GEOPHYSICAL INVESTIGATIONS OF A RURAL WATER POINT INSTALLATION PROGRAM IN NAMPULA PROVINCE, MOZAMBIQUE

Abstract

There are many projects in Mozambique for poverty reduction. One of these projects is funded by Millennium Challenge Account (MCA) and is aimed to install a total of 600 rural water points in the province of Nampula and Cabo Delgado in crystalline rock zone. Each water point consists of a drilled well, a water pump and a communal washing basin. Vertical Electrical Sounding (VES) was used for assessing the suitability of the drill sites but despite this many boreholes have come out with an insufficient yield and the failure rates in certain areas are as high as 50%. Continuous Vertical Electrical Sounding (CVES), also known as Electrical Resistivity Tomography (ERT), was carried out in an attempt to explain the high failure rate of boreholes. In total, nine boreholes with sufficient yield, and five boreholes with insufficient yield were investigated. In both VES and ERT, the resistivity values indicate 3 different layers. One surface layer with resistivity between 220-5000+ Ωm, a second layer with lower resistivity value, varying from 10-220 Ωm, less than 10 Ωm in some places, and a third layer with high resistivity values, 220-5000+ Ωm, increasing with Depth. Due to lateral variation, the geology in study area is best described in 3D therefore ERT appears to be a suitable method for groundwater exploration and could probably lower the failure rate. (Less)