Landslide impacts and management in Nanka area, Southeast Nigeria

Ogbonnaya Igwe,Chuku Okoro Una

doi:10.1186/s40677-019-0122-z

Ogbonnaya Igwe, Chuku Okoro Una

Open Access

https://doi.org/10.1186/s40677-019-0122-z

Copy DOI

Abstract

The devastating impacts and mitigation measures for landslides in Nanka, Southeast Nigeria were studied. A procedure encompassing field mapping, laboratory analysis and limit equilibrium simulations were employed in the study. A total of 120 landslides in this area were documented during the field study. They were mainly shallow landslides with depth range of 0.2 m – 1.8 m and slope angle range of 36o - 65o. This study revealed that landslides in this area occur mainly during the rainy season, and are triggered by water infiltration in slopes with high gradient, where poorly consolidated sands overlies less permeable silty clay units in the Nanka Formation. The increase in pore water pressure due to soil saturation leads to reduction of the shear strength and loss of apparent cohesion. Geotechnical laboratory analysis showed that the thin silty clay soils found in the area have very high plasticity, while the sands are non-plastic. The limit equilibrium simulations revealed that as the slope angle increases, the potential slip mass volume increases. Our study in Nanka revealed that landslides have negatively affected the topography/morphology, settlement areas, agricultural lands and vegetation/land cover of the area and many areas are also threatened by this phenomenon. Standard mechanical drainage system and biotechnical slope protection have been suggested as mitigation measures. Finally, we suggested that landslide hazard information should be incorporated into long-term plans for Nanka and other areas prone to landslides, the public should be aware of the hazards and preventive measures.

Highlights

Landslide occurs in different parts of the world, under all climatic conditions and environments
A procedure that involved field, laboratory and limit equilibrium simulations were employed in the study
The limit equilibrium simulations revealed that as the slope angle increases, the potential slip mass volume increases, which implies that areas with higher slope angles will possibly have more potential mass volume

Summary

Introduction

Landslide occurs in different parts of the world, under all climatic conditions and environments. In many regions of the world, the impacts of landslides have been cataclysmic with damages worth several millions of dollars in monetary losses, and are responsible for thousands of deaths and injuries annually. They cause long-term economic disruption, population displacement, and negative effects on the natural environment, (Ancuţa et al 2007; Highland and Bobrowsky 2008; Igwe, 2015). Though landslides can occur in different parts of the world, their mechanisms, impacts and management is often determined by the geology, hydrogeology and geomorphology of the area. It means that the risk associated with landslides is area dependent, which implies that mitigation techniques

Methods

Results

Conclusion