water harvesting in eastern coastal plains orissa ap tn l.
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Water Harvesting in Eastern Coastal Plains (Orissa, AP, TN). Sangati CPR Working group. Area of focus. Between Eastern ghats and Bay of Bengal Rainfall range: 1000-3000mm Subdivisions: Mahanadi delta Southern AP plains Krishna and Godavari deltas Kanyakumari coast Sandy littorals

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area of focus
Area of focus
  • Between Eastern ghats and Bay of Bengal
  • Rainfall range: 1000-3000mm
  • Subdivisions:
    • Mahanadi delta
    • Southern AP plains
    • Krishna and Godavari deltas
    • Kanyakumari coast
    • Sandy littorals
    • Madras/Coromandel coast
role of water harvesting
Role of Water Harvesting
  • Study by an organization known as PROGRESS
  • Area of focus: drainage basin of a few tributaries of Krishna river
  • Elevation difference between mouth of basin and topmost point: 290m
    • Heavy runoff
  • Main rainfall: July and August
  • Rainfall in 1988-90: ~900mm per year
  • Yet soil was moisture-deficient (drought conditions)
role of water harvesting4
Role of Water Harvesting
  • Study over two years with:
    • Water-absorbing cropping techniques
      • Intercropping, organic farming, etc.
    • Water harvesting
      • Runoff conserved through interconnected water structures, so that overflow in one gets collected in another
      • 170 structures, covering 4% of the basin area
    • Harvested 25% of total rainfall
  • Conclusions of study:
    • Drought is not because of lack of rainfall but because of mismanagement of existing rainfall
    • Traditional water structures if revitalized can harvest 75% of the runoff
    • Worst-affected by lack of over-reliance on individual wells (as opposed to tanks) are the small farmers. Leads to the usual cycle of indebtedness
orissa ap
Orissa, AP
  • Area: Mahanadi delta, Palar basin
  • Tanks, percolations tanks, etc.
tamil nadu
Tamil Nadu
  • Drought-prone state
  • Artificial irrigation imperative
  • Classic example: Tanjore
    • “For the most part, the soil is naturally poor, and it is irrigation alone which makes the province such a scene of fertility” (British irrigation authority)
  • Annual Rainfall: 750-1000mm – NE monsoon, 250mm – SW monsoon
anicuts
Anicuts
  • Small to medium size dams
    • Length: 329m, width: 12-18m, depth: 4.5m
  • Mainly around the Cauvery delta to channel water
  • Silting/scouring of the riverbed was a problem (not carefully engineered to prevent this)
  • Prevented by controlling the water flow into the Cauvery delta, by constructing centralized “regulators” or kallanais at the head of the Cauvery delta in Srirangam
  • Serpentine structure for kallanai to resist floods better
slide8
Eris
  • Ancient tanks
  • Approximately one-third of the irrigated area of Tamil Nadu is watered by eris (tanks).
  • Eris have played several important roles in maintaining ecological harmony as flood-control systems, preventing soil erosion and wastage of runoff during periods of heavy rainfall, and recharging the groundwater in the surrounding areas.
  • The presence of eris provided an appropriate micro-climate for the local areas. Without eris, paddy cultivation would have been impossible.
history of eris
History of Eris
  • Till the British arrived, local communities maintained eris.
  • Historical data from Chengalpattu district indicates that in the 18th century about 4-5 per cent of the gross produce of each village was allocated to maintain eris and other irrigation structures.
  • The early British rule saw the enormous expropriation of village resources by the state
    • Eris managed by centralized Public Works Department
    • Led to the poor maintenance and degeneration of eris
oorani
Oorani
  • Smaller tanks (compared to eris) containing just enough water to cultivate the few acres of land dependent on them.
  • Major source of water for drinking and domestic use where groundwater not sufficient
  • Generally excavated to depths ranging from 2-5 m below ground.
  • In many cases, rehabilitation of neglected village tanks saves approximately 365 hours or 45 working days per household
    • Which is the total time spent each year to fetch water from neighboring villages.
  • Especially applicable where groundwater is saline
kudimaramath
Kudimaramath
  • Voluntary labor undertaken by village communities traditionally to maintain the eris / ooranis
    • Checking the growth of weeds on tank bunds
    • Clearing away underwood from tank bunds
    • Clearing out deposits/silt
    • Blocking breaches through ring bunds
  • Came to an end when the British forced eris under PWD
    • Eri maintenance was contracted out, leading to the usual cycle of negligence, corruption, etc.
decline of tank irrigation in tn
Decline of tank irrigation in TN
  • Old records: 39000 tanks in TN!
  • Sharp decline, esp. in North Arcot, South Arcot and Chengalpattu
  • Traditional Irrigation Institutions (TIIs) that perform maintenance have reduced in effectiveness
    • Centralization of tank maintenance
    • Emergence of wells and electricity, also leading to cuts in payments of maintenance workers
    • Transfer of land / redistribution of land means more owners of land, more castes own land
      • Caste-based factions of TIIs, more people means less effectiveness
    • Many tanks in TN are fed by an anicut system; Palar anicut system supplies water to 317 tanks in N. Arcot and Chengalpattu
      • Here, the tanks close to the head have more effective TIIs, tail-reach tanks are less effective
chennai
Chennai
  • Annual rainfall: 1200mm, which is sufficient
  • Lack of facilities to store this water
  • Current capacity: 100 million cu. M, or ~2700 million cu. Ft. or ~76,356 million liters
    • 124 tanks, plus 39 temple tanks (or kulams) (?)
      • 5.5% of Madras Metropolitan area
    • Include tanks in Cholavaram and Red Hills which are used only for domestic needs (~28000 million liters)
  • Rough demand: ~283 million liters a day, or ~100,000 million liters a year
  • Clearly, the current capacity to store rain water needs to be fully utilized!
    • RWH crucial!
chennai14
Chennai
  • However, traditional temple tanks (and other tanks too) have degenerated
    • Storm-water courses that refill these tanks have disappeared
    • Water runs off into the sea
  • Slum resettlements on tank and lake beds
    • “When World Bank gave TNHB Rs. 600 crore as aid for slum improvement schemes, we had no land to implement them on. Hence, we had to think of tank beds” (deputy planner, MMDA)
  • As a result, ground-water depletion heavy
    • Salt water front of the sea has advanced by 800m in 20 years (10-year old data, probably even worse now)