Habibah Lateh

Landslide hazard mapping of Penang island using probabilistic methods and logistic regression

This paper summarizes landslide hazard mapping of Penang Island, Malaysia using probabilistic methods and logistic regression. Probabilistic methods such as frequency ratio, statistical index, certainty factor and landslide susceptibility analysis, and logistic regression were applied to produce landslide hazard maps. Correlations were used to determine effects and contributions of landslide-causative factor to landslide. Factors that show low correlations or proven to negatively contribute to the final results were ejected. Final results show logistic regression as the best method to predict landslide occurrences in Penang Island with an accuracy of 80.05%, followed by frequency ratio with 79.68%, landslide susceptibility analysis with 79.6%, statistical index with 79.38% and certainty factor with 79.37%.

Meteorological drought in Bangladesh: assessing, analysing and hazard mapping using SPI, GIS and monthly rainfall data

This study focused on assessing and analysing meteorological drought characteristics of Bangladesh based on rainfall, standardized precipitation index (SPI) and geographic information system (GIS). SPI and monthly rainfall time series dataset for the period of 1971–2010 were used to define the drought years and severity. GIS techniques, along with inverse distance weighted interpolation, were used to determine the spatial pattern of drought. Drought occurrences with severity were analysed based on 3-month (SPI-3 January and SPI-3 April) and 6-month (SPI-6 April) time scales. Drought occurrence maps were generated in GIS environment by summarizing the percentage of drought occurrence for each category and for each time scale. For drought hazard mapping, a drought hazard index was computed from 34 observation stations using analytical hierarchy process, weighted sum method and drought occurrence with different severities at different time scales. Afterwards, index values were interpolated and classified into four hazard levels viz. low, moderate, high and very high. This study pointed out that 1972, 1978, 1981, 1982, 1995, 1997, 1999, 2004, 2006 and 2010 were the most drought-affected years since 1971, and 1972, 1978, 1982, 1995, 1999 and 2006 were the worst drought years based on severity. In the last two decades, Bangladesh had high numbers of severe and extreme droughts. Drought occurrences showed that during the study period, comparatively moderate drought occurred more frequently than severe and extreme. The time scale SPI-3 January was more prone to severe drought occurrence while the time scale SPI-3 April was more prone to extreme drought occurrence. The northern, north-western, western, south-western and central parts were the most drought-prone areas of the country in terms of occurrence and severity. Low annual and seasonal rainfall, high variability in rainfall and climate change impacts, and particularly increased maximum temperatures greatly influence droughts in Bangladesh. On the other hand, drought hazard maps of SPI-3 January, SPI-3 April and SPI-6 April showed that high and very high hazardous areas were located in the north-west, west and south-west parts of the country. The Rajshahi, Dinajpur, Rangpur, Bogra, Kushtia were the most drought-prone districts (under very high hazard zone) of the country. The districts Jamalpur, Pabna, Jessore, Khulna, Mymensingh and Tangail were also identified as drought hazardous districts (under high hazard zone). Thus, these parts of the country require urgent intervention on a priority basis to mitigate drought impacts.

Landslide Hazard Mapping Using a Poisson Distribution: A Case Study in Penang Island, Malaysia

Landsliding is one of the most destructive natural geohazards in Malaysia. Landslide hazard maps are very useful for urban development planning. This paper presents landslide hazard mapping using a new approach, i.e. a Poisson distribution, and compares the result with previous probabilistic approaches, i.e. frequency ratio (FR), statistical index (SI) and landslide nominal susceptibility factor (LNSF). These approaches were implemented in Penang Island to produce landslide hazard maps. The landslide causative factors considered are elevation, slope gradient, slope aspect, curvature, land cover, vegetation cover, distance from nearest road, distance from nearest stream, distance from nearest fault line, geology, soil texture and precipitation. Landslide hazard maps were assessed using the Receiver Operating Characteristics (ROC) method. Accuracy obtained for FR, SI and LNSF are 78.52 %, 78.12 % and 72.93 % respectively. Poisson distribution approach gives high accuracy of 78.51 % as FR.

Bivariate Probabilistic Modelling of Hydro-mechanical Properties of Vegetated Soils

Vegetation retains soil suction, which significantly affects the shear strength characteristics of soil and slope stability. However, because of uncertainties (heterogeneous root distribution, spatial variability) associated with vegetated soil, probabilistic analysis on the hydro-mechanical properties of vegetated soil is a necessity. Moreover, mechanical (cohesion, c, angle of internal friction, ϕ) as well as hydrological properties (suction, ψ, water content, θw) are correlated in nature, and this has a significant effect on the reliability of geotechnical structures. However, these studies investigated the dependence structure of mechanical parameters only. The main objective of this study is to evaluate the dependence structure of both mechanical (c, ϕ) as well as hydrological (ψ, θw) parameters of homogeneously compacted vegetated soil on the basis of measured field data. This is done by using copula theory to map the copula density functions (copula probability distribution functions [PDFs]) of (c, ϕ(ψ, θw) to their respective marginal distributions (PDFs) in order to simulate their bivariate distributions. The novelty of this work further lies in analysis of time-dependent behavior of θw by generating its PDFs, utilizing the concept of average mutual information (AMI). Thus, the information attained in this study about the inherent behavior of hydro-mechanical parameters of soil can be further utilized to estimate the reliability of vegetated slopes under varying climatic conditions.

Plant Root Reinforcement Against Local Failure Mechanism of Natural Slope

The effectiveness of plant root reinforcement in protecting shallow landslide was analyzed using a method of slope stability analysis. The study has investigated the effective contribution of roots to the local safety factors as well as over-all safety factor. The roots of natural plants increased the local safety factor by providing additional shear strength locally to at failure plane. During propagation of failure, the strength of soil at certain location along the shear plane drastically reduced to a residual level and the failure was imminent locally, it was found that the roots significantly contributed additional strength locally and increased the safety factor at the place. The shear strengths of roots were determined with root diameters, number of roots and tensile strength of roots. The shear strengths of plants were incorporated as reinforcements into the slope stability analysis. The analysis calculated the local as well as over-all safety factor with such reinforcement of roots. Existing published data regarding the roots were used in the analyses. An example case of slope stability analysis was done with different root reinforcement situation on the slope. Effects of different cases considering the positions of root reinforcements on the safety factor and the shear strength were also examined.

Comparison of fuzzy filters on Synthetic Aperture Radar image

The Synthetic Aperture Radar (SAR) image with its advantages is becoming more popular than the optical image in earth observation in using the remote-sensing techniques. However, the speckle noise that occurs in the SAR image causes difficulties in image interpretation. Thus, speckle noise reduction needs prepossessing procedure prior to the use of the SAR images. This study is done by proposed fuzzy filters that utilize SAR data. From the comparison, the combination of Frost-Triangular Moving Average (TMAV) has the best performance in the ability to reduce speckle noise than other filters. This filter improved the Frost filter performance for speckle noise reduction parameters measurement, shows that 13.41% for Equivalent Number of Looks (ENL) and 6.07% for Speckle Index (SI). While Frost-Asymmetric Triangular Moving Average (ATMAV) has a relatively good performance for preserved texture. This filter improved the texture parameters such as Standard Deviation improved 4.33% and improved Variance for 8.46%. However, for the Mean parameters, Frost-Triangular Median Center (TMED) combination has the best performance compared to other filters, which improved the mean value for 7.10%. The comparative study it has been verified that the fuzzy approach has the robustness in the reduction of speckle noise and preserving the texture when applied in SAR image.

Landslide hazard mapping of Penang Island using dominant factors

Landslide is one of the natural disasters in Malaysia and precipitation is the triggering factors for landslide in Malaysia. Besides rainfall factors, topographical factors also play key role in the susceptibility analysis of landslide. Since there are many available landslide-causative factors involved, selection of dominant factors is a crucial steps in landslide susceptibility analysis. This paper reports the landslide hazard mapping using Frequency Ratio (FR) approach with selected dominant factors in the area of Penang Island of Malaysia. Landslide hazard map of Penang Island is first generated by taking into account of twenty-two (22) landslide-causative factors. Among these twenty-two (22) factors, fourteen (14) factors are topographic factors. They are elevation, slope gradient, slope aspect, plan curvature, profile curvature, general curvature, tangential curvature, longitudinal curvature, cross section curvature, total curvature, diagonal length, surface area, surface roughness and rugosity. The other eight (8) non-topographic factors considered are land cover, vegetation cover, distance from road, distance from stream, distance from fault line, geology, soil texture and rainfall precipitation. After considering all twenty-two factors for landslide hazard mapping, the analysis is repeated by removing one factor at one time to identify the dominant landslide-causative factors. Twelve dominant factors are selected from the twenty-two factors. Landslide hazard map was segregated into four categories of risks, i.e. Highly hazardous area, Hazardous area, Moderately hazardous area and Not hazardous area. The maps was assessed using ROC (Receiver Operating Characteristic) based on the area under the curve method (AUC). Landslide hazard map produced by including all 22 factors has an accuracy of 77.76%. By removing 10 irrelevant factors and employing only 12 dominant factors, the generated hazard map achieves better performance with accuracy of 79.14%.

Investigation of Root Distribution and Tensile Strength of Acacia mangium Willd (Fabaceae) in the Rainforest

The purpose of this study is to complement the existing body of knowledge on the root system of tropical plants and their contribution to slope stability. For this reason, four trees of Acacia mangium selected as randomly in rainforest along East-West Highway, Malaysia. Root area ratio (RAR) and tensile strength (Tr) data were collected and analyzed. RAR data were measured with the whole root system and Tr were measured by individual roots. The results showed that there is a power law equation between root diameter and Tr, with an average of 44.11 Mpa (in average root diameter of 0.9mm). There was a wide variation in the RAR in relation to soil depth. Generally, RAR reduced with the increasing soil depth. Similarly, additional cohesion by plant roots conducted by Tr and RAR. In conclusion, in order to assess soil reinforcement by vegetation roots, root distribution and tensile strength data with soil depth in different vegetation and sites is necessary.

The prevalence of post-traumatic stress disorder among landslide victims

Landslides have resulted in large numbers of casualities and huge economic loss in hilly and mountainous areas in Malaysia. Due to a rapid development since the 1980s, strategic and suitable low-lying areas for development have become incresingly and resulted make unavailable in Malaysia. Hence, the development of highland or hilly terrain has increased, particularly in areas adjacent to densely populated cities thereby exposing urban communities to an increased risk of landslides occurrence. Malaysia lies in a geologically stable region which is free from earthquakes, volcanic activities and strong winds such as tropical cyclones which periodically affect some of its neigbors. It lies geographically just outside “Pacific Ring Of Fire”. But, that does not mean Malaysia is totally “Free” from natural disasters and calamities, as it is often hit by floods, droughts, landslides, haze, tsunamis and humanmade disasters.1 Hence, the most tragedy disaster that hit Malaysia is landslide that affecting almost all continents of the world causing damage to life and property damage to life and property and massive distruption in transport/ supply network. A landslide is geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments. Landslide can be categorizes based on the movement of soil mass, landslides failure surface and the duration of the movement. In general, soil mass moves failure surface from the original area to the lower depositional area. 2 National Slope Master Plan 3 landslides are a massive mass of soil and rock debris that move downhill because of the action of gravity. The sheer mass of material involved and the speed at which they occur make them potentially disastrous as a consequences because of the massive damage that can cause to property and lives.

The Role of Local Authorities in Communicating Landslide Hazard to the Orang Asli (Indigenous) Community in Cameron Highlands

Landslides have caused large numbers of casualties and huge economic losses in mountainous areas around the world. Rapid movement of rock mass, debris or earth down a slope, has the potential to cause extensive damage to infrastructure such as roads, bridges, human dwellings, agricultural lands and forests, thus resulting in economic losses.