EGYPTIAN JOURNAL OF AQUATIC RESEARCH ISSN 1110-0354
VOL. 31., 1. 2005.
ELECTRIC RESISTIVITY INVESTIGATION AT NUWEIBA
HARBOUR GULF OF AQABA, SOUTH SINAI, EGYPT
MAHMOUD ISMAIL ISMAIL MOHAMADEN
National Institute of Oceanography and Fisheries, Alexandria, Egypt.
Key wards: Resistivity, Vertical electric sounding (V.E.S.), cathodic.
ABSTRACT
The results obtained from the interpretation of the V.E.S.’s gave information regarding
the geological situation in the Nuweiba Harbour, Gulf of Aqaba south Sinai, Egypt. A total
of 20 vertical electrical soundings (V.E.S.’s) were conducted along 6 profiles. The
geoelectrical field emphasis some knowledge about structural geology and lithology of the
subsurface formations of the study area. In this work, the Schlumberger array with
maximum current electrode half spacing (AB/2) of 75 m was applied. This spacing is
sufficient to reach adequate depths for this study. The established geoelectric sections
reveal the presence of the following geoelectric units: (a) A superficial unit characterized
by electric resistivity value ranging from 2.47 to 106 ohm-m., and with a thickness ranges
from 0.7 to 9.7 m. (b) A second unit with electric resistivity values (0.82 - 24 ohm-m.) and
of depths from 0.35 to 5.8 m. (c) A third unit characterized by electric resistivity values
ranging from 0.7 and 6.5 ohm-m. This third unit has a maximum thickness of 22m. which
disappears at some localities. (d) A basal unit characterized by lower electric resistivity
values that ranging from 0.2 to 0.6 ohm-m.
Location for cathodic protection necessary for construction of civil engineering harbour
project is determined by the lowest values of resistivity values.
INTRODUCTION electrical soundings (V.E.S.’s) were
The geoelectric survey is one of the conducted along 6 geoelectric profiles, in
cheapest tools applied in the solving civil order to evaluate the geological setting of the
engineering problem (Reynold, 1997). The Nuweiba Harbour, Gulf of Aqaba, south
geoelectrical field clarifies some knowledge Sinai, Egypt (Fig. 1). Schlumberger electrode
about lithology and structural geology of the arrangement has been used in this study. It
study area. Electrical resistivity techniques covers an area for about 5 Km2.
are used extensively in the engineering Many authors as Koefoed (1965),
surveys to locate subsurface cavities, faults Meinardus (1970), Ghosh (1971), and Zohdy
and fissures, permafrost, mineshafts, etc. The (1975 and 1989) discussed the quantitative
aim of the current geoelectric study at interpretation of the earth resistivity
Nuweiba Harbour is to fulfill the following measurements. The interpretation of the
goals: apparent resistivity data was achieved using
1-Identification of the subsurface formations, two methods. The first is based on curve
with respect to it’s lithological and structural matching technique using Generalized
features. Caginard Graph method constructed by
2-Localization of conductive zones favorable Koefoed (1960), in which the results obtained
for cathodic protected stations used for are subjected to a direct method using an
caviling engineering projects. algorithm constructed by Hemeker (1984)
A total number of 20 vertical which based on Gosh (1971).
MAHMOUD ISMAIL ISMAIL MOHAMADEN
preparing the isoapparent electric resistivity
The results of the interpretation are map and the geoelectric cross sections. These
represented in the form of the apparent sections reflect both lateral and vertical
electric resistivity values that can be used for variations in resistivity.
Electric Resistivity Investigation at Nuweiba Harbour Gulf of Aqaba, South Sinai, Egypt
METHODOLOGY surface effect and increase the depth of the
The geoelectric resistivity measurements current penetration. The AB spacing begins
performed within the present study are with a distance equal to 3 meters and extends
executed applying U.S.A. made digital up to 150 meters. The ratio between the MN
electric voltameters of the type Fluke - 27 distance and AB distance ranges between 1/3
allowing filtering the self potential of the to about 1/10 (Parasnis, 1997).
earth. Accordingly, it is possible to measure The layers parameters (True
simultaneously, the potential difference (ΔV) Resistivity & Thickness) obtained from the
due to fed current (I). quantitative interpretation are shown in Table
Schlumberger array used in the field (1). These parameters are therefore,
survey is found to be more suitable for this integrated with the available geological
study (Reynold, 1997). The advantage of the information (Flathe; 1976) to construct the
array is to minimize the lateral variation geological picture of the study area.
changes in geology as well as the near
Table (1) Geoelectrical parameters for Different V.E.S.'s
Layer 1 Layer 2 Layer 3 Layer 4
V.E.S.
ȡ1 d1 ȇ2 d2 ȡ3 d3 ȡ4
1 23.3 0.79 5.6 1.8 0.98 9.5 0.36
2 17.1 0.75 7.86 2 0.86 9.5 0.72
3 67.6 2.6 13.6 5.8 0.74 23.7 0.26
4 7.13 0.87 1.31 9.6 0.48
5 9 1.6 6.5 1.7 0.98 17.4 0.37
6 10.2 2.4 0.55
7 12 2 10.9 2.1 0.97 5.2 0.6
8 10.4 1.4 0.49 4.2 1.13 6.4 1.73
9 2.69 1.5 0.59 27.1 17.8
10 49.3 1 1.98 3.8 0.9 12.5 0.47
11 17.9 0.7 0.82 2.4 0.9 16.3 0.43
12 2.33 1.6 1.04 3 0.96 14.1 0.52
13 3.22 0.52 24.4 1.2 0.59 2.7 1.12
14 0.6 0.49 4.94 1.6 0.68 15.8 0.58
15 6.32 2.1 2.94 2.4 1.23 7.5 1.01
16 10.3 0.35 2.67 2.8 3.01 9.8 0.76
17 106 0.51 24.5 9.7 0.68
18 32.2 1.3 1.98 5.8 0.91
19 0.77 1.5 0.67 31.7 0.36
20 2.47 2.2 1.56 10 0.55
ȡ= True resistivity ( ȍ. m.) d = Depth (meter)
MAHMOUD ISMAIL ISMAIL MOHAMADEN
RESULTS AND DISCUSSION Isoapparent Electric Resistivity Map for
The field results obtained within the AB/2 = 15 m. (Figs. 3)
present study are presented in the form of This map reflects the lateral
qualitative interpretation (isoapparent electric variation over a horizontal plane at a depth of
resistivity maps) and quantitative about 5 meters. It shows the effect of
interpretation (geoelectric sections). transported filling materials still existed, but
Isoapparent Electric Resistivity Maps it tends to be vanished. The electric resistivity
Three isoapparent electric resistivity values decrease from west to the east towards
maps are constructed at AB/2= 3, 15, and 50 the Gulf and increase towards the land which
m. The choice of such spacing depends on the indicates that the invasion of the sea water in
variability between them. These maps reflect land decrease towards west. Also, gradation
the lateral variations of the electric resistivity from coarse sediments to finer sediments near
at a depth of about 1, 5, and17meters, the Gulf.
respectively. (Roy and Elliot; 1981) Isoapparent Electric Resistivity Map at
Isoapparent Electric Resistivity Map for AB/2 =50 m. (Fig. 4)
AB/2 = 3 m. (Figs. 2) This map reflects the lateral variation
This map reflects the lateral over a horizontal plane at a depth of about 17
variation over a horizontal plane at a depth of meters. It shows that a nucleus of relatively
about 1 meters. It shows some sort of high electric resistivity values exists at the
transported filling material around of location of V.E.S.’s 3 and 17 at the present
V.E.S.’s 3, 17, and 8, with relatively high temporary platform of Nuweiba Harbour
apparent electric resistivity values. which is believed to be due to the transported
filling materials.
Electric Resistivity Investigation at Nuweiba Harbour Gulf of Aqaba, South Sinai, Egypt
Geological Investigation V.E.S. 4 or covered by the superficial unit
The quantitative interpretation of the east of V.E.S. 4.The depositional conditions
different points reveals the following results: prevailed is similar to the first unit. It is
Profile A-A\: characterized by relative moderate electrical
Profile A-A\ runs from east to the resistivity values (5.6-13.6 ohm-m) and of
west perpendicular to the Gulf of Aqaba. It is depth ranges from 0.87 to 5.8 m. Partial
crossing five vertical electrical sounding sedimentation of the land filling material with
(V.E.S.’s) namely 1, 2, 3, 4, and 5 (Fig. 1). salt water may be responsible for such a
The geoelectric section has been constructed situation.
according to the quantitative interpretation of The third unit is characterized by
V.E.S.’s which leads to the following relatively low electric resistivity values
observations as indicated in Figure 5 and (0.735 - 6.5 ohm-m) and of depths ranging
Table 1: from 1.7 to 23.7 m. It may consisted of sand
A superficial unit is detected contaminated with clay and rock fragment
between V.E.S.’s 2 and 4 which consists of and coral fragment.
dry transported land filling. It is characterized At the maximum depth of
by its thin thickness (0.75-2.6 m.) and penetration a layer has detected from sandy
relatively high electric resistivity values (17.1 clay contaminated with coral and marine
- 67.6 ohm-m). This situation may be shell fragment. It is characterized by very low
attributed to the topographic condition electric resistivity values (0.261-0.369 ohm -
prevailed during sedimentation. m).
The second unit has variable depths
where it reached the ground surface west of
MAHMOUD ISMAIL ISMAIL MOHAMADEN
Profile B-B\: platform 3 (Fig 1). This profile is crossing by
Profile B-B\ is located to the north of four vertical electrical soundings namely
profile A-A\. It extends to the platform. The V.E.S’s 12, 11, 10, and 9. The quantitative
geoelectric section is constructed according interpretation of this V.E.S.’s leads to
to the quantitative interpretation results of construction of geoelectrical section as shown
V.E.S.’s number 6, 7, and 8, which are in figure 7 and Table 1. It leads the following
correlated with V.E.S.’s 3, 4, and 5, observations:
respectively (Fig.1). The results of this The land filling material is shown at
section is indicated to the following the ground surface around of V.E.S.’s 10 and
observations (Fig.6 &Table1): 11. It’s thickness is ranging from 0.7 to 1m
While the fist unit is missed, the with resistivity ranges from 17.9 to 49.3 ohm-
second and third units previously mentioned, m. While that filling material charged with
are still observed along this section. The salt water is considered as the second
superficial unit consists of (partial saturated geoelectric resistivity unit. It various
with seawater), land filling material attains its maximum calculated depths (1.5 – 3.8 m.)
maximum thickness around of V.E.S. 6 (2.4 and various electrical resistivity values (0.82
m.). This unit is thinning towards the western – 2.69 ohm-m.). This unit covers the ground
direction (1.4 m.) with moderate electric surface around V.E.S.’s 12 and 9. The third
resistivity values (10.2-12 ohm-m). geoelectric unit can be detected at maximum
At the maximum depth of depth various from 12.5 to 16.3 m or to the
penetration a sand layer is contaminated with maximum depth of penetration at the east of
clay and rock fragment and coral fragment V.E.S. 9. This unit is formed of sand
with relatively low electric resistivity values contaminated with clay and rock fragment
(0.493-1.73 ohm-m). The increase in the and coral fragment with variable electrical
electric resistivity values can be interpreted resistivity values from 0.589 to 0.96 ohm-m.
due to the increase of the percentage of coral At the maximum depth of
reef fragments at such depth, which may be penetration to the east of V.E.S. 9 the fourth
attributed to an old beach existing under the geoelectric unit can be detected that forms of
recent sedimentation. This unit is supposed to sandy clay contaminated with coral and
be fully saturated with seawater. marine shell. It is characterized by very low
Profile C-C\: electric resistivity values (0.429 to 0.522
Profile C-C\ is located to the north of ohm-m.).
profile B-B\; it is perpendicular to the
Electric Resistivity Investigation at Nuweiba Harbour Gulf of Aqaba, South Sinai, Egypt
V.E.S. 18 it attains a thickness of about 1.3
Profile D-D\: meters. The ohmic values characterizing this
Profile D-D\ is running at the south unit show big difference ranges from about
fence of Nuweiba Marine Harbour. It is 24.5 ohm. m to about 106 ohm-m. The
crossing V.E.S.’s 13, 14, 15, and 16 (Fig. 1). intermediate unit appears underneath the
The geoelectric section can be explained as superficial one where it is characterized by
shown (Fig. 8 & Table 1): electric resistivity values ranging from 1.98
The superficial electrical unit to 0.679 ohm-m. The basal unit is not reached
characterized by high electric resistivity along this section.
values (4.94 - 24 ohm-m.) and formed from Profile F-F\:
land filling material. The thickness of this This section is located along the
unit varies from 0.35 to 1.6 m. The second northern fence of Nuweiba Harbour (Fig. 1).
electrical unit is characterized by moderate It is constructed due to the quantitative
electrical resistivity values (1.12 – 3.01 ohm interpretation results of V.E.S.'s 19 and 20.
– m.) and is formed from land filling material The study of this geoelectric section (Fig. 10)
filled charged with salt water. shows that: The superficial transported filling
The third electric unit is located at unit is absent at the site of V.E.S. 19, whereas
the maximum depth of penetration with it attains a thickness of about 2.2 m at the site
various electrical resistivity values (0.58 - of V.E.S. 20 and it is characterized by an
1.01 ohm-m.). It forms of sandy clay ohmic value equivalent to about 2.47 ohm-m.
contaminated with coral and marine shell It seems that, a crest of an andulation exists at
fragment. the site of V.E.S. 19. The land filling material
Profile E-E\: with salt water (second unit) is located at the
This geoelectric section is running ground surface around of V.E.S. 19 and is
along the temporary platform (Fig. 1). Where charged with located beneath the fist unit
a nucleus of relatively electric resistivity around of V.E.S. 20.
values exits (Fig. 9 & Table 1) and probably The third electric unit is located at
explained by the presence of big thickness the maximum depth of penetration with
from land filling material at this locality. The various electric resistivity values (0.546 –
quantitative interpretation of V.E.S.17 0.667 ohm-m.). It forms of sandy clay
indicates that, this unit attains a thickness of contaminated with coral and marine shell
about 9.7 meters, whereas, at the site of fragment.
MAHMOUD ISMAIL ISMAIL MOHAMADEN
Electric Resistivity Investigation at Nuweiba Harbour Gulf of Aqaba, South Sinai, Egypt
CONCLUSION 5- It seems that, some sort of andulation may
According to the previous discussion affect sedimentation at the area of study. As a
of the results of the geoelectric survey result of sea water movement along the shore
executed at Nuweiba Marine Harbour, it is during the sedimentation.
possible to reach the following conclusions: 6-The area favorable for cathodic protection
1-The isoapparent electric resistivity maps stations is that characterized by low ohmic
constructed yield that sedimentation took values i. e. the northeastern zones of the area
place in a normal condition. The nucleus of of the study.
high electric resistivity at the location of V.
E. S.’ s 3, 17, and 8 (Fig. 2,3,and 4), may ACKNOWLEDGEMENTS
indicate the land filling material attains a big Thanks are extends to Professor Dr.
thickness at this locality. Also electric Ibrahim Meaiza for supplying the author with
resistivity values appearing at depth at the the field data and permit him to work this
sites of VES 8 and 9 may be due to an old paper. Thanks to Dr, William K. Awad for
beach existing before more recent his continuous encouragement and for
sedimentation took place. offering much of devices for all works.
2-The geoelectric sections constructed reveal
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