IGCP 565 Project Workshops

IGCP 565 Workshop 5: Water Security for Africa: Bringing Together Research, Monitoring, and Managing October 29-30, 2012 Johannesburg, South Africa

Time series analysis of rainfall events and the gravity response at the Southern African Geodynamic Observatory, Sutherland

Mahed, G^1,3, Blume, T², Gunter, A², and de Wit, M^3
1 AEON (Africa Earth Observatory Network), and Department of Geosciences, Faculty of Science, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa
² Helmholtz Centre for Geosciences, GFZ, Potsdam, Germany
³ AEON (Africa Earth Observatory Network), Nelson Mandela Metropolitan University, Port Elizabeth, South Africa.

We examined the subsurface water level, precipitation, and gravity residual data at one well in the study area to determine the correlation between the water level and gravity residual. Single rainfall events were separated from those comprising more than one rainfall event (e.g. amalgamated events). Two cases of weak direct correlation (e.g. 0.63 and 0.68) were found between the water level data and gravity residual data for amalgamated events, comprising multiple episodes of precipitation. On the other hand strong correlations, up to 0.9 were identified between the water level in the well and the gravity residual following single rainfall events. These variable correlations shed light on the variability of the hydrological regime. In both cases weak and inverse correlations were also present between the water level and gravity residual. This suggests that multiple reservoirs contribute to the mass storage in the subsurface. However the possibility that this well acts merely as a conduit for through-flow, and that the correlations reflects an instantaneous response to precipitation and subsequent instant drop in water level, is another possibility. This point is further substantiated by the sulphur stench of the anoxic water in the well.