Paper presented at the Seminar on Cascade Irrigation Systems for Rural Sustainability
held on 9th December 2010 at SLFI, Colombo, organized by Plan Sri Lanka.
Essential Components of Traditional Village Tank Systems
P.B. Dharmasena
Interceptor
Interceptor (Kattakaduwa)
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Three land phases (water hole, marshy land
and dry upland)
Reduce tank seepage
Prevent entering Na, Mg, Fe into the paddy
land
Safeguard the tank bund
A common village garden and agro-forestry
system – medicine, fuel wood, timber, fencing
materials, farm and household materials, food,
fruit, vegetable, fodder
Raw materials for cottage industry
Plant diversity (77 species – 13 species
specific to kattakaduwa
Three land phases of Kattakaduwa
Wetakeya
Gotukola,
mukunuwenna,
kiriala, Vewel
Pan, kohila,
wadakaha, kankun
Thal, puwak, milla, teak
Patabeli, kumbuk,
kohomba, divul, mee,
amba
Tree species
Forest 76
10
Home garden 148
70
34
9
Interceptor 77
23
13
21
Plant species in the interceptor
Function/use
Medicine
Fuel wood
Timber
Fencing materials
Farm and domestic tools
Food
Fruits
Vegetables
Fodder
No. of
species
52
52
40
31
15
12
11
9
5
Four phases of the traditional tank
Waangilma (High flood phase)
Wev thaula (shallow phase)
Jalagilma (deep phase)
Madakaluwa (dead storage)
Four phases of the traditional tank
Waangilma (High flood phase)
Wev thaula (shallow phase)
Jalagilma (deep phase)
Madakaluwa (dead storage)
Four phases of the traditional tank
Waangilma (High flood phase)
Wev thaula (shallow phase)
Jalagilma (deep phase)
Madakaluwa (dead storage)
Cropping Intensity and Rainfall
Anuradhapura District (1970-2003)
2
1.8
1.6
1.4
1.2
Rainfall (m)
1
0.8
0.6
0.4
0.2
0
Cropping Intensity
Geometry of water body affects the loss
Percent water loss
100.0
90.0
y = 59.471x-1.3351
80.0
R2 = 0.786
70.0
60.0
50.0
40.0
30.0
0.7
0.9
1.1
Capacity/area (m)
1.3
1.5
PARTIAL DESILTING CONCEPT
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Reduces water losses
Makes upstream area free of water
Reduces salinity in the upstream area
Allows to re-establish gasgommana and perana
Avails water during dry period
Increases cropping intensity
Area (ha)
PARTIAL DESILTING CONCEPT
FSL
Elevation (m)
FSL
Sill level
Proposed
PARTIAL DESILTING CONCEPT
Catchment area
Natural streams
Old tank bed
Removed sediment
New tank bed
Tank bund
Interceptor
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Thisbambe –
Buffer zone of
hamlet, resting
place of buffalo,
protection from
malaria and wild
animals, sanitary
activities, nutrient
source to paddy
field
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Kiul-ela
Common
drainage of paddy
tract, disposal of
saline water from
kattakaduwa, biodiversity, habitats for
predators
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Iswetiya –
Soil erosion
control, prevent
sedimentation, acts
as a temporary water
pond
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Godawala –
Sediment trap,
drinking water for
cattle and wild
animals
Gasgommana and Peraana
• Wind barrier – reduces
evaporation
• Reduces temperature
• Habitat of some species
• Fish breeding points
• Territory between man and
wild animals
• Reduce sedimentation