1. Barber, W. 1965. Pressure water in the Chad Formation of Bornu and Dikwa Emirates. northeastern Nigeria. Geological Survey of Nigeria Bulletin No 35.
2. Study of the infiltration and recharge through the sand dunes in arid zones with special reference to the stable isotopes and thermonuclear tritium
3. du Preez, J. W. & Barber, W. 1965. The distribution and chemicala quality of groundwater in northern Nigeria. Geological Survey of Nigeria Bulletin No 36.
4. Edmunds, W. M., Darling, W. G. & Kinniburgh, D. G. 1987. Solute profile techniques for recharge estimation in semi arid and arid terrain. In Simmers, I. (ed.) 1987. Paper presented at NATO Advanced Research Workshop on Estimation of Natural Recharge of Groundwater with Special Reference to Arid and Semi-Arid Zones, Antalya, Turkey, March 7–15, 1987. D Reidel, Dordrecht, 139–157.
5. FAO 1984. Agroclimatological Data for Africa. Plant Production and Protection Series No 22, FAO, Rome.