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0Egyptian Journal of Aquatic Research (2015) 41, 165-176
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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
Effect of flooding on distribution and mode c^m^
of transportation of Lake Nasser sediments, Egypt
Hassan I. Farhat *, Salem G. Salem
Geology Lab., National Institute of Oceanography and Fisheries (NIOF), Cairo, Egypt
Received 18 January 2015; revised 9 March 2015; accepted 9 March 2015 Available online 28 March 2015
KEYWORDS
Bottom sediment;
Lake Nasser;
Mode of transportation;
Flooding
Abstract Sediment samples have been collected from Lake Nasser during drought and flooding periods to study the effect of flood season on bottom sediment distribution and mode of transportation. Ten sectors with three sites in each sector were chosen from upstream of Aswan High Dam to Adindan. The study showed that Lake Nasser sediments are heterogeneous and are mainly silty clay and clayey silt. Eastern and western sides of the lake include more sand. Depth controlled distribution of grain size (deeper is finer). Sands increase with the starting of the flood season. During drought periods suspension was the most predominant mode of transportation; i.e. sediments transported by a medium of considerable density. During flooding period siltation and suspension were most predominant modes of transportation; i.e. environment with a high energy, various overlapping processes, and variety of depositional environments. C-M diagram indicates that sediments during drought periods behaved as pelagic suspension in which sediments settled from a suspension in stagnant water, rolling; overbank facies suspension and uniform suspension were of less importance. During the flooding period there was no clear trend for studied sediments of pelagic suspension; rolling, graded suspension, overbank facies suspension, suspension, and uniform suspension were widely distributed.
© 2015 National Institute of Oceanography and Fisheries. Hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction
Many factors control sedimentation in the High Dam Lake such as annual effective base level for each flood, distribution and characteristics of rocky islands, the valley Lake bends, the old river terraces, and the plankton induced deposition, water
* Corresponding author at: Fresh Water and Lakes Division, National Institute of Oceanography and Fisheries (NIOF), 101 El Kasr El Eini St., Cairo, Egypt. Tel.: +20 1008616048.
E-mail address: hf_geo@hotmail.com (H.I. Farhat). Peer review under responsibility of National Institute of Oceanography and Fisheries.
discharges especially during flooding periods, sediment loads and their gradation. During high water level the influence of these factors can be exemplified by the large scale sediment deposition at the lake entrance, while during a lower water profile sediments would mainly deposit further downstream (Aboul-Haggag; 1977; El-Manadely et al., 2002). At lake entrance (Gomi and the Second Cataract (Abca)) silt layer was 17 and 20 m respectively. Further downstream it was 2 m at Adindan and 1 m at Abu-Simbel within Lake Nasser (Aboul-Haggag, 1977; El Dardir, 1984, 1987). 90% of deposited sediment between 1964 and 1998 is within the Sudanese side of the reservoir (El-Manadely et al., 2002). Hafez (1977) stated that some microorganisms act as filtering organisms in
http://dx.doi.org/10.1016/j.ejar.2015.03.009
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This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
the reservoir which feed on finer materials suspended then digest the organic content in the fine materials and coagulate the suspended particles to bigger droplets. These filtering organisms are believed by Entz and Latif (1974) to be the main reason for the turbid water not reaching the northern section of the reservoir.
Before the construction of the Aswan High Dam the sediments discharged into the Mediterranean Sea, and quantity of these sediments greatly increases at the beginning of Nile flood. Since 1964, this amount of sediments has been held in the Aswan High Dam Reservoir (Hurst, 1952). Aswan High Dam acts as a good trap by which; under normal conditions; only the finest fractions of the suspended load are transported to the downstream. During the flood season 98% of the annual sediment load occurred; (2% in July, 45% in August, 38% in September, 12% in October, and 1.5 in November), Quelennec and Kruk (1976).
Different methods are widely used for determining the source material of sediments, as well as the environment and dynamics of their transport and deposition such as: grain-size distribution (Mycielska-Dowgiao and Ludwikowska-Kedzia,
Figure 1 A map showing sampling sites of Lake Nasser (General
2011; Woronko, 2012; Farhat, 2013), rounding and surface morphology of quartz grains in sand and silt (Mycielska-Dowgiao and Woronko, 2004), the petrographical composition of the light minerals (Mycielska-Dowgiao, 1995, 2007; Woronko et al., 2013), and composition of heavy-mineral assemblages (Marcinkowski and Mycielska-Dowgiao, 2013). The joint analysis of all previous textural features is the best method for determining the environment and dynamics of their transport and deposition as well as the source material of sediments. Each of them provides its own information, which supplements the other data. (Morton et al., 2013; Wachecka-Kotkowska and Lu-dwikowska-Kedzia, 2013).
Distributions of gravel, sand and mud fractions are used as good indicators for studying of all textural properties of deposits. Different interpretations of grain size distributions led to numerous discussions (e.g. Friedman and Sanders, 1978; Mycielska-Dowgiao, 2007; Flemming, 2007; Hartmann and Flemming, 2007; Szmanda, 2007; Weltje and Prins, 2007; Mycielska-Dowgiao and Ludwikowska Kedzia, 2011). Grain size depends on several factors such as: transport processes, the sedimentation conditions and transport related features,
location of Lake Nasser in Egypt is shown in the top left corner).
all of previous factors are better expressed in the structural features (Flemming, 2007; Hartmann and Flemming, 2007).
The aim of this study is to show the effect of flood season on bottom sediments of Lake Nasser, which could help in understanding the differences between sediments' grain size distribution and mode of transportation during drought (DDP) and flooding periods (DFp).
Materials and methods
Area of study
The largest man-made lake in Africa; the High Dam Lake; is formed after the construction of a rock-filled dam on the River Nile (17 km south of Aswan, 900 km from Cairo). The lake extends from the dam itself in the north to the Cataract at Dal, to Sudan in the south. The major portion of the lake lies in Egypt and is known as Lake Nasser and Lake Nubia on the Sudanese side. Lake Nasser extends between latitudes 22°00'-23°58' N and longitudes 31°19'-33°19' E (Abou El Ella and El Samman, 2010; Heikal, 2010).
Egypt is classified as a water scarce country, in addition to an increase in population it is preoccupied with a shortage of water resources. The Nile River and Lake Nasser are the principal arteries of life in Egypt (Flakenmark et al., 1989; Hassan and Al Rasheedy, 2007). Lake Nasser has a long and narrow shape particularly at its southern part (Lake Nubia), more than 95% of the Egyptian freshwater budget is coming from Lake Nasser (El Shemy, 2010).
The whole reservoir extends about 496 km, 292 km for Lake Nasser and 204 km for Lake Nubia. The area of the reservoir at 180 m vertical level is about 6275 km2 of which Lake Nasser occupies about 5248 km2. The mean depth of Lake Nasser at 160 m vertical level is 21.5 m as compared with about 25.2 m at 180 m vertical level (Abou El Ella and El Samman, 2010; El Shemy, 2010).
Geographical and geological settings
Most of the topographic features located in Lake Nasser date back to the Pliocene, while the present deep gorges and khors
(wadis) together with the relief are probably of the Pleistocene or Recent age. The channel of old River Nile followed different directions starting southward from Wadi Halfa until Aswan northward. It was divided into Wadi Halfa - Thomas (SW-NE direction) and Thomas - El-Diwan (NW-SE), El-Diwan -Korosko (W-E). North to Korosko, the channel of the old River Nile followed two directions, (SW-NE) and (SE-NW). Kalabsha High Dam channel followed almost one main trend (S-N) which was controlled by igneous and metamorphic rock exposures on both sides. Deep canyon with highly slick-sided is located at El-Madiq area (Issawi, 1968, 1978; Hassan et al., 2010).
The area of Lake Nasser belongs to the so-called Arabo-Nubian massif. Four main geomorphological and geological units are found which are (1) Aswan Hills extend along the eastern bank of Lake Nasser with rugged topography, (2) The old Nile valley and the High Dam Reservoir are extended along the western edge of Aswan hills. (3) The Nubian Plain covers most of the low lands west of the old Nile valley. And (4) The Sinn El-Kaddab Plateau is a vast limestone capped table land (Issawi, 1968).
Faulting is the most important geologic feature in Lake Nasser area. The largest faults are Kalabsha and Seiyal faults; trending in E-W direction; with predominant faults in N-S direction. NW-SW and NE-SW are subordinate faults. Up-arching is found as a result of uplifting of basement rocks. Folding is a less predominant structure. Small domes and several basins were created according to the up-arching of the basement (Issawi, 1968, 1978; Wycisk, 1987; Morgan, 1990; Klitzsch and Wycisk, 1999).
Sampling
Sampling was undertaken through a comprehensive program of the National Institute of Oceanography and Fisheries (NIOF) (Fresh Water and Lakes Division-FWLD) in order to study environmental conditions and Fisheries of Lake Nasser. The sampling program was done during 2013.
Sediment samples were collected using Ekman grab sampler semi-annually during drought (DDP) and flooding periods (DFP) during spring and autumn, 2013. Samples were
Figure 2 Showing distribution of sand fraction of Lake Nasser sediments. DDP: Before flood season, DFP: After flood season (M: main channel, E: eastern bank, W: western bank).
Figure 3 Showing distribution of mud fraction of Lake Nasser sediments. DDP: Before flood season, DFP: After flood season (M: main channel, E: eastern bank, W: western bank).
collected from ten sectors in the main channel of the lake from south to north; Adindan, Abu-Simbel, Tushka, Amada, Korosko, El-Madiq, Wadi-Abyd, Kalabsha, Dahmit and upstream of High Dam, respectively. Each sector consists of three sites; main channel (M) in addition to eastern (E) and western (W) banks (Fig. 1).
Analysis
Sediment samples were prepared using the decantation method (Folk, 1980), where grain size analysis was done by the dry sieving technique (Folk, 1980). Samples containing more than 5% fine fraction (finer than 40) were analyzed using the pipette method described by Krumbien and Pettijohn (1938), Griffiths (1951) and Carver (1971). Sediment textural classes were deduced according to Folk (1980). The sedimentological parameters were derived according to Folk and Ward (1957). The grain size of the sediments is indicated according to the Udden-Wentworth scale (Udden, 1914; Wentworth, 1922). Sediment modes of transportation were interpreted using Characteristic of truncation lines at inflection points of cumulative lines and C-M diagram according to Visher (1969), Bartholdy et al. (2007), Opreanu et al. (2007), Mycielska-Dowgiao and Ludwikowska Kedzia (2011), and Passega (1964). One Way ANOVA statistical analysis was carried out using Statistica© program version 8 and correlation analysis was carried out using SPSS© program version 20.
Results
Grain-size analysis Grain-size distribution
Both weight-percentage frequency curves and cumulative weight-percentage frequency curves have been constructed in order to identify possible trends. Comparison of these curves for the sediments of the two seasons indicates that there were clear trends of Lake Nasser sediments, the main channel sediments consisted mainly from mud fraction with variable amount of sand (fine and very fine sand), whereas the bank
sediments have no clear trend just depending on topographical features, which may lead to increase gravel to 100% (sites 2W and 3E BFS). Sand fractions (fine and very fine sand) were widely distributed at bank sites especially westwards reaching 94.40% at site 1W AFS and 79.10% at site 10E BFS. Clay fraction has a clear trend; increases southward; it reached up to 90.34 and 72.65% at sites 9M DDP and DFP, respectively. Silt fractions increase toward both banks and northward. It reached to 57.60% at site 2E (DDP), while (DFP) it recorded 52.65% at site 6M (Figs. 2 and 3; Tables 1 and 2).
The Main channel (M) sediment textural classes are mainly silty clay southward DDP, while DFP was sandy mud. Sediments of the bank sites (E & W) were sandy mud and muddy sand northward DDP, while southward they were silty clay and clayey silt. DFP they were sandy mud and muddy sand.
Results illustrate that depth controlled the distribution of grain size. Mud increased with increasing depth while sand fractions decreased in the same trend. Mud fractions are correlated positively and significantly with depth (r = 0.48 , p = 0.05 ( : significant at 0.05%)), while sand fractions are correlated negatively and significantly with depth (r = -0.48*, p = 0.05 (*: significant at 0.05%)), but some sites deviate from this pattern.
To find out whether the population variances are equal or there are insignificant differences between the means of several variables, statistical tests must be carried out (Dean and Voss, 1999; Walpole et al., 2004; Srivastava et al., 2012). A one-way ANOVA was applied between the grain size fractions (gravel, sand, mud, and clay) and the studied periods (during drought and flooding periods). Table 3 shows the calculated values. Results indicate that gravel fraction is insignificant with seasons (p = 0.52) it may be due to local topography factor. Sand and mud fractions are significant with seasons (p = 0.0065, and 0.0117 for sand and mud, respectively), which indicate that the distribution of sand and mud fractions were affected by flood season.
Grain-size parameters
The grain size parameters of Lake Nasser sediments were calculated from cumulative curves and given in Tables 4 and 5.
Table 1 Sediment fraction percent and textural classes of Lake Nasser sediment during the drought period.
Station Gravel V.C. Sand C. Sand M. Sand F. Sand V.F. Sand C. Silt M. Silt F. Silt V.F. Silt Gravel Sand Silt
Mud Sediment type
1M 0.00 0.00 0.00 0.00 0.00 0.00
1E *** *** *** *** *** ***
1W 0.00 0.00 0.00 0.00 23.09 31.20
2M 0.00 0.00 0.00 0.00 0.00 0.00
2E 0.00 0.00 0.00 0.00 0.00 0.00
2W 100.00 0.00 0.00 0.00 0.00 0.00
3M 0.00 0.00 0.00 10.17 13.41 19.33
3E 95.71 0.00 0.00 0.00 0.00 0.00
3W 0.00 0.00 0.00 0.00 14.27 25.42
4M 16.59 0.00 0.00 0.00 0.00 19.91
4E *** *** *** *** *** ***
4W 30.78 0.00 0.00 0.00 8.74 18.08
5M *** *** *** *** *** ***
5E *** *** *** *** *** ***
5W *** *** *** *** *** ***
6M 0.00 0.00 0.00 0.00 0.00 0.00
6E 0.00 0.00 0.00 0.00 0.00 0.00
6W 0.00 0.00 0.00 0.00 0.00 0.00
7M 0.00 0.00 0.00 0.00 0.00 0.00
7E 0.00 0.00 0.00 0.00 0.00 0.00
7W 0.00 0.00 0.00 0.00 0.00 7.24
8M 0.00 0.00 0.00 0.00 0.00 14.19
8E 0.00 0.00 0.00 0.00 0.00 0.00
8W 0.00 0.00 0.00 0.00 0.00 9.63
9M 0.00 0.00 0.00 0.00 0.00 0.00
9E 0.00 0.00 0.00 0.00 0.00 0.00
9W *** *** *** *** *** ***
10M 0.00 0.00 0.00 0.00 0.00 0.00
10E 1.71 2.30 4.69 15.94 31.93 24.23
10W 47.00 12.73 11.93 8.51 9.12 7.01
13.93 ***
26.56 11.02 46.55 0.00 14.17
3.35 ***
6.03 ***
1.64 6.99 5.89 0.00 4.33
2.80 ***
2.23 6.88 1.06 0.00 9.34
6.66 5.56 0.67 11.29
15.34 3.72 3.29 1.42
*** *** *** ***
6.71 9.28 0.38 3.68
*** *** *** ***
*** *** *** ***
*** *** *** ***
5.91 1.57 0.47 4.01
7.65 2.19 1.81 39.33
9.44 0.24 37.50 5.88
6.43 3.38 1.64 2.98
7.94 6.13 3.29 20.43
8.91 3.96 27.05 0.90
3.04 1.61 2.87 0.70
4.53 1.73 8.04 5.99
3.94 1.48 5.97 11.40
3.41 1.76 1.34 3.15
12.80 12.14 1.54 7.87
*** *** *** ***
7.59 4.78 7.31 6.60
7.58 4.30 0.08 0.32
0.00 ***
0.00 0.00 0.00 100.00 0.00 95.71 0.00
16.59 ***
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.00 ***
0.00 1.71 47.00
0.00 26.11
54.29 0.00 0.00 0.00 42.91 0.00 39.69 19.91
33.98 27.73 57.60 100.00 30.97
0.00 0.00 0.00 0.00 0.00 7.24 14.19 0.00 9.63 0.00
0.00 ***
73.89 ***
100.00 0.00 45.71 100.00 100.00 0.00 57.09 3.29
Mud (Silty clay) ***
Muddy sand Mud (Silty clay) Mud (Silty clay) Gravel Sandy mud Muddy gravel
24.17 36.13 60.31 Sandy mud
23.76 39.73 63.50 Gravelly sandy mud
*** *** *** ***
20.05 22.35 42.40 Sandy gravelly mud
*** *** *** ***
*** *** *** ***
*** *** *** ***
11.96 88.04 100.00 Mud (Silty clay)
50.97 49.03 100.00 Mud (Clayey silt)
53.06 46.94 100.00 Mud (clayey silt)
14.43 85.57 100.00 Mud (Silty clay)
37.80 62.20 100.00 Mud (Silty clay)
40.83 51.94 92.76 Sandy mud
8.21 77.60 85.81 Sandy mud
20.29 79.71 100.00 Mud (Silty clay)
22.80 67.57 90.37 Sandy mud
9.66 90.34 100.00 Mud (Silty clay)
34.34 65.66 100.00 Mud (Silty clay)
*** *** *** ***
26.28 73.72 100.00 Mud (Silty clay)
12.29 6.91 19.20 Muddy gravelly sand
0.00 65.66 3.70 Gravelly muddy sand
sample with mud fraction less than 5%;
Not collected sample; VC: very coarse; C: coarse; M: medium; F: fine; VF: very fine.
Table 2 Sediment fraction percent and textural classes of Lake Nasser sediment during the flooding period.
Station Gravel V.C.
C. M. F. V.F.
Sand Sand Sand Sand
C. Silt
M. Silt
F. Silt
V.F. Silt
Gravel Sand Silt Clay Mud Sediment type
0.00 0.00 0.00 0.00 0.00 0.00
2.07 1.33 10.88 44.35 25.92 11.93
0.00 0.00 31.36 68.64 100.00
2.07 94.40
Mud (Silty
clay) ***
Gravelly muddy sand
2M 0.00 0.00 0.00 0.00 0.00 13.45 8.42 18.08 11.04 9.15 39.86 0.00 13.45 46.69 39.86 86.55 Sandy mud
2E 0.00 0.00 0.00 19.05 20.70 20.51 20.81 3.80 3.06 0.84 11.23 0.00 60.25 28.52 11.23 39.75 Muddy sand
2W 0.00 0.00 0.00 23.51 37.43 20.72 1.63 3.48 1.54 2.48 9.21 0.00 81.66 9.13 9.21 18.34 Muddy sand
3M 0.00 0.00 0.00 0.00 27.85 42.94 7.98 6.37 4.09 2.26 8.51 0.00 70.79 20.70 8.51 29.21 Muddy sand
3E *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
3W 0.00 0.00 0.00 0.00 26.32 38.95 2.33 4.50 5.08 4.67 18.15 0.00 65.27 16.58 18.15 34.73 Muddy sand
4M 0.00 0.00 0.00 0.00 0.00 32.54 13.14 15.55 9.33 4.56 24.88 0.00 32.54 42.58 24.88 67.46 Sandy mud
4E *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
4W 0.00 0.00 0.00 0.00 0.00 22.67 4.24 18.61 8.66 10.90 34.93 0.00 22.67 42.40 34.93 77.33 Sandy mud
5M 0.00 0.00 0.00 0.00 13.55 22.61 12.67 12.24 9.15 5.24 24.54 0.00 36.16 39.30 24.54 63.84 Sandy mud
5E *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
5W *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
6M 0.00 0.00 0.00 0.00 0.00 0.00 7.19 17.88 18.78 8.81 47.35 0.00 0.00 52.65 47.35 100.00 Mud (Clayey
6E *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
6W *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
7M 0.00 0.00 0.00 0.00 0.00 34.55 10.76 8.61 7.34 8.10 30.64 0.00 34.55 34.81 30.64 65.45 Sandy mud
7E 0.00 0.00 0.00 0.00 25.06 29.15 14.71 1.74 1.45 1.88 26.02 0.00 54.21 19.77 26.02 45.79 Muddy sand
7W 0.00 0.00 0.00 0.00 10.41 27.15 16.50 15.79 10.82 5.54 13.78 0.00 37.56 48.66 13.78 62.44 Sandy mud
8M 0.00 11.43 12.85 8.51 4.96 3.71 12.63 9.96 8.99 19.77 51.35 0.00 7.19 41.46 51.35 92.81 Sandy mud
8E 0.00 0.00 0.00 0.00 12.11 48.54 11.66 10.83 4.63 2.37 9.86 0.00 60.65 29.49 9.86 39.35 Muddy sand
8W 0.00 6.42 5.84 3.52 2.62 2.99 7.44 4.22 3.63 1.21 62.11 0.00 21.39 16.50 62.11 78.61 Sandy mud
9M 0.00 0.00 0.00 0.00 0.00 0.00 11.41 4.10 0.58 11.26 72.65 0.00 0.00 27.35 72.65 100.00 Mud (Silty
9E 0.00 0.00 0.00 0.00 0.00 27.86 13.15 0.91 9.61 0.96 47.50 0.00 27.86 24.64 47.50 72.14 Sandy mud
9W *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
10M *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
10E *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
10W *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
-: Sample with mud fraction less than 5%; ****: Not collected sample; VC: very coarse; C: coarse; M: medium; F: fine; VF: very fine.
The mean grain size is a parameter related to the overall grain size, sorting or the uniformity of the grain-size distribution, Skewness is a measure of symmetrical distribution, i.e. the proportion of coarse or fine fractions. A symmetrical curve with excess fine material shows a positive value, whereas one with excess coarse material shows a negative value; a zero value is indicated by a symmetrical curve, while the kurtosis expresses the peakedness of the grain-size distribution (Srivastava et al., 2012). During the drought period, the main size ranged between gravel and clay (—1.30 to 8.220), while during the flooding period it ranged between medium sand and very fine silt (1.98-7.60). DDP sorting ranged between medium well
sorted and very poorly sorted (0.63-3.780), where it was moderately sorted to very poorly sorted (0.98-2.180) DFP. The skewness was symmetrical to strongly fine-skewed and near symmetrical to strongly fine-skewed DDP and DFP, respectively. Kurtosis varied between very platykurtic to extremely leptokurtic during both periods.
Sediment mode of transportation
Visher (1969) related the modes of sediment transportation; by traction, saltation and suspension; by distinguishing three distinct sectors of the cumulative curve in the form of straight lines of different lengths and slopes. Lake Nasser sediments DDP indicate a prominent truncation between traction and saltation at a range of —1.1 and 5.00 ± 0.20 with percentage ranged between 1.9% and 47.0% except at site 3 E that was — 1.00 with percentage of 95.5% due to access of gravel fraction. Truncation between saltation and suspension was more than 40 which ranged between 4.0 and 8.000 with percentage ranged between 6.0% and 91.0%. Suspension load ranged between 4.5% and 90.5%. DFP results indicate a prominent truncation between traction and saltation at a range of —1.0 and 5.0 ± 0.20 with percentage ranged between 2.0% and 34.0%. Truncation between saltation and suspension was more than 80 with percentage ranged between 11.0% and
Table 3 One-way ANOVA between fractions (gravel, sand, clay, and mud) and studied periods (during drought and flooding periods).
Fraction One-way ANOVA
p value Outcome
Gravel Sand Clay Mud 0.5224 0.0065 0.0076 0.0117 Non-significant Significant Significant Significant
Table 4 Sedimentological parameters of Lake Nasser sediment during the drought period according to Folk and Ward (1957).
Station Mean size (Mz) (assorting Skewness (SKj) Kurtosis (KG)
Value(0) Type Value(0) Type Value Type Value Type
1M 7.35 Very fine silt 1.25 Poorly sorted -0.80 Strongly coarse-skewed 1.68 Very lepto-kurtic
1E ****** ****** **** ** ****** ****** ****** ***** * ******
1W 4.27 Coarse silt 1.61 Poorly sorted 0.46 Strongly fine-skewed 1.41 Very lepto-kurtic
2M 7.57 Very fine silt 1.06 Poorly sorted -0.79 Strongly coarse-skewed 2.53 Very lepto-kurtic
2E 6.32 Fine silt 1.44 Poorly sorted 0.27 Fine-skewed 0.47 Very platy-kurtic
2W 5.03 Medium silt 2.38 Very poorly sorted 0.23 Fine-skewed 0.54 Very platy-kurtic
3M 5.70 Fine silt 2.12 Very poorly sorted 0.00 Near symmetrical 0.50 Very platy-kurtic
3E -1.30 Gravel 0.19 Very well sorted -0.07 Symmetrical 1.23 Very lepto-kurtic
3W 4.07 Coarse silt 3.76 Very poorly sorted -0.28 Coarse-skewed 0.85 Platy-kurtic
4M 3.50 Very fine sand 3.78 Very poorly sorted -0.03 Near symmetrical 0.47 Very platy-kurtic
4E ****** ****** **** ** ****** ****** ****** ***** * ******
4W 8.20 Clay 0.66 Medium well sorted -0.39 Strongly coarse-skewed 6.07 Extremely lepto-kurtic
5M ****** ****** **** ** ****** ****** ****** ***** * ******
5E ****** ****** **** ** ****** ****** ****** ***** * ******
5W ****** ****** **** ** ****** ****** ****** ***** * ******
6M 7.80 Very fine silt 0.78 Moderately sorted -0.69 Strongly coarse-skewed 1.91 Very lepto-kurtic
6E 7.20 Very fine silt 1.03 Poorly sorted -0.16 Coarse-skewed 0.90 Meso-kurtic
6W 8.20 Clay 0.63 Medium well sorted -0.43 Strongly coarse-skewed 5.74 Extremely lepto-kurtic
7M 7.65 Very fine silt 0.96 Moderately sorted -0.75 Strongly coarse-skewed 1.79 Very lepto-kurtic
7E 7.07 Very fine silt 1.48 Poorly sorted -0.85 Strongly coarse-skewed 0.95 Meso-kurtic
7W 6.98 Fine silt 1.70 Poorly sorted -0.87 Strongly coarse-skewed 7.62 Extremely lepto-kurtic
8M 7.90 Very fine silt 0.76 Moderately sorted -0.75 Strongly coarse-skewed 5.08 Extremely lepto-kurtic
8E 7.45 Very fine silt 1.26 Poorly sorted -0.81 Strongly coarse-skewed 1.96 Very lepto-kurtic
8W 8.22 Clay 0.49 Well sorted -0.33 Strongly coarse-skewed 5.43 Extremely lepto-kurtic
9M 7.17 Very fine silt 1.30 Poorly sorted -0.81 Strongly coarse-skewed 0.67 Platy-kurtic
9E 7.62 Very fine silt 1.00 Poorly sorted -0.79 Strongly coarse-skewed 4.16 Extremely lepto-kurtic
9W ****** ****** **** ** ****** ****** ****** ***** * ******
10M 7.22 Very fine silt 1.30 Poorly sorted -0.82 Strongly coarse-skewed 0.67 Platy-kurtic
10E 2.85 Fine sand 1.87 Poorly sorted 0.23 Fine-skewed 2.12 Very lepto-kurtic
10W 0.37 Coarse sand 1.91 Poorly sorted 0.77 Strongly fine-skewed 0.69 Platy-kurtic
******. Not collected sample.
Table 5 Sedimentological parameters of Lake Nasser bottom sediment during the flooding period according to Folk and Ward (1957).
Station Mean size (Mz) (aI)Sorting Skewness (SKI) Kurtosis (KG)
Value(0) Type Value(0) Type Value Type Value Type
1M 7.60 Very fine silt 0.98 Moderately sorted -0.69 Strongly coarse-skewed 1.59 Very lepto-kurtic
1E ****** ****** **** ** ****** ****** ****** ****** ******
1W 1.98 Medium sand 1.00 Poorly sorted 0.09 Near symmetrical 1.12 Lepto-kurtic
2M 6.50 Very fine silt 1.66 Poorly sorted -0.40 Strongly coarse-skewed 0.64 Very platy-kurtic
2E 3.72 Very fine sand 1.90 Poorly sorted 0.31 Strongly fine-skewed 1.13 Lepto-kurtic
2W 3.23 Very fine sand 1.78 Poorly sorted 0.59 Strongly fine-skewed 1.65 Very lepto-kurtic
3M 4.05 Coarse silt 1.56 Poorly sorted 0.62 Strongly fine-skewed 1.43 Lepto-kurtic
3E ****** ****** **** ** ****** ****** ****** ****** ******
3W 4.83 Coarse silt 2.11 Very poorly sorted 0.70 Strongly fine-skewed 0.64 Very lepto-kurtic
4M 5.70 Medium silt 1.75 Poorly sorted 0.34 Strongly fine-skewed 0.46 Very lepto-kurtic
4E ****** ****** **** ** ****** ****** ****** ****** ******
4W 6.13 Fine silt 1.75 Poorly sorted -0.18 Coarse-skewed 0.53 Very lepto-kurtic
5M 5.42 Medium silt 2.07 Very poorly sorted 0.17 Fine-skewed 0.51 Very lepto-kurtic
5E ****** ****** **** ** ****** ****** ****** ****** ******
5W ****** ****** **** ** ****** ****** ****** ****** ******
6M 7.17 Very fine silt 1.18 Poorly sorted -0.61 Strongly coarse-skewed 0.67 Platy-kurtic
6E ****** ****** **** ** ****** ****** ****** ****** ******
6W ****** ****** **** ** ****** ****** ****** ****** ******
7M 5.82 Medium silt 1.77 Poorly sorted 0.21 Fine-skewed 0.46 Very platy-kurtic
7E 4.93 Coarse silt 2.15 Very poorly sorted 0.63 Strongly fine-skewed 0.46 Very platy-kurtic
7W 5.20 Medium silt 1.89 Poorly sorted 0.32 Strongly fine-skewed 0.79 Platy-kurtic
8M 7.17 Very fine silt 1.18 Poorly sorted -0.61 Strongly coarse-skewed 0.67 Platy-kurtic
8E 4.33 Coarse silt 1.56 Poorly sorted 0.58 Strongly fine-skewed 1.10 Meso-kurtic
8W 7.45 Very fine silt 1.12 Poorly sorted -0.71 Strongly coarse-skewed 2.39 Very lepto-kurtic
9M 7.60 Very fine silt 1.03 Poorly sorted -0.80 Strongly coarse-skewed 3.74 Extremely lepto-kurtic
9E 6.30 Fine silt 1.78 Poorly sorted -0.34 Strongly coarse-skewed 0.46 Very platy-kurtic
9W ****** ****** **** ** ****** ****** ****** ****** ******
10M ****** ****** **** ** ****** ****** ****** ****** ******
10E ****** ****** **** ** ****** ****** ****** ****** ******
10W ****** ****** **** ** ****** ****** ****** ****** ******
******. Not collected sample.
94.5%. Suspension load ranged between 3.5% and 84.0% (Table 6).
C—M patterns
The results obtained from grain-size analyses are presented in a Passega C-M diagram (Passega, 1964; Passega and Byramjee, 1969; Mycielska-Dowgiao and Ludwikowska-Kedzia, 2011), where the values of "C" the first percentile are plotted against the "M" median grain diameter.
C-M application is used widely to interpret different depositional environments. (Ludwikowska-Kedzia, 2000; Szmanda, 2002; Ostrowska et al., 2003; Bartholdy et al., 2007; Opreanu et al., 2007; Mycielska-Dowgiao and Ludwikowska-Kedzia, 2011; Farhat, 2010, 2013; Srivastava et al., 2012; Pisarska-Jamrozy, 2013; Ramamohanarao et al., 2003). There was a clear trend of the sediment of Lake Nasser during the drought period showing that most of sediments fall in pelagic suspension (T) (especially main channel M) in which sediments are settled from suspension in stagnant water. It may be due to the great depth as wave and current activity decrease toward deeper parts of the lake. According to Fig 4, sites 2W and 3W fall in field 3 (i.e. rolling), 4M and 10E fall in field 2 (i.e. rolling), 3M and 10W fall in field
1 (i.e. rolling), 1W falls in uniform suspension and 3E falls in overbank-pool facies suspension. During flooding period there was no clear trend for the studied sediments, most of the main channel (M) samples fall in pelagic suspension (T), 1 W falls in field 2 (i.e. rolling), 2E and 2W fall in graded suspension (transported mainly by siltation), 4M, 7M, and 7W fall in overbank facies suspension, 5M falls in suspension, and 3W, 3M, 7E and 8E fall in uniform suspension.
Discussion
The field description of the bottom sediments under concern indicates that the darkest color of sediment was observed near Aswan; this may be due to relatively old sediments and the anoxic conditions during stagnation period before flood season; while light color was observed southward; especially during the flooding period; this may be due to deposition of fresh sediment southward. The sediments of Lake Nasser are heterogeneous. The main channel sediments are mainly silty clay and clayey silt, while the eastern and western sides include more sand and depend on the local topography. Deposition of sand from the adjacent sand dunes scattered along the western bank of Lake Nasser takes place as aeolian deposits. The highest percentage of clay was recorded in the main channel of the
Table 6 Characteristics of truncation lines of Lake Nasser bottom sediment during 2013. Station Spring 2013 Autumn 2013
Traction/Saltation Saltation/Suspension Suspension Traction/Saltation Saltation/Suspension Suspension
0 Wt% 0 Wt% Wt% 0 Wt% 0 Wt% Wt%
1M 5.00 14.00 7.50 72.00 14.00 4.00 9.00 8.00 36.50 54.50
1E *** *** *** *** *** *** *** *** *** ***
1W 3.00 23.00 4.90 57.00 20.00 -1.00 2.00 8.00 94.50 3.50
2M 5.00 12.00 8.00 15.00 73.00 4.00 13.00 8.00 47.00 40.00
2E 5.00 47.00 8.00 10.00 43.00 2.00 19.00 8.00 70.00 11.00
2W 2.00 11.00 8.00 63.00 26.00 2.00 23.00 8.00 67.50 9.50
3M 4.00 39.50 8.00 24.50 36.00 3.00 27.00 8.00 64.50 8.50
3E -1.00 95.50 4.00 0.00 4.50 *** *** *** *** ***
3W 1.00 16.00 8.00 44.00 40.00 3.00 26.00 8.00 55.00 19.00
4M -1.00 30.50 8.00 47.00 22.50 4.00 32.00 8.00 43.00 25.00
4E *** *** *** *** *** *** *** *** *** ***
4W 5.00 6.00 8.00 6.00 88.00 4.00 23.00 8.00 42.00 35.00
5M *** *** *** *** *** 3.00 14.00 8.00 61.00 25.00
5E *** *** *** *** *** *** *** *** *** ***
5W *** *** *** *** *** *** *** *** *** ***
6M 5.00 8.00 8.00 42.00 50.00 5.00 7.00 8.00 46.00 47.00
6E 5.00 9.00 8.00 45.00 46.00 *** *** *** *** ***
6W 5.00 6.50 8.00 7.50 86.00 *** *** *** *** ***
7M 5.00 8.00 8.00 30.00 62.00 4.00 34.00 8.00 35.00 31.00
7E 4.00 7.00 8.00 42.00 51.00 3.00 25.00 8.00 49.00 26.00
7W 4.00 14.00 8.00 8.00 78.00 3.00 10.00 8.00 76.00 14.00
8M 5.00 4.50 8.00 15.50 80.00 5.00 7.00 8.00 14.50 78.50
8E 4.00 9.50 8.00 22.50 68.00 3.00 12.00 8.00 78.00 10.00
8W 5.00 3.50 8.00 6.00 90.50 4.00 5.00 8.00 11.00 84.00
9M 5.00 15.00 8.00 29.00 56.00 5.00 11.00 8.00 15.00 74.00
9E 5.00 7.50 8.00 17.50 75.00 4.00 27.00 8.00 29.00 44.00
9W *** *** *** *** *** *** *** *** *** ***
10M 5.00 13.00 8.00 22.00 65.00 *** *** *** *** ***
10E -1.00 1.90 8.00 91.10 7.00 *** *** *** *** ***
10W -1.00 46.00 4.00 30.00 24.00 *** *** *** *** ***
Not collected sample.
southern sites at Tushka, Abu Simbel and Adindan (Entz and Latif, 1974; Philip et al., 1977; Scott et al., 1978; El Dardir, 1984, 1987, 1994; Fishar, 1995; El-Manadely et al., 2002; Iskaros and El Dardir, 2010).
In agreement with Liggza and Smal (2002) who studied the sediment of the Dobczyce reservoir, and Teeter et al. (2001) and Wetzel (2001) who studied Myslenice Basin, it is clear that depth is controlling the distribution of grain size. Fines increased with increasing of depth while sand fractions decreased. This indicates less current effects on deeper sediments. Re-suspension of fine particles from a shallow area and its re-deposition in a deeper part of the water body affect significantly the texture of sediment in the shallow part of the reservoir, but some sites deviate from this pattern due to geo-morphic features of the reservoir. Concentration of suspended sediments decreases northward. The lake sediments are consisting of sand, silt and clay, with non-uniform composition pattern. The variation in the sediment composition is due to both time and topographical features characterizing deposited sediment particles. After drought periods, high floods decrease the dead storage zone of Lake Nasser by filling it with re-deposited sediments coming from southern zones (El-Manadley et al., 2002).
The decreasing of fines and increasing of sand fraction DFP; than DDP; indicate that the percent of sands increased as the flood season started, it may be a result of washing of bottom sediments by high energy water current caused by the flood which carries fine as suspended material leaving sand fractions. It agrees with El-Manadely et al. (2002) who stated that proportion of sand tended to increase as the flood season progressed.
Grain-size distributions are widely used to study various sedimentary facies and environments of deposits. Sand fraction part of the cumulative curves is considered to be a normal distribution, admixtures of coarser and finer grains occur, which do not form normal distributions (Tanner, 1964). Nevertheless, their presence or absence is important for the interpretation of the sedimentary environment (Mycielska-Dowgiao and Ludwikowska-Kedzia, 2011).
Most ofthe cumulative curves ofthe sediments ofthe present study have clear different sectors with clear straight line and inflection points. During the drought period, it can be deduced from the curves that suspension was the most prominent form of transport, followed by siltation, while truncation was of minor importance. It means that curves most closely resemble the second group of cumulative curves in which sediments are
Figure 4 C-M Pattern diagrams showing mode of transportation of Lake Nasser sediments. (A) During the drought period, (B) During the flooding period.
transported by a medium of considerable density. During the flooding period siltation was most predominant mode of transportation, followed by suspension and truncation was of less importance, which means that curves most closely resemble the third group of cumulative curves, (transitional group including mixed sediments formed by short-lived depositional processes, deposits resulting from various overlapping processes and depositional environments) (Mycielska-Dowgiao and Ludwikowska-Kgdzia, 2011; Srivastava et al., 2012; Wachecka-Kotkowska and Ludwikowska-Kgdzia, 2013).
The mode of transportation of Lake Nasser sediments during the drought period was pelagic suspension in which sediments were settled from suspension in stagnant water, while rolling, overbank facies suspension and uniform suspension were less important. During the flooding period there was no clear trend for the studied sediments, most of the main channel samples fall in pelagic suspension, while rolling, graded suspension, overbank facies suspension, suspension and uniform suspension were widely distributed. Passega C-M diagram is helpful for the study of fluvial deposits, even though it was elaborated initially for the marine environment. It has been useful for the study of fluvial and coastal deposits, because both formed from different lithofacies, by which the diagram is useful to explain the depositional sub-environments. Different transport and depositional histories can thus be
distinguished (Ludwikowska-Kgdzia, 2000; Mycielska-Dowgiao and Ludwikowska-Kgdzia, 2011; Szmanda, 2002).
Conclusion
The present study results conclude that Lake Nasser sediments are heterogeneous. The main channel sediments are mainly silty clay and clayey silt, while the eastern and western sites include more sand which depends on the local topography. The highest percentage of clay was recorded in the main channel southward. Depth controlled distribution of grain size (deeper is finer) with some sites deviates from this pattern. Sand fractions increased as the flood season started.
Cumulative curves indicate that during the drought period suspension was the most prominent form of transportation, followed by siltation, while truncation was of minor importance, which means that sediments were transported by a medium of considerable density. During the flooding period siltation was most predominant mode of transportation, followed by suspension, while truncation was less important, which means that this environment has a high energy and variety of depositional environments.
C-M pattern diagram indicates that sediments of Lake Nasser during the drought period were pelagic suspension in
which sediments were settled from suspension in stagnant water, while rolling, overbank facies suspension and uniform suspension were less important. During the flooding period there was no clear trend, most of the main channel samples fall in pelagic suspension, while rolling, graded suspension, overbank facies suspension, suspension and uniform suspension were widely distributed for banks.
Further studies are recommended, just like roundness and surface morphology of quartz grains of sand and silt, the petrographical composition of the light minerals, and composition of heavy-mineral assemblages for determining the source material of Lake Nasser sediments, as well as the environment and dynamics of their transport and deposition.
Acknowledgements
This work was supported by the research plan of the Environment of Freshwater and Lakes Division, National Institute of Oceanography and Fisheries, Egypt in order to identify and evaluate the environmental and fisheries status of Lake Nasser during 2013.
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