Agriculture Reference
In-Depth Information
Anayari catchment will be 371ha (0.8%), in the Atankwidi catchment 5.4ha
(0.05%) and in Yarigatanga 578ha (1.6%). This results in reducing
streamflow in the Anayari River by 3.8x10
6
m
3
/a (3.7%), in Atankwidi by
0.8x10
6
m
3
/a (1.2%) and in Yarigatanga by 2.6x10
6
m
3
/a (3.2%).
Impact of ground water irrigation
Current groundwater irrigation in the Anayari catchment is 840ha (1.80%),
in Atankwidi catchment 191ha (0.69%) and in Yarigatanga catchment 5ha
(0.01%). If current irrigation would grow at 5% then by 2025, groundwater
irrigation in Anayari would have reached 4.86%, 1.86% in Atankwidi and
0.03% in the Yarigatanga catchment. These result in evaporation losses of
21.2x10
6
m
3
/a in the Anayari catchment, 4.6x10
6
m
3
/a in the Atankwidi
catchment and 0.14x10
6
m
3
/a in the Yarigatanga catchment. These
evaporation losses stem from groundwater that otherwise would contribute
to streamflow in the basin. Therefore, streamflow contribution from the
catchment is reduced by these evaporation losses. However, these
evaporation lossess are conservatively very high estimates. The fact remains
that not every drop of water that is not used for irrigation would have made
it to the Volta Lake.
Impact of upscaling irrigation in the White Volta sub-basin
The study area covers about 1% of the White Volta sub-basin. The trend of
irrigation observed in the study area is similar to those in other catchments
within the sub-basin. Therefore upscaling the results in the study area, gives
a large-scale assessment of the impact of irrigation development in the sub-
basin.
The White Volta sub-basin contributes 25% (9.57 x 10
9
m
3
/a) of the annual
inflow into the Volta Lake. Thus a reduction in the streamflow from the
White Volta sub-basin has a reduction factor of 0.25 on the total flow into
the Volta Lake.
Using the 5% annual growth in irrigation as the benchmark for this analysis,
the total water loss due to surface water and groundwater irrigation when
the irrigation level in 2025 is attained equals 33.1 x 10
6
m
3
/a in the Anayari,
Atankwidi and Yarigatanga watersheds. This is the total water loss due to
irrigation in 1% of the total catchment area of the White Volta sub-basin.
Upscaling to the entire White Volta sub-basin, results in annual streamflow
reduction of 3.31 x 10
9
m
3
/a (35% of total streamflow) from the White Volta
sub-basin. This is equivalent to 8.8% of mean annual water inflow into the
Volta Lake; the largest water user being hydropower production at the
Akosombo dam.
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