Agriculture Reference
In-Depth Information
A measure of the water use efficiency can be defined as the overall irrigation
efficiency of the irrigation scheme. The overall irrigation efficiency is the
ratio between net irrigation requirement and the water released from the
headwork (ICOUR, 2009).
Net
Re
Irrigation
Re
quirement
Overall
Irrigation
Efficiency
=
Water
leased
from
the
headworks
(Equation 4.1)
Records obtained from ICOUR on water use, irrigated crops and their
corresponding areas were used together with crop water requirements to
compute the irrigation efficiencies. The net irrigation water requirement was
computed using CROPWAT (see Appendix A for CROPWAT input data).
The water released from the headworks is supposedly based on the irrigated
area but in actual fact this has not always been the case. This is because the
irrigation system has several malfunctioning water control systems which
make it impossible to effectively control the release of water for irrigation.
In Vea the irrigation efficiency was based on dry season irrigation. Also in
Tono where both dry and wet season irrigation are practiced the irrigation
efficiency was based on dry season irrigation. The reason was that, during
the rainy season, rainfall is the major source of water.
Figure 4.11: a) Irrigation efficiency for dry season irrigation; b) Water
productivity for dry season irrigation
Figure 4.11a shows low irrigation efficiencies at both schemes: Vea has an
average of 24% irrigation efficiency and Tono 30%. The ongoing
rehabilitation of the canals and laterals at Tono is expected to improve its
irrigation efficiency significantly.
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