The document discusses the importance of maintaining ecological balance within tank cascade systems in Sri Lanka. It begins by defining tank cascades and cascade ecology. It then explains key ecosystem principles and the various ecosystem services and functions provided by tanks cascades, including regulating services like drought/flood control; supporting services like nutrient cycling; provisioning services like food/water; and cultural services. The document emphasizes the need for restoration of tank ecosystems through participatory planning, awareness, training, and planting campaigns to sustain these services.

1. The importance of maintaining the ecological
balance within tank cascades
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
https://scholar.google.com/citations?user=pjuU1GkAAAAJ&hl=en
Short Course on Tank Rehabilitation and Cascade Development
CES, University of Peradeniya
30th May, 2022

2. The importance of maintaining the ecological balance
within tank cascades
• Tank cascade systems – Unique to Sri Lanka
• Cascade ecology – Effective not only within the cascade boundary
• Ecosystem principles
• Ecosystem services and functions - Benefits of ecosystems, regulating,
supporting, provisioning and cultural
• Regulating services - Drought, flood, cyclone, epidemics
• Supporting services - Nutrients, habitats, ecosystem sustainability
• Provisioning services - Food, fruits and vegetables, timber fuel wood
etc., materials for cottage industries, animal feed, medicine, bio-
pesticides
• Cultural services - Recreation and mental and physical health, aesthetic
appreciation, spiritual experience, agro-ecotourism
• Restoration of tank ecosystems - Participatory planning, awareness and
training, planting campaigns
CONTENT

3. Water Management Master Plan of Sri Lanka
Country level
Inter-river basin level
Inter-reservoir level
Sub-watershed
Village level
Field
level
Tank cascade level

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

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

6. • Inter-river basin water resources
sharing
• Dambulu Oya - Malwathu Oya
diversion canal (860 AD)
• Malwathu Oya - Kanadara Oya
diversion canal (860 AD)
• Yoda Ela - Nachchduwa feeder
canal (540 AD)
• Inter-reservoir water resources
sharing
– 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

7. River basins – Annual Water Losses to Sea
River Basin Basin
Area
(km2)
Length
(km)
Rainfall
(mil.m3)
Drainage to
Sea
Major
tanks
Minor
tanks
Cascades
(mil.m3) %
Deduru Oya 2,616 142 4,794 1,608 34.0 4 2,408 164
Kala Oya 2,772 148 4,424 587 13.0 3 1,015 91
Malwathu Oya 3,246 164 4,592 568 12.0 5 1,731 189
Yan Oya 1,520 142 2,269 300 19.0 2 80 746
Kelani Ganga 2,278 145 8,692 5,474 62.0 0 9 0
Gin Ganga 922 113 3039 1903 62.0 0 0 0
Kalu Ganga 2,688 129 10,122 7,862 77.0 0 3 0
Walawe Ganga 2,442 138 9,843 2,165 22.0 12 750 49
Mi Oya 1,516 109 2,176 338 16.0 1 750 47

8. How did they
locate ancient
reservoirs?
Kantale
Huruluwewa
Minneriya
Giritale
Parakrama Samudra
Maduruoya
Mapakadawewa
Udawalawe
Kalawewa &
Balaluwewa
150 m
contour
Nachchaduwa

9. Network of tanks and streams in the form of cascades
Vilachchiya
Kanadarawewa
Nachchaduwa
Huruluwewa
Kalawewa and Balaluwewa

10. Tank clusters or cascades
Source: Kadupitiya, 2018

11. Distribution of tank
cascades in Sri Lanka
North and North Central
North Western
Southern
Dharmasena, 2019

12. 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

13. Definition of the Tank Cascade
Hydrology based definition
• 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
Ecology based definition
• Tank cascade is 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, 2017

16. Cascade Ecology
• Ecology is the study of the relationships
between living organisms, including
humans, and their physical environment.
• Cascade ecology does not confine to the
cascade boundary.
• Ecological influence spreads radially.
• Studies should be extended to outside
areas of the cascade
• Influence is of multifaceted (social,
ecological, cultural)
• Cascade ecology knowledge is still like a
just born child
Ecological
nuclei
Knowledge on ecology will pave the way
to system resilience and sustainability

17. Definition of Tank Cascade Ecology
Tank Cascade Ecology is the study of the interactive
relationships between living organisms (flora and
fauna), including humans, and their physical
environment (soil, water and geo-morphology) within
the cascade boundary as well as its surrounding area
of influence.
Dharmasena. P.B., 2021
Area of influence depends on various factors such as
types of organism, human intervention, biodiversity
richness, surrounding environment etc.

18. Organization of life
Organisms
Populations
Communities
Ecosystems
Biosphere
Biosphere
Ecosystems
Communities
Populations
Organisms
Ecosystem Principles

19. Scales of Ecological organization

20. Individual, population, community and
ecosystem
A
B
C
D

21. Ecosystem Principles

22. connectivity, interaction and complexity of ecosystem
Ecosystem Principles

23. What you can learn from this picture?
1. Population
2. Genetic
diversity
3. Interaction

24. How do we take care of ecosystems?
1. Knowledge on
ecosystems
• Investigation
• Awareness
• Training

25. How do we take care of ecosystems?
1. Knowledge on
ecosystems
2. Participation in
ecosystem
activities
• Collective
efforts
• Individual
behaviour
• Participatory
ecosystem
management
programmes

26. How do we take care of ecosystems?
1. Knowledge on
ecosystems
2. Participation in
ecosystem activities
3. Management of
ecosystems
• Planning
• Implementation
• Maintenance

27. Ecosystems in Sri
Lanka

28. Ecosystems in Sri Lanka
• Forest and related
ecosystems - tropical
forest types, riverine dry
forest, grasslands etc.
• Inland wetland
ecosystems - flood
plains, swamps,
reservoirs, wet villus
• Coastal and marine
ecosystems - mangroves,
salt marshes, sand dunes
and beaches, lagoons and
estuaries, coral reefs
• Agricultural ecosystems -
paddy land, fruit
cultivations, small crop
holdings or other field
crops, vegetables, export
crop plantations, home
gardens, chena lands

29. Agro-ecosystems

30. Property Agro-
ecosystem
Natural ecosystem
Productivity High Low
Species diversity Low High
Genetic diversity within species Low High
Plant life cycles present Few Whole, more
perennial
Competition Negative Tolerable
Flowering, plant maturing synchronized seasonal
Nutrient cycles open closed
Permanence Short Long
Human control High Low
Ecological maturity Early,
immature
Mature (climax)
Comparison of natural and agro-ecosystems

31. NUTRIENT CYCLING
 Inputs:
Plant residue
Animal wastes
Animal residue
Atmosphere
Nitrogen fixation
 Outputs:
Plants animals
grazing on plants
Denitrification
Run-off
leaching
NATURAL ECOSYSTEM
AGROECOSYSTEM
 Using the soil as a
pool of nutrients:
 Inputs:
Fertilizers
Crop residues
Atmosphere
Nitrogen fixation
 Outputs:
Crops  then
removal from
area
Erosion
Leaching
 Run-off
Nutrients cycling

32. Special Features of Agro-ecosystem
• Productivity - the quantity of food, fuel or fiber that
an agro-ecosystem produces for human use.
• Stability - consistency of production.
• Sustainability - maintaining a specified level of
production over the long term.
• Equity - sharing agricultural production fairly.
• Independence – agro-ecosystem self-sufficiency.

33. Tank-based agro-ecosystems
Components

34. Water
Rain
water
Surface
water
Ground
water
Drinking and
domestic water
Rain-fed
farming
Agro-well
farming
Tank irrigated
farming
Fishery
Homestead
farming
Livestock
Tank-based agro-ecosystems
Interaction

35. Tank-based agro-ecosystems
Co-existence

36. Godaw
ala
Perahana
Gasgommana
Iswetiya
Tank water resource – no pollution, no sedimentation: safe drinking
water, good storage
Tank-based agro-ecosystems
Soil and water
resources,
recycling

37. Landa
Thisbambe
Gangoda
Kattakaduwa
Kiul-ela
Paddy field soil resource - no salinity, good fertility: High productivity
Tank-based agro-ecosystems
Soil and water
resources,
recycling

38. • Natural components –
forest, shrub lands, natural
streams, habitats
• Human influence – tanks,
paddy fields, hamlets,
religious places
• Management – sharing
water, sharing lands,
conjunctive water use
• Sustainability – regulatory
measures, farming under
water stress, balance
between rain-fed and
irrigated farming
Tank cascade - based agro-ecosystems
Natural components, human influence, management, sustainability

39. Ecosystem Functions/Services
• Ecosystem Functions/Services are
the conditions and processes
through which natural ecosystems
and the species that make them up,
sustain and fulfill human life.
• Biophysical necessities for human
life provided by natural ecosystems
• Functions provide goods and
services
• Currently threatened by most
human activities
• Important (but new) conservation
tool

40. • Cover a wide range of
processes and scales
– Global scale
• Carbon sequestration
• Global warming
– Landscape scale
• Water purification
• Erosion prevention
– Community scale
• Crop pollination
• Pest control
– Field, plot or individual
person scale
• Local nutrient levels
• Disease and pest prevention

41. • The combined activity of soil
organisms results in ecosystem
functions that sustain life on the
planet. Ecosystem functions
that generate benefits to society
have been defined as ecosystem
services. The centrality of
belowground biodiversity to
global sustainability is because
soil organisms of different
types, shapes and colours are
responsible for different
ecological functions…
• Complex
• Dynamic
• Interact
• Multiple within an ecosystem

42. 1. Supporting
• Habitat
• Biodiversity
• Photosynthesis
• Soil formation
2. Provisioning
• Food
• Clean water
• Fish
• Wood
• Pollination
• Cool temperature
3. Regulating
• Control flooding
• Purify water
• Store carbon
• Clean air
4. Cultural
• Education
• Recreation
• Aesthetic
• Stewardship

44. Distinguish: ecosystem services and
functions
• The terms ‘functions’
and ‘services’ can be
confusing.
• Usually, functions are
considered as the
biological processes
underpinning and
maintaining the
ecosystem, while
ecosystem services are
defined as the direct and
indirect contributions of
an ecosystem to human
well-being

45. Three steps to study an ecosystem
• Step 1:
Classification of
Services
• Step 2:
Identification of
species and
processes
• Step 3: Valuation
of services using
economic
evaluation

46. Step 1: Classification of Services
Different approaches
A) Approach - 1
– Supporting
– Provisioning
– Regulating
– Cultural
B) Approach - 2
– Regulation functions
– Habitat functions
– Production functions
– Information functions
C) Approach - 3
– Provision of production inputs
(inputs from environment)
– Sustaining plant and animal life
(life support services)
– Provision of existence value
(Amenity services)
– Provision of option value (future
services)

47. Approach – 1
1. Supporting
– Nutrient cycling
– Soil formation
– Primary production
2. Provisioning
– Food
– Wood
– Fresh water
– Fuel
3. Regulating
• Climate regulation
• Flood prevention
• Disease prevention
• Water purification
4. Cultural
• Aesthetic
• Spiritual
• Recreational
• Educational

48. Approach – 2
Regulation functions, Habitat functions, Production
functions, Information functions
1. Regulation functions – Maintenance of essential ecological
processes and life support systems.
– gas regulation (UVB regulation, climate, air quality)
– climate regulation (maintaining favorable climate)
– disturbance prevention (Storm prevention, flood prevention)
– water regulation (drainage, natural irrigation)
– water supply (provision of water for consumptive use)
– soil retention (maintenance of arable land)
– soil formation (maintenance of productivity)
– nutrient regulation (maintenance of healthy soils)
– waste treatment (pollution control – detox)
– Pollination (pollination of crops)
– biological control (control of pests and diseases

49. 2. Habitat functions
– Refugium function (maintaining harvested species)
– Nursery function
3. Production services
– food – conversion of solar energy into edible plants and
animals, food and energy
– raw materials
– genetic resources (drugs and pharmaceuticals)
– medicinal resources (drugs and pharmaceuticals – and others)
– Ornamental resources (resources for fashion, etc)
4. Information functions
– Aesthetic value (enjoyment of scenery)
– Recreation (travel to natural ecosystems)
– Cultural and artistic information (use of nature as a motive)
– Spiritual and historic information (use for religious purpose)
– Science and education (use for schools)

50. Step 2: Identification
• Identify what species and
processes are required to
perform each service
– Depends on the ecosystem
– Scale issues
– Separability
Step 3: Valuation
• Value the importance of those services using economic evaluation
• E.g. the value of carbon sequestration
• Different methods for different services

51. Landscape of aVillage –Tank System

53. Drought –
water storage,
reduced
seepage and
evaporation,
clean water
Flood –
rainwater
absorption,
excess water
drainage, flow
regulatory
mechanism
Cyclone –
gasgommana,
kattakaduwa,
tis-bambe,
forest
Epidemics –
malaria, water
purification,
waste
recycling
Regulating services

54. Nutrients –
tis-bambe,
gan-goda
landa, mee
tree
Habitats–
kattakaduwa,
gasgommana
perahana, wew
thawula
Supporting services

55. Cottage
industry –
materials
from
kattakaduwa
Consumables –
food, fruits,
vegetable from
kattakaduwa,
gasgommana and
wewa
Materials – timber,
fuel wood, farm
implement,
household
implement
Others –
medicine, bio-
pesticides,
animal feed
Provisioning services

56. Recreation and
mental and physical
health - Agricultural
landscapes
recreational
opportunities
Aesthetic
appreciation and
inspiration for
culture, art and
design
Spiritual experience
and sense of place -
Natural heritage,
spiritual sense of
belonging, traditional
knowledge, and
associated customs.
Tourism -Farm
tourism allowing
urbanites to
reconnect with
nature.
Cultural services

57. Participatory planning
• Field visits to identify tank ecosystem
components
• Discussion with village champions
(experienced adults who have special
skills)
• Social mapping with selected active
villagers
• SWOT analysis (Strength,
Weaknesses, Opportunities and
Threats)
• Assessment of restoration needs
• Participatory tank restoration planning
• Identification of risks and assumptions
• Identification of training needs
Restoration of tank ecosystems

58. Awareness and training
Restoration of tank ecosystems
• Field visits to tank cascade systems
• Awareness on the importance of
tank cascade systems and
ecosystems
• Field identification of regulating
services
• Field identification of supporting
services
• Field identification of provisioning
services
• Field identification of cultural
services
• Training on tank ecosystem
restoration

59. Planting campaigns
• Planning planting
programmes
• Identification of list
of plant species
• Collection of plants
from available
agencies
• Establishment of
village nurseries
• Awareness for school
children
• Conducting planting
campaigns
Restoration of tank ecosystems

60. Contemporary risks to cascades and probable impacts
• Land use changes - Increasing demand for land, encroachment,
destruction of ecosystems, mismanagement of land resource
• Soil erosion and sedimentation - Soil erosion from tank catchments,
sediment flow into tanks, tank capacity reduction, change in tank
geometry
• Depletion of groundwater - Groundwater movement in the cascade,
changes in the system water balance, causal factors for groundwater
depletion
• Water pollution - Soil erosion, use of chemical fertilizer, application
of agro-chemicals, threat to human health
• Threat to bio-diversity - Floral diversity, faunal diversity, Issues
threatening the biodiversity
• Human - elephant conflict - What is human elephant conflict and
why does it happen?
– The best solution: Let them to enjoy their resources,
– Other solutions: Traditional bio-fence with Palmyra trees; Bee hive fence;
Electric fence; Siren drone

61. Decline in forest
cover in Tank
cascade system areas
- 1992
1. Land use changes
Increasing demand
for lands due to:
• Population
increase
• Increased value of
lands
• Commercial
cultivation
• Development
activities

62. Decline in forest
cover in Tank
cascade system
areas - 2010
1. Land use changes
Increasing demand
for lands due to:
• Population
increase
• Increased value of
lands
• Commercial
cultivation
• Development
activities

63. 1. Land use
changes
Encroachment
of lands for:
• Paddy
cultivation
• Rain-fed
cultivation
• Agro-well
farming
• New
residential
areas

64. Encroachment of lands for new
residential areas
1. Land use changes

65. Destruction of
ecosystems
• Biodiversity
reduction
• Loss of
ecosystem
services and
functions
• Loss of flora
and fauna
species
• Drought and
flood due to
ecological
imbalance
Home garden 148
Forest 76
Kattakaduwa 77
70
34
9
23
10
21
13
Ecosystem biodiversity
1. Land use changes

66. 1. Land use changes
Mismanagement of
land resource
• Land suitability for
crops – ignored
• Soil conservation –
not adopted
• Irrigation planning
without considering
drainage
• Use of agro-
chemicals and
chemical fertilizer
• Traditional
practices – given
away

67. 2. Soil erosion and sedimentation
Soil erosion from tank catchments
Land use Soil loss
(t/ha)
Runoff
(mm)
Chena cultivation 11.73 388
Field with
conservation bunds
8.33 124
Scrub vegetation 0.25 7
Forest 0.04 7
Example: Maha 1989/90 season
Source: Dharmasena, 1994

68. 2. Soil erosion and sedimentation
Sediment flow into tanks – Results of a tank
sedimentation survey
Tank Year Catchment
(ha)
Capacity
(ha.m)
Sediment
(ha.m)
% silted
Paindikulama 1984 123 30.2 9.7 24.3
1987 123 28.0 11.9 29.8
1990 123 25.8 14.1 35.3
Siwalagala 1990 62 19.9 8.6 30.2
Marikaragama 1986 70 36.2 9.6 21.0
1990 70 35.3 10.5 22.9
Source: Dharmasena, 1992

69. 2. Soil erosion and sedimentation
Tank capacity reduction
• Tank water storage -
reduced
• Paddy cultivation –
affected
• Dead storage –
disappeared
• Invasive weeds – covered
the water surface
• Fish population – affected
• Rain-fed farming -
increased

70. Soil Erosion
Tank
Sedimentation
Rain-fed
Farming
Tank Capacity
Tank Irrigated
Farming
Vicious circle in tank-village farming
Population
Pressure
2. Soil erosion and
sedimentation

71. Four strata of tank water body
Madakaluwa
Diyagilma
Vaangilma
Thawulla
2. Soil erosion and sedimentation
Change in tank geometry

72. Madakaluwa
Diyagilma
Thawulla
Vaangilma
2. Soil erosion and sedimentation
Change in tank geometry
Sediment deposited on
tank bed

73. 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
2. Soil erosion and sedimentation
Change in tank geometry
Tank water loss
is high if the
capacity/ water
spread area ratio
is low

74. 3. Depletion of groundwater
Groundwater movement in the cascade

75. 3. Depletion of groundwater
Groundwater movement in the cascade
Source: Muditha Perera, 2016

76. 3. Depletion of groundwater
Changes in the system water
balance:
• High surface evaporation
from tanks due to large water
spread area and invasive
aquatic weeds;
• Quick surface runoff from
chena in the tank catchments
lowers the subsurface water
movement;
• Silted up tanks cut off the
groundwater flow along the
cascade;
• Increased use of groundwater
through agro-wells

77. 3. Depletion of groundwater
Causal factors for
groundwater depletion:
• Extensive use of groundwater
for farming
• Forest removal of tank
catchments for rain-fed
farming (chena)
• Changes in the water balance
due to soil erosion and
sedimentation
• Changes in rainfall behaviour
due to climate change

78. Water is a very limited resource
0.03%
4. Water pollution

79. Environmental
pollution
Sound
pollution
Radioactive
pollution
Heat
pollution
Soil
pollution
Light
pollution
Electro
magnetic
pollution
Water
pollution
Air
pollution
Water is the most disastrous pollution among
environmental pollutions of the world
4. Water pollution

80. Water Pollution in tanks – Example from Vavuniya

81. 4. Water pollution

82. 4. Water pollution

83. USE OF CHEMICAL FERTILIZER IN SOUTH ASIAN COUNTRIES
Country Use in farm lands
(kg/ha)
Sri Lanka 284.3
Bangladesh 164.5
Pakistan 163.3
India 153.5
Bhutan 9.0
Nepal 7.7
4. Water pollution

84. 4. Water pollution
Water Pollution in tank cascade systems:
• Soil erosion from tank catchments –
tank water is polluted with eroded
sediments due to absence of godawala,
perahana and iswetiya
• Chemical fertilizer applied in upstream
cultivated lands – N, P, Cd dissolved in
water flowing into tanks
• Eutrophication affects aquatic life
• Weed infestation increases
evaporation
• Human health issues
• Agro-chemicals in water especially with
hard water
• Threat to human health

85. 5. Threat to biodiversity
Tank and environs
Cultivation
areas
Natural/semi-
natural areas
Habitat
Gasgommana
Kattakaduwa
Other
associated
area
Tank
water
body
Tank
bund
Chena
Home
gardens
Paddy
fields
Forests
Scrublands
Number of Flora
species recorded
201 153 68 40 153 55 42 17 123 32
Biodiversity in Tank cascade systems - floral diversity
in Kapiriggama tank cascade (2013-2015)

86. 5. Threat to biodiversity
Animal Group
Recorded Faunal Species
Total Endemic Migrant/ Exotic Domestic
Land snails 7 3 1 0
Dragonflies 20 1 0 0
Butterflies 46 1 0 0
Crabs 1 1 0 0
Fishes 25 4 3 0
Amphibians 13 1 0 0
Reptiles 26 3 0 0
Birds 117 8 14 0
Mammals 29 2 0 4
Total 284 24 18 4
Biodiversity in Tank cascade systems - faunal diversity in Kapiriggama tank
cascade (2013-2015)

87. 5. Threat to biodiversity
Issues threatening the
biodiversity:
• Agricultural expansion into
non-target areas;
• Spread of Invasive Alien
Species (IAS);
• Unsustainable biomass
extractions and loss of
vegetative cover;
• Pollution and siltation of
water bodies; and
• Lack of awareness among
communities

88. 6. Human – elephant conflict
What is human elephant
conflict?
Human elephant conflict
occurs when elephants and
people live together in an
area where they share the
same resources. Therefore,
they compete for the same
food, space and water.
Why does it happen?
HEC occurs when people
change elephant habitat into
people habitat by clearing land
to grow crops, building villages
and adding roads.

89. 6. Human – elephant conflict
The best solution:
Let them to enjoy their
resources
Other solutions
• Traditional bio-fence
with Palmyra trees
• Bee hive fence
• Electric fence
• Siren drone