Agriculture Reference
In-Depth Information
groundwater exploitation. Modelling results show that sustainable
groundwater use can be achieved if not more than about 8% of the
catchment is irrigated, at an irrigation efficiency of 70%. This ceiling is
sensitive to groundwater recharge rates, which are affected by changing land-
use practices and climate variability and change.
The outcomes of the WEAP model have been validated using a simple water
balance approach. The validation revealed that the WEAP model ignores
water losses due to groundwater abstraction, which is a serious weakness.
Thus losses due to groundwater abstraction were computed using the water
balance approach.
Based on the observed 5%/a growth rate in the White Volta sub-basin, the
irrigated area is likely to more than double by 2025. When this occurs,
inflows into the Volta Lake will be reduced by 8.8%. This has potential
consequences on hydropower production at Akosombo dam.
Comparing the benefits of upstream irrigation to the losses suffered by
hydropower production downstream of the sub-basin, vegetable farmers
would make a profit of about 429 million US$/a while hydropower
production at Akosombo would loose 42.5 million US$/a. The socio-economic
benefits of irrigation upstream of the Volta Lake thus significantly exceed the
financial loss to hydro-power production. This implies that if current
development trends as studied in the three small catchments continue to
develop for the coming 15 years, and are upscaled to the entire White Volta,
then the negative downstream impacts are relatively small compared to the
upstream benefits.
However, these conclusions are made based on reproducing historical
electricity generation patterns. A much more detailed investigation is
required that would include explicit operating policies of the Akosombo dam,
and would be able to optimise operating rule that could minimise electricity
losses in the face of reduced inflows.
The study has not considered the possible future developments in other sub-
basins and the combined impacts of all upstream developments on the
Akosombo dam. To be able to assess the impact, the following has to be
done: (1) to conduct analysis similar to the present in all other sub-basins;
and (2) to develop a dynamic water resources model to accurately assess the
impact.
Finally objective criteria have to be developed, that are derived from
policies, with which maximum upstream abstraction levels can be
established, based on the above input data and models.
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