Control of Tropical Landcover and Soil Properties on Landslides’ Aquifer Recharge, Piezometry and Dynamics

Abstract

Among the processes controlling landslide dynamics, piezometry plays a major role. The characterization of a landslide’s aquifer recharge (=inflows) is thus indispensable for predicting displacements. In this research, the recharge of the large Grand Ilet landslide in the humid tropical, Reunion Island was characterized through a multi-disciplinary and robust hydrological approach, notably comprising a precise water budget of the landslide (outflows = inflows). Surface processes play a major role in the landslide recharge regime. Runoff is less than 1% of rainfall (2400 mm/year) due to the soil’s high permeability. A large quantity of water (250 mm) is adsorbed in this shallow layer. This reservoir is submitted to high real evapotranspiration (1500 mm/year) due to the dense tropical broad-leaved vegetation. This explains the low aquifer recharge (860 mm/year), the fact that only major rainfall episodes during the rainy season induce recharge, with a consequent increase in landslide velocity, and finally low outflow from the landslide. Therefore, among other operational recommendations, it is necessary to maintain natural vegetation cover over such landslide surface in order to limit aquifer recharge and thus displacements. This study provides a methodological framework for landslide studies, particularly for modeling their recharge/piezometry, and key parameters of their dynamics.

Keywords

• groundwater
• water budget
• climate
• slope instability
• evapotranspiration
• spring
• hydrogeology
• hydrology
• volcanic rocks