Vulnerability Assessment Methods for Land Subsidence Prone Areas – A Case Study: Matale Municipal Council Area DS Munasinghe Human Settlement Planning and Training Division, NBRO EE Wijegunarathne Human Settlement Planning and Training Division, NBRO ABSTRACT : Hazard, Vulnerability and Risk are generic terms in disaster management that are used frequently for taking decisions in development planning. Vulnerability assessment requires gathering of various data that are consist of various fields and various methods are used to calculate the vulnerabilities. Several incidents of land subsidence were recorded in the Matale Municipal Council Area and it became necessary to assess the vulnerability of the settlements for developing a resilient built environment. This paper discusses the vulnerability assessment methodology used and the results of the assessment that were conducted in the Matale Municipal Council Area. Two types of vulnerability assessment methods were developed; community based vulnerability assessment and computer based vulnerability assessment. Community based vulnerability assessment describes the community ideas and how they feel uncertainties on their buildings and territory. The data were obtained through a community survey, which was conducted in a systematic random sample in the Matale Municipal Council Area. Technical assessment is based technical evaluations based on available secondary data and its analysed outputs. Based on the analysis few recommendations were made to reduce the vulnerabilities of the Matale Municipal Council Area. Key Words: Vulnerability Assessment, Land Subsidence 1 INTRODUCTION 2 PRESENT SITUATION OF MATALE The first landslide incident was recorded in 1995 Matale District is located in the Central Province in Matale area and thereafter a land subsidence and a large proportion of the district belongs to the incident was recorded in 2005. Several months after dry zone. Geomorphologically, the study area lies 2004 tsunami, the observation of unusual water virtually at the centre of Sri Lanka and has an fluctuation in existing wells, tube wells in Nagolla, undulating topography. The area lies on Western Madawala, Ulpotha and Ukuwela area in Matale foothill of well-known Knuckles mountain range was made. National Building Research and an eastern foothill of Makulessa range. Sudu Organisation (NBRO) started the land subsidence Ganga is flowing in the eastern side close to study investigations and social surveys to identify the area. The major rock types found in the areas are possible impact areas in Matale. As a result, in 2008 Garnet-Sillimanite-Biotite with interlayered NBRO developed a land subsidence hazard Charnokitic gneiss. Dolamitic Marble is the susceptibility map of the affected area. prominent rock type in the area, which are inter The technical coorperation with Norwegian layered or mobilized into surrounding rocks. Geotechnical Institute (NGI), Oslo- Norway was While considering the existing statistics of the started in 2012 November to enhance the area and the population size, a map of the land professional and technical capacities of NBRO to subsidence area was generated by using the data identify and assess the land subsidence and obtained from Census and Statistics Department landslide hazards in Matale area. Ground Penetrate (2001) and NBRO field survey data. According to Radar (GPR) system had been donated to NBRO to statistics, the whole Matale Municipal Council area investigate the land subsidence hazards and appear to suffer from the land subsidence incidence; numbers of automated rain gauges were installed in therefore, the total population of 41,929 is suffering identified locations to monitor the rainfall, soil from the direct threat. Based on the preliminary moisture, temperature and other parameters which survey conducted by NBRO, the following areas of are relevant to assess the ground conditions in Grama Niladhari Divisions (GN Divisions) in problematic areas. Matale MC Area are facing the land subsidence hazard. Table 1: Land area according to Grama Niladari In this survey, 94% of houses were recorded to Divisions have cracks in walls and 45% of the cracks were GN Name GN code Area (Sq wider than 10mm. Following observations were Km) also made; Oya Pahala 352H 0.1119 1. 71% of houses have no tie beams Gongawala 352B 0.3451 2. 53% of houses have not lintels Sinhala Town 352A 0.3061 3. 36% of houses were built with large bricks and Hulangamuwa 353 0.1417 among them 97% of houses were cracked. South Hulangamuwa 353B 0.3868 North 3 METHODOLOGY Diyabubula 352F 0.3950 Nagolla 353A 0.0870 The disaster “Crunch Model”, is used to Maligathenna 352C 0.3251 understand and react to people’s vulnerability to Malwatta 352D 0.0262 disasters. The model is able to take into Kaludewala 350C 0.2623 consideration how the community experience Aluvihare 327 0.9524 different levels and types of vulnerability to Harasgama 350 0.0002 disasters. The model has two dimensions; hazard Mandandawela 350A 0.3638 and vulnerability. It indicates that a disaster happens Parawatta 350B 0.5602 only when a hazard affects vulnerable people which influence the disaster risk. Therefore the level of Land use types are the key factors affecting to disaster risk depends on the magnitude of the hazard the economy. According to the preliminary survey and degree of vulnerability of the people. by NBRO, following amounts of land are affected Three layers of social processes that cause on land subsidence. Therefore, most of the vulnerability are: cultivation lands are found to be affected by land Underlying/ root causes that include pre subsidence. conditioning factors such as poverty and lack of Table 2: Land area as a percentage to total cultivation access to resources brought about by the nature of Land Area Area (Sq Percentage to prevailing power structures and political/economic m) total Land Uses systems. (in Matale) Coconut 100.0% Forcing factors/ Dynamic pressures that include 6,863.20 lack of necessary institutions, training, skills and Chena 100.0% investment, population growth, urbanization, 235,469.20 decline in soil productivity and environmental Home 45.2% degradation. Garden 407,247.27 Fragile/ unsafe conditions that include Fragile Other 18.0% physical environment: risk prone location, Plantations 43,974.51 unprotected buildings and infrastructure, Fragile Paddy 91.4% local economy: livelihoods at risk, low income 30,206.85 levels, Vulnerable community members and lack of Rubber 70.8% disaster preparedness. 129,665.38 The root causes lead to dynamic pressures that Streams 90.4% explain how the unsafe conditions have arisen and 30,731.53 persisted. In the previous studies conducted covering nearly 3000 houses in seriously affected GN 4 VULNERABILITY ASSESSMENT divisions of Matale district, the following structural problems were identified. Vulnerability is a planning perspective on the 1. Foundations of 53% of the total buildings settlements which helps to identify the settlements surveyed are found to be cracked as result of behavior during the hazard situation. More often, land subsidence settlements issues were the exact vulnerabilities 2. 63% of the houses had marble foundations and during rise in the hazard situation. This argument 54% among them were found to be damaged. formed to assess the settlements vulnerability in the 3. 30% houses has plinth beams and cracks were hazard prone environment. not reported in these houses. Two methods were used to calculate the 4. 70% houses did not have plinth beams out of vulnerability at the site; 1. Computer based analysis, which 77% were found to be cracked. 2. Community based analysis 4.1 Computer Based analysis of Vulnerability pattern in detail to identify the vulnerability. This analysis will be conducted in grid base and In the thesis reviewed to determine the minimum size of the grid will be 50 m. methodology for the vulnerability assessment, the Indicat Measurements Method of following components have been suggested. or Analysis 1. Societal Analysis Plot If answers should There are lack of 2. Economic Analysis Size be more than 300 data to identify 3. Environmental Analysis sq m (12 p) then it the exact plot 4. Critical Facility Analysis achieve the sizes. Therefore, 5. Mitigation Opportunity Analysis standard. make Theysian Regular building: polygon from 4.1.1 Societal Analysis 300 sq m (12 p) or existing building In this analysis, consider the social elements 150 sq m (6 p). pattern (by using which affect from the landslide and land subsidence. High rise cadastral maps) Under this analysis following sub – analysis will be buildings:1000 sq and then identified. m (40 p) calculate: (Area of Theysian 4.1.1.1 Settlement Hierarchy (Scalogram) polygon)/ (# of Settlements hierarchy is needed to conduct buildings) identification of the settlement level. The higher Road If answer equal or Calculate: (Area ranked settlements have various activities and it has Frontag less than 25 then of Theysian es it is up to polygon)/ (Road higher vulnerability than lower ranked settlement. standard. length) This hierarchy will be conducted by sub region/ Building frontage: node vice. 150 sq m to 6 m Each settlements have different activities and frontage. 300 sq based on the availability the settlement defining will m to 12 m be analyzed. Mostly, settlements are concentrated to Plot Regular buildings Calculate: ( Area the road node areas. Covera standard : less or of building)/ ge equal to 66% (Area of 4.1.1.2 Demographic Condition Commercial and Theysian Demographic condition of the area is needed to industrial standard Polygon) % : less or equal to consider in detail level. The vulnerability of human 80% settlements means analysis of human settlements by Elevati Human Identify the its characteristics. Therefore, considering the on of settlements should elevation levels previous analysis, following characteristics will be buildin not developed with the analyzed in this assessment; g more than 1000m buildings. 1. Gender ratio elevations. 2. Age groups Slope Buildings cannot Identify the 3. Disability of the be constructed slope angles and 4. Growth rate buildin more than 60% building 5. Type of employment gs slopes.