G.M. Bandaranayake

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• G.M. Bandaranayake
• Department of Geography
• University of USJP
• Sri Lanka

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Tank Cascading System of Sri Lanka

• What is a tank cascade ?
• A Cascade is a chain of tanks connected by
  water, flows from one to another, located in the
  downstream.
• A tank cascade is a connected series of tanks
  organized within the meso-catchment of the dry
  zone landscape
• cascade is a system of water storage, using the
  drainage courses within a definite watershed
  boundary
• cascade is a means of storing,conveying,distribu
  ting and utilizing water from first or second
  order empherenial streams
• cascade is a small storage reservoir system
  with hydrologic interlinkage by water, flows
  through the same valley
• Irrigation tanks, interconnected forming
  cascades allowing surplus flow from the upstream
  tanks(s)and return flow from the upstream commond
  area, to reach the tank that is immediately
  downstream.

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A typical tank cascade
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How cascades originated

• Early settlers who settled down in river
  valleys, first used water directly drawn
• from the streams
• Latter, they made small tanks, like ponds in
  valley bottoms to store water. Streams
• were dammed and converted water through canals
  to tanks.
• When population expanded and when they realized
  that water is a seasonal resource
• they constructed tanks damming accross
  rivers. Settlements attached the tanks
• spread over the valleys from lower to the
  upper parts.
• When Buddhism and paddy culture were
  incoporated, a hydraulic civilization
• based on triple elements called tankvillage
  temple was developed
• Ancient kings main task was the building of
  tanks and temples, considering it as a
• meritatious task
• When ancient people got a well awareness on the
  topography of the land
• they built tanks at every possible sites of
  the valleys for different purposes in
• different size

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Tank types
Choronicles refer 3 types of tanks 1.Kulu wew
(spring tanks) 2.Rada wew(very deep tanks)
3.Talaka wew (ponds in the jungle) 4.Dana
wew(large tanks) Parker (1909) and Brohier
(1941) identified different ancient tanks made by
ancient people for many purposes 1. Jungle
tanks for wild creatures 2. Mountian tanks for
chena (shifting) cultivation 3. Slope
tanks for soil erosion controlling 4. Village
tanks for human settlements
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Location of tanks
1.In the uppermost parts of rivers small tanks
2.in the middle parts
midium tanks 3.in lower valleys
larger tanks
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Evolution of the Cascading System

• Most jungle tanks were destroyed when shifting
  cultivation was extensively practiced
• By the 11th centuray, most tanks had been
  destroyed by outside invations and abandoned
• as the kingdom shifted to the wet zone
• During the period of Dutch administration
  (1650-1796), some attempts were made to
• restore canal anicuits irrigation systems, but
  tanks in the dry zone were completely
• neglected.
• When British occupied the country (1796), the
  tank irrigation system was badly in
• function . They made a vigorous effort on
  restoration and repairing of tanks .They wanted
  
• the North Central Province to be re-created.
• They launched an immense program on tank
  restoration, but used an approach of
• selecting individual tanks rather than the
  whole cascade system.
• During the period of post- independence,(1948-19
  54) local political leaders made a special
• attention on the buiding of large scale river
  diversion projects called colonization schemes.
  
• Therefore, small tank systems were further
  neglected

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Recent trends

• Recently, some development programs have focused
  attention on villge tanks
• Integrated Rural Development Program(IRDP) 1986
  
• (Selected village tanks were restored)
• Village Irrigation Rehabilitation Progeam(VIRP)
  1990
• (irrigation channels, anicuits and sluices of
  tanks)
• Village Community Rehabilitation (VCRP) 1994
• (community participation on restoring of
  tanks)
• All these programes dealt with individual tank
  restoration, not utilized an approach of overall
  cascade
• Today, SriLankan Government has launched a
  program of Thousands Tanks Restoration. It is
  also based on the restoration of selected tanks
  island wide, not concerns with the tank cascading
  system.

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Previous researches undertaken on tank
cascading systems

• Brohier (1946) studied the technical set-up of
  tank systems from an irrigation and engineering
  perspectives.( location,dam characteristics and
  irrigation channels.
• Parker(1909),Nicholas(1960) studied the
  historical backaground of the tank systems. How
  originated?
• MaddumaBandara(1985) - significance of tank
  catchments. Some aspects of land and water
  resources managements
• IIMI of Sri Lanka conducted many researches on
  the view of making framework for rehabilitation
  of tanks within cascades. Based on basin
  hydrology.
• Somasiri (1997) emphasised the importance of
  village tanks as an agricultural resources.A case
  study.Water crops and land relationship.
• Panabokke(1999) dealing with the nature and
  properties of small tanks, has attempted to
  identify the sustainable production threshods of
  village tanks. Calculation of water and crop
  yield.

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Previous researches cont..

• Itakura(1995) attempted to build a water balance
  model for planing rehabilitation of tank
  cascades. A similar study has been done by
  Shinori (1998). Utilizing Hydrological parameters
  
• Tasuma (1999) has studied how return flows of
  tanks act as an input of water to other tanks of
  the cascade system (water behaviour)
• IIMI of Sri Lanka studied the the possibility of
  predicting water availability of cascade system
  using a water balance model.
• Author (2003) has carried out a reaesrch on
  socio-ecological significance of tank villages of
  Sri Lanka based on a case study concerning with
  some social and environmental values of tank
  villages.

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Gaps and missing aspects of previous researches

• Most researches emphazised the produtivity of
  tanks,irrigation and water management, physical
  renovations,rehabilitation dealing with
  technical,physical or human aspects alone,
  regarding mostly with individual tanks,sometimes,
  based on cascades
• But the problem of efficient use of water is a
  combination of many factors of physical and
  social relating to the whole system.
• Therefore, it is more essential to adopt an
  integrated approach concerning both physical and
  social aspects
• Most practically, in the context of dry zone tank
  cascades, there is a tight interationship of
  physical and social factors
• As shown in the next slide.

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Inter-relationship of Physical and social factors

Land form changes
Catchment land use
Changes in stream flow
Sedimentation in tanks
Less water storage
Increasing Landuse under tanks
Increasing population
Increasing demand on water
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Many researches have missed this integration of
the water problem of cascade system
thus My research problem
is How the past functional mechanism of the
cascading system was operated to be achieved the
sustainable use of water
and How the system has been changed due
to integrated socio- physical factors at present
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Methodology

• Initial set-up and physical formation of tank
  systems will be studied
• by topo-maps, sattellite images, and
  archaeological evidences
• Initial functional characteritics of tanks
  will be examined by historical
• evidences,
• present land use, stream runoff, landform
  changes will be studied by field
• observation, aerial photo and sattellite
  images interpretation
• Sedimentation of tanks is measured at the
  field
• infomation on present water and land
  utilization are collected by field
• surveys

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Outcome and Importance of the research

• Findings of experiences from the past,constrains
  in the present, could be jointly used in making
  an appropiate framework for the sustainable
  water resources development planning for the dry
  zone Sri Lanka.