rocks and clastic rocks, and the annual rainfall is between1000 ~1400 mm.

Landslides and collapses occurred in this area. There are 37 debris flows, and the distribution density of debris flows is about1.16/100km2.

(8) Debris flow prone area at the foot of Tianshan Mountain (M8)

Including Xinjiang Ili Valley, Turpan-Hami region, South Xinjiang, Grand Valley, West Kunlun Mountain and its important traffic arteries.

Neotectonic movement caused Tianshan Mountain to uplift strongly, faults developed, metamorphic rocks and magmatic rocks were widely distributed, Quaternary sediments were abundant, and loess was distributed in the foothills. Glacier snow covers a large area. There are more heavy rains in warm seasons.

Landslides and collapses developed, and there were 32 large and medium-sized mudslides.

(9) The debris flow prone area (M9) in the alpine valleys of southeast Tibet.

Including the middle and lower reaches of the "Three Rivers" in eastern Tibet, the Yarlung Zangbo River basin in the east of Sangri and the Himalayas in the south.

Both rainstorm-type and glacier-type debris flows are well developed in this area. Slope debris flow is dominant, with high frequency and strong activity.

Low debris flow prone areas in 4.4.2.3.

(1) debris flow prone area in eastern mountainous area (L 1)

Including Changbai Mountain, Luzhong Mountain, Dabie Mountain and Jiangnan-coastal hilly areas.

Topographically, it is located on the third step of China's topography. Mainly for the Neocathaysian, zonal tectonic system, low mountains and hills, with long-term heavy rain.

(2) Low debris flow prone areas in the central mountain basin (L2)

Include Daxing 'anling, Xiaoxing 'anling, Wei Fen Valley, eastern Sichuan Basin and western Guangxi.

This area is located in the transition zone between the second and third levels of Chinese topography. Mainly for the Neocathaysian, zonal tectonic system, low mountains and hills, with long-term heavy rain.

(3) Debris flow prone area in western plateau mountainous area (L3)

Including the Qinghai-Tibet Plateau and Altai Mountain.

This area is located in the transition zone between the first and second levels of Chinese topography. The Qinghai-Tibet Plateau belongs to the Mesozoic-Cenozoic strong uplift area, with an average elevation of over 3,000 meters and a cold climate. Active faults are widely developed, mostly distributed in the piedmont of major mountains or along some rivers. Active faults are active, the horizontal displacement rate is generally above 6mm/a, and some of them exceed 10mm/a, and the frequency and intensity of seismic activity are high, second only to Taiwan Province Province.