Content uploaded by Hetti Arachchige Hemachandra Jayasena
Author content
All content in this area was uploaded by Hetti Arachchige Hemachandra Jayasena on Mar 18, 2021
Content may be subject to copyright.
Jayasuriya and Jayasena /Int.J.Econ.Environ.Geol.Vol. 10(1) 00-00, 2019
1
c
Refined GIS Mapping to Reinvestigate Groundwater Mining Potential Surrounding the
Manmade Reservoirs and Tributaries in the Deduru Oya Basin, Sri Lanka
C. Jayasuriya,1 H.A.H. Jayasena2
1Geological Survey and Mines Bureau, 569, Epitamulla Road, Pitakotte, 10100, Sri Lanka
2Department of Geology, University of Peradeniya, Peradeniya, 20400, Sri Lanka
*E mail: cjayasena@pdn.ac.lk
Received: 06 April, 2019 Accepted: 31 January, 2020
Abstract: A hydrogeologic study was carried out to understand the influence of Man-Made Reservoirs (MMR),
tributaries and fracture intensity on well yields within the Deduru Oya Basin (DOB), Sri Lanka. A number of cascaded
MMRs interconnected by tributaries are distributed throughout the basin. Fracture traces, lineaments and reservoir
boundaries were initially demarcated using aerial photographs, however, subsequently re-plotted them on to a Google
Earth map with corrections to rectify the distortion. The GPS based well locations were regenerated and plotted to obtain
accurate dimensions. ArcGIS was used to redraw the buffer zones from 0-200, 200-400 and 400-600 m away from the
MMRs and tributaries. After eliminating dry wells, box plots were prepared where lower and upper quartiles indicate
yield variations from 18-470; 15.8-165 and 12.8–55 liters/minute respectively. It clearly exhibits decreasing yields with
respect to distance away from the MMR. However, wells drilled within the alluvial plains of tributaries after filtering
those controlled by the MMRs and eliminating dry wells indicate different yield variations, viz: 7-36.8; 12.8-67.5 and
6.5-142.5 liters/minute. The results assigned higher yields to the wells located away from the tributaries with steep
hydraulic gradients whereas lower yields to the wells closer to the tributaries with gentle hydraulic gradients. Moreover,
wells drilled at fracture interconnections indicate a potential for high yields compared with those drilled along with a
single fracture. The study concludes that the potential for groundwater mining can be enhanced by identifying high
recharging areas such as MMRs, zones of steeper hydraulic gradients and high fracture interconnectivity.
Keywords: Deduru Oya, Fractures, Reservoirs, Recharge, GIS mapping, Groundwater Mining.
Introduction
With the increasing demand for the available surface
water, the emphasis is now being laid on the extraction
of shallow and deep-seated groundwater in crystalline
rocks (Jayasena et al., 1986; Jayasena, 1989; Jayasena,
1993; Jayasena, 1995; Jayasena and Dissanayake,
1995). During the driest periods of the year, shallow
groundwater extracted from the regolith aquifer
(average up to 10 m) through dug wells may dry up.
Therefore, government and private agencies pay special
attention to extract deep groundwater (fractured aquifer
average up to 30 m and deep lineaments) (Jayasena et
al., 2018). The availability of groundwater in crystalline
rocks is generally less because of the extremely low
primary porosity and low interconnectivity (Bell, 1980;
Jayasena et al., 1986). However, fractures, joints, deep
lineaments, faults and shear zones developed due to
local and regional tectonic events could generate a
dense fracture network facilitating the movement and
occurrence of a significant amount of groundwater.
The overall objective is to investigate the hydrogeologic
behavior of a fractured crystalline rock terrain, with
special reference to identifying areas with high potential
for groundwater. It specifically aims at understanding
the influence of fracture distribution, manmade
reservoirs and diversion canals on groundwater yield in
the Deduru Oya Basin (DOB) with the support of
ArcGIS (Fig. 1).
Hydrogeologic and geomorphic background of the
study area
The DOB originates from the headwater around 850 m
above mean sea level (MSL) in the central highlands
and lies between the latitudes 7° 19’ N and 7° 51’ N and
the longitudes 79° 47’ E and 80° 34’ E. The elevation
drops towards the northwest, and the ridge and valley
topography give way to an area of isolated ridges and
rock knobs near the center of the basin (Jayasena, 1989;
Jayasena, 1998). The mainstream length is about 115
km and the basin covers approximately 2,600 km2
(Somaratne et al., 2003) which mainly underlain by
Precambrian metamorphic rocks. However, recent
deposits formed during the Quaternary period cover as
a mantle consist of alluviums about 3 km wide
floodplain at the western end of the DOB, colluviums
flanked by isolated ridges and rock knobs near the
center of the basin (Jayasena, 1989; Jayasena, 1998) and
regolith as thick as 10 m (Jayasena et al., 2018). The
regolith plays a significant role in retaining a substantial
amount of groundwater except in the north-central part
of the basin. In terms of groundwater exploration,
smaller geologic units such as Pegmatites, Dolerites and
the sequence of Jurassic sedimentary rocks occur in the
northwestern faulted basins significantly control the
groundwater occurrence, movement and quality
throughout the fractured rock environment (Jayasena et
al., 1986; Jayasena, 1993; Jayasena, 1995; Jayasena and
Dissanayake, 1995).
Open Access
ISSN: 2223-957X
Int. J. Econ. Environ. Geol. Vol. 10 (4) 00-00, 2019
Journal home page: www.econ-environ-geol.org
Copyright © SEGMITE
Jayasuriya and Jayasena /Int.J.Econ.Environ.Geol.Vol. 10(1) 00-00, 2019
00
Fig. 1 Map of Sri Lanka showing the location of the DOB and its
hydrological elements
Climatic, geologic and morphologic implications on
MMR distribution
The DOB receives rainfall from the Northeastern and
Southwestern monsoons. The mean annual rainfall
gradually decreases from South to North with an
average annual rainfall (ARF) of 1730 mm (Singh and
Jayasena, 1984; Jayasena, 1993). The basin falls under
three major climatic zones (Panabokke and Kannangara,
1975; Madduma Bandara, 1985; Jayasena, 1998). The
major part, 94% of the DOB falls in the intermediate
zone (ARF between 1,750 to 2,500 mm) while 5% and
1% respectively fall in the wet (ARF over 2,500 mm)
and the dry zones (ARF less than 1750 mm).
Rainfall and flood irrigation water infiltrates to
replenish groundwater reserve while streamflow
supports for surface storages at MMR’s constructed
within minor or meso-catchments. Lowlands in the dry
and the intermediate zones are characterized by rolling
topography defining such meso-catchments. These
catchments with reservoirs set up in the cascade system
have been identified as Tank Cascade Systems (TCS)
(Madduma Bandara, 1985; Mahatantila et al., 2008;
Jayasena and Gangadhara, 2014). The average area of
such unit is 21 km2 with a range from 13 to 26 km2
(Panabokke, 1999). The remnants of geological
formations and rock knobs play a vital role in siting and
governing the tank distribution (Jayasena et al., 1986;
Jayasena, 1993). Most tanks were constructed on this
basement where rock exposures have been used as
bunds, spillways and embankments (Cooray, 1984).
Tank beds cover either alluvial deposits or weathered
overburden with varying thickness (Jayasena et al.,
1986).
Fig. 2 Schematic diagram showing the progression of check dam-
based water ponds to TCS and associated man-made features
(Jayasena et al., 2011).
A recent study by Jayasena et al. (2011) delivered a
strong relationship between the tank distribution in
cascades and rainfall variation in the DOB. These
cascades with their boundaries demarcated using
topographic maps consist of 4633 small tanks for which
sequence numbers were assigned (Fig. 2). The sequence
numbers within the respective rainfall regimes
graphically represent a log-linear relationship with the
number of tanks, which resulted in “Degree of
Cascading” (DOC). Theoretically, DOC could vary
from 1 to infinity, however, in the DOB, it varies from
1.6 to 4.5 (Jayasena et al., 2011), indicating an
increasing number of tanks in gently sloping terrains
characterized by higher annual rainfall. On the contrary,
tanks with larger surface extent are common in the flat
areas with low rainfall indicating lower tank density
towards the tail-end of the basin. Moreover, the TCS
seems an outcome of organized planning rather a
haphazard construction.
Groundwater potential through lineaments and
fracture network
Investigation of lineaments and fracture network has
considerable importance on groundwater exploration
(Mallik et al., 1983; Palacky et al., 1981; Singhal et al.,
1988). Lineaments are indicative of secondary porosity,
and if intersected by a well, it will have the potential to
supply significant and reliable quantities of water
(Bruning et al., 2011). Since fractures and joints serve
as passageways for water movement, a dense network
of fracture system could enhance groundwater storage
and production (Hossam et al., 2011). One method of
identifying potential area is fracture trace analysis
(Krothe and Bergeron, 1981), where Lattman and
Nickelson (1958) defined the “fracture trace” as a
natural linear feature less than one mile (1.6 km) long.
A lineament is defined as a similar linear feature longer
than a mile (1.6 km). Fracture traces and lineaments can
be generated by tectonic activities or stratigraphic
discontinuities. In a previous study, fractures and
Jayasuriya and Jayasena /Int.J.Econ.Environ.Geol.Vol. 10(1) 00-00, 2019
00
lineaments formed due to tectonic activities were
considered around Wariyapola resulted in high yielding
wells with high fracture density (Jayasena, 1989;
Jayasena, 1993).
Materials and Methods
Fracture traces, lineaments and boundaries of reservoirs
and DOB were initially demarcated using aerial
photographs, however, subsequently re-plotted them on
to a Google Earth map with necessary corrections to
rectify the distortion. After the rectification, the GPS
based well locations (338) were regenerated to obtain
accurate measurements. Structural geologic control of
well yields within the DOB was examined with respect
to the axes of major antiforms and synforms, faults and
shear zones. The ArcGIS package has been used to
analyze relations between these features. “Add path”
was used for linear features while “Add polygon’ was
used for aerial boundaries. The generated “KML” files
were converted into a “shapefile” using the
“ArcToolbox” option.
Three buffer zones with 200 m interval up to 600 m
around MMR’s and tributaries were created, merged
and dissolved using ArcGIS. The input features based
on geometric intersection were computed as overlap for
all layers before written to the output. The intersect tool
was used to separate yields from each buffer zone before
calculating respective lower and upper quartiles. The
interquartile range (IQR) of well yields with respect to
distance away from the MMR’s and tributaries were
tabulated and box plots were prepared.
Results and Discussion
GIS-based study on DOB
ArcGIS, Google Earth and three-dimensional images
gave contrasting results for the basin area (2728.37
km2), basin perimeter (280.29 km) and the mainstream
length (approximately 137 km). The mainstream was
designated into the sixth order (Strahler, 1957) which,
originates from 850 m above MSL and runs adjacent to
Kurunegala before discharging its waters to the sea at
Chilaw lagoon. The slope of the mainstream varies
between 1.1% to 1.7%.
Fracture distribution
Fracture traces of the DOB have been transferred onto
ArcGIS from the Google Earth for frequency analysis.
The highest percentage of 7.1 is observed in the 3300 -
3400 direction, whereas, the lowest percentage of 3.7
follows in the EW direction (Fig. 3). A large number of
field scale joints in different rocks within the
Wariyapola area, however, indicated prominent E-W
direction (Jayasena, 1989).
Moreover, many of these joint traces are not commonly
observed on the aerial photographs and/or Google Earth
images, except at few places within the central part of
the Wariyapola area, which may suggest that they are
not wide enough to be observed as linear fractures. The
fracture trace density (based on length/km2) is high in
the southern flank of the DOB. However, only a few
fractures are observed on the western lowlands due to
the denudation produced surficial materials (Fig. 3).
Fig. 3 Google Earth-based fracture trace/lineament distribution and
the respective frequency diagram (Rose diagram) of the DOB.
Analysis of tube well data
Analysis of 338 domestic water supply tube wells in the
DOB gives the following results. The minimum and the
maximum depths are 7.5 and 140.15 m, respectively.
The average depth is about 53 m with a standard
deviation of 18.3 m. The lower and upper quartiles vary
from 39 to 63 m. The minimum and maximum yields
are 0 and 1200 liters/minute. The average well yield is
about 95 liters/minute with the standard deviation of
165.3 liters/minute. The lower and the upper quartiles
vary from 11.7 to 100 liters/minute. The lower yields
may result due to wells drilled away from the tectonic
fractures and joints. Further, it could also be due to
incomplete or improper drilling and construction
failures subjected to reducing well efficiency. The
recharging area includes headwater regions with
elevated central highlands on the south-eastern side of
the DOB. The distributary drainage system with a thick
pile of alluvial deposits in the discharging zones located
in the western lowlands of the Deduru Oya floodplain
could support for high yielding wells (Fig. 4).
Structural geologic control of yield in the DOB
The axes of major antiforms and synforms have a
general NW-SE trend. The analysis shows that the wells
drilled near the axes of synforms generally have lower
yields. In contrast, wells located close to the axes of
antiforms have higher yields (>30 liters/minute). Most
of the faults are concentrated in the eastern part of the
DOB covering the central highlands of Sri Lanka with
traces aligned in the NNE-SSW direction.
Jayasuriya and Jayasena /Int.J.Econ.Environ.Geol.Vol. 10(1) 00-00, 2019
00
Fig. 4 Distribution of tube wells and respective yield variations in the
DOB.
These faults could be generated due to neotectonic
movements parallel to the proposed arcuate axis of
upliftment in the central island (Vitanage, 1972; Silva et
al., 1983). The shear zones which run in the NW-SE
directions contribute more to high yielding tube wells
(Fig. 5). In this analysis clusters of high yielding wells
associated with the MMRs are eliminated.
Fig. 5 Distribution of structural geologic features and tube wells in the
DOB.
Analysis of well yield variations within the buffer
zones
ArcGIS package was used to redraw the buffer zones
with an interval of 200 m up to 600 m away from the
MMRs (Fig. 6) and tributaries (Fig. 7). After
eliminating dry wells, box plots were prepared for each
case with respect to well yields recorded within 200,
200-400 and 400-600 m intervals (Fig. 8). The
respective lower and upper quartiles with the Inter
Quartile Ranges are presented in Table 1. The results
undoubtedly exhibit the decreasing yields away from
the MMR. It is clear that such yield variations were
supported by the local recharging of the MMRs thus
those zones could be potentially promising areas for
groundwater mining. However, wells drilled in the
alluvial plains of the tributaries after filtering those
controlled by the MMRs and eliminating dry wells
indicate different yield variations. The results indicate
that the wells located 400-600 m away from the
tributaries with steeper hydraulic gradients provide an
appreciable amount of groundwater whereas with gentle
hydraulic gradients towards the tributaries resultant
with lower yields (Fig. 9). However, based on the
common notion, well yields closer to a tributary should
be higher than that away from it. Since the analysis even
eliminates the manmade reservoir (MMR), the output
should be attributed to the differences associated with
geologic formations. The wells drilled in the alluvial
formations closer to the tributary may have appreciable
amounts of clayey matter which inhibit the groundwater
inflow. However, within 400-600 m, the network of
fractures in the bedrocks facilitate recharge to the wells
through the tributaries where groundwater flow with
ease. In addition, groundwater flowing through such
rock fractures may improve the well efficiency
supporting for high yielding wells. Overall analysis
indicates that the well yields generally decrease beyond
600 m. Further scrutiny on a case by case is expected in
order to provide a concrete recommendation.
Fig. 6 The generated buffer zones with an interval of 200 m up to 600
m away from the MMRs.
Table 1 Yield variations within the respective buffer zones away from
the MMRs and the tributaries.
MMRs
Tributaries
Distance (m)
Distance (m)
0
to
200
200
to
400
400
to
600
0
to
200
200
to
400
400
to
600
Upper quartile
(liters/minute)
470
165
55.0
36.8
67.5
142.5
Lower quartile
(liters/minute)
18.0
15.8
12.8
7.0
12.8
6.5
Jayasuriya and Jayasena /Int.J.Econ.Environ.Geol.Vol. 10(1) 00-00, 2019
00
Fig. 7 The generated buffer zones with an interval of 200 m up to 600
m away from the tributaries (reservoirs have been eliminated in the
analysis).
Fig. 9 Schematic diagram showing the cross-section of Deduru Oya
with the possible water table and flow line distributions. Hydraulic
gradients at 200 m intervals along with TW distribution are also given
Conclusion
It is recommended that E-W fractures or lineaments
from the fractured rock regime should be avoided when
locating wells to extract a large quantity of groundwater.
Wells constructed near NW trending shear zones, along
the axes of antiforms and at locations where fractures
are interconnected could provide higher yields. Wells
having higher recharging potential close to the MMRs
clearly exhibit potential for groundwater mining. Well
yields within the 600 m peripheral area of the tributaries
exhibit a gradual increase; higher yields to the wells
located away from the tributaries with steep hydraulic
gradients whereas lower yields to the wells closer to the
tributaries with gentle hydraulic gradients. Beyond 600
m, the yields are generally low except for localized
pockets. The regional recharging areas mainly include
headwaters in the elevated Central Highlands on the
Southeastern segment of the DOB. The distributary
drainage system with a thick pile of alluvial deposits in
the discharging zones of the Deduru Oya floodplain
could support for high yielding wells. Further analysis
including modeling with the R software is planning.
Acknowledgement
This research was partially supported by the National
Water Supply and Drainage Board and the Ministry of
Technology and Research in Sri Lanka. The authors are
indebted to the reviewers and the chief editor for their
constructive comments. Prof. Rohana Chandrajith and
Bhanuka Hettiarachchi are mentioned for their editorial
supports. The second author acknowledges the support
given to him by Orbit Engineering, Canada during the
writing stage of this paper. Prof. Viqar Husain was
mentioned with his continuous encouragement given to
the authors to submit this paper.
References
Bell, F. G. (1980). Engineering Geology and
Geotechnics, Newnes Butterworths, Sevenoaks,
Kent., 498p.
Bruning, J. N., Gierke, J. S., Maclean, A. L. (2011). An
approach to lineament analysis for groundwater
Fig. 8 Box plots showing the yield variation at 200 m intervals up to 600 m away from (a). the MMRs and (b). the Tributaries.
0
200
400
600
800
1000
1200
200 400 600
Yield (liters/min)
Distance (m)
0
100
200
300
400
500
600
200 400 600
Distance (m)
a
b
Jayasuriya and Jayasena /Int.J.Econ.Environ.Geol.Vol. 10(1) 00-00, 2019
00
exploration in Nicaragua. Photogrammetric
Engineering & Remote Sensing, 77(5), 509-519.
Cooray, P. G. (1984). An introduction to the Geology of
Sri Lanka (Ceylon) (2nd edition) National Museums
of Sri Lanka publication, Colombo, 340p.
Hossam, H., Elewa, A., Quaddah, A. (2011).
Groundwater potentiality mapping in the Sinai
Peninsula, Egypt, using remote sensing and GIS-
watershed-based modelling. Hydrogeology
Journal, 19, 613-628.
Jayasena, H. A. H. (1989). Hydrogeology of basement
complexes - A case study from the Kurunegala
District of Sri Lanka. MS Thesis. Colorado State
University, Fort Collins, CO 80525, U.S.A., 121p.
Jayasena, H. A. H. (1993). Geological and structural
significance in variation of groundwater quality in
hard crystalline rocks of Sri Lanka. In S. Banks and
D. Banks (Eds). Hydrogeology of Fractured rocks,
Memoirs of XXIVth IAH Congress Oslo, Norway,
C8, 450-471.
Jayasena, H. A. H. (1995). An analysis of fluid flow
through fractured rocks. In K. Dahanayake (Ed),
Handbook on Geology and Mineral Resources of
Sri Lanka, Second South Asia Geological Congress
Souvenir Publication, Colombo, Sri Lanka, 87-90.
Jayasena, H. A. H. (1998). Hydrologic Assessment of
the Deduru Oya Basin in Sri Lanka. Multi-
Disciplinary International Conference on the
Occasion of 50th Anniversary of Independence of
Sri Lanka. University of Peradeniya, Sri Lanka.
Section – G, Science and Technology, 13p.
Jayasena, H. A. H., Chandrajith, R., Gangadhara, K. R.
(2011). Water management in ancient Tank
Cascade Systems (TCS) in Sri Lanka: Evidence for
systematic tank distribution. J Geol. Soc. Sri
Lanka, 14, 29-34.
Jayasena, H. A. H., Dissanayake, C. B. (1995). Analysis
of hydrochemistry in the groundwater flow system
of a crystalline terrain. Memoirs of XXVIth IAH
Congress Edmonton, Canada., 12p.
Jayasena, H. A. H. and Gangadhara, K. R. (2014). A
review on the qanats in Iran and the Tank Cascade
System (TCS) in Sri Lanka – Parallel evolution
based on Total Environment. Journal of the
Geological Society of Sri Lanka, 16, 75-91
Jayasena, H. A. H., Mohammadi, K., Shamsi, R.,
Ahmad, H. M., Hettiarachchi, B. (2018). The
outcome of construction dewatering associated
with glacial and hard rock terrains: need of a
regulatory framework for future megacity
development, (Abstract) Proceedings of the 34th
Annual Technical Session, Geological Society of
Sri Lanka.
Jayasena, H. A. H., Singh, B. K., Dissanayake, C. B.
(1986). Groundwater occurrences in the hard rock
terrains of Sri Lanka―A case study. Aqua, 4, 214-
219.
Krothe, N. C., Bergeron, M. P. (1981). The relationship
between fracture traces and joints in a Tertiary
Basin, southwest Montana. Ground Water, 19, 138-
143.
Lattman, L. H., Parizek, R. R. (1958). Photographic
fracture trace mapping in the Appalachian plateau.
Amer. Assoc. Petro. Geol. Bull., 42, 2238-2245.
Madduma Bandara, C. M. (1985). Catchment
ecosystems and village tank cascades in the dry
zone of Sri Lanka. Strategies for tributary basin
development, 99-113.
Mahatantila, K., Chandrajith, R., Jayasena, H. A. H.,
Ranawana, K. B. (2008). Spatial and temporal
changes of hydrogeochemistry in ancient tank
cascade systems in Sri Lanka: evidence for a
constructed wetland. Water and Environment
Journal, 22(1), 17-24.
Mallik, S. B., Bhattacharya, D. C., Nag, S. K. (1983).
Behaviour of fractures in Hard rocks- A study by
surface geology and radial VES method.
Geoexploration, 21, 181-189.
Palacky, C. J., Ritsema, I. L., De Jong, S. J. (1981).
Electromagnetic Prospecting for groundwater in
Pre Cambrian Terrains in the republic of Upper
Volta. Geophy. Prosp., 29, 932-955.
Panabokke, C. R., Kannangara, R. P. (1975). The
identification and demarcation of agro ecological
zones of Sri Lanka. Sri Lanka Association of
Advancement of Science Proceedings, 31(3), 49.
Panabokke, C. R. (1999). The Small Tank Cascade
Systems of the Rajarata; Their setting, distribution
Patterns and hydrography. Mahaweli Authority of
Sri Lanka.
Silva, K. K. M. W., Karunaratne, W. M. A. A.,
Amunugama, S. M. B. (1983). Comparison of
different methods of lineament analysis used in the
recognition of structural anomalies of the central
fold belt of Sri Lanka. Proceedings of the 4th Asian
Conference on Remote Sensing Colombo, Sri
Lanka, 8, 1-8.
Singh, B. K., Jayasena, H. A. H. (1984). Hydrogeology,
exploratory drilling and groundwater resources
potential in the Kurunegala District. Water
Resource Board Report, Colombo, Sri Lanka.,
293p.
Singhal, D. C., Sri Niwas, Singhal, B. B. S. (1988).
Integrated approach to aquifer delineation in hard
Jayasuriya and Jayasena /Int.J.Econ.Environ.Geol.Vol. 10(1) 00-00, 2019
00
rock terrains - A case study from the Banda District,
India. Journal of Hydrology, 98(1–2), 165-183.
Somaratne, P. G., Jinapala, K., Perera, L. R., Ariyaratne,
B. R., Bandaragoda, D. J., Makin, I. (2003).
Developing effective institutions for water
resources management: A case study in the Deduru
Oya Basin, Sri Lanka. Vol. 58. IWMI.
Strahler, A. N. (1957). Quantitative analysis of
watershed geomorphology. Transactions of the
American Geophysical Union, 38(6), 913-920.
Vitanage, P. W. (1972). Post Precambrian uplift and
regional neotectonic movements in Ceylon 24th
International geological Congress section 3,
Montreal, Canada, 642-654.
