The Eastern Cape Province has been severely impacted by the current drought period, particularly within the Butterworth town and surrounding communities. This study, conducted within the Mnquma Local Municipality of the greater Amathole District Municipality, presents the approach undertaken in mitigating and augmenting the current water shortage. The area generally experiences annual rainfall of 596 mm and is mostly reliant on surface water with a population of over 250 000 residents. The supply of water to the communities is abstracted from the Gcuwa, Toleni and Xilinxa dams with water levels at 44, 21 and 0.6% respectively. Groundwater source development remained the most feasible solution to alleviate the drought within the area.
The geophysical techniques that were applied include the airborne technique (aeromagnetic and gamma[1]ray spectrometric) and the ground geophysical techniques (magnetic and em34) at the targeted airborne sites to verify the dolerite structures. The airborne method was used to obtain more in-depth knowledge of the geological and hydrogeological conditions within the study area. The total distance in kms’ flown for the airborne survey amounted to ~1200 km. The flight-line pattern was (N-S) and tie-line pattern (E[1]W) of the survey was conducted by AeroPhysX, and the flight-lines were flown at a 200m line spacing and tie-lines at 750m spacing at 60m flying height.
The study area consists of a vast network of E-W trending geological structures such as regional dolerite dyke and sill intrusions, faults and lineaments. Although many dykes are present within the lower Ecca and Dwyka Formations and even the Nama age basement, the bulk of the dykes are strata bound and concentrated in the Upper Ecca and Beaufort Group (Chevallier and Woodford, 1999; Woodford & Chevallier 2002). The airborne geophysical technique assisted by accurately mapping out prominent and inferred dolerite dykes located at inaccessible areas due to steep undulating hills.
The drilling success rate on the airborne sites is 98% so far with depths ranging from 60 to 300 m with blow yields of between 2 and 50 l/s. A total of 25 prioritized drilling positions have been identified based on the airborne survey.
The hydrochemical status of the successfully developed boreholes is indicative of class 3 water quality according to the SANS 241-1:2015 minimum standards due to turbidity, sodium, chloride, iron and fluoride as common constituents in the developed boreholes. The developed boreholes will be connected to the existing bulk water supply to the Water Treatment Plant (WTP) for treatment prior human consumption.
Airborne survey has proven to be a useful method in locating new groundwater potential areas as well as identifying unmapped dolerite structures. This paper is based on quantitative and factual findings of actual work conducted on site so far.