Interaction between canal water and groundwater in the uda walawe irrigation system hydrochemistry...
-
Upload
international-water-management-institute-iwmi -
Category
Education
-
view
1.725 -
download
4
description
Transcript of Interaction between canal water and groundwater in the uda walawe irrigation system hydrochemistry...
Water for a food-secure world
Interaction between canal water and groundwater
in the Uda Walawe irrigation system:hydrochemistry and isotopes
Mauro Prado, Kevin Hiscock, Lorraine Rajasooriyar, Eline Boelee
Universities of East Anglia , Jaffna&
International Water Management Institute
Presented at Session C “Innovation and Technologies” of International Symposium 2010, Ruhuna University, Sri Lanka
November 16, 2010
Water for a food-secure worldWater for a food-secure world
Outline
• Approach• Study area: geology and sampling points• Sampling results and analysis• Discussion, conclusions and
recommendations
Water for a food-secure worldWater for a food-secure world
Approach• Isotope study; part of a larger research project• Objectives
– Understand determining factors of groundwater quality– Interactions between surface waters and groundwater– Consequences for management
• Mapping– Water infrastructure, geology, land use– Results
• Sampling• Analysis
Water for a food-secure worldWater for a food-secure world
Study area: Uda Walawe irrigation system
• Average Temp 28°C• Humidity 77%• ETpot 1988 mm• Rain 1979 mm
Source: IWMI, 2002 Etpot :Potential Evapotranspiration
Water for a food-secure worldWater for a food-secure world
N
Uda Walawe
Habaraluwewa
Kirribanwewa
Suriyawewa
Ridiyagama
Hambantota
Ambalantota
Left Bank Canal
Right Bank Canal
The study areaWalawe river
StreamsMajor StremasMinor StreamsCanals
ReservoirsSea
Liyangastota
Uda Walawe irrigation system < 400 km2
Source: L. Rajasooriyar, 2003
Water for a food-secure worldWater for a food-secure world
Sub-basins and sampling points• Two sub-basins
– Uda Walawe– Ridiyagama
• Three sampling rounds– Tube wells / boreholes– Shallow dug wells– Canals
• Chemical analysis– Ion specific electrodes, ion
chromatography, titration, spectrophotometry
• Isotope analysisSource: MCCM .Prado, 2002
Water for a food-secure worldWater for a food-secure world
Results - I• Small sample size for isotope analysis• Combining with data from hydrochemical study (fluoride)• Variation between surface and groundwater in terms of
physical and chemical featuressurface water groundwater
dissolved oxygen 4.6-6.7 mg/l 1.1-5.4 mg/l
pH 7.6-8.5 6.4-7.9
Eh 101-228 mV -26-180 mV
electrical conductivity <450 μS/cm <3910 μS/cm
chloride <0.1-24.8 mg/l 4.4-921.4 mg/l
fluoride 0.15-0.56 mg/l 0.25-4.66 mg/lSource: Created by Eline Boelee for the purpose of this presentation
Water for a food-secure worldWater for a food-secure world
Results - II• Contrast between surface and groundwater• More pronounced for deeper groundwater
0
2
4
6
8
-100 0 100 200 300
Eh (mV)
D.O
. (m
g/l
)
Surface water
Shallow groundwater
Deep groundwater
Source: Created by Eline Boelee for the purpose of this presentation
Water for a food-secure worldWater for a food-secure world
Results - III• Trend towards enrichment in heavier isotopes
towards coast
-7
-6
-5
-4
-3
-2
-1
0
0 10 20 30 40
Distance (km)
Oxy
gen
-18
(‰)
Surface water
Deep groundwater
Shallow gw - unlined areas
Shallow gw - lined areas
Source: Created by Eline Boelee for the purpose of this presentation
Water for a food-secure worldWater for a food-secure world
Results - IV
• Trend towards enrichment – possible explanations– Surface water: increasing evaporation– Groundwater:
• Enrichment in discharge areas close to the sea• Lower rainfall in south• Influence sea spray
• Mapping various data to understand better
Water for a food-secure worldWater for a food-secure world
N
Landuse PaddyCoconutOther PlantationGardenMarshScrubForestGrasslandChenaReservoirsPondsWater HolesRock OutcropsSand or BeachInland Lagoons
Uda Walawe land use
Source: L.Rajasooriyar, 2003
Water for a food-secure worldWater for a food-secure world
hjhgjkhsjkhg
Uda Walawe geology
N
1 0 1 Km
Not classifiedGranite GneissCharnockitic Gneiss and Charnockitic Biotite GneissCharnockiteMarble (Dolomite)Biotite GneissGametiferous Quartzofeldspathic GneissPegmatiteHornblende-biotite Gneiss & hornblende biotite migmatiteHornblende Gneiss or AmphiboliteGarnet-sillimanite-biotite GneissBiotite-hornblende Gneiss and Biotite-hornblende MigmatiteQuartziteMetagabbro
Walawe riverReservoirs
Shear ZonesFault, Fracture or Major joint
A
B Geosutur
Source: L.Rajasooriyar, 2003
Water for a food-secure worldWater for a food-secure world
N
Walawe riverReservoirs
10 m interval contours
Uda Walawe groundwater flow
Source: L.Rajasooriyar, 2003
Water for a food-secure worldWater for a food-secure world
Uda Walawe fluoride
Source: L.Rajasooriyar, 2003
Water for a food-secure worldWater for a food-secure world
Uda Walawe fluoride related to canal recharge
Source: L.Rajasooriyar, 2003
Water for a food-secure worldWater for a food-secure world
Discussion• Groundwater is recharged from paddy fields,
unlined canals and tanks• Isotope analysis limited in sample size• Results in line with those from hydrochemical
analysis • Important implications for groundwater quality and
drinking water supply• No quantification of surface – groundwater
interactions• Actual situation may have evolved…
Water for a food-secure worldWater for a food-secure world
Conclusion• Groundwater recharge dilutes contaminants, e.g.
fluoride• Shallow wells are preferred sources of drinking water• Recharge = seepage = leakage?• Lower irrigation efficiency?• Integrated approach required for efficient and
equitable management of surface and groundwater in Uda Walawe
Water for a food-secure worldWater for a food-secure world
Related Publications
• Rajasooriyar L (2003). A study of the hydrochemistry of the Uda Walawe Basin, Sri Lanka, and the factors that influence groundwater quality. Ph.D. thesis, University of East Anglia, UK
• Prado MCCM (2002).Contribution of irrigation canal water to aquifers in
South Sri Lanka. M.Sc. Thesis, University of East Anglia, UK
Water for a food-secure worldWater for a food-secure world
Thank you!
IWMI - www.iwmi.org
University of Jaffna - www.jfn.ac.lk/
University of East Anglia - www.uea.ac.uk
For more information please visit: