Effects of Soil Moisture Content on Electrical Resistivity Tomography Values Survey in Irrigation Paddy Field, Tanjong Karang, Malaysia

EFFECTS OF SOIL MOISTURE CONTENT ON
ELECTRICAL RESISTIVITY TOMOGRAPHY VALUES
SURVEY IN IRRIGATION PADDY FIELD, TANJONG
KARANG, MALAYSIA

NURMALA SARI

GRADUATE SCHOOL
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
2015

DECLARATION OF THESIS AND
INFORMATION SOURCES AND PATENT
I hereby declare that this thesis entitled ―Effects of Soil Moisture Content on
Electrical Resistivity Tomography Values Survey in Irrigation Paddy Field,
Tanjong Karang, Malaysia‖ is based on my original work, under supervision of Dr
Ir Prastowo, MEng and Dr Ir Yuli Suharnoto, MEng, except for quotations and
citations which have been duly acknowledged. I also declared that this thesis has
been submitted for master degree at SupAgro – Montpellier, France, as
qualification to obtain Master Degree in Double Degree Indonesia – Prancis

(DDIP) Program 2013-2014, under supervision of Gilles Belaud and Jean
Stéphane Bailly.
I delegate the patent of this thesis to Bogor Agricultural University and
SupAgro – Montpellier, France.
Bogor, February 2015
Nurmala Sari
NIM F451120131

RINGKASAN
NURMALA SARI. Pengaruh Kelembaban Tanah Terhadap Nilai Resistivitas
Elektrik Tomografi Pada Pengamatan Areal Sawah Tanjong Karang, Malaysia.
Dibimbing oleh PRASTOWO, YULI SUHARNOTO, GILLES BELAUD, JEAN
STÉPHANE BAILLY dan MOHAMMED AZWAN MOHAMMED ZAWAWI.
Survey resistivity elektrik tomografi (ERT) telah dilakukan pada area irigasi
padi di Tanjong Karang, Malaysia sebagai salah satu survey untuk pencarian
akuifer air bawah tanah. Akuifer air bawah tanah ini diharapkan dapat menjadi
sumberdaya air alternatif untuk irigasi padi di samping penggunaan sumber air
permukaan. Berdasarkan hasil yang didapat dari survey ERT yang telah
dilakukan, sistem irigasi yang diartikan dengan kondisi kelembaban tanah
disinyalir memberikan pengaruh terhadap nilai resistivitas elektrik dan juga

terhadap profil lapisan tanah yang dihasilkan dari survey ERT. Tujuan dari
penelitian ini yaitu untuk membuktikan adanya keterkaitan antara kelembaban
tanah dengan nilai resistivitas elektrik dan untuk menentukan level kelembaban
tanah yang tepat untuk dilakukannya survey ERT.
Survey ERT dilakukan dengan menggunakan alat survey ABEM Terrameter
SAS 4000 dengan susunan elektroda Wenner – Schlumberger. Jarak antara
elektroda untuk kabel bagian dalam dan kabel bagian luar masing – masing adalah
5.0 meter dan 10.0 meter. Profil lapisan bawah tanah yang dihasilkan dari analisis
ERT memperlihatkan bahwa kelembaban tanah mempengaruhi nilai resistivitas
elektrik. Dari beberapa kondisi kelembaban tanah yang berada pada rentang
16.96% hingga 27.50%, nilai resistivitas elektrik menurun pada beberapa titik dan
pada kedalaman tertentu seiring dengan meningkatnya kelembaban tanah. Ini
dibuktikan dengan uji analisis Anova dan Duncan yang memberikan nilai Pr > F
sebesar < 0.0001 yang menunjukkan bahwa nilai kelembaban tanah berpengaruh
signifikan terhadap nilai resistivitas elektrik. Lebih jauh lagi dengan uji Chisquare, menunjukkan bahwa kelembaban tanah pada tingkat 22.54% memberikan
nilai resistivitas elektrik yang lebih tepat jika dibandingkan dengan nilai
resistivitas elektrik pada borehole pada lokasi survey.
Kata kunci: air tanah, areal sawah, irigasi, kelembaban tanah, resistivitas elektrik
tomografi

SUMMARY
NURMALA SARI. Effects of Soil Moisture Content on Electrical Resistivity
Tomography Values Survey in Irrigation Paddy Field, Tanjong Karang, Malaysia.
Supervised by PRASTOWO, YULI SUHARNOTO, GILLES BELAUD, JEAN
STÉPHANE BAILLY and MOHAMMED AZWAN MOHAMMED ZAWAWI.
Electrical Resistivity Tomography (ERT) surveying method has been
conducted in Irrigation Paddy Scheme, Tanjong Karang, Malaysia as part of
investigation on groundwater potential aquifer to provide an alternative water
resource for paddy irrigation. Based on recent studies on soil water resistivity in
paddy field, irrigation system mentioned as soil moisture content was observed to
affect the value of electrical resistivity and subsurface geological profile resulted
from ERT surveying method. The objective of this study was to proof any
correlation between soil moisture content and electrical resistivity values and to
determine at what level of soil moisture content which will be the best condition
to conduct ERT survey.
ERT analysis was conducted by using ABEM Terrameter SAS 4000 of
Wenner-Schlumberger array with 5.0 meter and 10.0 meter for minimum and
maximum electrode spacing. Visually, based on subsurface geological profile
resulted from ERT analysis, soil moisture content affected (changed) electrical
resistivity values. With all different treatments of soil moisture ranged from

16.96% to 27.50%, electrical resistivity values decreased in certain points and in
certain depth along with the increase of soil moisture content. This was proofed
by Anova and Duncan’s multiple range tests showing that Pr > F value was less
than 0.0001. Further on Chi-square test showed that at soil moisture level of
22.54%, it was the best condition which gave more correct counts of electrical
resistivity values compared to well lithology sited on site survey location. This
was assumed to be the best condition to conduct ERT survey.
Keywords: electrical resistivity tomography, groundwater, irrigation, paddy field,
soil moisture

© Copyright of Bogor Agricultural University, 2015
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not give any disadvantage on behalf of Bogor Agricultural University.
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External examiner in final examination: Dr Ir Roh Santoso Budi Waspodo, MT

EFFECTS OF SOIL MOISTURE CONTENT ON
ELECTRICAL RESISTIVITY TOMOGRAPHY VALUES
SURVEY IN IRRIGATION PADDY FIELD, TANJONG
KARANG, MALAYSIA

NURMALA SARI

Thesis
in fulfillment of the requirement for the degree of
Master Science in
Study Program of Civil and Environmental Engineering

GRADUATE SCHOOL
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
2015

Thesis title : Effects of Soil Moisture Content on Electrical Resistivity
Tomography Values Survey in Irrigation Paddy Field, Tanjong

Karang, Malaysia
Name
: Nurmala Sari
NIM
: F451120131
Approved by
Supervisory committee

Dr Ir Prastowo, MEng
Committee chairman

Dr Ir Yuli Suharnoto, MEng
Committee member

Authorized by

Civil and Environmental
Engineering Study Program
Chairman,

Dean of Graduate School

Dr Satyanto K. Saptomo, STP, MSi

Dr Ir Dahrul Syah, MScAgr

Date of Final Examination:
7 January 2015

Date of Graduation:

FOREWORD
In the name of Allah SWT, the Most Gracious and the Most Merciful God
who has helped, guided and blessed me through all the way to complete my
Master study. Peace is upon my prophet Muhammad SAW who has fought for his
entire life for Islam and brought Islam to light our lives. This study was intended
as requirement to graduate in Master degree in Bogor Agricultural University,
Indonesia. Groundwater was taken as topic for this study entitled ―Effect of Soil
Moisture Content on Electrical Resistivity Tomography Values Survey in
Irrigation Paddy Field, Tanjong Karang, Malaysia‖.

Allow me to express my special appreciation and deepest gratitude to my
supervisors, Dr Ir Prastowo, MEng and Dr Ir Yuli Suharnoto, MEng who have
supervised and guided me in fulfilling my thesis. For my internship supervisor,
Mr. Mohamed Azwan bin Mohamed Zawawi, who has helped and assisted me in
internship program for 6 months in Universiti Putra Malaysia (UPM), Malaysia.
Thank you to all engineering assistants and colleagues in Soil and Water
Conservation Engineering laboratory, UPM. I dedicate my sincere appreciation to
my supervisors Mr. Gilles Belaud and Mr. Jean Stéphane Bailly for guiding and
assisting me in completing my Master 2 program in SupAgro-Montpellier, France,
in Double Degree Indonesia – Prancis (DDIP) program 2013 – 2014. Thank you
to Directorate of Higher Education of Indonesia (DIKTI) and Government of
France (BGF) who had granted me a full scholarship in 2012-2014, so that I could
complete and finish my study in appropriate time.
I am deeply indebted to my beloved family, my husband, Jumhar Febriko,
and my family in Persatuan Pelajar Indonesia (PPI) Montpellier and PPI – UPM,
thank you so much for your endless love, prayers and encouragement. Lastly, I
would like to thank whoever who is indirectly contribute to this research and gave
me possibility to complete this research. Thank you so much.
May this study be blessed..

Bogor, February 2015
Nurmala Sari

TABLE OF CONTENTS
LIST OF TABLES

vi

LIST OF FIGURES

vi

LIST OF APPENDIXES

vi

1 INTRODUCTION
Background Study
Problem Statement
Objectives of Study

Benefits of Study
Scope of Study

1
1
2
2
2
2

2 LITTERATURE REVIEW
Groundwater Investigation
Geophysics Method for Groundwater Investigation
Electrical Resistivity Tomography (ERT)
ERT Surveys in Several Studies

3
3
6
6

9

3 MATERIALS AND METHODS
Study Site
Research Procedure
Calibration of 5TE Soil Moisture Sensor
Preliminary ERT survey
Site Survey
Materials
Instruments
Data Analysis Procedure

11
11
13
14
15
16
16
17
18

4 RESULT AND DISCUSSION
Calibration of 5TE Soil Moisture Sensor
Preliminary ERT survey
Site Survey

18
18
19
21

5 CONCLUSION AND PERSPECTIVE
Conclusion
Perspective

25
25
26

REFERENCES

26

APPENDIX

29

BIOGRAPHY

41

LIST OF TABLES
1
2
3
4
5

Data requirements for a groundwater investigation
Gephysical methods used in groundwater exploration
Comparison of dipole-dipole, Schlumberger, square and Wenner
electrode arrays
Categories of possibility to extract groundwater
Electrical resistivity of well lithology in Block F

3
7
9
23
24

LIST OF FIGURES
1 Flow diagram showing the sequence of tasks in groundwater
2 Arrangement of electrodes for a 2-D electrical survey and the
sequence of measurements used to build up a pseudosection
3 Common arrays used in resistivity surveys and their geometric
factors
4 Study site of Sawah Sempadan - Irrigation Scheme, Tanjong Karang
- Malaysia
5 Block C of Sawah Sempadan, Tanjong Karang, Malaysia
6 Block F of Sawah Sempadan, Tanjong Karang, Malaysia
7 Soil moisture measurement using 5TE sensor
8 ERT installation of preliminary study on Block C
9 ERT installation of site survey on Block F
10 ABEM Terrameter SAS 4000
11 5TE Soil moisture sensor
12 Calibration graph of 5TE soil moisture sensor
13 Soil moisture content changes in preliminary study on Block C
14 Comparison of subsurface geological profile on preliminary study.
Treatment with normal condition, soil moisture of 25.6 % (a), soil
moisture of 46.8 % (b), and soil moisture of 48.1 % (c)
15 Soil moisture content changes in site survey Block F
16 Comparison of subsurface geological profile on site survey.
Treatment with normal condition soil moisture of 16.96 % (a), soil
moisture of 22.54 % (b), and soil moisture of 27.50 % (c)
17 Soil moisture changes in paddy planting seasons

5
8
9
11
13
14
15
16
16
17
17
19
19
21
21
22
25

LIST OF APPENDIXES
1
2
3
4
5
6

Irrigation Schedule in West Selangor, Malaysia
Soil types in Block C and Block F, Tanjong Karang, Malaysia
5TE Soil Moisture Sensor Calibration
Soil density measurement
Well schematics and lithology in Block F
Chi – square analysis results

29
30
32
38
39
40

1 INTRODUCTION
Water resource is definitely one of the most important factors in
agricultural activities. Especially for paddy plantation, irrigation is important
to be managed and scheduled in order to fulfill the needs of water for each of
paddy plantation stages. The most commonly used water resource for paddy
plantation was surface water such as rivers and ponds. The use of surface
water as water resource nowadays is facing the problem of draught, pollution
and the amount of surface water itself which is limited to fulfill the need of
agricultural activity (irrigation) (Hock 2008). Water shortage was due to the
unbalance condition of supply and demand of water resources for agricultural
activities and industrialization, especially in dry season. Due to this problem,
it is necessary to find other alternative water resource to substitute surface
water for agricultural activities.
Groundwater stored in the subsurface aquifer throughout Malaysia is
estimated at 5000 billion m3, or 90% of Malaysian freshwater resource which
is stored as groundwater (Azhar 2000). Recently, many researches have
studied about the availability of subsurface water (groundwater) to take place
as an alternative water resource, especially in Malaysia. One of studies was to
find the potential location of subsurface aquifer by using Electrical
Resistivity Tomography (ERT) surveying method on the site, where it was
expected to be water resource for agricultural activities. ERT was confirmed
to be one of geophysical methods which was efficient to provide detailed
distribution of electrical resistivity to characterize the lineament such as
quartz reef in granite host rock (Chandra et al. 2010).

Background Study
One study has given another opportunity to explore and investigate
how electrical resistivity works on groundwater investigation. The study of
several ERT surveys on paddy field in Sawah Sempadan, Tanjong Karang,
Malaysia has been conducted and came up with results that electrical
resistivity values, in same survey line, would change for every time sampling
and every paddy planting season, due to irrigation activities. First ERT
survey method was conducted in ploughing season meaning that there was no
irrigation applied. Second ERT survey was conducted in saturation (after
sowing) season, meaning that there was irrigation applied.
This study is necessarily to be done as consideration to whoever who
wants to use ERT method for different kind of purposes, taking into account
the soil moisture content condition before applying electrical resistivity
analysis. For example, the use of electrical resistivity method to find potential
location of groundwater aquifer, which is described as electrical resistivity
values (Ωm) in a given subsurface geological profile with certain depths,
resulted from ERT inversion. This is then followed by drilling process in
certain distance and depth to have production well. If the subsurface profile
resulted from this method does not give the correct profile as it is in the field,

2
then proposed well will be incorrect and that would cause loses in times,
financial, labors, etc. This study aims to help the use of electrical resistivity
method in order to achieve a more correct subsurface geological profile.

Problem Statement
As one of the most important factors, water resource has to be
maintained and sufficient to meet water needs in agricultural activities,
especially for paddy plantation. Several problems which may occur like
water pollution, salinity and water drought may give negative impacts to
paddy plantation in term of irrigation activities. Therefore, one way to
maintain water resource for irrigation is by finding alternative water resource
like using groundwater. One way to find potential location for groundwater
aquifer is by using ERT method. But in several ERT surveys which have
been conducted, the results of electrical resistivity values would change in
different condition of soil moisture (depends on irrigation on the field). This
phenomenon offered two hypotheses; 1) the use of water (irrigation activity),
in this study mentioned as soil moisture content, during paddy planting
seasons influences the results of electrical resistivity analysis, in term of
electrical resistivity values and 2) correct values of electrical resistivity will
be achieved at an appropriate level of soil moisture content.

Objectives of Study
General objective of this study is to find potential location of
groundwater aquifer in paddy plantation area. The specific objectives of this
study are; 1) to find correlation between soil moisture content and electrical
resistivity values in groundwater investigation, and 2) to determine the
appropriate level of soil moisture content in paddy soil to conduct ERT
survey.

Benefits of Study
This study was intended to improve the use of electrical resistivity
surveying method by taking into consideration the condition of soil moisture
content before applying ERT survey. Furthermore, this would help
stakeholders to minimize loses in time, budget, and labor consuming.

Scope of Study
The use of electrical resistivity method in this study was objected to
determine potential location of groundwater aquifer, based on electrical
resistivity values resulted from ERT analysis. The application limit of this
study was only applied for paddy soil having three different soil layers; top
soil (depth 0 cm – 7 cm), hardpan (depth 8 cm – 69 cm), and subsoil (depth

3
70 cm – 80 cm) (Shazelia 2011). Several studies would be necessary in order
to apply this study in other different type of soil.

2 LITTERATURE REVIEW
Groundwater Investigation
Groundwater investigation is focused on production wells – for
drinking water, irrigation or other supply purposes, but also focused on
locating other type of wells for other purposes – aquifer cleanup, artificial
recharge, and groundwater monitoring. The objectives of the groundwater
investigations should be to find locations where wells can be designed and
constructed to supply the required demand of water, of a quality suitable for
the intended use, at reasonable cost and with least impact to either fellow
groundwater users or to the aqueous environment. Environmental impacts to
be avoided include: (i) significant reductions in soil water flow to
ecologically important wetlands, spring areas or base flow-supported rivers;
(ii) saline intrusion in coastal aquifers; and (iii) ground subsidence caused by
large drawdowns in unconsolidated, compressible aquifers or by dewatering
organic-rich sub soils or sediments.
Flow diagram illustrating the sequence of groundwater investigations
for locating well sites and planning a well scheme is shown in Figure 1.
While several data are required in groundwater investigation as given in
Table 1.
Table 1 Data requirements for a groundwater investigation
Data requirements
Topographic maps
Bedrock geology maps
Soils, subsoils and land use maps
Hydrogeology and groundwater
vulnerability maps
Geology, hydrogeology, site
investigation and other relevant
reports
Aerial photographs, satellite imagery

Well and borehole records

Main data sources
National state mapping agency
Geological survey
Geological survey, agriculture
ministry
Geological survey, water ministry,
environmental agency
Geological survey, water ministry,
environmental agency, local
authorities, consulting firms,
nongovernmental organizations
National mapping agencies plus
international agencies for distribution
of Landsat, SPOT and other satellite
imagery (e.g NASA)
Geological survey, water ministry,
environmental agency, consulting
firms, drilling firms,
nongovernmental organizations

4
Data requirements
Water level and water quality
monitoring data

Main data sources

Geological survey, water ministry,
environmental agency,
environmental health office, local
authorities
Existing groundwater abstractions
Geological survey, ministry of water,
rural development, irrigation or
public works
River flow records
Ministry of water, hydrometric
agency, environmental agency,
consulting firms, electricity
(hydropower) authorities
Climate data, including rainfall and
Meteorological office, hydrometric
evapotranspiration
agency, water ministry,
environmental agency
Source : (Misstear, Banks, and Clark 2006)

5

Figure 1 Flow diagram showing the sequence of tasks in groundwater

6
Geophysics Method for Groundwater Investigation
Geophysical surveys can provide useful data on geology, aquifer
geometry and water quality. Geophysical surveys are sometimes undertaken
without proper planning, but rather in the hope that they will show something
useful. It does not lead to a unique geological model; more than one
interpretation of the data is possible. Borehole control is essential to reduce
this ambiguity. Therefore, geophysical surveys should be carried in
conjunction with exploratory boreholes rather than as a replacement for a
drilling program. The combined use of geophysics and drilling can produce
results more cheaply than relying on drilling alone, since the number of
exploratory boreholes can be reduced (Misstear, Banks, and Clark 2006).
There are several methods used in geophysical groundwater
investigation as mentioned in Table 2. Different methods provide data on
different geophysical properties on the ground and therefore, the best survey
results are usually achieved by using more than one method (Misstear, Banks,
and Clark 2006).
Electrical Resistivity Tomography (ERT)
ERT surveying method is one tool in geophysical method used in
groundwater investigation, which uses the principle of electrical resistivity.
Among other principles used in groundwater investigations are
electromagnetics (EM), magnetometry, seismic, ground penetrating radar
(GPR), and gravity (Misstear, Banks, and Clark 2006). Each of these
principles has different in main applications in groundwater investigations.
This study will focus on ERT surveying method, because more researches
used this method due to its low cost, simple operation, and efficiency in areas
with high contrasting resistivity (Muchingami et al. 2012).
Method of electrical resistivity is basically aimed to determine
subsurface resistivity distribution by making measurement on the ground
surface. This measurement will then be inverted to get true electrical
resistivity values of subsurface.
Basically the concept of ERT survey is by passing an electrical current
(I) into the ground between two electrodes and measuring the potential (V)
difference between two other electrodes. Then, apparent electrical resistivity
(pa) can be calculated as,
Source: (Loke 2000)

Where k is geometric factor which depends on electrode arrangement
of ERT survey line. Since resistance (R) is equal as V/I, then, apparent
electrical resistivity could be calculated as,
Source: (Loke 2000)

The apparent result as called pseudosection was generated by several
measurement as described in Figure 2.

Table 2 Gephysical methods used in groundwater exploration
Principle
Electrical resistivity

Electromagnetics (EM)

Magnetometry
Seismic
Ground penetrating
radar (Georadar)

Gravity

Method

Main applications in groundwater exploration

Vertical Electrical Sounding
(VES)

Depth to bedrock, thickness of superficial deposit, depth to water table,
depth of weathering in crystalline rock aquifers, depth to saline water
interface in coastal aquifer, aquifer properties
Electrical resistivity profiling Location of buried valleys, detection of vertical/near vertical fracture
(constant electrode separation zones, depth of weathering in crystalline rock aquifers, location of
traversing)
contaminant plumes
Electrical Imaging
Two-and three-dimensional imaging combines many of the applications of
(tomography)
VES and resistivity profiling. Time lapse (or four dimensional) imaging
can monitor water movement in the subsurface
Ground conductivity profiling Similar application to resistivity profiling
(frequency-domain EM)
Time-domain EM (TDEM)
Similar application to VES, but often used for greater depths of
investigation
Very low frequency (VLF)
Mainly for location of vertical/near vertical fracture zones, also to
determine depth to bedrock, depth to water table
Surface nuclear magnetic
Aquifer geometry, aquifers properties
resonance (SNMR)
Total magnetic field anomaly Location of igneous dykes, location of fracture zones
Seismic refraction
Depth to bedrock, thickenss of superficial deposits, depth to water table,
depth of weathering in crystalline rock aquifers, location of fracture zones,
Thickness of sand and gravel aquifers, depth to bedrock, depth to water
table, location of sub-horizontal fractures or cavities in karst limestones

Gravity and microgravity
surveys

Source: (Misstear, Banks, and Clark 2006)

Gometry of extensive sedimentary aquifers, location of buried valleys,
location of cavities in kars limestones (microgravity)

Figure 2 Arrangement of electrodes for a 2-D electrical survey and the
sequence of measurements used to build up a pseudosection
The first step is to make all the possible measurements with the Wenner
array with an electrode spacing of ―1a‖. For the first measurement, electrodes
number 1, 2, 3 and 4 are used. Notice that electrode 1 is used as the first
current electrode C1, electrode 2 as the first potential electrode P1, electrode
3 as the second potential electrode P2 and electrode 4 as the second current
electrode C2. After completing the sequence of measurements with ―1a‖
spacing, the next sequence of measurements with ―2a‖ electrode spacing is
made. First electrodes 1, 3, 5 and 7 are used for the first measurement. The
electrodes are chosen so that the spacing between adjacent electrodes is ―2a‖.
For the second measurement, electrodes 2, 4, 6 and 8 are used. This process
is repeated down the line until electrodes 14, 16, 18 and 20 are used for the
last measurement with spacing ―2a‖.
The results of apparent resistivity were then inverted by using
RES2DINV (Geotomo software, 1995) software to perform an analysis and
generate subsurface geological profile in a .DAT file format to describe the
real subsurface geological profile (Loke 2000). There are several types of
array (electrodes) arrangements (Loke 2000); Wenner, Schlumberger,
Dipole-Dipole, Pole-Dipole, Wenner-Schlumberger, and Equatorial DipoleDipole. These arrangements are presented in Figure 3.

9

Figure 3 Common arrays used in resistivity surveys and their geometric
factors
Where C, is injected current, P, is calculated difference of potential, a,
is distance between electrode, k, is geometric factor (depends on array), and n,
is the distance difference between C and P. Each of these arrays has different
advantages and disadvantages as shown in Table 3.
Table 3 Comparison of dipole-dipole, Schlumberger, square and Wenner
electrode arrays

Moderate
Moderate
Good
Yes

Dipoledipole
Poor
Good
Poor
Good
Moderate

Moderate
Moderate
Good
No

High

Moderate

Moderate

Low

Yes
Good

Moderate
Good

Moderate
Moderate

Yes
Poor

Criteria

Wenner

Vertical resolution
Depth penetration
Suitability to VES
Suitability to CST
Sensitivity to
orientation
Sensitivity to lateral
inhomogenities
Labour intensive
Availability of
interpretational aids
Source: (Reynolds 1997)

Good
Poor
Moderate
Good
Yes

Schlumberger

Square

ERT Surveys in Several Studies
Many studies related to electrical resistivity method have been
conducted throughout countries to solve and overcome water resource,
management and conservation problems. In Zimbabwe, study on the potential
location of subsurface aquifer has been conducted by using a combination of

10
ERT surveying method (Wenner-Schlumberger) and Vertical Electrical
Sounding (VES) method (Muchingami et al. 2012). It was mentioned that
ERT surveying method provided a more detailed interpretation of the
subsurface hydro-geological features from which potential sites for
successful borehole (well) location are identified. This study applied Wenner
– Schlumberger array of 100 meter survey line with 5 meter distance of
electrode spacing in four different survey lines. Here, it was concluded that
electrical resistivity values for high potential groundwater was in value of
less than 50 Ωm and for low potential groundwater location was in value
higher than 500 Ωm. And here, they found suitable borehole location which
could be used for long term groundwater prospecting.
Groundwater, soil pollution and salinity were also presented as problem
that could be solved by using resistivity method (Jiang et al. 2013) (Mcinnis
et al. 2013) (Yogeshwar et al. 2012). On their research (Jiang et al. 2013),
high-electrical resistivity surveying method was used to locate contaminant
source causing groundwater pollution in Nanjing chemical plant, China. By
using four different types of array; Wenner Array, Schlumberger Array, PoloPole Array and Dipole-Dipole Array, the results mentioned that the
contaminant was in level exceeding 100 Ωm of electrical resistivity values,
and the distribution of contaminant in subsurface layer was delineated by
profile map resulted from inversion of apparent electrical resistivity values.
This result was verified by chemical analysis of soil and water sampling
which was taken from observation borehole along electrical resistivity survey
line. The profile map could be used as guidance to determine location point
where to conserve area which was already polluted.
Investigations on the occurrence of potential subsurface aquifer have
also been done by some researches to provide an alternative water resource
for irrigation instead of using water surface (Chandra et al. 2010) (Tronicke
et al. 1999). In (Chandra et al. 2010), the study was focused on geophysical
modeling of geological discontinuities in a granitic aquifer in Hyderabad,
India. The research integrated ERT method of Wenner-Schlumberger array
with 10 meter electrode spacing, electrical resistivity values from well drilled
along survey line, and well lithology, and came up with results of 2D profile
of geological set up of quartz reef in granite host medium, and among the
results it showed that deepening of fracturing fronts over the quartz reefs as
well as generation of fractures inside the body would turn into groundwater
potential zones. Other study on groundwater exploration was conducted in
northern Germany on Spiekeroog Island (Tronicke et al. 1999). This study
was conducted by joining ERT (Schlumberger array with maximum of 150
meter electrode spacing) and Ground Penetrating Radar (GPR) survey. In this
study they were able to map contour of freshwater lens trapped in subsurface
layer, based on values of water level reading from groundwater boreholes and
groundwater level as reflected by GPR. This map described the location of
potential freshwater (in unit meter over mean sea level) and also showed the
effect of water exploitation in that island that caused in decrease of water
table values. In Malaysia, one of the uses of resistivity method was used to
calculate and figure freshwater lens on an island of Carey (Baharuddin et al.
2013). Other case, there was once applied resistivity measurement for

11
groundwater investigation in dry area of Northern Kuwait (Al-ruwaih and Ali
1986). In this study, due to dry nature of the surface soil and presence of
highly cemented gravels and sandstone at shallow depth, contact resistance at
the current electrodes was high and current penetration was a major problem,
therefore it was necessary to wet current electrodes (or best conducted after
rainfall). These studies, among other studies, have given a broader and deeper
knowledge of the usefulness of ERT method in agricultural and
environmental field.

3 MATERIALS AND METHODS
Study Site
The study site was in Sawah Sempadan Irrigation Scheme, Tanjong
Karang, Malaysia, which covers an area approximately of 2,300 ha. This
area, among other areas, is under supervision of IADA (Integrated
Agricultural Development Area), Ministry of Agriculture and Agro-based
Industry Malaysia, which concerns on developing integrated agricultural
activities all over Malaysia. Map of Sawah Sempadan is presented in Figure
4.

Block F

Figure 4 Study site of Sawah Sempadan - Irrigation Scheme,
Tanjong Karang - Malaysia
Paddy varieties which are commonly planted throughout Malaysia are
MR 84, MR 167, MR 185, MR 159. Normally certified paddy seeds
(certificate of Malaysian Standard MS 469:1993) are planted and sold by
Department of Agriculture, under Ministry of Agriculture and Agro-Based

12
Industry to all farmers in Malaysia. Paddy seeds are planted in soil with pH
of 5.0 – 6.0, nitrogen of 2% – 3%, phosphor of > 40 ppm, potassium of > 0.1
mEq/100 gram, CEC of > 20 mEq/100 gram and carbon organic of 2% - 3%
(Pertanian 1999). Other soil properties which should be maintained for paddy
planting are soil slope of 0% - 2%, soil depth of >25 cm, and soil texture of
sandy loam or very fine sand.
Normally there are three different paddy planting methods such; direct
sowing in dry paddy plot, direct sowing in wet paddy plot and indirect paddy
planting. The most commonly practiced method is indirect paddy planting,
meaning that paddy seeds are sowed in a 1 – 2 meter wide plot and any
desirable length. After 15 days after sowing, it is recommended to give
fertilizers (urea: 80 kg/ha N, 30 kg/ha P2O5, 20 kg/ha K2O - for west coast of
Malaysia) to paddy seeds with concentration of 45 – 50 gram/m2. And after
18 to 21 days paddy seeds are ready to be planted in paddy plot.
For indirect paddy planting method, land preparation is applied
normally 27 days before planting, starting from dry ploughing activity. Paddy
plots are ploughed using mechanized tractor which could be rent and
subsided by government. After dry ploughing, next activity is weeding in 1723 days before planting. This activity prevents paddy pests and diseases from
attacking area. Next activity is second ploughing (dry or wet) on 7-10 days
before planting, followed by wet ploughing and soil leveling on 1 day before
planting. Last ploughing activity is to irrigate paddy plot until water level
reaches 10 cm above ground. After being irrigated, water excess on paddy
plot is flowed in to drainage canal, and plot is ready to be planted.
Paddy seeds are planted with distance of 25 cm x 25 cm for optimum in
growing and food gaining. Fertilizing activity is continued for three times
after paddy being planted in paddy plot. First in 15 days after planted with
concentration of NPK is 35 kg/ha, 30 kg/ha and 20 kg/ha, respectively.
Second in 35 days after planted with only 23 kg/ha N. Third in 55 days after
planting with 22 kg/ha N. Paddy will be harvested after 125 – 135 days after
sowing.
Irrigation activities on Sawah Sempadan are applied by using integrated
irrigation canal systems of primary and secondary canal. Main water resource
is from surface water of river near paddy plots and water is delivered along
main canal and distributed along in secondary canal. Once the paddy plot is
fulfilled with irrigation water, excess water will flow out over the drainage
canal. The needs of irrigation water depend on each paddy planting stages.
More water is required on after sowing and mid-season stage for
approximately 10 cm of high water level inside paddy plot (Pertanian 1999).
Details of irrigation schedule are presented in Appendix 1. Irrigation
schedule is managed and controlled fully by IADA.
Sawah Sempadan is divided into 24 blocks namely Block A to X
(Wayayok 2006). The study will be conducted in Block C and Block F as
experiment site. Block C was contained of two different soil series namely
Telok series and Jawa series (Wayayok 2006), while Block F was contained
of one soil series namely Sabrang series (IADA 2009). Details of the series
are presented in Appendix 2.

13
Research Procedure
Several preliminary studies have taken place in order to support this
study, including 1) calibration of 5TE soil moisture sensor, 2) preliminary
ERT survey, and 3) site survey. The calibration of 5TE sensors was taken
place in laboratory of Soil and Water Conservation, Faculty of Engineering,
Universiti Putra Malaysia (UPM) – Malaysia. While preliminary and site
surveys were conducted in Block C and Block F, Sawah Sempadan, Tanjong
Karang, Malaysia in May – June 2014. Study Block C and block F are shown
in Figure 5 and Figure 6.

Figure 5 Block C of Sawah Sempadan, Tanjong Karang, Malaysia

14

Figure 6 Block F of Sawah Sempadan, Tanjong Karang, Malaysia
Calibration of 5TE Soil Moisture Sensor
This calibration was intended to see the performance of 5TE soil
moisture sensor to measure soil moisture content, compared to oven dried
method. Soil samples used for this calibration were randomly selected in
laboratory area. Thirty different conditions of soil moisture were measured
by 5TE Soil moisture sensor and by using oven dried method. These
conditions were achieved by adding water into the soil so that soil moisture
would be varied. The 5TE sensors read soil moisture content in volumetric
based (%), while oven dried method was soil moisture measurement on
weight based (%).
Thirty different samples of soil were placed in a beaker and 5TE sensor
was put in each beaker. All sensors were then connected to Em50 ECH20
Logger. Measurements by 5TE soil moisture sensor were recorded in 30
minutes in Em50 logger with interval reading of 2 minutes. So for every
sample there would be 15 reading of soil moisture sensors which would then
be averaged to get average soil moisture sensor. Data stored in data logger
were downloaded in ECH2O software (Decagon Device Inc, 2006) in
spreadsheet file format. Soil moisture measurement using 5TE sensor was
presented in Figure 7.
While for oven dried method, 5 samples of each soil conditions was
placed in a beaker with approximately 50-80 gram soil sample. Soil sample
was oven dried for 24 hours and soil moisture was calculated based on
difference of wet soil sample and dried soil sample (weight based). Since
oven dried method gave weight based measurement, the results should be
multiplied by soil density to find volumetric soil moisture results, as
measurement unit of 5TE soil sensors. Soil density (ρ) was determined in
manual method; by compacted random soil sample in a beaker and measure

15
beaker weigh (gram) as soil weight and beaker volume as soil volume (cm3).
Soil density was calculated by using equation below:

Figure 7 Soil moisture measurement using 5TE sensor
Preliminary ERT survey
The preliminary ERT survey was conducted in Block C - Irrigation
Scheme, Tanjong Karang, Malaysia. ERT measurement was set by using a
400 meter survey line of Wenner-Schlumberger array with minimum and
maximum electrode spacing of 5.0 meter and 10.0 meter. WennerSchlumberger array was chosen because based on several journals on
groundwater resistivity analysis this array gives greater sensitivity in vertical
and horizontal profile of subsurface than other arrays do (Loke 2000),
(Muchingami et al. 2012).
This preliminary study was intended to see the changes of electrical
resistivity results in relation to soil moisture content. In this case, resistivity
measurement on the field was conducted in 3 different treatments, varied by
amount of water injected into the electrode, but still using the same survey
line. FIEL0, FIEL1, FIEL2 are those treatments with normal condition,
additional of 200 ml water and another additional of 200 ml water,
respectively for each treatment. ERT measurement was run each time for
each treatment and took time for approximately 45 minutes for 781 points
reading, while soil moisture measurement was run in mean time of ERT
measurement. The measurement of soil moisture sensor in survey line was
conducted by installing 5 5TE soil moisture sensors on a depth of 5 to 8 cm
in distance of 2.5 meter at 100 meter survey line (data logger A), and another
5 sensors at 300 meter of survey line (data logger B). Survey line was
arranged as shown in Figure 8.

16

Logger A

100 m

Logger B

100 m

100 m

100 m

Figure 8 ERT installation of preliminary study on Block C
Site Survey
After preliminary studies have been conducted, site survey was held by
using the same method as preliminary study of ERT; using WennerSchlumberger array with 5 meter and 10 meter of minimum and maximum
electrode spacing. This survey was conducted in Block F, Irrigation Scheme,
Tanjong Karang, Malaysia. This survey was intended to see how soil
moisture content affects electrical resistivity values by comparing electrical
resistivity values to well lithology sited nearby the survey line. Three
treatments were applied in this survey; 1) normal condition (FIEL0a), 2)
addition of 100 ml water (FIEL1a), and 3) addition of 100 ml water for every
30 minute (FIEL2a). These treatments were applied in order to vary soil
moisture content. Five 5TE sensors were installed in center of survey line in
distance of 2.5 meter between each sensor. Survey line was arranged as
shown in Figure 9.

Logger A

100 m

100 m

100 m

100 m

Figure 9 ERT installation of site survey on Block F

Materials
Materials used in this study were randomly disturbed selected soil
sample which were used for 5TE soil sensor calibration in Soil and Water
Conservation Engineering Laboratory.

17

Figure 10 ABEM Terrameter SAS 4000

Figure 11 5TE Soil moisture sensor
Instruments
Some hard wares and soft wares were used in this study. For hard ware
instruments, it was used 5TE soil moisture sensor from Decagon Company,
with 70 Hz dielectrics wave frequency. Other hard ware was 1 unit of oven
and instruments used to measure soil moisture content in manual method;
oven dried method. While for electrical resistivity method, it was used 1 unit
of ERT instrument ABEM Terrameter SAS 4000. Hard wares are shown in
Figure 10 and Figure 11.
Instruments in soft wares used in this study were; 1) software ECH2O
Utility version 1.12 from Decagon Company to download result measured of
soil moisture recorded in data logger sensor 5TE, 2) software SAS 4000
(ABEM Instrument AB, 1999) to download values of electrical resistivity
recorded in instrument ABEM Terrameter SAS 4000, and 3) software
RES2DINV version 3.71 (Geotomo software, 1995-2011), to analyze results
of electrical resistivity and 4) software for statistical analysis, Minitab
version 16.1 (Minitab Inc, 2010).

18
Data Analysis Procedure
Statistical analysis was done to provide a deeper analysis and to proof
the hypothesis that soil moisture content will affect electrical resistivity
values. Analysis using ANOVA and Duncan’s multiple range tests on SAS
9.3 software were used to proof this hypothesis. Another study which would
be conducted was to determine level of soil moisture content which will give
correct values of electrical resistivity compared to well lithology. This was
done by using Chi-square test method in Minitab 16 software. This analysis
was to compare electrical resistivity values from different conditions of soil
moisture content to electrical resistivity values of well lithology, and see
which level of soil moisture which gave the closest electrical resistivity
values to well values.
In statistical analysis, it was focused on 102.5 meter inner survey line
with 1,800 points of ERT values. This was due to the electrode distance in
inner survey line which was set closer to each other (5 meter instead of 10
meter). The closer the electrode spacing the deeper the profile and the more
points of ERT will be produced.

4 RESULT AND DISCUSSION
Calibration of 5TE Soil Moisture Sensor
Em50 data logger will automatically transfer file of soil moisture
content values in excel spreadsheet once it was downloaded. Each treatment
has 15 readings, and should be averaged to find the value of soil moisture
content for each. Along with this, oven dried method has also 5 samples of
each treatment and should be averaged to find weigh based of soil moisture
content, and multiplied by density of soil. Soil moisture measurements by
oven dried method and 5TE soil moisture sensor were presented in Appendix
3. Density of sample soil was 1.312 gr/cm3. Details of soil density
measurement were presented in Appendix 4. Results of 5TE soil moisture
sensors and oven dried method are plotted in Figure 12.

19
Soil moisture content
(volumetric measure)
Oven dried method (%)

45
40
35
30
25

y = 0.9946x
R² = 0.8182

20
15
10
5
0
0

5

10

15

20

25

30

35

40

45

5TE sensor (%)

Figure 12 Calibration graph of 5TE soil moisture sensor
The calibration of 5TE soil moisture sensor was resulted in value of R 2
of 0.8182 with y = 0.9946x. This gives satisfaction that 5TE soil moisture
sensor was able to measure volumetric soil moisture content directly with
percentage of correctness was approximately 81.82%.
Preliminary ERT survey
Based on three different treatments applied in preliminary study of
ERT, the result of soil moisture content showed that maximum soil moisture
was in range of 46-48 %. The changes in soil moisture content along these
treatments are shown in Figure 13.
Volumetric water content changes in paddy field
using 5TE soil moisture sensor
100
90

Volumetric Water Content (%)

80
70
60
50
40
30
20
10
0
0

20

40

60

80
100
120
Time interval (minute)

140

160

180

200

Figure 13 Soil moisture content changes in preliminary study on
Block C

20
Generally the data obtained during ERT measurements were classically
presented as apparent resistivity pseudo-section, which gave an approximate
picture of the subsurface resistivity. Apparent electrical resistivity values
obtained from site were inverted by using RES2DINV software for each
treatment. Before the inversion process, to obtain true model representing
continuous distribution of calculated electrical resistivity in the subsurface,
data were concatenated and the noise and spiky values were edited by using
RES2DINV software. The inversion procedure was based on the regularized
least-square optimization method (Metwaly and Alfouzan 2013). Using 7
iterations and Root Mean Square error of less than 100 %, subsurface
geological profile of three different soil moisture conditions are shown in
Figure 14.
Figure 14 (a) was subsurface geological profile in Block C resulted
from ERT inversion results with normal condition (no water added). This
profile gave ERT value in range of 0 – 40 Ωm on depth of 74.7 meter. When
water added in survey line, and changed soil moisture content to 46.8%
(Figure 14 (b)), subsurface profile was still in same pattern as normal
condition, but ERT values in depth of 10 meter, dropped to majority 10 Ωm
from previously was 40 Ωm on the same depth. While for last treatment
(Figure 14 (c)) with adjusted soil moisture of 48.1%, subsurface geological
profile was still in the same pattern with the first two treatments but with
ERT values on depth of 10 meter ranged from 0 – 70 Ωm, and in several
points ranged from 0 – 250 Ωm. Overall, soil moisture content descriptively
will not affect subsurface geological profile but affects values of ERT.
a)

(a)

(b)

21

(c)

Figure 14 Comparison of subsurface geological profile on preliminary study. Treatment with
normal condition, soil moisture of 25.6 % (a), soil moisture of 46.8 % (b), and
soil moisture of 48.1 % (c)
Results of ANOVA tests showed that these treatments were highly
significant different at level 1%, with Pr value was less than F value of
0.0001. Further on Duncan’s multi range test showed that treatment 1 and 2
were not significantly different, but treatment 3 was significantly different
compared to other treatments. It was approved that electrical resistivity
values would change along with soil moisture content.
Site Survey
Soil moisture content in this survey ranges in average of 17-31% as
shown in Figure 15. Based on inversion of apparent electrical resistivity
values with RES2DINV software, subsurface geological profile of three
different treatments in Block F are shown in Figure 16.
Average volumetric soil water content for site survey #2
in 4 different treatments
36
34

32

100 ml water added
every 20 minute

Volumetric water content (%)

30
28
26

100 ml water added
every 30 minute

24
22

100 ml water
added

20
18
16

normal
condition

14
12

10
0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

Time interval (minute)

Figure 15 Soil moisture content changes in site survey
Block F

22

(a)

(b)

(c)

Figure 16 Comparison of subsurface geological profile on site survey. Treatment with
normal condition soil moisture of 16.96 % (a), soil moisture of 22.54 % (b), and
soil moisture of 27.50 % (c)
From Figure 16 at certain depth (red circle), Figure 16 (a) gave
electrical resistivity values in range of 50-500 Ωm, Figure 16 (b) gave
electrical values in range of 50-100 Ωm, Figure 16 (c) gave electrical
resistivity values in range of 10-50 Ωm. It can be concluded that electrical
resistivity values decreased along with the increase of soil moisture content.
But this condition is limited to field capacity preference. When soil reaches
its field capacity, it is assumed that electrical resistivity values would be
steady. The decrease of electrical resistivity along with the increase of soil
moisture content happened because high soil moisture content will increase
electrical conductivity of soil, which in turn will decrease electrical resistivity
values (Baharuddin et al. 2013), as mentioned in equation below:
σ=

1
ρ

Where σ is electrical conductivity (mS/m) and ρ is resistivity (Ωm).
This condition was also emphasized that low electrical resistivity would
occur in weathered zones, that were formed due to the weathering effects of
surface and groundwater inside the limestone, as these zones had high
moisture content (Metwaly and Alfouzan 2013). Figure 16 also described that

23
there was different condition of electrical resistivity between top layers (0 m
– 26 m) – having high electrical resistivity values, and sub layers (> 26 m) –
having low electrical resistivity values, because as current flows from top
layers towards sub layers, current density would increase and the potential
gradient at the potential electrode would decrease. This explained why sub
surface profiles were different among layers (Reynolds 1997).
Since the purpose of groundwater investigation is to determine
potential location for