1. Engineer, Water Resources Commission of Ghana, P. O. Box CT 5630, Accra, Ghana (corresponding author).
2. Professor, Institute of Geography and Geology, Univ. of Copenhagen, Øster Voldgade 10, DK-1350, Denmark.
3. Professor, Dept. of Geology, Univ. of Ghana, P.O. Box 58, Legon, Accra, Ghana.