Mekong Forum on Water, Food and Energy. 2012. Presentation from Session 2: The Values of Multiple Uses

1. GEOGRAPHIC AND SEASONAL DISTRIBUTION
OF WATER AVAILABILITY IN THE SESAN
CENTRAL HIGHLANDS
Tarek Ketelsen, Mai Ky Vinh, Jorma Koponen
MK2: Valuing Multiple uses of reservoir waters: WorldFish – ICEM –IFPRI – CIEM – DLOF - CEPA

2. Sesan Vietnam: land use
2005-2009
• forested areas rapidly converted
into agricultural land with the
expansion of industrial crops
– cassava, rubber and coffee
• cashew, rubber, cassava and
black pepper are the fastest
growing crops (growth of 8-12%
p.a.)
• Irrigated rice growing at 3.9%p.a.
• Rainfed rice & maize shrinking at
5-7% p.a.

3. Sesan Vietnam: catchment characteristics
• 3S catchments are highly
productive catchments
• 10% of the total Mekong
Basin area but contribute
20.5% of the total flow
• Strong monsoon climate =>
water availability is a
question of timing rather
than quantity
• Sesan catcment:18,684km2
• Sesan Mean annual
outflow: 651m3/s (20.5
billion m3/yr)

4. Purpose of the water balance
Assess:
• Surface water resource availability in the
Sesan Vietnam
• Contribution of reservoirs (Yali) to surface
water availability
• Identify which areas of agricultural land could
benefit from reservoir irrigation

5. Modelling methodology
• VMod model (Koponen et al, 2010)
• area-based distribution of hydro-
meteorological impacts of climate change
• Computes water balance for grid cells
(5x5km)
• Baseline:1981 – 2005
• Can predict changes in:
– Rainfall
– Runoff
– Flows
– Infiltration
– evapotranspiration

6. water balance components
• Moisture budget
– Surface water
availability
– Relationship between
Precipitation precipitation and PET
• Soil water availability
Transpiration
– Moisture stored in the
surface and subsurface
Evaporation
layers
Surface run-off
Surface layer water availability
Subsurface layer water availability
Infiltration
Groundwater availability

7. Sesan Vietnam: Rainfall

8. Sesan Vietnam: moisture budgets
precip. - PET

9. Sesan Vietnam: Water availability

10. Sesan Vietnam: Soil moisture availability

11. Sesan Vietnam: “Agricultural drought”
Precipitation < 0.5* PET
• Districts surrounding Sesan
hydropower are ‘hotspots’ for
agricultural drought during the
dry and transition seasons
– Sathay
– Ia Grai
– Kon Tum
– Chu Pah
• Agricultural land in these areas
could benefit from reservoir
irrigation to:
– Expand agriculture into new areas
– Reduce rising demand for
groundwater irrigation in the
Sesan

12. Catchment water availability
• Northern mountainous districts
in Kon Tum are wettest (e.g. Dak
Glei)
• Southern districts in Gia Lai are
driest (e.g. Chu Se)
• Central districts of Sesan
Vietnam are more prone to
water stress or extreme dry
periods

13. Reservoir contribution to water
availability
• Reservoirs regulate the
seasonal availability of
water increasing
productivity for electricity
generation
• Can they also improve
agricultural productivity?
• Which contribution is more
valuable?

14. Yali Buffer zone
• Within 2km of the
reservoir
• Sa Thay, Kon Tum and
Chu Pah districts

15. Yali buffer zone

16. Yali: inflow hydrology
• Contributing catchment:
3,878km2
• Mean annual flow:
262m3/s (40-950m3/s)
• Annual inflow volume:
47,327 – 175,434 m3
(average: 98,724m3)

17. Yali reservoir storage
• Drawdown :25m (515-490masl)
• Drawdown area: 30.2km2
• FSL Vol: 981.5mcm
• LSL Vol: 215.5mcm
• Live storage: 766mcm
• Evaporation losses: ~50mcm/yr
• => ~700mcm of ”productive water”
Source: (Räsänen et al, 2012

18. Reservoir water productivity
• ~700 mcm of productive water
• => 3,600-3,800GWh
• => USD ?
• How much water could be used in surrounding agricultural
land?
• How productive would this water be compared to hydro-
electric generation?
Source: (Räsänen et al, 2012

19. Thank you!