Model-based estimation of land subsidence in Kathmandu Valley, Nepal

Pallav Kumar Shrestha,Narendra Man Shakya,Vishnu Prasad Pandey,Stephen J Birkinshaw,Sangam Shrestha

doi:10.1080/19475705.2017.1289985

Abstract

ABSTRACTThis study is the first to assess land subsidence in the Kathmandu Valley, Nepal. Land subsidence simulations were based on a fully calibrated groundwater (GW) flow model developed using a coupled surface–subsurface modelling system. Subsidence is predicted to occur as a result of deep aquifer compaction due to excessive GW abstraction. The north and north-east areas at the periphery of the GW basin are hotspots for this subsidence. The estimated subsidence is most sensitive to changes in land cover within the recharge areas. The model shows the Melamchi water supply project assists in the control of subsidence to some extent. In the absence of land subsidence measurements, this paper highlights the location and the potential levels of the subsidence hazard which will be useful for hazard prevention management. Additionally, this work provides a basis to design field investigations, monitoring networks for land subsidence and upgrading the present GW monitoring network. Although the study has presented a preliminary analysis, a more comprehensive model inclusive of clay subsidence is required to address the subsidence vulnerability of the central densely populated core of the valley, which reflects the need for a comprehensive database of the hydrogeology in the valley.

Highlights

Land subsidence is the movement of the Earth’s surface as it shifts/ sinks/ settles downward relative to a datum
We calibrated and validated a SHETRAN model to simulate groundwater flow in the study area; developed three future scenarios for land cover, two for groundwater abstraction pattern, and future meteorological conditions; and estimated land subsidence based on change in effective stress due to fluctuation in groundwater table (GWT) for current and future conditions
The values of 0.25 for forest and 1 for arable cover are comparable to the range of 1–10 applied for a grass and forest dominant cover using the same model in Bathurst et al (1998)

Summary

Introduction

Land subsidence is the movement of the Earth’s surface as it shifts/ sinks/ settles downward relative to a datum. Land subsidence can have severe impacts in terms of the water sector. This can include reduction in groundwater storage capacity of a geologic strata, deterioration in groundwater quality, restrictions on groundwater pumping, intensification of the movement of ground fissure, destruction of natural drainages, exposing the land to flooding, and river channel distortion (Balogun et al 2011). It can cause structural damage to highways, buildings, etc. Fluid withdrawal has been found to be the most important one (Poland et al 1972, Larson et al 2001, Hu et al 2004, Xue et al 2005). In China, it has affected an area of 90,000 km (Xue et al 2008)

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