Verification of Surface-Groundwater Connectivity in an Irrigation Canal Using Geophysical, Water...

Water Resour Manage (2011) 25:2837–2853DOI 10.1007/s11269-011-9841-y

Verification of Surface-Groundwater Connectivityin an Irrigation Canal Using Geophysical, WaterBalance and Stable Isotope Approaches

Najihah Dor · Syafalni Syafalni · Ismail Abustan ·Mohd Tadza Abdul Rahman · Mohd Ariff Ahmad Nazri ·Roslanzairi Mostafa · Lakam Mejus

Received: 27 July 2010 / Accepted: 2 May 2011 /Published online: 24 May 2011© Springer Science+Business Media B.V. (outside the USA) 2011

Abstract Descriptions of the surface–groundwater interactions are required forenhanced water resource management in the irrigation canals of the Kerian Scheme.The current study aims to find the hidden aquifer, determine the water loss/gain in anirrigation system, and identify the hydraulic interconnection between aquifer systemsusing geophysical, water balance, and stable isotope methods. The Resistivity ImageProfiling (RIP) method is a common geophysical survey technique used to find apotential groundwater bearing zone in the study area. RIP results show that thethickness of the aquifer varies between 5 and 10 m at a depth of 10–30 m. Theresults are compared against borehole drilling data. Water loss and/or water gain inan irrigation system is an important component of the water balance for planning andoperation. The water level at the Selinsing Canal system increases, clearly indicatingthat the catchment is very responsive to rainfall events. The use of stable isotopesto trace water movement in hydrology, including surface water and groundwater, isan important task within the environmental field. Thus, the results plotted for bothwater samples from Selinsing Canal and groundwater are linearly similar to those inthe Global Meteoric Water Line and the Malaysian Meteoric Water Line. Thus, thesamples are revealed to come from evaporated samples. This indicates that there is aconnection between the surface and the groundwater in the catchment area.

Keywords Groundwater · Irrigation · Resistivity image profiling · Stable isotopes ·Water balance

N. Dor · S. Syafalni (B) · I. Abustan · M. A. A. NazriSchool of Civil Engineering, Engineering Campus, Universiti Sains Malaysia,14300 Nibong Tebal, Penang, Malaysiae-mail: [email protected]

M. T. A. Rahman · R. Mostafa · L. MejusMalaysian Nuclear Agency (Nuclear Malaysia) Bangi, 43000 Kajang, Selangor, Malaysia

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1 Introduction

Irrigation is an artificial application of water on land for agricultural production,landscape maintenance, and bed soil revegetation in dry areas and during periodsof inadequate rainfall. In Mediterranean countries, irrigated farming accounts fora large share of total water withdrawals (83% in Greece, 68% in Spain, 57% inItaly, and 52% in Portugal; Berbel et al. 2011). An irrigation system uses water ina completely uniform manner, allowing each part of the irrigated area to receive thesame amount of water. However, achieving this is impossible because even naturalrainfall is not completely uniform. Ideal water management is defined as the deliveryof the right amount of irrigation water to the fields at the right time to increase cropyield (Lee et al. 2004).

With population growth and economic development, water scarcity and demandfor various purposes especially agriculture and consequently food production isincreasingly becoming a crisis that constraints regional sustainable development(Montesinos et al. 2011; Song et al. 2011). The greater emphasis is given to theplanning and managing of the most favorable utilization of water resources. This haslead to studies on other alternatives, such as groundwater exploration. Geophysicalmethods are particularly suitable, and they have been widely applied in geotechnicaland geo-environmental investigations. Geophysical methods are involved in theinterpretation of soil properties, layering, and composition of the subsurface, cavities,and structures or bodies generally found underground that have different physicalproperties from their geological surroundings (Kneisel 2006). These are the impor-tant preliminary steps in any groundwater investigation. In the current study, Resis-tivity Image Profiling (RIP) was implemented to identify subsurface structure and tofind hidden water in geophysical survey due to its different electrical properties. Theresistivity imaging method has now become more popular in electrical explorationbecause of its efficient and effective non-destructive mode of implementation inproducing subsurface images (Soupios et al. 2008). Furthermore, RIP results havebeen correlated and calibrated with the available geotechnical borehole data toprovide a higher level of reliability on the interpretation and location of undergroundstructures.

In most of the countries around the globe, open channels system is the dominantwater supply technique in the off-farm irrigation system—from a diversion point tothe farm gates (the delivery points; Asghar et al. 2011). Water loss and/or gain inan irrigation system are important components of water balance for planning andoperation. Water loss represents a major portion of non-revenue water for a watersystem. Therefore, water balance techniques, such as determining the total waterloss in a river basin, were developed to solve theoretical and practical water lossproblems (Chung and Syafalni 2009). Understanding the water balance technique isvery important for studies on the operational management of reservoirs and riverbasins. Moreover, water balance studies provide an evaluation of an unknown waterbalance component from the difference between the known components.

The assessment on the origin of water, particularly of the groundwater sys-tem, often uses stable isotope methods to evaluate the hydraulic parameter. Themost commonly stable isotopes used are Oxygen-18 (18O) and Deuterium (2H).Both isotopes involve replenishment processes, estimating the mixing proportionsof different sources or component flows, and studying hydraulic interconnections

Geophysical, Water Balance and Stable Isotope Approaches 2839

between groundwater and surface waters or between different aquifer units within agiven groundwater system (Yurtsever and Araguas 1993).

Surface–groundwater connectivity proceeds in two ways. Groundwater flowsthrough the streambed into the stream (gaining stream), whereas stream waterinfiltrates through the sediments into the groundwater (losing stream). Groundwaterprovides a more stable water resource and rich groundwater areas play a vital rolein regional water resources (Chang et al. 2011). The connectivity is controlled bythe permeability of the streambed and the aquifer and by the channel position asregards the groundwater, as well as by the geometry and size of the contact area.Under low and intermediate flow conditions, the contact area is usually determinedby the channel geometry. However, during flood situations, the river water level mayrise above the river bank, and the geometry of the floodplain controls the exchangeinterface (Sophocleous 2002; Woessner 2000).

The overall aim of the current study is to gain a better understanding of thehydrologic settings of the surface and groundwater system in the irrigated area ofthe catchment. Based on a series of systematic analyses and interpretations of theresistivity technique, water balance method, and stable isotope method, conclusionsare drawn for improving water resources management and increasing the availabilityof good quality water for agricultural and other uses. Therefore, water shortage isalleviated, and sustainable water supply and regional development are ensured.

2 Methodology

2.1 Study Area

The Kerian Irrigation Scheme is a typical irrigation scheme in Malaysia situated atthe northwest corner of the state of Perak in Peninsular Malaysia (Fig. 1). The KerianIrrigation Scheme is one of the oldest schemes with granary areas in Malaysia. It hasan area of 23,560 ha.

The scheme is divided into eight irrigation compartments designated by A–H(Fig. 2). The main source of water is the Bukit Merah Reservoir, where water isdrawn from the reservoir feeding compartments E–H through gravity. The BogakPumping Plant, a major pumping station, is located at the downstream portion of theirrigation system; it supplements compartments A–D at the tail end of the scheme.Two primary canals, namely, the Main Canal and the Selinsing Canal, transportwater from the Bukit Merah Reservoir to compartments A–F and compartmentsG–H, respectively. The Main Canal is split into the Tanjung Piandang Canal and TitiSerong Canal at the downstream area. These feed the secondary canals through aConstant Head Orifice (CHO) at the off-take (Rowshon et al. 2003).

The scheme has a humid tropical climate with a high rainfall precipitation of about2,420 mm and temperatures around 27–28◦C. Moreover, the terrain in the schemeis mostly located along the coastal fringe areas, where the flat marine alluvial soilprovides a favorable environment for agricultural activities such as paddy growing(Valera and Desa 1991).

About 20% of the land in Malaysia is currently utilized for agriculture, ofwhich more than two-thirds are for industrial crops, mainly rubber and oil palm,whereas paddy cultivation covers 660,000 hectare (2% of total land area; Ghazalli

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Fig. 1 Location of the study area in the Kerian Irrigation Scheme of Perak State, PeninsularMalaysia

1998). Irrigation water management in all irrigation schemes is a crucial issue, andthe Kerian irrigation scheme is no exception. As a consequence of development,followed by the increasing number of population, the need for water resources hasincreased ten folds. The alternative method is to withdraw water from the groundbecause the provision of irrigation water from the surface water is not enough tofulfill the overall irrigation demand during the dry season. The focus of the currentwork is along the Selinsing Canal. There are two locations of the resistivity surveythat give an image of the subsurface resistivity distribution. Another 10 differentlocations of boreholes are used for the comparison of the soil layer as well as forwater sampling data.

2.2 Materials and Methods

Resistivity measurements are normally done by injecting a small value of directcurrent (1–1,000 mA) into the ground using two current electrodes (C1 and C2). Theresulting voltage difference at two potential electrodes (P1 and P2) is measured andcontrolled by the resistivity meter through a microprocessor-controlled electronicmodule (Fig. 3). Commonly, in a geophysical resistivity survey, the entire electrodeis placed in a line with a constant spacing via a multicore cable (Dutta et al. 2006).The SAS4000 resistivity meter and ABEM LUND electrode selector system wereused for data collection. Terramater SAS4000 was used as a medium to collectand present the aquifer layer resistivity value as well as to choose which electrodeconfiguration is compatible to be used as a measuring method. The Lund system,which consists of a multielectrode arrangement for high resolution two-dimensional


Fig. 2 Location of CHO, RIP, and boreholes along the Selinsing Canal

(2-D) and three-dimensional (3-D) resistivity surveys, is used for defining geolog-ical structures (Ewusi et al. 2009). Both are connected to measure the substanceresistivity using several commonly used electrode configurations, such as Wenner,Schlumber, Dipole–Dipole, and Pole–Dipole configurations.

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Fig. 3 A conventionalfour-electrode array is used tomeasure the subsurfaceresistivity (Loke 1999)

To determine the true subsurface resistivity, an inversion of the measured appar-ent resistivity values using a computer program must be carried out. The resistivitydata acquisition used a 2-D resistivity imaging technique. The data processing ofthe measured sets of the apparent resistivity was performed by filtering out poorquality data. Fresh data were used as input to the RES2DINV inversion software(Samsudin et al. 2006). RES2DINV is a least-squares inversion technique that usessmoothness constraints. It tries to reduce the difference between the calculated andmeasured apparent resistivity values by adjusting the resistivity of the model blocks.When the resistivity of different material types is known, converting the resistivityimage to an image of the subsurface consisting of different materials is possible.The conventional method of plotting the results for interpretation is conducted usingthe so-called pseudo section, which gives an approximate image of the subsurfaceresistivity distribution. The shape of the contours is dependent on the array geometryand the subsurface resistivity (Kneisel 2006).

Water balance techniques have been extensively used to make quantitative esti-mates of water resources and effect of the activities of man on the hydrologic cycle.The study of water balance is defined as the systematic presentation of data on thesupply and use of water within a geographic region for a specified period. Waterbalance of the Selinsing Canal reach between the Bukit Merah Reservoir and theend of the system was carried out using the following simple equation:

�S = I − O − D − Eν (1)

where �S is the net gain or loss; I represents the inflow to the system; O stands for theoutflow from the system; D is the authorized diversions; and Ev is the evaporationfrom the canal surface. All units are represented in m3/s.

The Ev term is negligible due to the relatively small magnitude. The “net gainor loss” represents the surface–groundwater interaction, flow measurement, anddiversion error (Abbas et al. 2009). The schematic diagram of CHO shown in Fig. 4illustrates the movement of inflow, outflow, and discharge of water from the BukitMerah Reservoir, which contributes to the water loss/gain for the Selinsing Canal.

In the current study, the inflow–outflow method is the preferred method fordetermining the loss occurring during water conveyance in open canals withoutobstructing the seasonal irrigation operation of the selected canals. At the same time,this method allows sufficiently accurate measurements (ANCID 2003). Through theuse of Acoustic Doppler Current Profiler (ADCP), the limitations of the inflow–outflow method can address the resulting high quality, replicable, and efficientmeasurements of canal seepage. The SonTek RiverSurveyor Live, Version 1.5 systemis a robust and highly accurate Acoustic Doppler Profiler (ADP) system specificallydesigned to measure river discharge, 3-D water currents, depths, and bathymetryfrom a moving or a stationary vessel.


Fig. 4 Schematic diagram of CHO for an authorized diversion system

The RiverSurveyor system is equipped with Bluetooth radio telemetry that allowscommunication and data transmission between the ADCP and a personal computer(PC) or mobile device (using cell phone technology). The maximum range using thesupplied Bluetooth dongle plugged into a PC is up to 200 m, whereas the range is60 m for a mobile device. These approximate ranges assume a clear line of sightwith no obstruction or poor weather (SonTek/YSI 2010). This distance significantlydecreases as the battery power in the ADCP also decreases. The ADP is mountedto the boat and ensured to be mounted deep enough. Therefore, the transducers willremain submerged for the entire measurement. Bank-operated pulley set-ups allowa more uniform pull, reduced boat motion, and consistent edge measurements. Asingle moving boat measurement of the discharge is divided into three components:start edge, transect, and end edge. These three components are shown in Fig. 5 below.

Measurements were conducted along the Selinsing Canal at every intake (CHO).A total of 17 CHO have used water from the canal for the rice irrigation scheme.The inflow–outflow method is based on creating water balance in an irrigation canalwhere the inflow and outflow are separated at a certain distance, as well as onensuring that no surface abstractions occur over the measurement reach (Kinzli et al.2010).

Stable isotopic analyses were carried out at the Malaysian Nuclear Agency usinga VG prism stable isotope ratio mass spectrometer. The 18O in the samples wereanalyzed via equilibration with CO2. The 2H values were produced from the watersamples by reduction over heated Zn under vacuum (Zhang et al. 2007). The stableisotopic composition of 18O and 2H is expressed as per mil deviation (δ ‰) of theratio 18O/16O or 2H/1H with reference to the Standard Mean Ocean Water. δ ‰ iscomputed using Eq. 2:

δ(‰) =[

Rsample − Rstandard

Rstandard

]× 1,000 (2)

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Fig. 5 Measurement sections in the Selinsing Canal from the left to the right bank

where R represents the ratio of 18O/16O or 2H/1H. The analytical errors for δ18O andδ2H are ±0.1‰ and ±1.0‰, respectively.

The isotopic composition of groundwater is generally controlled by meteorologi-cal processes and is intended for the analyses of δ18O and δ2H in groundwater system.The result of the isotope exchange process using the δ18O–δ2H diagram is a deviation

Fig. 6 Isotope exchange processes that modify the isotopic composition of meteoric water


from the meteoric water line along a line with a lower slope, which depends onthe relative humidity. However, there exist some extreme geological environmentswhere the reaction between groundwater and the aquifer matrix or subsurface gasescould change the meteoric signature of the water. Some typical processes are shownin Fig. 6.

3 Results and Discussions

3.1 RIP

The interpretations of the resistivity imaging using RES2DINV in the characteriza-tion of the subsoil was plotted both in the vertical and horizontal directions. Figures 7and 8 show the inversion model resistivity sections of fieldwork conducted in theRIP using the 2-D electrical imaging technique. The results obtained from RIP wereanalyzed and used to identify potential borehole drilling sites. After these sites weredetermined, drilling was conducted to confirm the presence or absence of water.

The soil types are different due to the location of the sub-scheme and because theKerian irrigation has two sub-schemes. The coastal portion is mostly located in theareas of compartments A–D, which are mainly composed of alluvial soils of marineorigin. Marine clay is characterized by a thin, brown, and sticky clay surface layercovering the subsoil, which is structureless greenish-gray clay. The inland areas inthe parts of compartments E–H are mostly composed of alluvial soils of river origin.About 5,000 ha of land along the Bagan Serai–Parit Buntar Road is overlain byslightly acid organic clay muck soils. These soils are in portions of compartmentsA, B, D, and F (Valera and Desa 1991).

The natural background resistivity of the three different entities can be defined.These are also marked on the profiles due to the several ranges of resistivity values.There is a very conductive substratum with very low resistivity values (∼5–80 �m)composed of marls, a conductive layer corresponding to the unconfined aquifer(∼80–200 �m), and a very shallow resistive zone (>200 �m) corresponding tothe vadose zone. Thus, these values served as guidelines during the data analyzingprocess.

In Fig. 7, the first layer shows a very low resistivity range of 5–80 �m. The range isobserved to be beneath station 30–120. Although the resistivity value is suitable forthe presence of groundwater, it is not suitable for drilling targets. The existence ofthis layer may be due to the infiltration process from the nearest channel. The second

Fig. 7 Resistivity model profile for Selinsing 4

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Fig. 8 Resistivity model profile for Kuala Selinsing

layer profile indicates that there are two comparatively low resistivity zones withvalues of 80–200 �m observed beneath stations 290–340 and 380–400 in the secondlayer. The aquifer layer can be seen at a depth of 10 m, where the resistivity value iswithin 100–150 �m. These two low resistivity zones are geophysically interpreted asprobably due to the fracturing in the bedrock as well as in the sandy layer. Therefore,these areas are potentially good targets for borehole drilling.

The resistivity model illustrated in Fig. 8 is underlain by low to moderately highresistivity soil ranging from 5–3,000 �m. Lower resistivity value (less than 75 �m)on the surface indicates that the layer is mostly clay, followed by the aquifer layer ata depth of 20 m. From the resistivity image shown above, a low resistivity zone witha long thin layer (blue color, with resistivity values of 10–75 �m) can be observedby varying the depth from 20–50 m below the subsurface and interpreting beneathstation 420–450. Therefore, the resistivity model is predominantly underlain by thesandy layer with a lower resistivity structure, representing the zones of potentialgroundwater occurrence.

The resistivity imaging result is well supported by the litholog data, which addadditional information on the local lithology. These electrical images can be con-verted to a geological section. Soil samples were taken every 3 m up to the end ofthe borehole depth during the drilling process. Drilling was done until the sand layer(shallow groundwater) was reached; it was stopped when the clay layer was reached.Figure 9a, b shows the lithologic section of borehole Selinsing 4 and borehole KualaSelinsing located near the study site, respectively.

Figure 9 illustrates the geotechnical profile at two borehole sites within the surveyarea. A success rate of 80% was obtained to determine the drilling sites for theborehole sitting. This information interpreted the boundary between these mainunits, which serves as a control (reference) to determine the soil layer types. A typicallithologic section of borehole Selinsing 4, which is found to be different, is shown inFig. 9a. The aquifer is found to be shallower in the borehole results compared withthe results from the resistivity profiling technique. The groundwater potential can befound at a depth of 6–9 m. This situation may have occurred due to the intrusion ofseawater that can affect the resistivity value (less than 80 �m). In general, the rockmatrix, salinity, and water intrusion are the major factors controlling the resistivity ofthe formation. Moreover, this investigation shows that borehole drilling is conductedto determine the groundwater potential area and also to compare the result againstthe resistivity imaging technique.

The Kuala Selinsing borehole shown in Fig. 9b illustrates that sandy clay wasfound at a depth of 27–33 m and had a thickness of approximately 6 m of the aquifer


(a) (b)

Fig. 9 Lithologic section of the borehole data located near the study site. a Borehole Selinsing 4b Borehole Kuala Selinsing

layer. Figure 9b also shows that the clay type of soil with some decayed matter andtraces of gravel are present at the upper layer of the subsurface, whereas at the endof the borehole, the soil contains a dark grey silty clay layer until a depth of 36 m.The geological interpretation based on resistivity imaging indicates that the aquiferlayer is in the range of 20–50 m. This finding matches the lithologic section shown inthe borehole data, although the clay, sandy clay, and sand are clearly undefined.

3.2 Water Balance Method

The data collected and subsequent analysis resulted in a database that containsthe following information for each discharge measurement location (CHO): canallength, canal width, canal depth, canal cross-section, mean speed, and total discharge.The total discharge is the amount of water flow (or net flux) through a section.It is computed from the mean water velocity and the cross-sectional area of themeasurement section. ADCPs offer the benefit of reducing measurement errorand measurement time, provide high-resolution data collection, are non-intrusive,and allow for the collection of canal seepage data during normal canal operation.Coupled with a pressure transducer to ensure that canal fluctuations are limited,the presented methodology using ADCP offers the opportunity to determine canaldischarge quickly, accurately, and efficiently.

The surface water balance was estimated for the river system starting from theBukit Merah Reservoir to the end of the Selinsing Canal. This method was resolvedusing data collected within two days. The corresponding net gain/loss (�S) valuewas estimated using Eq. 1. The tributary runoff (precipitation) to the study area wasassumed to be zero because there was no rainfall during the survey for two days.Water molecules move very slowly; thus, the groundwater table fluctuation shows nodifference in readings during the data collection for two days. Moreover, Eq. 1 onlyconsiders the losses of surface water (canal water) per segment, where the losses aredetermined in every segment (from one CHO to the next CHO) calculated in m3/s.m.

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The analysis indicates that there is an imbalance between inflows, outflow, and actualdiversions as shown in Table 1.

The evaporation term in Eq. 1 is neglected because it is too small (for SelinsingCanal only). When the total water released from reservoir is more than the totalwater released through the CHO, there is a net loss in the canal system. This valueis considered positive. However, if the total water released from the reservoir is lessthan the total water released through the CHO, there is a net gain in the canal system.This value is considered negative (Jothiprakash 2004). The net loss/gain term alsoincludes the water that moved in/out of the aquifer system from/to the river systemdue to surface–groundwater interaction.

Based on Table 1, most of the CHO experienced water gain on the first day ofthe survey, whereas some of the CHO experienced water loss on the second day.The gain by the system indicates that the catchment is very responsive to rainfallevents due to the rainfall on the previous day before the survey activities. However,water loss is higher because of two conditions. The first is due to low rainfall duringthat time; hence, there are less or no tributary contributions. The second is due tothe previous day/season being hot with less canal release (less area under irrigation).Hence, most parts of the canal course will be quite dry compared with those of theprevious day. Moreover, as presented in Table 1, water loss at the CHO occurredbecause of seepage losses. The seepage losses for every CHO were high due to thechanging of the water table at different locations. Generally, seepage rate from theirrigation canal varies from site to site depending on the local conditions.

Losses from irrigation schemes to groundwater are often significant. In a typicalscheme, as much as 50% of the water released from the reservoir is lost to thegroundwater. These losses occur in the canals and distributaries, as well as in thefields. Results from the resistivity image show that some section along the canal has

Table 1 Water balance of the Selinsing canal (m3/s)

Date Chainage/Channel Inflow Outflow Actual diversions Inflow–outflow Net loss/gain

Head Orifice (CHO) (I) (O) (D) (I–O) (�S)

28/04/10 Bukit Merah Bridge 8.13 8.13 0.00 0.00 0.00CH 37 6.75 6.55 0.53 0.22 −0.31CH 71 6.34 6.28 0.16 0.06 −0.10CH 109 6.03 5.88 0.23 0.15 −0.08CH 161 5.74 5.33 0.44 0.41 −0.03CH 195 5.25 5.00 0.21 0.25 0.04CH 236 4.98 4.62 0.40 0.36 −0.04

29/04/10 CH 275 4.52 4.35 0.25 0.17 −0.08CH 315 4.31 4.11 0.22 0.20 −0.02CH 374 3.01 3.00 0.00 0.01 0.01CH 375 3.00 2.93 0.11 0.07 −0.04CH 403 2.78 2.75 0.03 0.03 0.00CH 444 2.74 2.66 0.20 0.08 −0.12CH 474 2.62 2.31 0.37 0.31 −0.06CH 1B 2.23 2.00 0.20 0.23 0.03CH 515 1.95 1.92 0.20 0.03 −0.17CH 539 1.90 1.20 0.98 0.70 −0.28CH 563 1.18 0.09 1.04 1.09 0.05


shallow aquifers. This becomes one of the reasons why much of the water losses occurin this area. This indicates that there was loss in the irrigation water occurring alongthe canal bank into the subsurface, showing that the shallow groundwater was mainlyrecharged from the canal itself. Table 2 shows the water losses for each section of theSelinsing Canal.

The analysis of the data in Table 2 indicates that most of the water loss occurredupstream of the Bukit Merah Reservoir. Most of the surface flow loss occurred alongthe Bukit Merah Bridge and chainage 37 (1.97 × 10−3 m3/s.m) section, followed bychainage 315 to chainage 374 sections (1.17 × 10−3 m3/s.m). The loss is due to thestrong interconnection between the surface and groundwater system, where waterfrom the canal is lost through seepage to the shallow aquifer just below the canalbank. Moreover, seepage loss from a canal in an unconfined flow condition is finiteand maximum when the potential difference is very large, i.e., when the water tablelies at a very large depth.

3.2.1 Interrelationship Between RIP and Water Losses

The loss of water due to seepage and evaporation from irrigation canals constitutesa substantial part of useable water. Seepage loss depends on the channel geometry,whereas evaporation loss is proportional to the area of the free surface. On accountof the complexities of analysis, the losses shown in Table 2 are compared with theRIP result in Figs. 7 and 8 due to the interrelationship between both of the analysisthat have been done. The resistivity profile in Fig. 7 is probably underlain by thinhorizontal lithologies with a corresponding very low resistivity (less than 80 �m) onthe surface to a depth of 10 m, followed by a higher resistivity layer in the range of80–200 �m. This layer was observed beneath several stations: 30–160, 220–360, and430–520. These layers may consist of shallow groundwater and therefore contribute

Table 2 Water losses for each section of Selinsing Canal

Section Channel Channel Inflow Outflow Ev ×10−3 Losses Losses ×10−3length (m) width (m) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s.m)

Bridge–CH 37 700 13.83 8.13 6.75 0.32 1.38 1.97CH 37–CH 71 770 13.02 6.55 6.34 0.34 0.21 0.27CH 71–CH 109 650 13.11 6.28 6.03 0.29 0.25 0.38CH 109–CH 161 1,000 13.46 5.88 5.74 0.45 0.14 0.14CH 161–CH 195 670 12.21 5.33 5.25 0.27 0.08 0.12CH 195–CH 236 800 11.12 5.00 4.98 0.30 0.02 0.02CH 236–CH 275 780 11.01 4.62 4.52 0.29 0.10 0.13CH 275–CH 315 750 10.69 4.35 4.31 0.27 0.04 0.05CH 315–CH 374 940 9.37 4.11 3.01 0.30 1.10 1.17CH 374–CH 375 220 9.04 3.00 3.00 0.07 0.00 0.00CH 375–CH 403 630 10.02 2.93 2.78 0.21 0.15 0.24CH 403–CH 444 720 9.63 2.75 2.74 0.23 0.01 0.01CH 444–CH 474 830 8.56 2.66 2.62 0.24 0.04 0.04CH 474–CH 1B 200 8.12 2.31 2.23 0.05 0.08 0.40CH 1B–CH 515 480 7.63 2.00 1.95 0.12 0.05 0.10CH 515–CH 539 500 7.87 1.92 1.90 0.13 0.02 0.03CH 539–CH 563 900 8.32 1.20 1.18 0.25 0.02 0.02

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to higher losses of about 0.13 × 10−3 m3/s.m between chainages 236 and 275, as shownin Table 2.

However, the resistivity distributions in Fig. 8 observe a geological structure withthe appearance of shallow groundwater beneath station 220–530, which reveal higherlosses of about 0.24 × 10−3 m3/s.m in Table 2. This occurred between chainages 375and 403 due to the water loss in the canal through seepage and evaporation process.Furthermore, seepage loss from canals is governed by the hydraulic conductivityof the subsoil, canal geometry, and potential difference between the canal and theaquifer underneath, which in turn depends on the initial and boundary conditions.

Seepage losses are also influenced by the clogging of the canal surfaces dependingon the suspended sediment content of the water and on the grain size distributionof the suspended sediment particles. The seepage discharge can be decreased boththrough the bottom and the slopes of the canal. Thus, the losses can change withintime and can diminish under certain conditions (Swamee et al. 2002). Seepage losscan be higher at the beginning of the canal operation and can be lower after a fewyears of operation.

3.3 Stable Isotopes

Isotope techniques are particularly effective in identifying the sources of salinityand inflow of fresh groundwater. The fundamental relationships between δ18O andδ2H and between δ18O and salinity have been used to identify the mechanisms andsources of salinization (Gaye 2001). The stable isotope analyses of the groundwatersamples for the Selinsing Canal study area are shown in Table 3. The stable isotopedata of δ2H and δ18O are plotted in Fig. 10, along with the Global Meteoric WaterLine (GMWL; δ2H = 8 δ18O + 10; Craig 1961) and the Malaysian Meteoric WaterLine (MMWL; δ2H = 8 δ18O + 13.255; Ayub 2005), which are drawn as a referenceline.

Figure 10 reveals that the slope of the regression line of the borehole data is lowerthan that of the GMWL and MMWL:

δ2 H = 6.695δ18 O − 5.760 (3)

This shows that the groundwater is affected by evaporation. The stable isotopiccompositions of the groundwater indicate that the shallow groundwater mainlyoriginates from precipitation, which falls in the Kerian Irrigation Scheme. Thestable isotope content of these groundwater samples shows that the value of δ18O

Table 3 Stable isotopeanalyses of groundwater inSelinsing

Borehole no. δ2H ‰ δ18O ‰ “d”

BH 1 −55.53 −6.98 0.31BH 2 −50.68 −6.89 4.44BH 3 −46.86 −6.72 6.90BH 4 −50.83 −6.74 3.09BH 5 −49.54 −6.53 2.70BH 8 −53.81 −6.90 1.39BH 9 −48.75 −6.19 0.77BH 10 −46.41 −5.94 1.11BH 11 −49.51 −6.29 0.81BH 12 −44.65 −6.38 6.39


Fig. 10 Relationship between δ18O vs. δ2H for the Selinsing Canal system

varies from −5.94‰ to −6.98‰, whereas the value of δ2H varies from −44.65‰ to−55.53‰. The effect of evaporation is clear in the groundwater samples because itsisotopic composition is slightly enriched with heavy isotopes.

According to Al-Ruwaih and Shehata (2004), another piece of evidence for theorigin of recharge of the investigated wells is obtained from the value of the excessdeuterium “d” and is calculated using Eq. 4:

d = δ2H‰ − 8δ18O‰ (4)

The “d” values are listed in Table 3, where the investigated groundwater samplesfrom the Selinsing borehole show low values of “d” (“d” less than 10‰). Thevariation of “d” values (0.3–6.9) was considered to have been caused by the temporalheterogeneity of the recharge and mostly affected by the evaporation process. Theevaporation was assumed to be negligible in the water balance method due to theconsideration of water solely at the Selinsing Canal (surface water). However, todetermine the isotopic composition in the groundwater sample, evaporation wasconsidered because of the influence of the water from paddy field (surface water)on the study area. The infiltration of the subsurface water during a rainfall event ispartly evaporated and condensed after the rainfall has ended. Therefore, the effect ofevaporation on the stable isotopic composition of the soil water remains. As a result,the groundwater is probably recharged by soil water, which is isotopically affectedby evaporation. Thus, the variation of d-excess value occurred in the groundwatersystem.

The groundwater samples from the study site are closely located in a singlemixing line irrespective of their temperature. In most cases, these waters have beeninterpreted as mixtures of local meteoric waters. Moreover, the groundwater samplesare enriched in 18O and chloride. Hence, distinct evidence shows that the maincontribution is from local rainfall and slightly evaporated surface waters. In otherwords, water in the groundwater samples (borehole) and in the Selinsing Canalsamples appears to be in the same cluster, indicating that it comes from the samesource as the water distributed in the range of the δ-diagram of precipitation and

2852 N. Dor et al.

comes close to the GMWL and MMWL. This situation indicates that there are closeinteractions between the Selinsing Canal (surface water) and shallow groundwateralong the irrigated cropland area.

4 Conclusions

A resistivity survey is a valuable aspect of modern geophysical techniques that givesan appropriate image of the subsurface resistivity distribution. Combination of thesedata with the borehole data will provide the best estimates of layer thickness foraquifer occurrences. The RIP and drilling results presented in this study illustratethe thickness of the aquifer, which varies between 5 and 10 m at a depth of 10–30 m.The upper and lower layers are made up of clay formations in the upper reaches ofthe canal.

Furthermore, a water balance estimate of the water loss/gain in the canal systemindicates that the catchment is very responsive to rainfall events and irrigationdiversions due to the water gain of the canal, although there are several occurrencesof seepage losses in the period time. The losses from the ADCP results are moreaccurate because the calculation of data was done for each segment. Moreover, waterlosses are also influenced by the occurrence of the shallow aquifer at the top soillayer, which are shown in the RIP results. The losses are mostly higher at that area.

In addition to the processes mentioned above, the stable isotopic composition ofwater in the Selinsing Canal shows the hydraulic interconnections between the canaland aquifer systems. This is proven by the water samples plotted in the δ-diagramsof 18O and δ2H that come close to the GMWL and MMWL. Furthermore, theevaporation effect during the recharge process in the study area causes the variationof d-excess value in groundwater. Therefore, the correlation between the RIP,water balance, and stable isotope methods can determine the surface–groundwaterconnectivity in the Kerian Irrigation Scheme.

Acknowledgements The authors would like to acknowledge the Ministry of Science, Tech-nology, and Innovation of Malaysia (MOSTI) for its financial support through grant No.305/PAWAM/6013374 and the Malaysian Nuclear Agency for the resistivity data acquisition andstable isotopes analysis.

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