Agriculture Reference
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when annual abstractions exceed annual recharge (Anayari = 31 x 10 6 m 3 /a,
Atankwidi = 18 x10 6 m 3 /a and Yarigatanga = 23 x10 6 m 3 /a) then an
unsustainable groundwater condition is created.
Table 8.12 : Comparison of Water losses between WEAP results and water
balance analysis
Streamflow Losses for Scenarios Relative (Absolute) to the
Reference Scenario (10 6 m 3 /a)
S cenarios
Anayari Catchment Atankwidi Catchment Yarigatanga Catchment
WEAP
Model
Water
Balance
WEAP
Model
Water
Balance
WEAP
Model
Water
Balance
Irrigation in 2025 @
5 %/a Growth
3.89
2.86
0.17
0.02
2.60
2.72
Irrigation in 2025 @
1 0%/a Growth
12.76
9.47
0.77
0.07
7.86
8.30
Groundwater &
surface water irrigation
@ 8% and 2% respectively
6.53
5.54
6.35
4.64
5.63
5.08
Table 8.12 shows a comparison between the WEAP model results and the
water balance analysis. Water losses from the WEAP modelling results are
streamflow losses relative to the reference scenario. Water losses from the
water balance analysis are evaporation losses from surface reservoirs and
surface water irrigation fields.
The results show that the streamflow losses in the WEAP model are higher
than that of the water balance for Anayari and Atankwidi catchments and
for all their scenarios. The relatively low water losses in the water balance
analysis results from the combined surface and groundwater use of the
Riverine Alluvial Dugouts irrigation technology. In the WEAP Model this
technology abstracts water from both the streamflow and the groundwater
source with streamflow use having priority over groundwater use because the
farmers exhaust the runoff in the streams before they start digging for
groundwater. Thus the surface water use by the riverine alluvial dugouts also
results in a reduction of streamflow. However, in the simple water balance
analysis, the water source of the riverine alluvial dugouts was assumed as
groundwater only.
The impact of the assumption made for the riverine alluvial dugout is
observed in the results of the Yarigatanga catchment. In the first two
scenarios (5% and 10% growth), the water losses estimated from the water
balance are higher than that of the model. This is because, in the first two
 
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