DESCRIPTION OF IRRIGATION TECHNOLOGIES IN THE WHITE VOLTA SUB-BASIN - Sustainable Irrigation Development in the White Volta Sub-Basin - page 113

of Ghana from 1990 to 1997 and another 36 under the Phase II of the same
project (IFAD, 1990, 2005).
A study conducted by Birner et al. (2005) found that, out of 16 communities
in the Upper East Region that had small reservoirs either constructed or
rehabilitated in recent years, only 7 communities cultivated the full area
designed for irrigated agriculture, 4 cultivated part of the area, and 5 did not
irrigate any land at all. The reason for this low performance was lack of
water which was associated with poor dam construction, lack of
maintenance, or due to wrong hydrological and climatic estimations.
The construction of a single small reservoir without irrigation development in
the late 1990's cost approximately US$130,000 (Birner et al., 2005). Between
2004 and 2007 newly constructed small reservoirs with irrigation
development by an NGO in the Upper West Region of Ghana cost between
$422,000/10ha 2 irrigable area and $500,000/20ha irrigable area (source:
personal communication).
Infrastructure and irrigation technology (water abstraction,
transportation and application)
An assessment conducted in the Upper East Region of Ghana in 1995 by
GIDA showed that the impoundments of small reservoirs in general are fed
with water from catchment areas ranging from 10-544ha; have storage
volumes ranging from 0.15x10 6 m 3 to 0.47x10 6 m 3 , full scale storage area of
3.5-28ha, a maximum depth of 2.0-6.5m, embankment length of 100-1,000m
and an earth/concrete channel spillway connected to one end of the
embankment (Figure 5.1) . The inner face of the embankment is typically
covered with boulders and in some cases with wire mesh to prevent
crocodiles from boring into the embankment. Restricted areas are created in
the catchment area by planting trees which are used to prevent farming
activities and thereby reduce the rate of siltation into the reservoir.
Generally, small reservoir irrigation schemes have developed irrigable fields
downstream of the impoundment, furnished with water abstracting and
transporting facilities (see Figure 5.1) . Water abstraction from the reservoir
to the developed irrigation field is by means of a water outlet point located
close to the lowest point in the impoundment comprising a tunnel fitted with
a sieve at the end and connected to a distribution point (furnished with
2 The units are not in per ha because of the scale factor in costing small reservoirs.
The cost of 20ha small reservoir cannot be automatically divided into two to
represent the cost of a 10ha small reservoir.