Seminar on Research collaboration opportunities with School of Environment and Rural Science, University of New England, Australia -  14th September 2018, NRMC, Peradeniya, Sri Lanka

1. Seminar on Research collaboration opportunities with School of
Environment and Rural Science, University of New England, Australia -
14th September 2018, NRMC, Peradeniya, Sri Lanka
Cascade Tank Village System and identification of novel post graduate
research themes:
P.B. Dharmasena, 0777-613234, 0717-613234
dharmasenapb@ymail.com, dharmasenapb@gmail.com
https://independent.academia.edu/PunchiBandageDharmasena
https://www.researchgate.net/profile/Punchi_Bandage_Dharmasena/contributions
http://www.slideshare.net/DharmasenaPb

2. Rajarata University of Sri Lanka
• Established on 31st January, 1996.
• At the inception:
• Faculty of Social Sciences and Humanities,
• Faculty of Management Studies,
• Faculty of Agriculture and
• Faculty of Applied Sciences
• In 2006:
• Faculty of Medicine and Allied Sciences.

3. Faculty of Social Sciences and Humanities
Departments:
• Archaeology and Heritage Management
• Environmental Management
• Social Sciences
• Humanities
• Languages
• English Language Teaching

4. Management of Water Resources - Ancient Model, Unique to Sri Lanka
River basin level
Inter-River basin level
Intra-River basin level
Cascade level
Village level
Field
level

5. Kevesastha (Northern)
Upulwangiri
Rakungiri
Mahagiri
Chalaka
Neelagiri
Kawasthalabha
Dhumaka Kaddeera
Indra
Agni

6. Kevesastha (Northern)
Upulwangiri (Kala Oya)
Rakungiri (Malwathu Oya)
Mahagiri (Samanala mountain
area) – Kelani, Kalu, Walawe,
Mahaweli
Chalaka (Mi Oya)
Neelagiri (Modaragam Aru) Kawasthalabha (Yan oya)
Dhumaka Kaddeera (Deduru Oya)
Indra (Maduru Oya, Mundeni
Aru, Gal oya)
Agni (Kumbukkan Oya, Menik
Ganga, Kirindi Oya

7. Kala Oya
Deduru Oya
Yan Oya
Malwathu Oya
Kelani Ganga
Gin Ganga
Kalu Ganga
Walawe Ganga
Mahaweli Ganga
River basins: 103 (16 major rivers)
Major reservoirs and dams: 80
Minor tanks: 14,204 (1,262 cascades)
Minor anicuts 12,942
Annual average rainfall: 2,000 mm
Total land area: 65,610 km2
Total volume: 131.22 billion m³
Lost to sea: 66.18 billion m³ (>50%)

8. River basins – Water losses to Sea
River Basin Total Basin
Area (km2)
River
lengths
(km)
Total Rainfall
(million m3)
Drainage to Sea
(million m3) %
Deduru Oya 2,616 142 4,794 1,608 34.0
Kala Oya 2,772 148 4,424 587 13.0
Malwathu Oya 3,246 164 4,592 568 12.0
Yan Oya 1,520 142 2,269 300 19.0
Kelani Ganga 2,278 145 8,692 5,474 62.0
Gin Ganga 922 113 3039 1903 62.0
Kalu Ganga 2,688 129 10,122 7,862 77.0
Walawe Ganga 2,442 138 9,843 2,165 22.0
Mahaweli Ganga 10,327 335 26,804 11,016 41.0

9. River Basin Total Basin
Area (km2)
River
lengths
(km)
Total Rainfall
(million m3)
Drainage to Sea
(million m3) %
Malwathu Oya 3,246 164 4,592 568 12.0
5 major reservoirs
1,731 rural tanks
189 tank cascade systems
Source: Dept. of Agrarian Development

10. River Basin Total Basin
Area (km2)
River
lengths
(km)
Total Rainfall
(million m3)
Drainage to Sea
(million m3) %
Kala Oya 2,772 148 4,424 587 13.0
Source: Dept. of Agrarian Development
3 major reservoirs
1,015 rural tanks
85 tank cascade systems

11. River Basin Total Basin
Area (km2)
River
lengths (km)
Total Rainfall
(million m3)
Drainage to Sea
(million m3) %
Kelani Ganga 2,278 145 8,692 5,474 62.0
Source: Dept. of Agrarian Development
No major reservoirs
9 rural tanks
No tank cascade systems

12. River Basin Total Basin
Area (km2)
River
lengths (km)
Total Rainfall
(million m3)
Drainage to Sea
(million m3) %
Kalu Ganga 2,688 129 10,122 7,862 77.0
Source: Dept. of Agrarian Development
No major reservoirs
3 rural tanks
No tank cascade systems

13. Inter-river basin water resources sharing
model
• Dambulu Oya -
Malwathu Oya
diversion canal (860
AD)
• Malwathu Oya -
Kanadara Oya
diversion canal (860
AD)
• Yoda Ela -
Nachchduwa feeder
canal (540 AD)
Mahakanadarawa
Nachchaduwa
Kalawewa-Balaluwewa
Dambulu oya
Malwathu oya
Kanadara oya
Kala Oya
Kala Oya
Malwathu Oya

14. • Kalawewa - Thisawewa
Yodha Ela (470 AD)
• Nachchaduwa -
Nuwarawewa feeder canal
(290 AD)
• Balaluwewa -
Siyambalangamuwa feeder
canal (290 AD)
• Basawakkulama - Maha
Vilachchiya feeder canal
(470 AD)
Kalawewa-Balaluwewa
Thisawewa
Siyambalangamuwa
Nachchaduwa
Nuwarawewa
Mahavilachchiya
Basawakkulama
Malwathu oya
Thalawa oya
Kala oya
Intra-river basin water resources
sharing model
Kala Oya
Malwathu Oya

15. Cascade Level Model

16. The cascade retains water
within the river basin:
• Irrigation,
• Minimize flood damage
• Mitigate drought impact
• Protect ecosystems
through enhanced
groundwater
Network of tanks and streams in the form of cascades – Anuradhapura District

17. Nachchaduwa
Kanadarawewa
Vilachchiya
Kalawewa and
Balaluwewa
Huruluwewa
Network of tanks and streams in the form of cascades
– Anuradhapura District
Anuradhapura District:
• 6 major reservoirs
• 457 tank cascades
• 3,000 rural tanks
Malwathu Oya river
Kala Oya river
Yan Oya river

18. Tank clusters or cascades
Source: Kadupitiya, 2018

19. Tank clusters or cascades
Source: Kadupitiya, 2018

20. Distribution of tank
cascades in Sri Lanka
Source: Dept. of Agrarian Development
Main factors:
1. Morphology (landscape)
• Lower elevation,
• Moderate undulation
2. Rainfall
• Bimodality
• 800 - 2000 mm/ year
3. Soil and geology
• Wanni and Vijayan complexes
• Regolith aquifers
• Low infiltration
• RBE – LHG and
some on RYP and IBL

21. Landscape of aTank –Village System
Village level model

22. Godawala
Perahana
Gasgommana
Iswetiya
Tank water – no pollution, no sedimentation: safe drinking water, good storage

23. Landa
Thisbambe
Gangoda Kattakaduwa
Kiul-ela
Paddy field - no salinity, good fertility: High productivity

24. Field level water management model
• Integrated water management
approach
• Groundwater on poorly drained
soil phase
• Maximum use of seasonal
rainfall
• Irrigation water:
• Minimum use in major (maha)
season saving tank water for minor
(yala) season
Spill water
Shallow water
Deep water
Dead storage

25. Field level water management model
• Water issue through keta horowwa or bisokotuwa

26. Field level water management model
• Water distribution through karahana

27. Water management under stressed conditions
• Very limited water in the tank: ‘Bethma’ practice
• It is a practice that temporarily redistributes plots of land among
shareholders (paddy landowners) in part of the command area (territory) of a
tank (reservoir)
• Expecting the risk of flood: ‘Pangu’ method – regular
maintenance to avoid disasters
• The tank had to be maintained properly to avoid breach, leak, and excess
seepage. Repair and desiltation of tanks and cleaning of canals during dry
periods are shared tasks assigned to each farmer proportionately to land
ownership.
• If rainfall is expected low during major season:‘Kekulama’
• Farmers advance the cultivation time using early seasonal rains whenever
they feel that tanks would not get enough water to cultivate the command
area. They have the experience that if September (2nd inter-monsoonal)
rains are high, the total seasonal rainfall is not adequate to fill the tank.
• No water in the tank – extremely dry: ‘Thawulu Govithena’
• Tank bed cultivation using little rains constructing a main soil bund between
deep phase and shallow phase of the tank bed