Contents Introduction 2 Base Concept on Damage Assessment & Drone Survey 2 Methodology 3 Major Landslide Location - 2017 4 Annexure 1: Landslide Damage Assessment Individual Reports I 1. Landslide: Wewalkandura (Kalawana DSD, Ratnapura District) IV 2. Landslide: Horangala (Nivithigala DSD, Ratnapura District) XIII 3. Landslide: Wanniwatta (Nivithigala DSD, Ratnapura District) XXII 4. Landslide: Neluwankanda (Nivithigala DSD, Ratnapura District) XXX 5. Landslide: Ambalapitiya (Dehiowita DSD, Kegalle District) XXXVIII 6. Landslide: Diddeniya (Kuruwita DSD, Rathnapura District) XLVI 7. Landslide: Thalawitiya (Eheliyagoda DSD, Rathnapura District) LIV 8. Landslide: Arabbada (Eheliyagoda DSD, Rathnapura District) LXII Annexure 2: Informative drone survey orthomosaic map LXIX 1 Introduction The wettest time of the year in Sri Lanka’s south is usually from May to September. The South- West monsoon unleashed torrential rains, which ravaged fourteen districts in the western and southern parts of the country in May 2017. Heavy rain caused raise of water level 300 mm - 500 mm in 24 hours on the 25th of May 2017, and it resulted raise of water level rivers, particularly the Kelani river water level raised by 15.44 meters. Thousands have been displaced and hundreds killed by the floods and landslides caused by the unprecedented rain. Disaster Management Center reports 631,346 people of 164,264 families had been affected by the weather calamity, 203 killed and 96 people had gone missing. The worst affected district in terms of the numbers affected is Galle. The objective of this report is assess the damages cause by landslides and cut slope failures using unmanned aerial vehicle (UAV). Team, comprised of four scientists from Human Settlements Planning and Training Division (HSPTD) of NBRO, engaged in data collection and site visits together with the Geologists of Landslide Research and Risk Management Division (LRRMD) of the NBRO Galle district office. The team also engaged in discussion with the staff of LRRMD Matara district office. Base Concept on Damage Assessment & Drone Survey DAMAGE ASSESSMENT Damage Assessment means preliminary but fairly accurate onsite evaluation of damage or loss caused by natural event before filing a formal claim or disaster declaration. Damage assessment records the extent of damage, what can be replaced, restored, or salvaged, and time required for their execution. DRONE SURVEY Remote Aerial Surveys combines the latest advances in Unmanned Aerial Vehicles (UAVs) with innovative uses of imaging equipment to perform a wide range of high quality mapping & aerial surveys. UAVs are the perfect solution to get up-to-date high resolution imagery filling in the gaps from other survey methods by providing more recent & more precise data. 2 Methodology Landslide Location & initial information collection Field Reconnaissance Survey Damage Assessment Survey Drone Survey Data to Develop Landslide Damage Data Develop Ortho mosaic Vulnerability Curves & Information and 3D images Develop Vulnerability Develop Informative Curves Ortho Map Report on Landslide Damage Assessment and Drone Survey 3 Major Landslide Location - 2017 NBRO had received information on 39 major landslides occurred in May 2017. List of landslide locations are as follows; Type of District DSD S/N GN Location failure 1 Maheengoda Thalawitiya watta Landslide 2 Kalatuwawa east Bogoda kanda Landslide 3 Asgangula South Palandahena Landslide 4 Pelpitiya Arabboda Landslide Eheliyagoda 5 Karadana north Landslide Cutting 6 Karadana west failure 7 Bopeththa Kukuleliyadda, Meemurewatta Landslide Kodithuwakkukanda, Kiriella 8 Handukanda Landslide Dolapallehena Rathanpura 9 Wanniwatta Horaketiyahena, kiribathgala Landslide 10 Horangala Udakaravita Nivithagala 11 Begotuwa Neluwankanda 12 Gamekanda Landslide 13 Weragama Alupathgala Landslide Elapatha 14 Batakada Girapagama (Palagama) Landslide Kalawana 15 Wewalkandura Horton watta Landslide Kahawatta 16 Bungiriya Bungirikanda Landslide Kuruvita 17 Pathberiya Diddeniya lowland area Ayagama 18 Ayagama Town area Landslide 19 Ambalanpitiya Ambalanpitiya Landslide Kegalle Dehiowita Slope 20 Welangalla K 90/2, Welangalle, Getaheta failure Kotapola 21 Morawaka Morawakkanda Landslide Matara Pasgoda 22 Rotubma east Idigalgoda kanda Landslide Walasmulla 23 Ranmale Saputhanthrikanda Landslide 24 824F, Karalidekma Thibbotukanda Landslide 25 Yatagampitiya Landslide Cutting 26 Bogahawatta Bulathsinhala failure 27 Kobowela Landslide 28 Paragoda west, Morawaka Landslide 29 Niggaha, Pahiyangala Landslide Near Kalawana Matugama Main 30 Athwelthota Landslide Road Upto Palan gaga Mawatta, Delkith part, Bellana 31 Landslide Kaluthara east 32 Diganna Diganna Landslide Baduraliya Kukuleganga - in front of 33 underground power station Kukuleganga - Kelinkanda area 34 (Located behind temple) 35 834A Bellana East Mawatha Watta Landslide Walallawita 36 843F, Weerakanda Landslide Muddy Agalawatta 37 833 -Kithulgoda Kithulgoda Kanishta Vidyalaya Water flow Colombo Padukka 38 Thummodara Pathagiwatta Landslide Duli Ella Tea Factory, Kosmulla, Galle Neluwa 39 Kosmulla Landslide Neluwa, 4 Annexure 1: Landslide Damage Assessment Individual Reports I II Wewalkandura Wewalkandura Kalawana Ratnapura Sabaragamuwa III 1. Landslide: Wewalkandura (Kalawana DSD, Ratnapura District) Introduction This damage assessment and drone survey report is on the landslide occurred in Wewalkandura area (Wewalkandura GND, Kalawana DSD, Ratnapura District, Sabaragamuwa Province) on May 26, 2017 at 0610 hrs. This report is developed bases on the data and information collected in the field and drone survey conducted on site. Name of the Village : Wewelkandura GND : Wewelkandura 175A DSD : Kalawana District : Ratnapura Province : Sabaragamuwa Global Position (GPS) : 6°31'53.4404"N 80°26'09.5205"E Previous and Current Condition of the Landslide Location Previous condition of landslide location (Source: Google Earth); IV Current condition of landslide location (Source: Drone Survey); Length of Landslide: 363m V Analysis on Landslide Basic information of the landslide as follows; Basic Information of Landslide Landslide type Debris flow Date of Occurrence May 26, 2017 / 0610 hrs Date of inspection May 31, 2017 / 1000 hrs Crown Width 96 m Crown Height 30 m Initiation Area length Maximum Width 94 m Length of Landslide 363 m Width at Middle 94 m Slope Type Concave Initiation Area Slope Angle 45-50 deg Deposited Area Slope Angle 8 deg Erosion Type straight Hydrology Pattern Stream VI LANDSLIDE BOUNDARY OVERLAY ON LANDSLIDE HAZARD MAP VII ANALYSIS ON ALONG LANDSLIDE FLOW PATH (LONGITUDINAL PROFILE) Based on drone survey, landslide had been analyzed for further information. Information and data acquired from Ortho image and Digital Elevation Model (DEM) developed through drone survey. LONGITUDINAL PROFILE DETAILS A - A’ Start Position 6° 31' 56.9340" N, 80° 26' 13.1897" E Start Height 97.731 m End Position 6° 31' 47.1382" N, 80° 26' 06.9127" E End Height 16.074 m Path Length 358.4 m Straight-Line Distance 357.41 m 3D Distance on Surface 383.47 m Vertical Difference (Start to Finish) -81.7 m Total Climbing 7.3 m over 66.071 m on surface Total Descending 89.0 m over 317.39 m on surface Minimum Elevation on Path 14.639 m Maximum Elevation on Path 97.731 m Azimuth 212° 39' 14.1" Slope/Tilt -12.87° Max Path Slope 70.88° [1.051 m along path] * Reference Point: 6° 31' 43.7726" N, 80° 26' 02.6654" E (Elevation of this reference point is considered as 0 meter) VIII ANALYSIS ON CROSS SECTION (CROSS SECTIONAL PROFILE) CROSS SECTIONAL PROFILE DETAILS B - B’ Start Position 6° 31' 53.4404" N, 80° 26' 09.5205" E Start Height 34.836 m End Position 6° 31' 51.8264" N, 80° 26' 12.1681" E End Height 41.929 m Path Length 95.26 m Straight-Line Distance 95.26 m 3D Distance on Surface 99.552 m Vertical Difference (Start to Finish) 7.1 m Total Climbing 13.9 m over 64.341 m on surface Total Descending 6.8 m over 35.211 m on surface Minimum Elevation on Path 31.013 m Maximum Elevation on Path 42.619 m Azimuth 121° 21' 46.6" Slope/Tilt 4.26° Max Path Slope 68.35° [0 m along path] * Reference Point: 6° 31' 43.7726" N, 80° 26' 02.6654" E (Elevation of this reference point is considered as 0 meter) IX Landslide Damage Assessment In the location, before landslide its main landuse is tea, cinnamon, arecanut, Jackfruit trees and residential uses. Current land value is Rs. 15,000.00 per perch. Other information of location as follows; Land use management Human Impacted Erosion type Straight Slope type Concave Initiation area Slope Angle 45-500 Deposited area slope Angle 80 Hydrology Pattern Stream LANDSLIDE IMPACT ON HUMAN LIFE Number of Deaths 13 Injuries Not Recorded Fully Damaged Buildings 04 Typical houses Partially Damaged Buildings Not Recorded Infrastructure Damages Road, Electricity ESTIMATED ECONOMIC LOSS AFTER A LANDSLIDE EVENT Crop # of plant Total yield Unit Price (Rs) Total Loss (Rs) Coconut 50 3500 nut/year 50.00 175,000.00 Arecanut 50 50000 nut/year 105.00/100nuts 52,500.00 Cinnamon (kg) 15 75 800.00 60,000.00 Jack fruit 30 450 50.00 22,500.00 For 1 ha total loss 310,000.00 Estimated area buried under landslide is 1.4 ha 434,000.00 Expected loss over 10 year period 4,340,000.00 Tea (ha) 1.6 1500 kg/ha/year 600.00 1,440,000.00 Expected loss over 10 year period by losing 1ha Tea land 14,400,000.00 Area of Building (m2) Construction cost/m2 # of houses Total Loss (Rs) Houses 160 10000.00 4 6,400,000.00 Length (m) width (m) Cost per (m2) Total Loss (Rs) Road (concrete) 100 1.5 8,000.00 1,200,000.00 Total Direct Loss* 9,474,000.00 * Total direct losses were computed only for one year. X XI Udakaravita Horangala Nivithigala Ratnapura Sabaragamuwa XII 2. Landslide: Horangala (Nivithigala DSD, Ratnapura District) Introduction This damage assessment and drone survey report is on the landslide occurred in Udakaravita area (Horangala GND, Nivithigala DSD, Ratnapura District, Sabaragamuwa Province) on May 26, 2017 at 0655 hrs. This report is developed bases on the data and information collected in the field and drone survey conducted on site.