Landslide Disaster Management in Sri Lanka and Nichola Oya as a Case study Group 16 Gamini Jayathissa Udeni Nawagamuwa
Taiwan Sri lanka >2582 mm, max >5000mm NE= Nov. to Feb 1750 2500 mm >2500 mm Central Highland SW = May to Aug.
Landslide disasters in Sri Lanka One of the major & frequent disasters in the country. During monsoon & intermonsoon seasons, Most pressing natural disaster in the Central Highland. Spreading over 10 major districts 20% of the total land area (13,000km 2 ). about 30% of the total population. Central Highland Every year huge economic and human losses are recorded & damages are on the rise.
Rupture Flow path Beragala-2009 Ladupita,Kiriwanella- Nuwara Eliya District 2007 Koslanda-1995 Deposition
Mitigation Structural Non-Structural Engineered Non-Engineered Mitigation measures may be structural or non structural ; structural measures may be Engineered or Non Engineered.
Non Structural Mitigation
1. Hazard Zonation Mapping Padiyapelella Munwatta Area Sheet 62/11, Scale 1:10000 Local authority level
2. Legal framework- implimentation of effective policies via Landslide Risk Assessment Process (LRAP) Enforcement of building codes and landuse regulations- LU planning, Hazard zoning (mapping), and the resulting zoning laws.
Properly designed building or slopes Introduction of suitable construction methods in hill slopes Design buildings according to the slope
3. Training, education and Awareness
4. Monitoring, Forcasting and Early Warning Strain Gauge Inclinometer
Warning and Evacuation In Sri Lanka Standard threshold limits of the Rainfall for landslides Alert 75 mm/day Warning 100mm/day (Get ready to evacuation under short notice) Evacuation, Off limit 75 mm/hour or 150mm/day
Dissimination of warning NBRO Traditional communication systems in villages LANDSLIDE WARNING Public Announcements through Radio, TV (Cyclones, Floods, Landslides) Public Evacuation
Structural Mitigation 1. Modification of slope geometry 2. Drainage of surface and Subsurface (GW) 3. Retaining structures 4. Internal slope reinforcement
Real case studies
Landslide at Nichola Oya Rattota -18 Dec 2012 Death - 6 Houses - 14 Max Flow height - 12m Debris volume - 42000 m3 Length > 4km
Landslide at Nichola Oya,Rattota 18 Dec 2012 Destroyed houses 4km below the LS Destroyed Bridge
Disaster Risk Management
Mitigation Measures taken prior to the impact of a disaster to minimize its effects. Disaster mitigation involves measures taken to reduce the effects of disaster causing phenomena 21
What we learnt to apply in our country - structural and non structural mitigation Possible applications for Nichola oya in Rattota, Matale, Sri Lanka http://www.youtube.com/watch?v=els wa8dgtg0
Models for Predicting Landslide Locations Rainfall thresholds relationships we learnt Tiranti and Rabuffetti (2010) - hourly rainfall Guzzetti et al (2008) - hourly rainfall Caine (1980) - hourly rainfall In Sri Lanka Threshold limits Alert Warning Rainfall exceed 75mm within 24 hours and continue Warning Rainfall exceed 100 mm within 24 hours and continue Evacuation warning Rainfall exceed 150mm within 24 hours or 75mm within an hour period and continue
What is lacking? Rain gauges are not installed in critical slopes rain gauges belong to met dept are at some other locations and the information we have got were from the closest weather station belongs to met dept. this gives sometimes false information to develop a threshold.
What we can apply for Nichola Oya from the summer school Lack of hourly rainfall data for future predictions needs to install rain gauges (at critical locations) and obtain community participation in collecting rain fall information When there is a prolonged rainfall for few days or after a landslide event, thresholds have to be reduced! More spatial techniques Proper communication with relevant agencies
Back analysis of previous debris flow at Nichola oya Models we practiced here such as 2D debris flow will be used to validate the model and to identify parameters; this will be important for future predictions. Lab and field experiments will be carried out to forecast the effect of a possible future debris flow We will have continuous communication with NTU.
Training, education and awareness present condition in Sri Lanka Already disaster studies are included up to some extent in the school (primary and secondary) and university curriculum (under grad and masters) Regular trainings are conducted for technical and administrative personnel Community based programmes are conducted
Nichola oya needs.. Debris flow/ landslide volunteer specialists They need an appreciation! Very Important Lessons learnt from Taiwan.
Structural mitigation applicable to Nichola oya What we have learnt.. Udeni Nawagamuwa, 2013
Landslide at Nichola Oya,Rattota 18 Dec 2012 Destroyed houses 4km below the LS Destroyed Bridge
Structural measures needed for.. debris control measures Bank protection Downstream area protection We can introduce (if financial condition is favorable); but further studies are needed. Debris barriers (location should be identified) Debris breakers and Debris basins Slit dams and Sabo dams (in mild slope areas ) Debris flow gullies Stream regulation (not a river, but a type of a creek) Detention ponds may not be suitable, but hydrological study has to be done * Tire dam and comb dam in Hsinchu county (in 1980s) would be an economical solution for a developing country like Sri Lanka!
We are very grateful to Taiwanese people. More than 35000 people died and several thousands of people are still missing after the devastating Indian Ocean Tsunami hit on the island on 26 th Dec 2004. Infrastructure was disappeared and gone to the ocean
You were with us after that devastating Tsunami.. More than 2000 houses were built by Taiwan Buddhist Association. You gave us a hope.
The most important lesson we learnt! Let s work together towards a society that Nature and Human can live together peacefully - Ko-Fei Liu (2013) Thank you very much Ladies and Gentlemen. Thank you for your hospitality at NTU and we welcome you all to the Pearl of the Indian Ocean, Sri Lanka!