Abstract
Land subsidence is identified as a global problem and intensive studies are being conducted worldwide to detect and monitor risk of this problem. Risk assessment of land subsidence is simply an evaluation of the probability and frequency of occurrence of land subsidence, exposure of people and property to the subsidence and consequence of that exposure. Remote sensing technology was used to extract information of land subsidence in Kathmandu Valley, Nepal. Also, Disaster Risk Index method and Analytic Hierarchy Process (AHP) along with Geographic Information System (GIS) tools were used to assess risk of land subsidence in Kathmandu Valley, Nepal. Subsidence volume for locations Central Kathmandu, Chauni, Lalitpur, Imadol, Thimi, Madhyaour Thimi, New Baneshwor, Koteshwor and Gothatar was calculated using a simple mathematical formula. The subsidence depth for these locations was found to be in a range of 1 cm to 17 cm and the maximum subsidence velocity was found to be 4.8 cm/yr. This study revealed that the location where maximum subsidence was observed (i.e. Central Kathmandu and Lalitpur) was found to be at high risk of experiencing land subsidence induced damage. Other location where subsidence was observed was found to be at medium risk and the rest of the Kathmandu valley was found to be at low risk with current data situation. This study can be considered as the first step towards other comprehensive study relating to land subsidence risk assessment. The outcome of this research provides a basic understanding of the current situation that can further assist in developing prevention and risk management techniques.
Highlights
This study revealed that the location where maximum subsidence was observed (i.e. Central Kathmandu and Lalitpur) was found to be at high risk of experiencing land subsidence induced damage
Land subsidence is just a geological phenomenon either triggered by natural or anthropogenic activities but when this phenomenon has the probability of resulting harmful consequences or the expected loss it is considered as risk [1]
Groundwater exploitation intensity data was used for hazard mapping of land subsidence and was provided by the Kathmandu Valley Water Supply Management Board (KVWSMB), Ministry of Water Supply and Sanitation, Government of Nepal
Summary
Land subsidence is just a geological phenomenon either triggered by natural or anthropogenic activities but when this phenomenon has the probability of resulting harmful consequences or the expected loss (of lives, property, livelihoods, economic activities or environment) it is considered as risk [1]. The physical damage caused by land subsidence can be mainly categorized into two forms: damage on artificial (manmade) infrastructures and damage on natural systems. Significant damage is seen in areas corresponding to land subsidence occurrence. The main damage on manmade infrastructure reported worldwide is mostly related to water transport structures [3] [4]. Since land subsidence affects the elevation of the ground, and because water transportation infrastructures are very sensitive to minor gradient changes, subsidence can hugely affect such structures. Other reported problems include damage to buildings and transportation facility (i.e. roads, bridges, railways)
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