THE WHITE VOLTA SUB-BASIN - Sustainable Irrigation Development in the White Volta Sub-Basin - page 13

2.3 T HE W HITE V OLTA SUB - BASIN
The total catchment area of the White Volta is 107,417km 2 distributed in
Ghana, Burkina Faso and Togo. Its main tributaries are the Nakambé, Red
Volta, Morago, Nasia, Kulpawn and Tamne. The area of the catchment
outside Ghana is 58,207km² which is about 54% of the total basin area. The
area of the catchment in Togo is less than 5% of the total.
The White Volta begins as the Nakambé River in Burkina Faso. The Red
Volta, referred to as Nazinon in Burkina Faso, and Sissili are tributaries of
the White Volta and have their source in Burkina Faso. In the White Volta
sub-basin, the following rivers originate from within Ghana: Nasia, Kulpawn
and the latter's tributary Sisili (WRRI, 1975).
The surface water resources in the basin consist of flows generated inside
Burkina Faso as well as flows from within Ghana. The mean annual flow of
the White Volta sub-basin is about 300 m 3 /s, of which 36.5% is generated in
upstream Burkina Faso (Barry et al., 2005). The discharges entering Ghana
are estimated from the border gauging stations. The border station on the
Red Volta is Nangodi with a measured average annual flow of 30m 3 /s and
the gauging station on the White Volta is Yarugu with a measured average
annual flow of 80m 3 /s (Opoku-Ankomah and Amisigo, 1997). The White
Volta sub-basin contributes about 25% of the annual total flows to the Volta
Lake. The mean monthly runoff varies from a maximum flow of 1,216m 3 /s to
a minimum of about 0.1m 3 /s (Barry et al., 2005).
Climate: The White Volta sub-basin stretches into three climatic zones:
1. The Sudan zone with an annual rainfall between 900 and 1,200mm/a
distributed on average over 74 rainy days. It is located South of the
11 o 30'N parallel. The mean temperature in this climatic zone is
always below 28 o C.
2. The Sudano-Sahelian zone with an annual rainfall between 600 and
900mm/a on average over 43 rainy days, located between the 11 o
30'N and 14 o N parallels. In this zone the mean temperature lies
between 28 o C and 29 o C.
3. The Sahelian zone located North of the 14 o N parallel with a mean
annual rainfall between 300 and 600mm/a over 38 rainy days. The
mean temperature in this climatic zone is always higher than 29 o C.
Hydrogeology: The White Volta sub-basin is composed of about 45%
crystalline rocks comprising the Birimian system and its associated Granitic
Intrusives and isolated patches of Tarkwaian formations. The remaining 55%