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0Egyptian Journal of Aquatic Research (2014) 40, 373-383
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National Institute of Oceanography and Fisheries Egyptian Journal of Aquatic Research
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Egyptian Journal of Aquatic Research
FULL LENGTH ARTICLE
Characteristic properties of seabed fluvial-marine c^ark sediments in front of Damietta promontory, Nile Delta, Egypt
A. Hamouda, S. El-Gharabawy, M. Awad *, M. Shata, A. Badawi
National Institute of Oceanography and Fisheries, Alexandria, Egypt
Received 11 November 2014; accepted 12 November 2014 Available online 24 December 2014
KEYWORDS
Seabed characteristics; Acoustic ground discrimination;
Bathymetry survey; QTC VIEW remote sensing
Abstract Acoustic bottom classification utilities have been developed in favor of routine investigation of the seabed texture and grain size, as well as type of sediments. Single beam echosounder, seabed classification systems and QTC VIEW series V were used to map out and identify sediment gradients offshore Nile Delta in front of Damietta promontory. The survey area has an asymmetric shape and of very gentle slope parallel to the shore line at Damietta promontory. Ground truth observation analyses were carried out for 24 grab samples using the classification technique. The acoustic survey data were analyzed with the QTC IMPACT software and classified into five acoustic classes namely (silty clay, clayey silt, silt, sandy silt and very fine sand). The fine sediments (clay and silt) cover the front area of Damietta outlet, forming a stream like shape cutting the center of the area of study, which composed mainly of fluvial sediments. While the sandy sediments, appear as small patches to the east and west. The dominant of the small mean size (fine fractions) is corresponding to the fluvial depositions that form the Nile Delta fan of mainly mud sediments. Actually, since the building of Aswan High Dam in 1964, sediment discharge at the Nile promontories has diminished to almost zero, the recent situation of seabed characteristics is related mainly to the effect of the oceanographic circulation regime dominating the study area.
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Introduction
Nile Delta is located on the Egyptian Mediterranean coast that extends offshore to about 240 km. The slope of the continental shelf of the Mediterranean Sea off the Nile Delta is gentle but not uniform. It does not show the even outward slope of the so-called graded profile but it has numerous terraces at a
* Corresponding author. Peer review under responsibility of National Institute of Oceanography and Fisheries.
variety of levels that extend to depths of at least 91 m. Dami-etta promontory is located in the eastern half of the Nile delta, and its shoreline extends to about 35 km. The large present day Damietta promontory was formed by the sediment discharged from the former Nile branches about 6500 years ago (Fig. 1) (UNESCO/UNDP, 1978; Stanley and Warne, 1993).
The backshore east of the Damietta promontory forms a series of accretion ridges delineating ancient shorelines. The nature and origin of these ridges are directly related to the processes that have taken place in shaping the delta morphology. These ridges are parallel and sub-parallel to the present shoreline
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(El-Banna and Frihy, 2009). The first protection structure -against erosion and wave actions - was built along the Damietta promontory sector in 1941 with the construction of a jetty at the western side of the Damietta mouth. In Damietta flank, a spit of sand, 12 km long, formed approximately at southeast of the mouth of the Damietta Nile branch is a complex system of sand bars developed as a series of narrow and parallel prograded shorelines grown from a common point at east of the promontory with hook-like arms trending south east.
Nile Delta is presently subjected to significant coastal changes because of reduction in the Nile discharge and sediment load to the Nile promontory mouths due to the construction of water control structures and dams along its course. Since building of the High Aswan Dam in 1964, sediment discharge at the Nile promontories has diminished
to almost zero (Frihy et al., 2003). Accelerated erosion of Egypt's Nile Delta coast during the last century has generally been attributed to construction of two dams at Aswan, entrapment of sediment in Lake Nasser behind the High Dam, and effects of barrages and river control structures on River Nile deposition below Aswan. Moreover, the natural hazard factors of delta subsidence, raising sea level and strong coastal current processes, have been contributing to erosive coastal processes of the Nile Delta coast, (Stanley and Warne, 1993; Fanos et al., 1995) (Fig. 2). This leads to special and essential needs to understand the recent situation of the seabed characteristics in front of Nile promontory mouth related to the effects of this limited sediment delivery since the 1964's.
Accordingly, the acoustic seabed classification (ASC) is a new technology for mapping surficial seabed characteristic
Figure 2 Morphological changes of the Damietta mouth from 1800 to 1991 after: Fanos et al., (1995).
Figure 3 The location of the collected samples and acoustic survey lines along the study area in front of Damietta branch.
properties and sediment distribution with echo sounders (Anderson et al., 2008). It is an important tool for shallow marine survey to provide a recognized seabed characteristic mapping (Freitas et al., 2008). The idea relies on the fact that any change in sediment composition implies a change in acoustic properties. The acoustic data enable to distinguish various types of sediment grain size, bathymetric relief and water depth. Acoustic signature diversity is successfully capturing a high variety of seabed types based on sediment grain size (Freitas et al., 2003; Han et al., 2011; Maida et al., 2011). It means that, the results from the acoustic sediment analyses are related mainly to the grain size distribution. This results in a systematic difference in the recorded echoes, provided that the data have been corrected for extraneous influences, e.g. variable water depth or instrument settings. ASC might resolve fine variations in seabed properties with a high spatial resolution, which makes it a valuable complement to sediment sampling to build seabed characteristic mapping (Brown and Blondel, 2009; Freitas et al., 2003; Haris et al., 2012), environmental monitoring (Medialdea et al., 2008) and geotechnical engineering (Bartholoma, 2006).
The study area is located in front of Damietta branch along the coast of the Egyptian Nile Delta, Mediterranean Sea. It is extending from the shore line to latitude 31.8 0N and in between longitudes 31.70E and 320E (Fig. 3).
The main objective of this study is to detect the recent distribution of the grain size and seabed characteristics along the study area by using marine acoustic survey with the ordinary sediment analysis tool. In addition, it is aimed to get recent bathymetric map to understand the seafloor variation along the study area. It provides additional detailed natural resource information.
Methodology
Field survey
The field survey has been carried out on September 2013, extending from near shore (5 m water depth) to about 100 km offshore (65 m water depth). Twenty acoustic survey cross lines, oriented north/south and east/west, were run at a vessel average speed of 3-4 knots for each area (Fig. 3). The marine acoustic survey was done by using the QTC VIEW series V, connected to a single-beam echosounder (SIMRAD EK-60) operating at 50 kHz and emitting pulses every 2 s. The echoes were transformed to the reference depth (i.e. average survey depth), before they were processed. Normalizing the echosounder waveforms to a reference depth allows signal sampling which corresponds to a standard set of incidence angles, as opposed to a set of linearly spaced time (Caughey et al., 1994). The navigation system provided with Differential Global Positioning System (DGPS), providing position accuracy of ±0.5 m, is connected to both the echosounder and the QTC VIEW system.
Sediment analysis
Twenty-four bottom samples were collected from the study area, using grab sampler (Fig. 3). The samples were subjected to the combined technique of dry sieving and pipette analysis according to the method described by Folk (1974). The procedure involves pipetting a weighed portion of sediment sample using 0.01 N sodium oxalate followed by sieving through a 4 U (63i) mesh screen to separate the sand from the silt and clay
fractions. The fractions retained on the sieve are washed, dried and sieved; on electrical shaker for 15 min. The sieves are arranged from top to bottom as one phi order as follows: —2, — 1, 0, 1, 2, 3, 4 U, which are corresponding to 4, 2, 1, 0.5, 0.25, 0.125 and 0.063 mm respectively. The graphic measures were employed for the results of the grain size analysis using the phi notation, where U = —log x, (x = given value in mm). The mean size has been evaluated according to Folk (1974).
The results of sand, silt and clay were combined in smooth continuous cumulative curves, from which grain size data (percentiles) were obtained. These percentiles were used in calculating the four statistical parameters; graphic mean size (MZ), inclusive standard deviation (sorting), skewness and kurtosis for each using the formulae of Folk (1974).
Acoustic analysis
The QTC VIEW has many functions such as; captures and digitizes the seabed echo from the conventional echosoun-der, processes analysis, displays and records an acoustic waveform data that is used to characterize the sea floor. The QTC VIEW software implements automatic gain control (AGC) to compensate for factors, other than absorption and spreading that affect echo amplitude. For example, as the bottom type changes, the echo amplitude will change. The depth pick is generally quite reliable as long as the echo amplitude is sufficiently greater than the background noise (Freitas et al., 2003; Riegl et al., 2005; Quintino et al., 2010).
At traditional echo-sounding of frequencies (~50 kHz) most of the acoustic information for bottom classification involves the topography and sediment characteristics. In the present survey the definition of the extent of acoustic seabed classification is about 2 m (or less) below the seabed. This zone was intended to include biogenic structures directly associated with the seabed characteristics (Hamouda and Abdel-Salam, 2009). The QTC VIEW series V system examines the shape characteristics of the first echo and uses a series of algorithms
to translate it to an array of 166 descriptive variables (Collins et al., 2002). These variables are clustered through principal component analysis (PCA) to five Q-values, Q1, Q2, Q3, Q4 and Q5 corresponding to the coordinates on the first 3 PCA axes (Wienberg and Bartholoma, 2005; Riegl et al., 2005) which generally account for 90% or more of the total variance in a data set. (Ehrhold et al., 2006; Freitas et al., 2008). Statistical methods search the data for systematic differences among distinct seabed types (Amiri-Simkooei et al., 2011; Haris et al., 2012; Madricardo et al., 2012). Acoustic clustering group (Q) space is partitioned into five distinct groups defined by their means and covariance (Fig. 4).
The QTC IMPACT™ is an Integrated Map Processing and Classification Toolkit for echo processing. It is a powerful tool for extracting information about the seabed from echosounder data. The IMPACT package provides tools to read sonar echo data from a variety of sources that perform quality assurance, analysis and classification. (Preston et al., 2006). IMPACT processes digitally recorded echo traces or QTC VIEW™ echo features to extract information on the nature of sea substrates. IMPACT enables the generation of bottom type maps from echo sounder data. Using the software QTC IMPACT this data matrix was then submitted to a cluster analysis to divide acoustically distinct bottom types into classes. It is expected to get distinct acoustic classes corresponding to distinct seabed types (Hamouda and Abdel-Salam, 2010. The obtained classes are then used to create a catalog of known seabed classes. The detailed procedure of the QTC IMPACT processing is described in Freitas et al. (2003, 2008). Ground-truth data, including sediment samples are necessary to understand these acoustic classes.
Results
Bathymetry survey
The bathymetric map of the study area in front of Damietta promontory shows the depth variation of the seafloor from
Figure 4 Five acoustic clustering groups - Q-space is partitioned into distinct groups defined by their means and covariance.
Scale (m)
Figure 5 The bathymetric map of the study area in front of Damietta promontory, and depth contour is marked in meters. The dot red line represents the navigation canal of Damietta harbor.
Scale (m)
Figure 6 3D morphology of seafloor of the study area in front of Damietta promontory.
shore line to depth of about 60 m (Fig. 5). There is asymmetry along the shore between east and west sides of the peak of the out flow of the Damietta branch. The southern part of the study area, in front of Damietta outlet, is characterized by gentle slope until a depth of 25 m. The slope increases toward the north direction where it becomes very steep.
The study area in 3D is shown in Fig. 6, where the dot line may represent the suggested extension of the old shore that is parallel to the present shore. The figure shows the steep slope at the northern part of the study area. It shows the extension of the fan sediment deposit in front of Damietta branch. The sediment border of the fan deposit has an asymmetric extension in
Latitude
31.56 31.60 31.63 31.66 31.69 31.71 31.73 31.75
Figure 7 The cross section for the sea floor for Damietta area - toward NE direction, the length of each profile about 20 miles from the shoreline.
Table 1 Percentages of sand, silt and clay for the sediment samples of Damietta study area.
Sample Sand (%) Silt (%) Clay (%) Nomenclature
D1 1.68 56.9 41.42 Clayey silt
D2 1.91 56.41 41.68 Clayey silt
D3 0.84 68.07 31.08 Clayey silt
D4 95.03 3.05 1.92 Sand
D5 1.81 40.98 57.2 Silty clay
D6 1.2 40.81 57.98 Silty clay
D7 0.17 43.71 56.12 Silty clay
D8 0.23 63.32 36.46 Clayey silt
D9 0.26 48.76 50.98 Silty clay
D10 0.91 41.27 57.82 Silty clay
D11 0.43 33.83 65.74 Silty clay
D12 17.82 25.37 56.81 Silty clay
D13 12.09 32.99 54.92 Silty clay
D14 6.5 38.57 54.94 Silty clay
D15 15.6 53.93 30.47 Clayey silt
D16 14.77 62.8 22.44 Sandy silt
D17 20.52 62.39 17.09 Sandy silt
D18 0.25 35.11 64.63 Silty clay
D19 0.56 48.99 50.45 Silty clay
D20 0.4 45.9 53.7 Silty clay
D21 0.39 31.32 68.3 Silty clay
D22 60.63 20.08 19.29 Silty sand
D23 60.29 20.63 19.08 Silty sand
D24 6.94 38.5 54.57 Silty clay
Average 13.38 40.75 45.86
Max 95.03 91.32 75.74
Min 0.17 3.05 1.92
front of the Damietta branch. Fig. 7 shows the cross section for the sea floor that extends from the shore line (latitude 31.53°) at Damietta outlet toward the NE direction until latitude 31.75°. The length of this profile is about 24.2 km. From the shore line at latitude (31.53) to latitude (31.55) where the depth does not exceed 10 m, within a latitude difference of 0.02 (about 2.2 km), the linear trend of the seafloor slope will be started close to the shore line at latitude 31.53.
Sediment distribution
The collected sediment samples from the study area are mainly characterized by five grained deposits. Their percentage
distribution of sand, silt and clay are shown in Table 1. Five main sediment types could be distinguished and a map of the surface sediment distribution was drawn (Fig. 8). The main sediment textures observed in the study area are silty clay, clayey silt, sandy silt, silty sand and sand. The fine sediments (silty clay and clayey silt) cover the area in front of Damietta outlet forming a fan like shape cutting the center of the area which is composed mainly of fluvial sediments. It is obvious that the sand fraction is very low especially near to the Damietta outlet. Sandy sediments appear as small patches located to the east and west of the study area. The sandy samples in the region usually contain abundant shell fragments and bryzoa that covers most of the off shore area in front of
Silty Sandy Sand Silty Clayey
Sand Silt Clay Silt
Figure 8 The map represents the distribution of the sediment characteristics of the seafloor along the study area in front of Damietta promontory by sediment analyses.
Table 2 The mean size, sorting, skewness and kurtosis of the sediment from Damietta study area.
Sample Mean Size Sorting Skewness Kurtosis
D1 Fine silt Poorly sorted Near symmetrical Platykurtic
D2 Fine silt Poorly sorted Near symmetrical Platykurtic
D3 Fine silt Poorly sorted Near symmetrical Platykurtic
D4 Medium sand Poorly sorted Fine skewed Platykurtic
D5 Fine silt Poorly sorted Strongly coarse skewed Mesokurtic
D6 Fine silt Poorly sorted Strongly coarse skewed Mesokurtic
D7 Fine silt Poorly sorted Strongly coarse skewed Mesokurtic
D8 Fine silt Poorly sorted Coarse skewed Mesokurtic
D9 Fine silt Poorly sorted Coarse skewed Mesokurtic
D10 Fine silt Poorly sorted Strongly coarse skewed Mesokurtic
D11 Very fine silt Poorly sorted Strongly coarse skewed Leptokurtic
D12 Very fine silt Very poorly sorted Strongly coarse skewed Mesokurtic
D13 Very fine silt Very poorly sorted Coarse skewed Mesokurtic
D14 Very fine silt Very poorly sorted Near symmetrical Platykurtic
D15 Medium silt Very poorly sorted Strongly fine skewed Platykurtic
D16 Very fine silt Very poorly sorted Strongly coarse skewed Mesokurtic
D17 Fine silt Very poorly sorted Strongly coarse skewed Mesokurtic
D18 Fine silt Poorly sorted Strongly coarse skewed Mesokurtic
D19 Fine silt Poorly sorted Strongly coarse skewed Platykurtic
D20 Very fine silt Poorly sorted Near symmetrical Mesokurtic
D21 Medium silt Poorly sorted Strongly fine skewed Very leptokurtic
D22 Very fine sand Very poorly sorted Strongly fine skewed Platykurtic
D23 Very fine sand Very poorly sorted Strongly fine skewed Platykurtic
D24 Very fine silt Very poorly sorted Near symmetrical Platykurtic
Figure 9 Sediment mean size (a), sorting (b), skewness (c) kurtosis (d) distribution in Damietta sediments.
Damietta promontory. Thus, these sediment types which occur in front of Damietta promontory are typical Nile Delta sediments (El-Gammal et al., 2013).
The sediment distribution and transport analysis along Damietta promontory zone were taken out according to the mean, sorting and skewness that of equal importance in defining transport trends. Graphic mean size (Mz) is used as indicator for the grain size distribution. The mean size of Damietta profile sediment samples is shown in Table 2 and their distribution is presented in Fig. 9a. The sediment cover of Damietta profile is of fine to very fine silt though, there are few number of stations having medium sand and very fine sand. Occasionally medium sands are derived mainly from shell fragments and foraminifera.
The standard deviation is reflecting general, poor and very poor sorting Fig. 9b. Generally speaking, the difference in the degree of sorting is probably related to the proportion of biogenic materials. Probably the factors resulting in the poor sorting of sediments were lack of any effective hydrodynamic as well as the production of the bulk of sedimentary materials that is coupled with the high rate of sedimentation.
The skewness of sediment is a particularly useful indicator for explaining its history. It is found that 62.5% of the sediment samples of Damietta study area is negatively skewed
which are coarse skewed and strongly coarse skewed while the other 37.5% are positively skewed which are fine skewed and strongly fine skewed Fig. 9c. The dominant negative skewness in the area may be due to the winnowing of fine material by currents and waves and to occasional area of erosion or non-deposition, as well as addition of coarse materials such as shell fragments to the sediments. While, the positive skewness is probably due to the unidirectional flow of transporting media from west to east along the sea shore (littoral current), it might reflect the existence of fine materials.
Kurtosis measures the ratio of sorting in the extremes of the distribution compared with sorting in the central part, which describes the departure of samples from the normality. In the Damietta study area it is found that 50% of the sediment samples are mesokurtic, 42% are platykurtic and 8% are leptokurtic Fig. 9d.
Acoustic survey
Results of the acoustic classification by the QTC VIEW are corresponding to five acoustic classes, A, B, C, D and E. These classes are obtained at the third split, when the total score tends to be stabilized at the minimum value. The joint geographic distribution of the acoustic classes and the
Figure 10 The map represents the spatial distribution of the acoustic classification of the study area in front of Damietta promontory (interpolated for the 200 kHz data). The sediment characteristics of the seafloor represented by 5 classes (silty clay, clayey silt, silt, sandy silt and very fine sand).
sedimentary groups are shown in Fig. 10. The output data indicate a close correspondence between the acoustic pattern and the main sediment characteristics.
The first acoustic class (class A; gray color) corresponds to very fine sand that covers high extension area at the eastern side of the Damietta survey area. The second acoustic class (class B; yellow color) corresponds to sandy silt that covers about thirty percent of the Damietta survey area. The third acoustic class (class C; green) corresponds to silt which is mainly predominant in the Damietta survey area. The fourth class (D; red color - dash line) corresponds to clayey silt that presented as cluster in the Damietta survey area especially in front of the out flow of the Damietta branch. The fifth class (brown color) corresponds to silty clay. It is representing mainly a small cluster near the out flows of the Damietta branch.
Current wave characteristics
The height and direction of the wave are affected by refraction, dissipation of energy and breaking during their propagation into shallow near the coast. The effect highly depends on the local bathymetry, which may allow only a limited direction to reach a certain location. Analysis of incident waves versus shoreline orientation revealed that about 80% of the waves
arrive from between dominant N and N-W frequency distribution associated with minor NNE, NE and WSW reversals at the study area coast (Frihy et al., 2003). At the western coast of the Damietta promontory, the N, NNW, NW (totaling 90j) and WWN (40j) waves are responsible for the generation of long shore current toward the southwest and northeast, respectively (Fig. 11). Conversely, small wave components approaching from W and NE move sediment to the NNE and west directions, respectively, along these coastal stretches.
Discussion and conclusions
The sediment types recorded in the study area are almost similar to those that had been recorded in 1977 by El Sayed (1977), although the distribution pattern had changed (Fig. 1). Recently, the silty clay sediment type is dominating the Damietta fan area. This silty sediment covers the area in front of Damietta outlet and extends to the off shore covering the old sandy deposits. The sandy sediments (sand, silty sand and sandy silt) are distributed to the east and west of the study area.
Acoustic seabed classification (ASC) is an important tool for survey area of marine science and will contribute significantly to both scientific research and ecosystem-based management of the marine environment. The acoustic technique has
Figure 11 Average wave direction-height distribution for total average for 16 months examined the Damietta harbor showing dominant north and N and N-W frequency distribution associated with minor NNE, NE and WSW reversals (Frihy et al., 2003).
attempted to provide reasonably acquired seabed characteristics mapping data of the study area. The acoustic data enabled to distinguish various types of sediment grain size, bathymetric relief and water depth. Acoustic diversity successfully captured a high variety of seabed types based on sediment grain size (Kenny et al., 2003, Freitas et al., 2003). This means that the results from the acoustic sediment analyses are mainly related to the grain size distribution. Damietta survey area is mainly dominated by silt with sandy silt intercalated by very fine sand. The gradient size varies from very fine texture near the shore to medium texture in the north and the west direction. The acoustic survey shows the intercalation boundaries between different textures. This variation of the grain size helps to get acoustic variability at the study area. The present study agrees with the facts that the QTC View seabed classification system is responsive to a variety of grain size characteristics. The critical inspection and processing of the available data, that include selected ground truth, acoustic seabed classification map can provide useful results. Its importance is to support marine-based surveying and mapping which is obvious and of widespread applications. Physical sampling of the seabed to determine bottom types is important but it adds to the effort and cost especially for a wide survey area. As such, to produce such map using sediment analysis only, we would need unlimited number of sediment samples.
The grain size analysis is one of the basic techniques in sediment studies. It provides useful information about the deposi-tional environments, source area and sediment composition. Since the particle size of sediment controls the physicochemical processes on the sediment particle surfaces, it was necessary to study the mechanical characteristics of the sediment collected.
The grain size of classic sediment is an indicator to the energy of the deposition medium, or the energy of its basin. In general, coarser sediments are found in higher energy environment and finer sediments are found in lower energy environment (Bell, 1998). This means the front of Damietta outlet is characterized by lower energy environment. The grain size analysis is done to evaluate the distribution and follow the variation of the grain size parameters along the study area.
The study area is dominated by small mean size (fine fractions). This is mainly due to the fluvial depositions that form the Nile Delta fan which is composed mainly of mud. The study area has standard deviation ranging from 1 to 3.07U reflecting generally poor and very poor sorting except for one station (D7) which is moderately sorted. This difference in the degree of sorting is probably related to the proportion of biogenic materials. Probably the factors resulting in the poor sorting of sediments are:
(i) The lack of any effective hydrodynamic (sorting agent); i.e. poor sorting of sediments reflects the low energy conditions and appearance of the biogenic materials with different growth stages and origin.
(ii) The production of the bulk of sedimentary materials is coupled with the high rate of sedimentation; i.e. the chances for the sediments to get sorted are very little.
The Damietta section is negatively skewed which are coarse skewed and strongly coarse skewed while the other (37.5%) are positively skewed which are fine skewed and strongly fine skewed. The dominancy of the negative skewness in the area may be due to the winnowing of fine material by currents and waves and to occasional area of erosion or non-deposition, as well as addition of coarse materials such as shell fragments to the sediments while, the positive skewness detected in the area is probably due to the unidirectional flow of transporting media from west to east along sea shore littoral current, as well as, reflects the existence of fine materials.
Kurtosis measures the ratio of the sorting in the extremes of the distribution compared with the sorting in the central part, which describes the departure of samples from the normality. In this measure, normal curves have KG of 1. If KG is over 1, the central portion is better sorted than the tails, and the curve is excessively peaked or Leptokurtic, and if KG is below 1 the tails are better sorted than the central portion, and the curve is flat-peaked or Platykurtic.
Maximum erosion for Damietta promontory is occurring at the tip of the promontory (10 m/year) while accretion takes place to the east along its flank at the neck of the sand spit. The spit acts as a buffer for sand transport farther southeast, further increasing sand starvation of down-spit coasts. On the west coast, a significant erosion (4 m/year) appears along Ras El Bar resort beach and decreases westward where it is changed to accretion (14 m/year) at the up drift of the Dami-etta harbor breakwaters (Frihy et al., 2003). These results are corresponding with the results shown in the 3D map representing the erosion and accretion pattern in the study area.
Conclusively, since building of the High Aswan Dam in 1964, sediment discharge at the Nile promontories has diminished to almost zero. The recent situation of seabed characteristics is related to the effect of the current circulation along the study area. In addition the effect of the seafloor morphology spatially in the southern part (shallow area) plays as another
parameter effect of the grain size distribution. Maximum erosion is occurring at the tip of the promontory (10 m/year) with accretion taking place to the east along its flank at the neck of the sand spit.
Acknowledgments
The authors would like to express their appreciation to the STDF, Egypt (www.stdf.org.eg), that supports finance of this study. Many thanks are also due to the Geophysicist team of the field survey (M. Nassar, A. Fekry and M. Salah) for their support and help.
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