THE WHITE VOLTA SUB-BASIN - Sustainable Irrigation Development in the White Volta Sub-Basin - page 14

of the White Volta sub-basin is composed of Voltaian Systems consisting of
the Upper Voltaian Sandstone, Obosum and Oti beds and Lower Voltaian
(Barry et al., 2005).
Aquifers: Two types of aquifers exist in the White Volta sub-basin. These are
the weathered zone aquifers and the fissured zone aquifers. These aquifers
are either phreatic semi-confined or confined depending on the clay and mica
content of the upper weathered layer (Kortatsi, 1997). The fractured zone
aquifers are normally discontinuous and limited in area. Due to the sandy
clay nature of the weathered overburden, the groundwater occurs mostly
under semi-confined or leaky conditions (Ministry of Works and Housing,
1998).
Generally the yield of boreholes vary from 0.03m 3 /h to 24.0m 3 /h with a
mean value of 2.1m 3 /h suggesting that most of the aquifers are low yielding
(Kortatsi, 1997). Yields from boreholes are highly variable because of the
lithological varieties and structural complexities of the rocks (Dapaah-
Siakwan and Gyau-Boakye, 2000).
Studies (Kortatsi, 1994; Ministry of Works and Housing, 1998) revealed that
the quality of groundwater in Ghana is generally good for multi-purpose use
except for thelow pH (3.5-6.0) values, and the presence of high level of iron,
manganese and fluoride in certain localities.
2.4 W ATER USES IN THE W HITE V OLTA SUB - BASIN
Agriculture is the main economic activity in the sub-basin. The agricultural
activities include rainfed agriculture, irrigated agriculture, livestock
production and fishing. Other notable water uses are domestic water supply
(for both rural and urban settlements), industrial water supply and
hydropower generation. Current surface water uses in the sub-basin are
estimated at about 0.11m 3 /s for domestic water supply and about 2m 3 /s at
numerous small-scale irrigation projects (Barry et al., 2005).
In Ghana there are about 200 small reservoirs and 800 dugouts developed in
the White Volta sub-basin for the purposes of livestock, fishing, domestic,
construction and irrigation farming. In addition there are three large-scale
irrigation schemes with a sum of 3790ha of developed irrigable area for
irrigation farming. Unmeasured areas of informal irrigation using various
irrigation technologies are spread within the basin along rivers and streams.
These irrigation developments are private-led and have been intensifying
during the past two decades.