Revival of village tanks in Sri Lanka

Revival of Village Tanks
P.B. Dharmasena
0777 - 613234, 0717 - 613234
dharmasenapb@ymail.com, dharmasenapb@gmail.com
Links to publications:
https://independent.academia.edu/PunchiBandageDharmasena
https://www.researchgate.net/profile/Punchi_Bandage_Dharmasena/contributions
http://www.slideshare.net/DharmasenaPb
https://www.youtube.com/channel/UC_PFqwl0OqsrxH1wTm_jZeg
Lecture delivered to Engineers and Engineering
Assistants on 2nd August 2021 held at Kurunegala,
organized by the Department of Agrarian Development

Covid – 19 Pandemic Situation
• Up to 1st August 2021:
• Cases: 198,964,808
• Deaths: 4,239,512
• Recovered: 179,588,198 (90%)
Country % recovered
USA 83.0
UK 76.9
Russia 89.5
India 97.3
Sri Lanka 89.6
Bhutan 94.7
Nepal 94.1
Food habits
Environment
• Reasons for the death of Covid-19 victims
• Low immunity
• High blood pressure
• Diabetics
• Heart diseases
• Respiratory diseases
First of all we must be healthy

Human health can be ensured by improving the ecosystem health
Risk reduction impact

Ancient Water Management Master Plan of Sri Lanka
Country level
Inter-river basin level
Inter-reservoir level
Sub-watershed level
Village level
Field level

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,
Maha Oya)
Indra (Maduru Oya, Mundeni
Aru, Gal oya)
Agni (Kumbukkan Oya,
Menik Ganga, Kirindi Oya
Decentralized Governance
Leadership

Water resources shared by River Basin Leaders
(600 BC – 1200 AD)
• 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
Inter-river basin level

Manewa cascade
Mahakanumulla cascade
• Single bank canal
• It runs along contour
• Water is collected from upstream
• Water is released to both sides
• Canal moves along tank upstream
• Tank cascade systems are fed
• Diyakaliya and wewa to ensure water
security
Kalawewa-Thisawewa Giant Canal

Left bank
Sedimentation
Diyakaliya
Natural rock
Soil mound
Mahailluppallama
Amunukole
Diyakaliya
Source: Dr. Ashoka Karunaratne, 2021

Upper land and Lower land sluice
gates of Yodha Ela
Position of Upper land Sluice gates
Position of lower land Sluice gates
B
A
Aluth wewa
Amunukole wewa
Koon wewa
Wewa

Diyakaliya Wewa
1 Placed above the canal Placed below the canal
2 Canal has been connected
to the diyakaliya
Constructed the canal running
above the wewa
3 Diyakaliya has been
connected to a natural rock
line or soil ridge
Bund of the wewa has been raised
to a higher contour
4 Issue of water through a
natural process
Release of water to wewa is
through sluice placed on the left
bank of Yodha Ela canal
5 Controlling the Sediment Controlling the sediment and
providing water to paddy tract
6 Providing water to upland
cultivation
Combined with human settlement
and cascade systems

April – May 2010
“Inconvenient Truth” behind
Engineering Designs of
Irrigation Projects developed
during the Last Century.
“……….Those days we thought
that the canal was planned to
avoid rock barriers as the ancient
people did not own the
technology to break them
……..”
- Eng. Mahinda Panapitiya

– 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
Water resources shared by Reservoir Leaders
(600 BC – 1200 AD)

Tank Cascade System (Village) – Collective
Leadership (Self governing system)
රාල leadership
• ගමරාල - Village leader
• කපුරාල - Leader for rituals
• දනුමැතිරාල - The most knowledgeable person in the village
• වෙදරාල - Medical practitioner
• නැකැත්රාල - Providing auspicious times
• (සිෙුරාල) - Religious knowledge

Kalawewa - Balaluwewa
Minneriya
Parakrama Samudraya
Maduruoya
Udawalawe
Kantale
All ancient reservoirs are found below 150 masl contour
Senanayake Samudraya
Huruluwewa
Nachchaduwa

Annual average rainfall: 2,000 mm
Land extent: 65,610 km2
Total volume of water: 131.22 bil. m3
Discharge to sea: 66.18 bil. M3 (>50%)
No. of river basins: 103
Major reservoirs and dams: 80
Small tanks: 14,421
Small anicuts: 12,773
Source: N. Eriyagama et al 2015
Shortage of water or wastage of water?

River basins – Water losses to Sea
River Basin Total Basin
Area (Km2)
Length of the
river (km)
Total Rainfall
(million M3)
Drainage to Sea
(million M3)
Percent Drainage
to Sea
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 %
Mee Oya 1,516 109 2,176 338 16.0 %

Area (km2)
River lengths
(km)
Total Rainfall
(million m3)
Drainage to Sea
(million m3) %
Kala Oya 2,772 148 4,424 587 13.0
Major reservoirs: 3
Minor tanks: 1015
Source: Dept. of Agrarian Development

River Basin Total Basin Area
(km2)
Total Rainfall
(million m3)
Drainage to Sea
(million m3) %
Yan Oya 1,520 2,269 300 19.0
Major tanks 2
Small tanks 746

River Basin Total Basin Area
(km2)
Total Rainfall
(million m3)
Drainage to Sea
(million m3) %
Mee Oya 1,516 2,176 338 16.0
Major tanks 1
Small tanks 750

Area (Km2)
Length of the
river (km)
Total Rainfall
(million M3)
Drainage to Sea
(million M3)
Percent
Drainage to Sea
Deduru Oya 2,616 142 4,794 1,608 34.0 %
Major tanks 4
Small tanks 2408

Area (Km2)
Length of the
river (km)
Total Rainfall
(million M3)
Drainage to Sea
(million M3)
Percent
Drainage to Sea
Malwathu Oya 3,246 164 4,592 568 12.0 %
Major tanks 5
Small tanks 1731

Area (km2)
River length
(km)
Total Rainfall
(million m3)
Drainage to Sea
(million m3) %
Walawe Ganga 2,442 138 9,843 2,165 22.0
Major/ medium reservoirs: 12
Minor tanks: 750

Area (Km2)
Length of the
river (km)
Total Rainfall
(million M3)
Drainage to Sea
(million M3)
Percent Drainage
to Sea
Kelani Ganga 2,278 145 8,692 5,474 62.0 %
Major tanks 0
Small tanks 9

Area (Km2)
Length of the
river (km)
Total Rainfall
(million M3)
Drainage to Sea
(million M3)
Percent
Drainage to Sea
Gin Ganga 922 113 3039 1903 62.0%
Major tanks 0
Small tanks 0

Area (Km2)
Length of the
river (km)
Total Rainfall
(million M3)
Drainage to Sea
(million M3)
Percent
Drainage to Sea
Kalu Ganga 2,688 129 10,122 7,862 77.0 %
Major tanks 0
Small tanks 3

Nachchaduwa
Kanadarawewa
Kalawewa and Balaluwewa
Huruluwewa
Network of tanks and streams in the form of cascades
Vilachchiya
There was no old term such as cascade
or ellanga. It was the whole village.
Therefore, the whole system was
managed by the village leaders

Tank clusters or cascades
Kendewa cascade
Kapiriggama cascade
Bandara Rathmale cascade
Kallanchiya tank

Nachchaduwa tank
Mahakanumulla cascade
Ulagalle cascade
Thirappane cascade

Horiwila tank
Palugaswewa cascade
Udakadawala cascade

Northern Zone
North Western Zone
South Eastern Zone
Tank cascades zones
of Sri Lanka

Searching for a Globally Important Agricultural Heritage System (GIAHS)

The first GIAHS declared in Sri Lanka by UNFAO on 19th April 2018 is the
Cascaded Tank-Village System and it is the 39th in the World.
Globally Important Agricultural Heritage System (GIAHS)

Old definition of the tank cascade system
New definition of the tank cascade system
• A „cascade‟ is a connected series of tanks organized within a micro-
catchment (meso catchment) of the dry zone landscape, storing,
conveying and utilizing water from an ephemeral rivulet‟. (Madduma
Bandara, 1985)
An ecosystem, where water and land resources are organized within the micro-
catchments of the dry zone landscape, providing basic needs to human, floral and
faunal communities through water, soil, air and vegetation with human intervention
on sustainable basis‟
– Dharmasena, 2019

Productivity Potential of Tank Cascade System
• Physical productivity potential:
• food, water, air, timber, fuel wood, medicine, raw materials for handicraft, …..
• Economic productivity potential:
• agriculture, fishery, livestock, handicraft, ………..
• Ecological productivity potential:
• habitats, biodiversity, aesthetic beauty, nutrient cycling, …………..
• Scio-cultural productivity potential:
• living environment, local knowledge, tourism, education, human health, rituals,
……………..

Therefore, I suggest it is essential to probe deeply the awakening of „Sri Lankan Water Culture‟
not only through a physical/ engineering point of view but also on the basis of a spiritual
dimension.
When we attempt to study the creations made by a human society nurtured in a spiritual environs
by using only physical and environmental principles we may understand only a fraction of it.

Tank-Village Ecosystem
Source: Dharmasena, 2010

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

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

Gasgommana
Perahana
Rootlet web
Rootlet web
Rootlet web
Terminalia arjuna

Traditional Vision of Water Management
 Integrated Water Management Approach (Rainwater, Irrigation water,
Groundwater)
Saturated soil zone
Capillary action
Water
table
fluctuation
Poorly drained soil
IWRM

Keta sorowwa – release surface water, self controlled
Traditional sluice

Diya keta pahana to measure tank water level
Traditional sluice

Karahan kote
Cuts are made in the log with different width and depth so that discharge is different. This
provides water for different extents and different soils during the same sluice opening time
Flow distribution structure

• ‘Bethma’ practice during drought periods
– 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) during drought periods
• ‘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.
• ‘Kekulama’ if the low rainfall maha is expected
– 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.
• ‘Thawulu Govithena’ during extremely dry situation
– Tank bed cultivation using little rains constructing a main soil bund
between deep phase and shallow phase of the tank bed
• ‘Goda wee hena’ due to inadequate tank storage
– Paddy and vegetables are grown on imperfectly drained soil with
available soil moisture
Water sharing and water recycling

Water sharing and water recycling
Water is recycled through
• Drainage from paddy fields (welpahuwathura)
• Tank seepage into common drainage (kiul ela)
• Lateral flow of groundwater supplying water to puranawela

Four strata of tank water body
Dead storage (Madakaluwa)
Deep tank bed (Diyagilma)
High flood area (Vaangilma)
Shallow tank bed (Thawulla)
Partial Desilting Concept

Madakaluwa
Diyagilma
Thawulla
Vaangilma
Change in tank geometry
Sediment deposited on tank bed
Partial Desilting Concept
A sedimentation study indicates that the amount of sediment deposited in minor
tanks is in the range of 20 - 35 percent, and half of the sediment is found within
one third of the tank bed area closer to the bund (Dharmasena, 1992).

0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Rainfall (m)
Cropping intensity and rainfall - Anuradhapura district (1970-2003)
Cropping intensity

0
10
20
30
40
50
60
70
80
90
100
0 0.2 0.4 0.6 0.8 1 1.2
Cropping Intensity
Probability
(%)
Probability of Cropping Intensity under minor irrigation in Anuradhapura District (1970-2003)

The expansion of water spread area and occurrence of a shallow water body
• Reduces the water use efficiency due to increased tank water losses.
• Disappearance of the tree strip (Gasgommana) and meadow
(Perahana) found along the periphery of the early water spread area.
This would enhance the water evaporation due to advection effect.
• Development of salinity in the upstream area around F.S.L especially
if the tank is second or third in the series.
• Inundation of upstream rice fields. This has caused conflict between
two village communities
• Disappearance of some of the fish species, which cannot survive in
shallow waters.

Disappearance of local fish species

Geometry of water body affects the loss
y = 59.471x-1.3351
R2
= 0.786
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
0.7 0.9 1.1 1.3 1.5
Capacity/area (m)
Percent
water
loss
A water balance study was carried out for two years in 8 small tanks

Partial desilting concept was first introduced in 1994 based on water
balance studies carried out in 8 tanks by Field Crops Research and
Development Institute, Mahailluppallama

PARTIAL DESILTING CONCEPT
Tank bund
Water
Sediment
Dead storage
Sediment

Area
(ha)
Elevation (m)
Designed curve
FSL
FSL
Sill level
DESIGN OF PARTIAL DESILTING CONCEPT

Old tank bed
New tank bed
Tank bund
Interceptor
Removed sediment
Natural streams
Catchment area
PARTIAL DESILTING CONCEPT

This Partial Desilting Concept was first tested in 2004 and then during 2013-
2015 in Kapiriggama tank cascade system
Madakaluwa
Diyagilma
Thawulla
Vaangilma

Benefits of Partial Desilting
• Cost can be minimized
• Storage capacity can be increased if needed
• Return to investment can be justified if all benefits (water, land,
environment, productivity potential) are considered
• Increased extent for cultivation
• More agriculturally productive lands
• Increased cropping intensity
• Opportunities for cottage industries
• Freshwater fishery

PARTIAL DESILTING METHODOLOGY
• Participatory Rural Appraisal is carried out to obtain farmers' views on tank
rehabilitation
• Tank bed level survey
• Tank bed sediment survey
• Partial desiltation design
• The required live and dead storage after completing the desilting process.
• The minimum requirement of sediment layer to avoid excessive percolation.
• The volume of soil required to repair the upstream side of the tank bund and
„isweti‟.
• The design is initially worked out on the area-elevation diagram and transferred
with relevant information to the tank bed contour map.
• Plans
• Design for silt removal
• A diagram showing the cross-sectional view of tank bund including the sill
level and dimensions of Kattakaduwa.
• Cross-sectional view of soil mounds and isweti.
• Plan of Kattakaduwa with improvements.
• Plan of Gasgommana area with proposed vegetation.

Revival of village tanks in Sri Lanka

Revival of village tanks in Sri Lanka

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