Agriculture Reference
In-Depth Information
Table 8.11
Total Evaporation from surface (E
SI
) and groundwater irrigation
(E
GI
) and Evaporation from reservoirs (E
R
)
Water Losses due to Evaporation from Surface water and Groundwater
Irrigation Fields and surface reservoirs (x10
6
m
3
/a)
Anayari Catchment
Atankwidi Catchment
Yarigatanga Catchment
Scenarios
Ground
Water
E
GI
Surface
Reservoir
E
R
Surface
Water
E
SI
Ground
Water
E
GI
Surface
Reservoir
E
R
Surface
Water
E
SI
Ground
Water
E
GI
Surface
Reservoir
E
R
Surface
Water E
SI
Reference
1.18
7.99
0.86
0.01
1.74
0.09
1.71
0.05
2.28
Irrigation in
2025 @ 5%/a
Growth
3.13
21.19
1.77
0.03
4.61
0.09
4.35
0.14
2.35
Irrigation in
2025 @ 10%/a
Growth
7.94
49.60
3.57
0.07
11.69
0.10
9.92
0.35
2.35
Groundwater
& surface
water
irrigation @
8% and 2%
respectively,
5.10
29.60
2.48
2.99
17.23
1.75
6.84
23.06
2.08
Evaporation losses from surface reservoirs and water abstracted from surface
reservoirs directly reduce surface water runoff for downstream water uses.
Groundwater abstractions directly affect streamflow in the catchment in the
situation where groundwater contributes to streamflow. However, the study
of Martin (2006) concluded that, baseflow in the study area is negligible.
This would imply that groundwater abstractions for irrigation do not impact
directly on the streamflow in the catchment. Meanwhile groundwater from
the aquifer is discharged at unidentified locations within the basin which
contributes to streamflow downstream. Therefore, groundwater abstractions
for irrigation do reduce groundwater discharge from the aquifer thereby
reducing streamflow downstream. However, the groundwater discharge
contributing to streamflow downstream of the catchment is currently
unknown.
Water abstracted from groundwater for irrigation results in a reduction of
groundwater storage which is replenished during the rainy season with
groundwater recharge. The groundwater recharge does not depend on the
abstraction but on the aquifer, catchment characteristics and rainfall. In
situations where annual abstractions exceed annual groundwater recharge,
the natural annual groundwater recharge does not automatically increase to
replenish the depleted groundwater resource. Therefore it is expected that
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