The purpose of this study is to develop and apply land use change (LUC) as a novel causative factor to produce landslide susceptibility map (LSM) by using frequency ratio (FR), certainty factor (CF), and logistic regression (LR) models in a geographic information system environment. In the study area, Upper Area of Ujung-loe Watersheds area South Sulawesi Indonesia, landslides were derived from aerial photography from time series data image of Google Earth ProTM during 2012-2016 and field survey. LSM were built by using FR, CF, and LR with eleven causative factors. The results indicated that LUC affects landslide susceptibility in the study area according to FR and CF method. It can be inferred from the results of FR and CF, LUC has the highest value on both at LUC from primary forest to open area and paddy field, it was observed that the change vegetation type to another landscape destabilize slopes. However, in logistic regression method, LUC has on 5th place from eleven causative factor, according to likelihood ratio test with chi-square value 85.065 after Slope, distance to river, distance to faults and aspect. Validation of landslide susceptibility was carried out by calculating the area under the curve (AUC) of receiver operating characteristic curve (ROC). Firstly, LR shows the highest accuracy in both success and predictive rate (85.6%). Secondly, the frequency of landslides in high to a very high class of susceptibility was calculated, which indicates the level of accuracy of the method. CF returns the highest accuracy of 85.28%.
Many techniques have been proposed for landslide hazard zonation (LHZ). They can generally be divided into two groups : direct or semi direct hazard mapping in which the degree of hazard is determined by the mapping expert and indirect hazard mapping in which either statistical or deterministic models are used to predict landslide prone areas based on information obtained from the interrelation between terrain factors and the landslide distribution. With the introduction of GIS, in particular indirect methods gained enormously due to its capacity to handle and analyze data with high spatial variability.
In the context of Sri Lanka, landslide hazard maps are prepared using a model developed under a research project conducted from mid-1989 to mid-1995. This model is based on the analysis of six major terrain factors with sub factors and factor classes collected from more than thousand landslides occurred in Badulla and Nuwaraeliya districts. For the zonation based on this model, field data is collected according to those factors and the corresponding weight maps are prepared manually. GIS is only used finally as an overlaying and reclassifying tool. In this workflow, very laborious effort is needed for the preparation of geology weight map, especially when complex terrain conditions and large amount of data are involved. One of the reasons is that, unlike all other factors where the basic mapping units are areas, the geology map consists of two major parts : lithological units as areas but structural attitudes as linear or point measurements.
In 2009, an approach was discussed how GIS capabilities can be used efficiently to integrate the influence of structural attitudes such as strike or dip directions and dip angles for the preparation of geology weight maps which is an essential part of the LHZ model used in Sri Lanka. Even though the original procedure was based on manual weighting since then, the newly introduced automated procedure has been used by National Building Research Organization to accelerate the mapping procedure.
Under this study, a statistical comparison and an assessment were done between the two procedures and necessary modifications to the latter, that is to the automated procedure is proposed to enhance the accuracy of the method.
On 29 th October, 2014 during a heavy rain event, a large landslide occurred in Koslanda, Badulla District, Sri Lanka. The landslide and associated debris flow destroyed several houses and killed more than 30 people. Following the landslide, an aerial survey by helicopter on 5 th November, 2014 and field survey on 19 th and 20 th November, 2014 were undertaken by JICA (Japan International Cooperation Agency) Project Team to understand the occurrence mechanism of the landslide and identify further hazard of the landslide. Further, we conducted numerical simulation to understand processes of these sediment disasters. This report summarizes the observation results conducted by the JICA Project Team, presents the geological explanation of the mechanism and causes of the landslide, and gives suggestions on emergency mitigation measure for further movements of the landslides.
The earthquake with a seismic intensity of seven hit Kumamoto Prefecture twice in April 2016, and caused immense damage in the prefecture. It brought about 158 sediment disasters which included slope failure and landslides, and 246 people died, (which includes the number of those who died of disaster related-death). Furthermore, as the slope in the affected area was loosened, the secondary disasters which might be caused by a rain were likely to occur. Therefore, Kumamoto Prefectural Government adopted various measures, and applied the Provisional Sediment Disaster Warning Standard, for instance, to prevent and mitigate damage from secondary disasters. Kumamoto Prefectural Government is now providing permanent measures to the affected locations to accelerate the recovery to ensure safety and security of the residents.