Water for a food-secure world

A positive effect of hydropower development on water availability for irrigation. The case of

the Nam Ngum River in the Lower Mekong Basin

Somphasith Douangsavanh, IWMI-SEA Guillaume Lacombe, IWMI-SEAJustin Baker, RTI InternationalChu Thai Hoanh, IWMI-SEAChanseng Phongpachith, MoNRE

The Mekong Forum on Water, Food and Energy Hanoi, Vietnam, November 13-14, 2012

Water for a food-secure worldWater for a food-secure world

Introduction

• Population growth and economic development in SEA induces increase in food & energy demand

• Several studies have focused only on negative impacts of hydropower dams

• In contrast, hydropower development could compliment irrigation development

Water for a food-secure worldWater for a food-secure world

Study Area

Nam Ngum Basin: one of the most important in Lao PDR (flow, population, food production & irrigation)

Upstream: hydropower dev

Downstream: irrigation dev in Vientiane Plain

Water for a food-secure worldWater for a food-secure world

Research Question

• What are the effects of existing and proposed hydropower development on water availability for irrigation in the Nam Ngum Basin

Water for a food-secure worldWater for a food-secure world

Methodology

• Assessed current and potential irrigation water demand from satellite images, cropping calendar & simple crop water balance

• Analysed flow data recorded over 1962-2009 in combination with an optimized reservoir system model

Water for a food-secure worldWater for a food-secure world

Methodology cont

Assessed irrigation water demand (WD)

where

Water for a food-secure worldWater for a food-secure world

Methodology cont

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Time periods:NN1 stages:

Hydrological years:

4 TURBINES1 DIVERSION 2 DIVERSIONS

5 TURBINESTP2

NO WATER DIVERSION

TP1NO DAM 2 TURBINES

Nam Song diversion

Na LuangTha Ngon

Pak KanhoungThalat

HinheupNN1 spillwayNN1 Turbine

Nam Leuk diversion

Analyzed flow data recorded since 1962-2008

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Structure and functioning of the model

Each dam represented by a water balance equation:

Δvolume = Σ inflow – Σ outflow

Power = Turbine flow × Diff water level × Constant

Water for a food-secure worldWater for a food-secure world

Results Seasonal variability flow at Tha Ngon gauging. (a) no dams_1962-1971; (b) existing dams; (c) full hydropower dev_2030

a b

c

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Results cont Water availability and water supply at the Tha Ngon gauging station in the Vientian Plain

WD2

203m3.s-1

227m3.s-1 155m3.s-1

WD3L

WD3H

a b

c

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Conclusions

• Water demand WD1 would not respect the environment flow requirement in the dry years if no dams existed in the Nam Ngum Basin

• Dry season flow is expected to increase by >200% and wet season, to decrease by 20%

• Full hydropower development could allow current irrigation water demand to triple ( 20,824ha-56,376ha)

Water for a food-secure worldWater for a food-secure world

Thank you