303
Detection of Shallow Subsurface Water by Processing Two-dimensional Electrical Imaging
Data With Multiple Iteration
Mervat Ayad Abd Al-khaliq Alaa Ezzat Hassen Firas Subhi Hameed
Abstract— In this research we used technician of 2D electrical imaging to detect shallow ground water at samara, by using ABEM LS tetrameter instrument (64 channel with multi electrode cable system) and choose three profiles, the first and second profiles are parallel, third is perpendicular of them .we processed the data of profiles by using (RES2DINV) program with multi iteration (five iteration) for each profile. the apparent resistivity for first profile (5.17-125) Ω.m, second profile (2.67-66.1) Ω.m,and third profile (2.26-65.4) Ω.m The shallow groundwater are detected at (0.75-6.3) m suspended water assemblage resulted from rain water and sewage leakage and not effect of aquifer because of the solid layer that separate , and the water table at(27.5)m the aquifer at(30)m.
Index Terms— 2D Electrical Imaging, Shallow Groundwater, Inverse Theory and Resistivity.
Inverse Theory and Resistivity.
I. INTRODUCTION
HE two-dimensional electrode imaging method has become widely used in recent years, and increasingly through environmental, hydrographic and geotechnical studies. These studies give a more accurate picture of the distribution of apparent resistivity under the surface and are more accurate than the measurement of electrical resistance one-dimensional (VERTICAL ELECTRICAL SOUNDING 1D). In this study, the 2D electrical imaging technique was used in three sections using the Wenner-Shlemberger protocol along the measurement path and using ABEM Tetrameter LS. The data collected and the practical side was carried out in the area that defined by latitude (22 '89 43) and latitude (12 '54 34), where the distance between dipoles (7,5,2.5) meters for sections (1,2,3), respectively The maximum depth of penetration 46 m .The data is analyzed and interpreted by using RES2DINV software , which is based on the theory of Inversion Theory. The research area (in one of Samarra's neighborhoods) is located within the unstable quay as it lies within the sedimentary plain (Buday, 1980) about (75%) of the research area.
The research aims to use two-dimensional electrical imaging technique to detect Sub-surface water pools at city of Samarra.
Corresponding Author: Mervat .A. Abd Al-Khaliq. Ministery of Science and Technology, Directorate Space Technology and Communication.
E-mail: Umervatali2005@ gmail.comU
II.The Climate
The climate of the region is subject to the climatic conditions of dry and semi-dry regions characterized by cold weather, summer is hot and dry with low rainfall according to the Iraq Climate Atlas for the years 1971-2000 (General Air Conditioning Authority, 2000), the research area has annual percentages of climate coefficients. The annual temperature percentage is 22.5 C, and the annual humidity percentage is 45%, the drying factor is 15 mm, the annual evaporation percentage about 3000 mm, the annual rainfall about 200 mm and the annual wind speed is 3.0.
(M / s), the climate must have an effect on the soil moisture level should be taken into account, the study was conducted in January, where the effect of the rain on the two-dimensional electrical images, which give low values of the nearby resistance to the surface).
III.Geologic Description of the study area
The geological formation Njana are produced the main aquifer that locates in the west of the Tigris River. The main aquifer is located in the area between the Tigris River to the west and the Hamrin mountain ranges from the north and the east mainly (Hamid Saeed Ahmed, 2005). The main aquifer was produced by (Bye Hassan) at the north of the Hamrin mountain ranges (Fig. 1).
The Quaternary sediments are forming the upper aquifer at the different areas of this study. Where these sediments have suitable thickness that helps to store water.
Fig 1: Satellite image
T
296 The groundwater movement is parallel to the terrain of the research area, which is southward (Falah Hassan Abbas, 2010).
There are high levels of pizometrics in the highlands, river and irrigation channels. There are also bizometric or drainage areas on the rivers and lowlands. This affects the quality of the groundwater, which is mostly sulfate with chloride and other quality of bicarbonate. The Ministry of Water Resources and the Department of Geological Survey in Iraq have reports by drilling number of wells to know the hydrographic situation of the research area, that gave more details about the main aquifer depth, movement direction of groundwater and quality, (Barwary and Slewa, 1995).
The western area research has included river and gravel deposits. (Araim et al., 1976).
V. Topographic search area
The research area is located in the city of Samarra, 120 km northwest of Baghdad and on both sides of the Tigris River. The area is characterized by varying heights. The western parts are composed of river deposits from the gravel deposits and are considered Old Alluvium and the real coastline (Actual Shore Line) characterized by low cliffs , in some areas are covered with surfaces of secondary gypsum, the eastern parts of the area are high sand dunes, the low part that covered with sand and silt characterized by wind ,it can follow the shape Low direction To the south in the form of drainage line connected to the Tigris River Valley, as these waters formed as a result of winter rainfall (Bolton, 1956).
VI. Theory
The two-dimensional electrical imaging depends on electric current flow in the earth by pair of metal electrodes placed on two points in the ground. The electric current is injection to the ground and the voltage difference is measured by two other poles according to the law of ohm. (Fig.2) shows the relationship between the voltage, current and resistivity of the current flow, the geometric factor of the distribution of the poles and the distance between them.
Zhou, et al., 1999).
Fig 2: Distribution of voltage and current Electrodes
The protocols are chosen according to study area conditions.
(Zhou, et al., 2002) (Fig.3)
Fig 3: the electrical device with a multi- electrode cable
The data are processing by inversion theory. The values are represent by number of rectangles, they distributed on a pseudosection. The area of these rectangles is based on the values of the apparent resistivity. (EA EI Zein, et al., 2005) (Fig. 4).
Fig 4: Distribution of apparent resistivity according to the inverse theory
The area of these rectangles Can be controlled by use multi iteration to reduce error percentage that called (RMS) (the apparent resistivity values of some materials may be overlapped) the layers are separated from each other, water table and aquifer (Rivers, Peter, 2003) (Fig. 5).
Fig 5: apparent resistivity for some material
297 VII. Field work
After studying the research area from the theoretical side, three profiles paths are fixed, the ABEM TERRAMETER LS instrument are used (64-channel) 600 volts with a volt output voltage of up to 1200 volts, which gives sensitivity to the few resistors at 0.2% accuracy and with a 3nV analytical capacity per second connected to a voluntary coupling containing 41 electrode (Fig.6)
Fig 6: A resistor with its accessories
The electrodes devices are distributed on three profiles depend on available study area to obtain electrical psedosection ,The first profile (length 280 meters) , second profile (length 200 meter ),the two profiles are parallel with interval distance 995 meters this setting is important to investigate the depth of the aquifer and collecting shallow groundwater . The third profile (length100 meters) perpendicular on (profile one, profile two) away from the second profile (379) meters. These interval distance are choice to cover the soil properties up to depth (46) meters. The electrodes setting with intervals distance of each two electrodes are (7, 5, 2.5) meters for the first, second and third profiles, respectively to cover changing in the distribution of the apparent resistivity for earth layers (Fig.7).
Fig 7: Field Work profiles
VIII. Discussion
The first profile located at longitude (43◦ 89′ 22″) and latitude (34◦ 20′ 3″). The apparent resistivity values are distributed between (5.17-125) Ω. m. The high values of the apparent resistivity are close to the surface that irregularly arrangement because of construction waste in the soil.
A number of iteration is selected in the model that covers all processing data. This depends on the data processor experience of the researcher (Fig.8).
A) Areas with high moisture soil are observed with Iteration 1ABS and error percentage (14.2%). The apparent resistivity values are distributed between (5.17 - 82.2) Ω. m, there are five areas of subsurface water at depth between (1.75-1.5) m .
B) Areas with high moisture soil are joined with each other.
The apparent resistivity values are distributed between (6.20- 84.5) Ω. m when Iteration 2ABS and error percentage (4.21%).
C) The effect of the lower aquifer is isolated from the surface water collecting areas. A clear distance is observed. The level of the aquifer is approximately (27.5)m. Groundwater collected at the bottom of the surface of about (1.5) m separate by a muddy layer.
The apparent resistivity values are distributed between (6.12- 85.6)Ω.m. Iteration 3ABS and error percentage of (2.6%).
D) The values of apparent resistivity were distributed between 104-6.24 Ω.m. Iteration (7ABS) and error percentage (1.69%). A higher apparent resistivity values are observed on the mathematical model and the depth of the aquifer at 30 m.
E) The apparent resistivity values between (5.91-125) Ω.m.
Iteration 10ABS and error percentage (1.63%). When comparing the iteration between D and E, there is a slight effect in the mathematical model, with a shallow groundwater located between two solid zones.
298
Fig 8: Multi-iteration data processing for the first profile
,B(Iteration 2ABS),C Iteration 3ABS,D(Iteration 7ABS), E (Iteration 10ABS ) )
Iteration 1ABS (
A
The second profile is located on the longitude (43◦ 89′ 71″) and latitude(34◦ 19′ 99″)The apparent resistivity values (2.67-66.1) Ω.m The length of the measurement path (200) meters, the number of electrodes (41) and the distance between the electrode and the other (5) meters, the data processed in several attempts using the available models. ( Fig.9)
A) Areas with high moisture soil are observed at depth of (3.76- 6.3) m with Iteration 1ABS and the error percentage was (9.3%).
The apparent resistivity values distributed between (3.19-61.6) Ω.m. A solid area located at the beginning of the profile.
B) At Iteration 2ABS and error percentage (4.1%) Apparent resistivity distributed between (2.67-57.8) Ω.m.. Two collected shallow groundwater at depths of (3.76-5) m .
C) At Iteration 3ABS and the error percentage of (2.3%), The apparent resistivity distributed between (4.14 to 61.7) Ω.m, the water table at depth (24.8 m) .
D) At Iteration 7ABS and error percentage of (1.23%), the Apparent resistivity distributed between (5.37-64.2)Ω.m. a solid area with depth of (4) meters and thickness (6) meters are observed.
E) At Iteration value (10ABS) and the error percentage (1.19%), the Apparent resistivity distributed between (5.64-66.1) Ω. m the a solid area at the end of profile and aquifer at (30 m) .
Water table
First profile
Groundwater aquifer
Solid area Shallow groundwater
299
Fig 9: Multi-iteration data processing for the second profile
, B (Iteration 2ABS),C Iteration 3ABS,D(Iteration 7ABS), E (Iteration 10ABS ) )
Iteration 1ABS (
A
The third profile, which is located at the longitude(43◦ 89′ 89″) latitude (34◦ 19′ 93″), The apparent resistivity values distributed between (2.26-65.4) Ω.m. The length of the measurement path (100 meters), the number of electrodes (41) and the distance between the electrodes and the other (2.5 meters) were processed by several attempts using the models available in the program ( RES2DINV). (Fig.10)
A) At Iteration 1ABS and error percentage (5.3%) Apparent resistivity distributed between (13.4-52.8) Ω.m. Three collected shallow groundwater at depths of (0.75-3.5) m .
B) At Iteration 2ABS and error percentage (2.3%) Apparent resistivity distributed between (6.59-52.5)Ω.m. A higher apparent resistivity values are observed (30-52) Ω.m of sub-
surface water and not penetrate Water for the upper layers the deep groundwater aquifer.
C) The apparent resistivity values distributed between (2.26- 47.32) Ω. m. Iteration (3ABS) and the error percentage was (1.71%).
D) At Iteration 7ABS and error percentage (0.92%) Apparent resistivity distributed between (3.8-63.1) Ω.m. The effect of the groundwater level of the deep aquifer (the poetic property) was 18.5 meters deep.
E) The apparent resistivity values distributed between (3.8 - 65.4) Ω.m (Iteration10ABS) and the error percentage was (0.81%).
Solid area Solid area
Solid area
Second profile
Water table
Solid area
Aquifer
300
Fig 10: Multi-iteration data processing for the third profile
, B (Iteration 2ABS),C Iteration 3ABS,D(Iteration 7ABS), E (Iteration 10ABS ) )
Iteration 1ABS (
A
Third profile
Not penetrate layer
Shallow groundwater
Aquifer effect area
Aquifer effect area
301 IX.CONCLUSIONS
The two-dimensional electrical surveying has proved efficient when used for the detection of underground water that are gathered in the form of what is geologically known as Lenses.
These lenses are surrounded by silt and gravel and considered as undesired underground regions of weakness. In order to get rid of these lenses, a well-designed drainage system must be built nearby to deplete the underground water The RES2DINV treatment program is used to separate the soil layers and analyze the data of the electric scanner and in several attempts for the first profile (12.5-5.17 m), the second profile (66.1,67,7) m and the third profile (65.4-2.26) Aquifer (30-27.5) meters as well as shallow groundwater (6.3-0.75) meters.
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