Landslide Risk Reduction in

Eng (Dr.) Asiri Karunawardena, Director General, National Building Research Organisation Sri Lanka Landslides in Sri Lanka

• Landslides have become a frequent natural hazard in central highlands of Sri Lanka, which disturbs its life, causes damage to property, constructed facilities and infrastructure. • Nearly 20% of the land area from 65,000 sq. km of total area in Sri Lanka is identified as landslide prone. Nearly 30% of total population live in these areas.

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2011 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2012 2013 2014 2015 2016 2017

Number of lives lost due to landslides/slope failures:2000-2017 Landslide Potential Area Landslides in Sri Lanka

Mulhalkele 1986 Watawala 1991-92

Paradeka - 2006 Ladupita,Kiriwanella- District 2007 Landslides in Sri Lanka

Peradeniya 2006 Kalawana 2003

Ratnapura 2003 2003

Reactivation of Beragala Landslide ( Padiyapelella 2007 District) 2009 Landslide along major roads

Outer Boundary Kahagolla Landslide Damages due to Unplanned Construction

Pilimathalawa 2007 Nildandahinna - 2007 Non Engineered Construction Leading to Cutting Failures Along Main Roads

Recent Cutting Failures Landslides in Sri Lanka Main triggering factor- Rainfall

2014-10-29, 2014-12-26 Meeriabedda

2014-06-01 Our Strategies In Landslide Risk Management

• Landslide identification and hazard zonation mapping • Integrate from Hazard to Risk management • Landslide monitoring and early warning and awareness • Landslide risk assessment for development and construction projects • Landslide Special Investigations • Structural mitigation works • Related policy development and planning Landslide Identification & Hazard Zonation Mapping Former Landslide * Key Ground Surveys Map Slope range and * slope category Field Investigations Bedrock geology and * Structure

Colluvium and Available Maps Residual soil * Landform and Unpublished materials Erosion Attribute Hydrology and Terrain factors & WeightingsMaps Drainage

• BEDROCK GEOLOGY - 20 Rainfall • SOIL COVER - 10 • SLOPE RANGE & CATEGORY - 25 Human Settlements & Infrastructure • HYDROLOGY & DRAINAGE - 20 Landuse &

Mapping Process Mapping • LAND USE & MANAGEMENT - 15 Management • LAND FORM - 10

Allocated weights for attributes and factor maps according to the statistical Final Product LANDSLIDE HAZARD MAP analysis and experts knowledge Landslide Hazard Zonation Maps

Landslide Hazard Zonation Maps at different levels, Regional, District & Local Authority level

Map of Municipal area

Mapped Area

A typical hazard zonation map

Map of Nawalapitiya Urban Council area Development of Flow paths Day 2016.5.17＿17:00 2016.5.18＿ 0:00 Damage 28dead,99missing

12 DEVELOPMENT INTEGRATED LANDSLIDE HARZED MAPS

BUILDING FOOTPRINTS INTEGRATED LANDSLIDE HAZARD ZONATION MAP BUILDINGS EXPOSURE TO LANDSLIDE HAZARD DATABASE ON ELEMENTS AT RISK – Data Base

Search option in different levels

Retrieve data from selected area or building Details of the Risk Levels of the landslide prone locations at all districts

Number of # Province District Houses in High Risk 1 Uva Badulla 6,418 Kandy 1,292 2 Central Nuwara Eliya 3,496 Investigation and 210 Identification of Rathnapura 757 Vulnerable 3 Sabaragamuwa Communities and 824 Matara 591 High Risk Settlements 4 Southern 343 5 Western 929 Real Time Landslide Monitoring & Early Warning

• 100 automated rain gauge stations in pre- selected catchments in landslide prone districts

DMC Dynamic Model Warning and Evacuation

DOM NBRO Standard threshold limits of the Rainfall for landslides Alert 75 mm/day Early Kalawana Warning Warning 100mm/day Pelmadulla Evacuation, Off limit 75 mm/hour or 150mm/day Nivithigala Elapatha Kahawatt Automatic Rainfall a Measurement System

Rainfall data is used in computer simulation and early warning is issued depending on threshold limits Site specific/CB Monitoring, Forecasting and Early Warning

Schematic diagram of the socio-technical management system on landslide early warning Extensometer

Tilt Sensor

Data Logger for tilt sensor Instrumentation and Monitoring

Protection Box

Invar Wire

Extensometer

Protection Pi pe Crack, Scarp

Landslide Movement

Movable Pile Protection Pipe

Extensometers and Groundwater Level for Badulla Landslide 40 10.0mm/2days 15.7mm/3days 30 (5.8mm/day) (7.6mm/day) 20

10 SB-1 0 SB-2

Displacement (mm) Displacement SB-3 -10 2016/7/6 Fire Incident(SB-3,4) 2016/8/1 Re-installation SB-4

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1200 Rainfall (mm/day) Horizontal Drainage Drilling 2016/6/15- Surface Drainage Ditch 2016/6/24- 1000 Cumulative Rainfall (mm) 8 Aug. -21 Dec. 2014 800 15- 27 Dec. 2014 Cumulative rainfall: Total 873mm Cumulative rainfall: Total 652mm 600 24 Dec 2014

400 218mm/day Railfall (mm/day) Railfall

Cumulative Rainfall (mm) (mm) CumulativeRainfall 200

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