IWMI’s Yoshiaki Inadi takes a closer look at Sri Lanka’s water storage reservoirs, locally known as “tanks”, and the growing importance of “agro-wells” for accessing groundwater.

1. Photo:DavidBrazier/IWMIPhoto:TomvanCakenberghe/IWMIPhoto:DavidBrazier/IWMI
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A water-secure world
The Tank Cascade System
and the Contribution of
Ground water to the
Livelihoods of the Dry Zone
in Sri Lanka
Yoshiaki Inada
6th November 2013
INWEP 10th Steering meeting and
Symposium at Centara Duangtawan
Hotel in Chiang Mai, Thai Land

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Today’s presentation
1.Review the past tank cascade system and ground
water recharge studies in IWMI
2. Agro-well development due to high ground water
level
3. Multiple benefits of high ground water level derived
from irrigation project

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Rainfall, Agro ecological zone

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Climate and cultivation season
• Climate seasons
• First inter monsoon – March to April
• Southwest monsoon – May to September
• Second inter monsoon – October to November
• Northeast monsoon – December to February
• Cultivation Season
• Yala: March to September – less rain in dry zone area
• Maha: October to February – major rainy season in dry zone area

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Location of the study site and tank
distribution in dry zone

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Average Month Total Rainfall &
Evaporation

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Water Balance and Groundwater
Studies in Tank Cascade
• Tank balance model in Thirappane Cascade System (TCS)
• Itakura 1995
• Shinogi 1997
• Shanthi 2002
• Sub-watershed balance (on going) – 2013 Ministry of Water Resource
Management/Water Resource Board of Sri Lanka
• JIRCAS conducting a utilization of water balance model study in
Thirappane (on going)
• Cascade study – upper Yan Oya - Matsuno -1996

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Thirappane Cascade
Located at Anuradhapra
district in the North Central
province
6 interlinked small tanks
are situated 8 km between
top and bottom tanks
Jun Itakura’s initiated Study
in 1991

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Tank water balance in Shinogi’s study

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Cross Sectional View of Meegassagama Tank
(Shanthi’s study)

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Seepage and percolation values found
in the Studies

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Agro-well development around tank

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Uda Walawe Irrigation and Resettlement
Project

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Economic benefits on recharging
ground water(home-garden produce)
Total value of US$14.4 million/year (Molle, F; Renwick, M
2005)
13,000 ha (satellite images)
Amount(sampling survey)
Value(local market price)
Fruit value US$8 million/year
Timber value of US$6.40 million/year

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Economic benefits on recharging
ground water(domestic water supply)
• value of drinking water is estimated at US$0.14 million/
year. (Molle, F; Renwick, M 2005)
average water supply cost of 15 Rs/m3 (recent
communal water supply projects)
average current usage of 20 liter/person/day and
population estimate of 120,000 (Irrigation Department)

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Multiple benefit derived from the Uda
Walawe Project

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Thank You