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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
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
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
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)
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
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
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)
Reservoirs with irrigation and
assessment scales
                                 Catchment
                                 scale with
                                 seven
                                 reservoirs

                                 Case study
                                 reservoir for
                                 more detailed
                                 assessment
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
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%
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
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
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
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

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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