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Đánh giá mức độ tổn thương do tai biến trượt lở tại Tỉnh Bắc Kan, tình hình trượt lở chung tại việt Nam, các phương pháp giảm thiểu và phòng chống, phương pháp đánh giá mức độ tổn thương, các loại hình
Landslide risk assessment The case study of landslide disaster vulnerability assessment in Vietnam Dr Nguyen Thi Thi Ha グググ ググ ググ ハハ Content of lecture Introduction Approach and methods Results and Discussion Conclusion Future works Seeking dead people Introduction 1.1 Concept of Landslide risk assessment • About 10 landslide disasters per year affecting residential lives, development and municipal infrastructure • Landslide accompanied with heavy rain/floods Before: usually occur in raining season (July – September); Now: in the whole year • Consequences have included: injury, fatality; damage to property and infrastructure; environmental impacts; increased development costs Damaged an industrial factory Specific Risk is the expected degree of loss (experienced by a given element) due to a particular natural phenomenon (Varnes, 1984) It is considered as the product of hazard and vulnerability, eg: Rs = H × V Rt = sum (E × Rs) = sum(E × H × V) Risk (R) Specific Risk, (RS) Vulnerability (V) Damage (D) Element (E) Hazard (H) Probability (P) Magnitude (M) 1.2 Study area Bac Kan Province ( ググググ ) located in the Northern mountainous area of Vietnam Geographical features: The name Bac Kan is ググ , total area of 4,859.4 km Its terrain has the highest altitude in the Northeast mountainous region, varies from 1,640 m (highest point in Khe Thuong mountain) to the lowest point of 40 m in Cho Moi There are numerous rivers and streams flowing through the province However, most of them have steep slopes and short lengths • Limestone topography: mainly distributes in Xuat Hoa commute; • Land/soil hill topography: distributes in almost commutes/wards with average height of 150 - 160 m; • Valley topography: mainly distributes in wards with relatively flat topography Rainfall in Bac Kan Town is higher than average rainfall of Vietnam Annual average rainfall is 1400 - 1600 mm; reaching 1800 - 2000 mm in rainy season and 250 - 300 mm in dry season Geologic feature Phu Ngu Formation (O-S pn): west, southwest, and center of Bac Kan Town, includes shale, sandstone and siltstone varying within 1100 - 1500 m thick, upper layer consists of black shale, silicic silt, and limestone Strongly deformed and Mia Le Formation (D1 ml): southeast of Bac Kan Town, includesblack shale, limestone, weathered and silic with 400 - 1000 m thick Na Quan Formation (D1-2 nq): southeast, includes of lime-shale, shake, limestone, and sand-siltstone of 300 -600 m thick Tam Hoa Formation (D2-3 th): east and southeast of Bac Kan Town The Formation consists of schist limestone, limestone, and sand-silt stone varying 350 m thick Materials for landslide Population (2008) • Total • Density 308,900 people 64/km (160/sq mi) Tày : 54%, Dao: 16,8%, Vietnamese:14% • Ethnicities Nung: 9% H’Mong: 5.5% Chinese/Ngai: 0.4% San Chi: 0.3% Results and Discussion 3.1 Residential vulnerability 3.2 Transportation vulnerability Map of landslide risk is established based on the following factors: (1) altitude, (2) slope, (3) petrography, (4) geomorphology, (5) rainfall, (6) rock inclination angle, (7) engineering geology, (8) deep intersect, (9) horizontal intersect, (10) lineament density, (11) crack density, (12) slope aspect, (13) crack inclination angle 1, (14) crack inclination angle 2, (15) weathering crust, (16) techtonics, (17) land use Landslide occurred in areas where: • Geology: black shalestone and silicic layer of Phu Ngu Formation • Geomorphology: integrated denudation surface • Engineering geology: cutting slope • Weathering crust: semi-weathered zone • Land use: un-used hills, transportation land, annual cultivation land, and rice field • Rainfall: average rainfall in 10 years range within 1086 - 1107 mm/year • Attitude: 150 - 177 m • 0 Slope: 15 - 35 • Aspect: northwest slope • Lineament density: 31,46 - 50,02 km/km • Crack density: 0,06 - 0,08 km/km • Horizontal intersect: high density of running water (7,61 - 14,02 km/km ) and strongly intersected topography • Deep intersect: high value of deep intersect: 15 - 33 m • Shear stress: low shear stress areas 2 3.1.1 Landslide risk level map Zone I - low risk level area: distributed mainly surrounding Song Cau Zone IV - very high risk level area : mainly distributes along 3B and River, is characterized by low occurrence frequency of landslide (3 257 Highways This zone is characterized by high potential of landslide small landslide sites per total of 250 landslides recorded and Zone III - high risk level area: mainly distributes in Song Cau, Phung risk as mentioned above Of the 250 landslide sites in the study area, observed in the study area) Chi Kien wards, and Duong Quang, Huyen Tung communes Of the 150 sites were observed and recorded in this zone 250 landslide sites in the study area, 77 sites were observed and recorded in this zone Zone II - medium risk level area: scatteredly distributes in the study area, mainly in Duc Xuan ward, Duong Quang and Huyen Tung communes 3.1.2 Vulnerable object density map Zone I – low vulnerable object density area: mainly distributes in Duong Quang, Huyen Tung, Nong Thuong, and Xuat Hoa communes This zone is characterized by far distance to the roads, scarce Zone II – medium vulnerable object density area: occupies narrower facilities, leading to lower density of people in general and the old, area than zone I This zone is characterized by scattered distribution Zone IV –and highfemale vulnerable object density area: mainly distributes in children, in particular with low density of population, low-educated people the center of Bac Kan Town (Minh Khai, Song Cau, Duc Xuan, and Phung Chi Kien wards) and along major transport routes due to high density of people Highest density of vulnerable female is found in the east of Song Cau ward Resilience capacity of human to landslide is assessed based on the following information: - house types; - supportive policies of local government; - education level, - number of persons at working age, - and income Households who have concreted buildings, high level of education and receive support from local government will be likely to respond to landslide better than others 3.1.3 Local resilience capacity Zones I– low resilience capacity: a large portion of the study area, including Minh Khai ward, Duong Quang commune, the southwest of Song Cau ward, Huyen Tung commune, Phung Chi Kien ward, and Xuat Hoa ward These Zones II- mediumresilience capacity: scatteredly distributed in center of Zones II- medium resilience capacity: scatteredly in center of zones are characterized by very rural area with lowdistributed uneducated and poor communes frastructure systemand is relatively developed and (thatched people livingwhere in scattered distribution houses communes where infrastructure system is unconsolidated relatively developed and Zones III- high resilience capacity: centered in the provincial town or along huts) completed, ratio of primary educated people is higher (60-70%) completed, ratio of primary educated people is higher (60-70%) the road where living infrastructure system is relatively developed and Primary school convenient, people are educated and supported by mass media Residential houses 3.1.4 Local residential vulnerability to landslide disaster Zone I – low vulnerability: distributed in the center of Bac Kan Town (area of intersection between four center wards) Small-scale landslide Zone IV - high in vulnerability: mainly distributes mainhigh roads Road was observed this zone However, high living along standard, Zone III – highwithout vulnerability : covers of a large in the north ofhas the construction caring enough slopearea stability problems awareness of hazard adaptation and protection of local people, Zone IIarea, medium occupies aand larger area than zone and study mainly distributes inthis Song CauMoreover, Phung Chi Kien wards posed a–high risk ofvulnerability: landslide in area awareness ofI the support from local government, and good infrastructure helps to distributes zone I, by such as: Duc Xuan ward, high Huyen Tung and This isaround characterized medium-to-relatively living standard localzone people on landslide risks is relatively low In addition, households increase human resilience Duong Quang communes of local people, poorobserved households, relatively living near talus many were also in this zone low intelllectual standard of people, and low awareness of local people on hazard adaptation and protection • Density of vulnerable transportation calculated by length and investment values: high density was found along road system, especially along 3B and 257 Highways The highest value was observed in areas where administrative offices of Bac Kan Town locate • Density of vulnerable bridges: high density was observed in the intersection between river/stream system and roads Highest value was found in Xuat Hoa commune 3.2.1 Vulnerable object density (road and bridge) map Zone I – low density of vulnerable roads and bridges: national road No.3 (Bac Kan town to Xuat Hoa) and No.3B (Bac Kan to Na Lai commune), provincial road No 257 in Duong Phong commune Zone I – high density of vulnerable roads and bridges: national road No.3 (Xuat Hoa - Hoa Muc, Bac Kan – Cao Bang) , other parts of No 3B and provincial road No 257 The transportation resilience capacity is calculated based on the factors restricting/limiting the ability to repair roads, including topographic talus, slope talus, and stream and river system Therefore, areas with high transportation resilience capacity to landslide are areas of low restriction factors 3.2.2 Transportation resilience capacity to landslide map Zone I - Areas with low transportation resilience capacity to landslide: scatteredly distributes in the study area, mainly in Nong Zone II - Areas with medium transportation resilience capacity to Thuong commune, Phung Chi Kien ward, the west of Huyen Tung landslide: distributes mainly in Duong Quang commune, and the commune and the center of Song Cau ward This zone is characterized southeast of Huyen Tung commune This zone is characterized by by high topographic and slope subgrade relatively low topographic and slope subgrade and relatively high Zone III - Areas with high transportation resilience capacity to density of river and stream system landslide: covers a small area and mainly distributes in the east of Song Cau ward and northwest of Duc Xuan ward 3.2.3 Local Transportation vulnerability to landslide disaster Zone III - Areas with high vulnerability level of transportation to Zone I - Areas with low vulnerability level of transportation to landslide: covers a relatively large area of Bac Kan Town, mainly landslide: covers a small area in Duong Quang, Huyen Tung communes, distributes along main roads, such as in Minh Khai ward, in the south of Zone Duc IV Xuan - Areas ward,with andvery in the high north vulnerability of Song Cau level ward of transportation to Song Cau ward, Duc Xuan anh Phung Chi Kien wards landslide: distributes along Highway such as Minh Khai, Duc Xuan, and Song Cau wards In this zone, infrastructure in general and transportation inZone particular is well invested However, high slope terrain in many areas II - Areas with medium transportation vulnerability: mainly poses high risk of landslide distributes in Xuong Quang and Huyen Tung communes, and Duc Xuan ward Conclusion Landslide often occurs in Bac Kan, particularly in rainy season (Jul-Oct) and along the provincial main roads (talus) due to physical condition, particularly features of topography, geologic setting and climate Bac Kan province is an area high venerable to landslide disasters due to low road building technology and low public awareness Future works ????? ... vulnerability assessment for landslide Vulnerability assessment of landslide in the present study includes: Human vulnerability to landslide is assessed based on components: 1) risk level of landslide; ... Rock mines: Phia Na Kong, Ban Tac Landslide disaster in Bac Kan 2006: 2008: heavy rain induced landslides and flood: houses were destroyed 18/5/2009: people dead, landslide occured along the road... a complete standstill Bac Kan Town 2010: 30 landslide sites along 257 road 2011 2012: 2013: landslide occured strongly in rainy season Approach and methods Vulnerability assessment equation (IPCC,