Identification of temporary evacuation sites and relocation of dangerous settlements in the Dolakha District: An approach by hazard mapping

Transcription

1 J-RAPID Workshop, June 2016 Identification of temporary evacuation sites and relocation of dangerous settlements in the Dolakha District: An approach by hazard mapping PI Nepal side: Lalu Paudel 1 PI Japan side: Teiji Watanabe 2 1. Central Department of Geology, Tribhuvan University 2. Environmental Earth Science, Hokkaido University

2 Members HU Team TU Team Teiji Watanabe Faculty of Environmental Earth Science Lalu Paudel Central Department of Geology Yusuke Kobayashi Graduate School of Environmental Science Narendra Raj Khanal Central Department of Geography Bhabana Thapa Graduate School of Environmental Science Motilal Ghimire Central Department of Geography Dhananjay Regmi The Himalayan Research Expedition

3 Study area Death toll by the earthquake Dolakha District source: Government of Nepal Dolakha District = eastern part of the damaged area of the country Tama Koshi = hydropower dam Trekking destination of Rolwaling

4 Objectives 1. To identify potentially dangerous sties in the Dolakha region through landslide susceptibility mapping. 2. To identify potentially dangerous sites in the case of future earthquakes and other hazards. 3. To map GLOF inundation along the main river. 4. To propose temporal evacuation sites in the case of future hazards.

5 EARTHQUAKE FACT SHEET Dolakha was the epicentre of the 12 May earthquake, while the 25 April earthquake caused widespread damage to the area. KEY FIGURES 280,874 total population 87% houses fully or partially damaged 50,284 houses fully damaged 305 houses partially damaged 134 dead 304 injured 2,037 people in nine sites (Temporary settlements) ( Source: Tamakoshi Hydropower 2014, 2 District Development Committee 03/07/2015, 3 IOM/CCCM 20/07/2015)

6 Many People are still living in temporary houses in temporary settlement sites

7 Flow of research Remote sensing & GIS Base maps (Land use and land cover map, etc.) Damage, dearth toll, etc. Field survey Distribution of landslides/rockfalls /other hazards Baseline survey UAV survey Photography for 3D mapping at seriously damaged sites Modeling HEC-RAS analysis for GLOF hazard Field survey Distribution of damages; social survey Landslide hazard map Training seminars for students Recommendation to local communities/gove rnment Labo. analysis Base-mapping for hazard map Landslide & GLOF hazard map Labo. analysis 3D-mapping (Structure from Motion) Labo. analysis Identifying evacuation sites Identifying evacuation sites

8 Topographc Maps Satellite Image Methodology Data Sources Input layer Analysis Contour line DEM Drainage line Slope Aspect Relative relief Curvature Drainage distance Reclassification Reclassification Landuse Land use IR & R NDVI Reclassification band Road map Road distance Reclassification Field survey: Geology Geological unit Feature class Google earth Image Field Survey Landslide Inventory Landslide Weighted value Cross tabulation Bivariate analysis Predictive rate evaluation Landslide Susceptibility

9 Procedure Landslide (both pre and post Earthquake) were inventoried from Google Earth Image and Field Survey Causative parameters were developed in Arc GIS Environment Inventoried pre earth quake landslide and the parameters were cross tabulated Landslide index was calculated by using formula (Van Westen, 1979) ln Wi = ln ( DDDDDDDDDDDD A (SS)/A (NN) ) = ln ( DDDDDDDDDD A(SS)/ A(NN) A (Si) = Number of evidence in a certain parameter class. A (Ni) = Total area, in a certain parameter class.

10 Landslide susceptibility was determined by summation of each factor s ratings using equation: Where, n LHI = i WW... Wi = Weight assigned to each i parameters N= Total number of parameters

11 Geology Field Survey was carried out for Geological mapping of the area

12 Geological map of the area Area (Sq Km) Landslide (Sq Km) Geology Wi Higher Himalaya (Gneiss) Graphitic Schist Garnet Schist Chlorite-Biotite Schist Gneiss (Orthogneiss) MCT

13 Gneiss Schist Quartzite

14 Landslide Inventory Landslide inventory was prepared using Google Image, topomap and field survey

15 Identification of earthquake induced landslides 3/3/2015

16 Earthquake-Induced 15/5/2015

17 Rockfall at Wosimpa village Debris flow at Buma Village Debris flow at Charnawoti area Jointed rocks at Olitar

18 Identification of unstable slopes Unstable jointed slope at Sigati bazar Cracks near Kalinchwok temple

19 Landslide Inventory Map

20 Slope Class Area (Sq Km) Landslide (Sq Km) Wi Slope Map < >

21 Relative Area Landslide Relief (Sq Km) (Sq Km) Wi Relative Relief

22 Drainage distance Area (Sq Km) Landsli de (Sq Km) Wi < > Drainage Distance

23 Landuse/ Landcover Landuse Area Landslide (Sq Km) (Sq Km) Wi Barren Land Cultivated Land Exposed Rock Forest Grassland Lake Landslide/Erosi on Riverbed Settlement Shrub/Bushes Snow Sparse Forest

24 Aspect Area (Sq Km) Landslid e (Sq Km) Wi Aspect North East South West

25 Curvature Area (Sq Km) Landslid e (Sq Km) Wi Concave Curvature Straight Convex

26 Road Distance Area (Sq Km) Landsli de (Sq Km) Wi < > Distance to road

27 Normalized Vegetation Index (NDVI) NDVI Area Landslide (Sq Km) (Sq Km) Wi

28 Landslide Susceptibility Map Susceptibility Area (sq Km) Percentage (%) Low Moderate High

29 Flow of research Remote sensing & GIS Base maps (Land use and land cover map, etc.) Damage, dearth toll, etc. Field survey Distribution of landslides/rockfalls /other hazards Baseline survey UAV survey Photography for 3D mapping at seriously damaged sites Modeling HEC-RAS analysis for GLOF hazard Field survey Distribution of damages; social survey Landslide hazard map Training seminars for students Recommendation to local communities/gove rnment Labo. analysis Base-mapping for hazard map Landslide & GLOF hazard map Labo. analysis 3D-mapping (Structure from Motion) Labo. analysis Identifying evacuation sites Identifying evacuation sites

30 UAV survey (Singati and Gongar only) Permission issued on: 26 Feb UAV:DJI Phantom 2 Camera:RICOH GR Attached to UAV GPS logs & flight sites Gave dimensions SfM: DSM, Ortho-map

31 Social survey: 13 settlements The number of interviewed households in Nov. 2015: Tamakosi Kattike Charikot Dolakha Singati Olital Bohle Suri Doban Jamune Purano Jagat Jagat Manthali Gongar Face-to-face questionnaire survey 25 questions: Income Length of residence Damage Knowledge about evacuation site and hazard map

32 Focuses of hazard map (1) Landslide hazard map (2) GLOF hazard map One of the dangerous glacial lakes, Tsho Rolpa: potential source of future GLOF Local residents, hydropower-related workers, and international trekkers to Rolwaling Himal (>3,000 per year). Tsho Rolpa (ICIMOD, 2011): Length=3.7 km Area=1.54 km 2 Vol=86 million m 3 Max depth=135.5 m

33 HEC-RAS model for mapping inundation area along the river Where, Q = discharge (m 3 /s) A = cross-section area (m 2 ) R = hydraulic radius (m) S = friction slope and n = Manning s roughness coefficient Manning s n for different land use (Chow et al., 2010) Land use Manning s n type Barren 0.03 Bush 0.05 Cultivation area Cutting 0.04 area Forest 0.1 Grassland Orchard River 0.04 Sand 0.03

34 Gongar Singati GLOF hazard and landslide hazard map

35 GLOF hazard and landslide hazard map: Dolakha, Charikot, Kattike, Tamakoshi

36 GLOF hazard and landslide hazard map: Purano Jagat, Jagat, Manthali

37 GLOF hazard and landslide hazard map: Jamune, Suri Dobhan, Bhorle, Olitar

38 GLOF hazard and landslide hazard map (Detailed): Singati

39 GLOF hazard and landslide hazard in Gongar

40 UAV and questionnaire surveys in Singati Nov. 2015: Interviewed household number: 66 Feb. 2016: Drone coverage: 16 households June 2016: More interviewed & drone covered all settlement area Drone coverage in Feb Singati: Population=1,618 Households=338

41 Earthquake damage survey in Singati 116 houses: 33 collapsed 5 partly damaged 4 emigrated to KTM (no use)

42 Damaged houses by the earthquake (by questionnaire survey) Completely Distroyed Condition of House Partly damaged No. of houses

43 Earthquake damage survey in Singati River terrace I (higher): quite OK II (middle): quite OK III (lower): more collapsed houses

44 GLOF hazard in Singati estimate by HEC-RAS Nov. 2015: 33 houses were used on the lower river terrace. The lower river terrace (III) should be avoided to reside: relocation suggested. Legend To be inundated Collapsed Partly damaged Currently used Rebuilt No use Storage Temple As of Nov. 2015, 4 houses have been rebuilt at the same site at lower river terrace. In June, 2016, there were more rebuilt houses.

45 Temple 1 st river terrace 2 nd river terrace 3 rd river terrace To be inundated 2 nd river terrace 3 rd river terrace To be inundated A-A section B-B section Safe site: 1 st river terrace Good for evacuation

46 Residents knowledge on hazard map in Singati Interviewed 66 households: Yes=1, No=65 Only 1.5% of residents know a hazard map *) The entire area: Yes=3, No=280 Legend To be inundated Do not know

47 Residents knowledge on the safe site for evacuation in Singati Interviewed 66 households: Yes=2, No=64 Legend To be inundated Do not know Know

48 Residents knowledge on the evacuation site and safe site Interviewed 66 households: Yes=2, No=64 No. of houses Yes No Evacuate to safe site Yes=7/283 Legend No. of houses To be 80 inundated 40 Do not know Know Yes Safe site near by place Yes=134/283

49 Evacuation routes in Singati *) Will work on the lower Singati area

50 Evacuation routes in Singati Stone steps: cm wide (max: 1.8 m) Existing evacuation routes are not enough

51 Preparedness for future hazards 100 No. of households Yes No 0 Governmental & UNDP s awareness projects after the earthquake

52 UAV and questionnaire surveys in Gongar Drone coverage in Feb Nov. 2015: Interviewed household number: 10 Feb. 2016: Drone coverage: 10 households Hydropower facilities Drone coverage in Feb. 2016

53 GLOF hazard in Gongar estimate by HEC-RAS Hydropower facilities To be inundated Collapsed Partly damaged Currently used Rebuilt No use Storage

54 To be inundated To be inundated To be inundated A-A section B-B section C-C section Relocation suggested Gongar: some risk of GLOF

55 Conclusions and policy recommendation Landslide inventory of pre- and post-earthquake event of April 2015 prepared. Landslide incidences were found to be higher on steep and rectilinear, and south facing slopes, high relative relief, barren, poorly vegetated slopes, closed to roads and small rivers. High relative relief areas are in high risk of earthquake induced landslides such as rockfall and rock slides. The susceptibility areas shown in the maps should be considered for relocating the settlements in future.

56 Conclusions and policy recommendation HEC-RAS modeling suggests that future GLOF from Tso Rolpa could affect some settlements such as Gongar (16 houses), Kattike (4 houses), Signati (13houses), and Tamakoshi (6 houses; 100%). Location of the reconstruction of buildings should avoid lower river terraces. Evacuation routes in Singati and Gongar were examined to point out the need of their improvement. Organizing local workshops is suggested to increase awareness of hazard map and to realize evacuation drills.

57 Additional outcome/effects 56 Transferring the methodology of the hazard mapping to Nepal (students of TU): training seminar will be conducted on 23 and 24 June 2016 and beyond.

58 Presentations 57 1) Kobayashi Y, Thapa B, Watanabe T, Paudel L, Khanal NR, Ghimire M & Regmi D: Survey on damage in settlements along the Tamakoshi river in Dolakha, Nepal, caused by earthquakes in April/May 2015, Annual Meeting of Japanese Geographers Association, Waseda Univ., Tokyo, March 21, ) Watanabe T, Paudel L, Kobayashi Y, Thapa B, Khanal NR, Ghimire M, & Regmi D: Floods Occurred by a Collapse of an Earthquake-Induced Dam, Gongar, Dolakha, Nepal in April International Geographical Congress, Beijing, August 22-23, ) Kobayashi Y, Thapa B, Watanabe T, Paudel L, Khanal N, Ghimire M, & Regmi D: Inhabitants Awareness of Prevention and Preparation towards Hazards in the Settlements along the Tamakoshi River, Dolakha, Nepal. International Geographical Congress, Beijing, August 22-23, ) Thapa B, Watanabe T & Kobayashi, Y: Risk assessment of flood Hazard in the Nepal Himalaya: Case studies of Seti River, Pokhara and Tamakoshi River, Dolakha. International Geographical Congress, Beijing, August 22-23, 2016.

59 Publication (to be submitted) 58 1) Watanabe T, Thapa B, Kobayashi Y, Paudel L, Khanal NR, Ghimire M, & Regmi D: Floods occurred by a collapse of an earthquake-induced dam, Gongar, Dolakha, Nepal. To be submitted. 26 th April 2015

60 Acknowledgements We are grateful to the following organizations and persons for their generous helps and support besides the funding support of the J-RAPID project: Hokkaido University and Himalayan Research Expedition provided additional funds, and Tribhuvan University provided necessary facilities, Mr. Niroj Timilsina, Mr. Kran Dahal, Mr. Shreekrishna Karki, Ms. Alina Karki helped in the field and data analysis.