Trading Off Hydropower Potential for Irrigated Agriculture-An Example from the Sesan River
1. Trading off hydropower potential for
irrigated agriculture – an example
from the Sesan river
Timo A. Räsänen, Olivier Joffre, Paradis Someth
and Matti Kummu
Aalto University, Finland
ICEM, Vietnam
ITC, Cambodia
timo.rasanen@aalto.fi
www.wdrg.fi
2. Background
• Sesan River
• Hydropower development
• 6 existing and 5 planned large hydropower
projects
• Agriculture and crops
• Cultivation of cash crops is increasing: Rubber,
Coffee, Cassava, Cashew, Soya
• Irrigated rice: 28,500 ha in Kontum and Gia Lai
and 4,350 ha in Ratanakiri
• In Cambodia rice is largely rainfed
• Food security
• Cambodia and Vietnam are hot spots for food
insecurity (UN ESCAP, 2009; FAO, 2012)
• Food demand is estimated to double by 2050 in
the region (FAO 2010)
• Climate variability has increased -> Challenges
for food production
• Multipurpose reservoirs could potentially
contribute to increased agricultural production
3. Aims, focus & approach
Aim: To assess the impacts of A) irrigation water abstraction
from reservoir on hydropower generation and B)
hydrological impacts of irrigation and hydropower
Focus: On 7 existing and 4 planned hydropower reservoirs
Approach: A) Detailed assessment with case study reservoir
and B) assessment of catchment scale irrigation
development
4. Assessment methodology
• Hydrological modelling (VMod)
• Hydropower modelling (CSUDP)
• Assessment of land use suitability for irrigated rice (LUSET)
• Assessment of crop water requirement (FAO CROPWAT 8.0)
• Assessment of irrigation potential of each reservoir
• Modelling of the trade off’s (CSUDP)
5. Assessment of land use suitability
for irrigated rice
• Land suitability was
estimated for 5 km
distance from the Sesan
River
• Results:
• Three land suitablity
classes
• Altogether 86,000 ha
indentified as potentially
suitable Highly suitable
Moderately suitable
• Assessment is on coarse Marginally suitable
scale and includes areas
already under cultivation
6. Assessment of crop water requirement
• Crop water requirement was
defined using for Weekly irrigation schedule
2500
• Dry season rice, 105 days Cambodia
• Wet season rice, 125 days 2000
Vietnam
• Average dry season irrigation
[m3/ha]
1500
volumes
• Cambodia: 13,200 m3/ha 1000
• Vietnam: 12,000 m3/ha
• Average wet season irrigation 500
volumes 0
• Cambodia: 2,700 m3/ha 1 5 9 13 17 21 25 29 33 37 41 45 49
[week]
• Vietnam: 2,200 m3/ha
7. Irrigation potential and scenarios
• Irrigation potential of each reservoir was based on
• Land suitability
• Crop water requirement
• Specific dry season water allocations: 3%, 5% and 7% of dry season water budget
• Seven reservoirs were selected for further assessment
• Three irrigation scenarios for Sesan 3A
• B2. 3,894 ha dry and wet season rice
• B3. 6,490 ha dry and wet season rice
• B4. 9,086 ha dry and wet season rice
• One catchment scale irrigation scenario for seven reservoirs
• 28,348 ha dry and wet season rice (rate of irrigation corresponds to B3)
8. Reservoirs with irrigation and
assessment scales
Catchment
scale with
seven
reservoirs
Case study
reservoir for
more detailed
assessment
9. Case study reservoir with high
irrigation potential
• Sesan 3A with high
downstream irrigation
potential
• An example where irrigation
from reservoir could have
been implemented
• Dowstream area has already
large irrigation projects
• Sesan 3A reservoir storage is
small, requires co-operation
with upstream dams Sesan 3
and Yali
10. Case study: Yali-Sesan 3-Sesan 3A cascade
• Simulated annual average
hydropwer generation of
Sesan 3A
• 425-428 GWh
• Reduction in annual
hydropower generation:
• 3,894 ha: -0.6…-0.7%
• 6,490 ha: -1…-1.2%
• 9,086 ha: -1.4…-1.7%
• Reduction in dry season
hydropower generation
• -1.8…-5.6%
11. Catchment scale irrigation scenario for seven
reservoirs: Hydropower
• Catchment scale reduction in annual hydropower generation
• 28,348 ha: -1.6 % (209 GWh)
• Most significant impacts were experienced in Lower Sesan 3
• -3.4% (56 Gwh) reduction in annual hydropower generation
Baseline annual Irrigated area Change in annual Baseline dry season Change in dry season
average hydropower average hydropower average hydropower average hydropower
generation generation generation generation
[GWh] [ha] [%] [GWh] [%]
Upper Kontum 1,057 600 -1.9 398 -4.1
Plei Krong 497 2,817 -1.4 149 -3.7
Yali 3,850 0 -0.6 1,333 -1.6
Sesan 3 1,228 0 -0.6 405 -1.6
Sesan 3A 454 6,490 -1.7 148 -5
Sesan 4 1,478 3,474 -2 449 -6.1
Sesan 4 A - 5,091 - - -
Sesan 1 641 0 -3.2 271 -7.5
Lower Sesan 3 1,634 7,843 -3.4 636 -8.6
Lower Sesan 2 2,218 2,033 -1.3 638 -4.3
TOTAL 13,056 28,348 -1.6 4,427 -4.2
12. Catchment scale irrigation scenario for seven
reservoirs: Hydrology
• The hydropower operations increased dry season flows and reduced wet
season flows
• Lower Sesan 3: dry season +167%, wet season -11%
• Irrigation of 28, 348 ha reduced the annual river flow by 0.39 km3 which
corresponds to 1.9% of the Sesan’s annual average flow
1800
Lower Sesan 3
1600
1400
1200
1000
[m3/s]
800
600
400
200
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
13. Catchment scale irrigation
scenario for seven
reservoirs: Land cover
• Hydropower reservoirs inundate land
• Existing reservoirs 198 km2
• Planned reservoirs 837 km2
• Lower Sesan 3 will inundate 45 000 ha of land
defined in this study as potentially suitable for
irrigated rice
• Expansion of agriculture has already caused
deforestation in Sesan catchment
• e.g. in Ratanakiri 40% reduction in forest cover
between 1997-2005
• Irrigation development from Sesan 4, Lower Sesan
3 and Lower Sesan 2 reservoirs have high
likelihood of causing further deforestation
14. Conclusions and final remarks
• Main finding: Irrigation from reservoirs contributed
to minor losses in hydropower generation
• Sesan 3A: 7.3 GWh (1.2%) were traded to 9,100 ha of
irrigated rice
• Catchment scale: 208.9 Gwh (1.6%) were traded to 28,400
ha of irrigated rice
• Impacts of hydropower on river flow were more
significant compared to irrigation and impacts were
cumulative downstream
• Co-ordination between hydropower projects may be
required for successful irrigation
• This study focused only on technical and
hydrological aspects
• Social, livelihood and political issues have a major role in
sustainable development
• Findings of this study prompt further investigations
on multi-purpose reservoirs