Effect of changing groundwater level on shallow landslide at the basin scale: a case study in the Odo basin of south eastern Nigeria

This study investigated the effect of changing groundwater level on the propagation and continued expansion of gully erosion and landslide in the Odo River sub basin (a major section of the Agulu-Nanka gully erosion and landslide complex located in south eastern Nigeria). A novel modified deterministic approach, loosely coupled stability (LOCOUPSTAB) framework which involves the development and linkage of groundwater recharge model, groundwater model (MODFLOW) and slope stability model (using Oasys slope, a program for stability analysis by limiting equilibrium) was used to determine the possibility of improving the stability of the study area. For the modelled scenario, reducing groundwater level through pumping from three boreholes at 300m3/day over one year, resulted in an increase in proportional change in factor of safety by an average 0.56 over the Odo river sub-basin. A stability risk map was also developed for the sub-basin. Useful information can be obtained even based on imperfect data availability, but model output should be interpreted carefully in the light of parameter uncertainty.