groundwater management: jaffna, sri lanka
DESCRIPTION
A presentation by Herath Manthrithilake at the Annual Research Meeting at IWMI HQ, Sri Lanka. December 2012. Groundwater management: Jaffna, Sri LankaTRANSCRIPT
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Groundwater Management: Jaffna/ Sri Lanka
Herath Manthrithilake
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Jaffna Peninsula
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Main Groundwater Aquifers in Jaffna Peninsula
Kayts
Chunnakam
Vadamaradchi
Thenmaradchi
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Annual average rainfall is 1250 mm, but 900 mm is received between months of October and December
• 50% of the northeast monsoonal rainfall is received within a very short time period
• 75% probability of rainfall in this district was 510 millimeters (mm) in Maha and 102 mm in Yala
• Evaporation of 45-48% of the annual rainfall
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Geology and condition of groundwater in the Jaffna Peninsula
Source: Sirimanne 1952(a) Red earth, (b) Jaffna limestone, (c) Granitic genesis, MSL (mean sea level), GWT (groundwater level), FWZ (zone
of freshwater saturation), BWZ (probable zone of brackish water); (1) dry well, (2) bottomless well or tidal well (Nilavarai), (3) ordinary successful well, (4) spring of Keerimalai type,
(5) solution cavern.
Infiltration 430 mm/hour
permeability high to very high
hydraulic conductivity 30 to 50 m/d
• Spatial variation of net groundwater recharge was observed to be in the range of 12 to 69% of the total rainfall,
• with an average of 37% during the short rainy season (i.e., during October, November and December).
• A significant volumes of run-off (43 -60%)is lost to the sea during monsoon months.
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Salt water
msl msl
Fresh water
Dry season lens
Wet season lens
Dry season water table
Wet season water table
Excess pumping
Excess pumping
(Ref. Prof.Y.D. Joshuva)
PROBLEMS ASSOCIATED WITH AVAILABLE WATER
QUANTITY Development of salinity
Over extraction
Rapid rate of extraction
Own property Digging of Deep wells
Salt water up coning
Salt water intrusion
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• Abstraction for irrigation varied from 9.4 to 15.7 mm/day with an average of 11.5 mm/day
• Daily ET in 2011 varied from 3.4 mm/day in December to 5.6 mm/day in May with an annual average of 4.7 mm/day
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Monthly deficits (i.e., Rainfall - ET) for 2011
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• Excessive irrigation was 51% over the peak demand of 5.6 mm/day; the major portion of which will eventually return to groundwater
• This limits the water availability and promotes saltwater intrusion
• Have serious consequences on groundwater pollution as the return flow could carry fertilizer and pesticide residues
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Fertilizer useCrop Avg. nitrogen
Applied (kg/ha)Recommended nitrogen (kg/ ha)
Excess nitrogen (kg/ha)
Onion 178.1 70 108.1
Carrot 230 150 80.0
Cabbage 142.6 150 -7.4
Beetroot 246 180 66.0
Tobacco 262.9 No recommendation -
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D
Farm
PublicD + H Paddy Banana Highland crops
Max Per
Concentration of nitrate- N during January 2011
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Agro-well density
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Hot-spots where agro-well density is very high
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Roof top Count
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Results
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Challenges
• Establishing caps on abstraction• Prevention of Contamination• Prevention of over irrigation• Increasing recharge & runoff reduction• CC challenges• Stakeholder cooperation
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Recommendations
• Awareness creation• Promotion of technologies• Investment on pollution control• Agrochemical use reduction• Rainwater harvesting & recharge• A policy framework for GW mgt.
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“There is a sufficiency in the world for man’s need but not for man’s
greed.”