NEAR SHORE AND BEACH NOURISHMENT’S EFFECTS ON THE STABILITY OF ROSETTA PROMONTORY, EGYPT

Eighteenth International Water Technology Conference, IWTC18SharmElSheikh, 12-14 March 2015

NEAR SHORE AND BEACH NOURISHMENT’S EFFECTS ON THE

STABILITY OF ROSETTA PROMONTORY, EGYPT

Ali Masria1, Kazuo Nadaoka

2, Yoshiaki Kuriyama

3, Abdelazim Negm

1, Moheb Iskander

4, and

Oliver C. Saavedra5

1Department of Environmental Engineering, Egypt-Japan University of Science and Technology E-JUST,

New Borg El-Arab, Alexandria, Egypt, E-mail: [email protected], [email protected] 2Department of Mechanical and Environmental Informatics, Graduate School of Information Science and

Engineering, Tokyo Institute of Technology, Tokyo, Japan, Email: [email protected] 3Director of Coastal and Estuarine Environment Field, and Director General of Asia-Pacific Center for

Coastal Disaster Research (APaC-CDR), Email:[email protected] 4Coastal Research Institute, Alexandria, Egypt, Email: [email protected]

5Department of Civil Engineering, Graduate School of Science and Engineering, Tokyo Institute of

Technology, Tokyo, Email: [email protected]

ABSTRACT

Rosetta promontory is located on the Mediterranean Sea where the Rosetta branch of Nile meets the

sea. Shoreline erosion and the river mouth sedimentation at Rosetta promontory were magnified after

construction of Aswan High Dam (AHD) in 1964 that dramatically decreased both water discharge,

and sediment transport to the sea. Many attempts to solve the erosion, and sedimentation problem were

performed. Hard protection works have been implemented since 1989 such as seawalls on the tip of the

promontory and several groins along the eastern and western shores of the promontory. Additionally

continuous dredging works were implemented within the river mouth. However, the shoreline along

Rosetta Promontory is still unstable and these measures has a limited effect on the promontory stability

where it transfers the problems to the adjacent areas.

Two techniques of coastal nourishment are proposed in this study to avoid further degradation of the

Rosetta coastal zone and to minimize erosion problems. These techniques include near shore and beach

nourishment.

A calibrated/verified Coastal Modeling System (CMS) was used to address the effect of the

nourishment on the morphology of the hot spot areas (erosion and accretion). Results of different

scenarios were discussed in detail. Beach nourishment on the western headland of the promontory will

modify the stability of the shoreline specially the western side of the promontory as well as decrease

the siltation problem inside the river mouth.

Keywords: Shoreline erosion, sedimentation, nourishment process, Rosetta.

1 INTRODUCTION AND STUDY AREA

The majority of coastlines‟ shape changes over time due to many factors such as ocean currents, rise

of sea level, wave action, sediment loads, and long shore drift. Coastal erosion occurs worldwide

along coastlines, and has been reported in the literature for several decades (Hamm et al. 2002;Castelle

et al. 2009; Spielmann et al. 2011; Shi et al. 2013 and Stive et al. 2013). Traditionally, eroded

coastlines have been protected by civil engineering structures involving revetments, groins, seawalls,

breakwaters and the like (Charlier et al. 2005). Major advances in the technology of beach nourishment

have been made over the past three decades (Houston 1996; Elko et al. 2005a), and spread widely. So,

not only coastal engineers are investigating beach nourishment, but also geoscientists(Hamm et al.

2002; Hanson et al. 2002). Nourishment and bypassing of sand are often required to mitigate the

unavoidable side-effects of engineering works. This „building with nature‟ approach requires a

profound understanding of the sediment transport processes in morphological systems Coastal erosion

(Van Rijn, 2004). This approach is recommended to apply in Egypt (Iskander 2010).

mailto:[email protected]


In general, beach nourishment involves the placement of sediment on an eroding beach to migrate

the shoreline seaward in order to promote storm protection, natural habitat and beach amenity. A wide

application of numerical models have been developed, both simple (Dean & Yoo 1992; Elko et al.

2005b) and more complex (Van Duin et al. 2004; Li et al. 2006; Lin et al. 2013; Kuroiwa et al. 2011),

to predict the impact of nourishment placement projects.

Coastal zone in Egypt in not an exception, especially at Damietta and Rosetta promontories. Rosetta

is one of the two main branched of the Nile River and will be the focus of this study. It is located 60

km east of Alexandria city as shown in “Fig.1”. After the construction of the Aswan High Dam, and

decrease in the discharge and sediment load the mouth of the two Nile Branches have faced many

environmental changelings. These include mainly sedimentation building up inside the outlet, and the

continuous erosion at both sides, (El Sayed et al. 2007;Masria et al. 2013; Masria et al. 2014b). The

main reason of Rosetta promontory instability is the lack of sedimentation and water flow from the

outlet due to execute the water control structures along the Nile River. Beach and nearshore

nourishment is one of the environmental friendly way to compensate the lack in sediment toward

sustainable stability of the promontory.

Analysis of incident waves versus shoreline orientation of the Rosetta promontory revealed that the

N, NNW, NW, WNW and NNE waves are jointly acting to transport sediment toward the southwest

and east along the western and eastern flanks of the Rosetta promontory, respectively. Conversely,

small wave components approaching from W and NE move sediment to the NNE and W directions,

respectively, along these coastal stretches(Frihy & Dewidar 2003). Many coastal protection measures

were executed to overcome the erosion problem, (Dewidar & Frihy 2008). Although the erosion rate

was decreased relatively in front of the revetments, it was shifted down drift, after 5 years, groins at the

eastern side, and 9 groins at the western one were constructed. Unfortunately, the situation in front of

the revetments, and down drift of the groins are still unstable. Periodically dredging projects

have been implemented along the river mouth to provide for minimum cross section for safe

fishing boats navigation and water drainage to the sea.

The objective of this work is to assess the influence of different proposed nourishment works at

Rosetta promontory stability. This work combines accurate bathymetric survey, wave, longshore drift,

and a morphological change modeling.

Figure 1. Study area location, land sat image ETM (2014).

2 MATERIAL AND METHOD

2.1 Numerical model

The CMS is a process-based suite of models that integrate hydrodynamics, sediment transport, and

morphological changes through the coupling of two modules, CMS-Flow and CMS-Wave, and they

a b a Rosetta promontory

Study area

Mediterranean Sea

Rosetta branch

Nile Delta

Study area


are coupled through steering module. It is conducted to simulate waves, interacting waves and currents,

water level, sediment transport, and morphology change at coastal inlets, entrances and nearby. The

CMS was developed specially for modeling outlet processes and morphology changes., (Demirbilek et

al. 2008). Model setup, calibration, verification and parameter sensitivity analysis were conducted by

using several hydrographic surveys during years 2005-2006, one year of wave and tide data as well as

bed sediment characteristics. The important parameter used in calibration; hydrodynamic time step,

Manning coefficient, different transport formulas, scaling factor for bed load and suspended load, total

adaptation length, and also the effect of smoothing the bathymetric contour. For more details see

(Masria et al. 2014a; Masria et al. 2013).

2.2 Nourishment Scenarios Set-up

Two different nourishment sets were simulated: beach nourishment, and near shore nourishment.

(Masria et al. 2014c) checked the availability of sediment resources for the nourishment and indentify

two main sources; offshore source with mean grain size range between 0.1 and 0.18 mm and land

source with mean grain size range between 0.24 - 0.32 mm. Also by using Particle Tracking Model

(PTM) he found that the sediment source come from El Khatatba which located 150 km from the site

landward with mean grain size 0.32 mm is more efficient within this area.

Based on the data availability, the simulation is conducted starting from October 2005 for one year

duration. The simulation is implemented to calculate the sediment transport using tide, and wave

forcing. These sediment volumes is presented in (CMS) as a uniform layer above the existing seabed

inside the placement area. Adding the nourishment is executed through interpolating the scatter of

placement site with the proposed nourished depth to the original grid, and using „linear‟ for

interpolation and „distance weighted‟ for extrapolation (to make sure the boundary depth is correctly

mapped).

(El Sayed et al. 2007) used multi-years hydrographic survey as well as GENESES model and found

that the needed quantity of sand nourishment for both western and eastern sides of the Rosetta

promontory, are about 500,000 m3/yr.

2.2.1 Beach nourishment group

The proposed placement sites are shown in ”Fig.2a”. The proposed geometry of placement sites is

similar to the old shape of the promontory before severe erosion occurred as shown in “Fig. 2b”

Different nourishment volumes of 100,000, 200,000 and 300,000 m3

are evaluated within this study.

For the sediment volume (100,000 m3), three scenarios were tested as shown in “Table 1”. These

scenarios are repeated for the other nourishment volumes (200,000, 300,000 m3).

Figure 2. a) The proposed placement sites for nourishment material, b)Shoreline retreat along Rosetta

promontory from 1900 to 2005, (El Sayed et al. 2007).

a b


Table 1. Scenarios assessed by CMS for different sediment volumes and locations

Scenario Description Total

sediment

volume(m3)

0 Do no thing 0

1 Placement site is at eastern side only. 100,000

2 Placement site is at western only. 100,000

3 Placement sites is at (eastern side + western side ), and

the volume is distributed equally between both sides. 100,000

2.2.2 Nearshore nourishment group

The proposed placement sites of the nourishment material are selected according to the hot spots

of the erosion ( represented in the negative values of morphology change map) as well as the point

where the current change its direction (nodal point) in the eastern side of the promontory where

longshore sediment transport is diverted to east and west “Fig.3”, (Masria et al. 2014a).The sediment

volumes evaluated are 100,000, 200,000 and 300,000 m3. Nourishment material will be placed at an

average depth 5m. For each sediment volumes, three scenarios were tested as shown in "Fig.3”: 1)

placement site directly at the right side of the nodal point (eastern side of the promontory); 2) the

placement site is centered above the nodal point at eastern side of the promontory; 3) the sediment

volume are distributed equally at the site east and west of the promontory.

Six profiles are selected at western and eastern sides of the outlet as shown in “Fig.3d” to evaluate

the effect of each scenario.

Figure 3. Three proposed nourishment placement sites scenarios a), b), c) for each sand nourishment, d)

Location of the selected profiles along eastern and western sides of Rosetta outlet used in bed evolution

analysis.

nodal point

nodal point

nodal point

a b

c d


3 RESULTS AND ANALYSIS

To evaluate the effect of the different nourishment scenarios, various outputs from one year

simulation implemented with Coastal Modeling System Software (CMS) are analyzed. The outputs

include morphology change, current velocity, and sediment concentrations.

3.1 Beach nourishment

Figure 4 shows an example of the morphology changes after one year along the study area. Figure 5

shows the bed changes east and west of the river mouth according to beach nourishment along the

western side of the promontory. The results illustrated that second scenario (Placement sand at the

western side of the river mouth) with sediment volume 200,000 m3 or more reduce the accumulation

of the sediments inside the outlet. Its function resembles the jetty function that decrease the wave

energy behind it, resulted in decreasing the strong eddy vortex which creates at the outlet due to the

interaction between discharge water and sea hydrodynamics. Also, increase the nourishment volume to

300,000 m3 will increase the accumulation of sediment west of the promontory. To accurately study

the effect of first scenario with different volumes, the hotspot area was divided into three subareas; the

eastern, middle and western as shown in “Figure 6 “.

Generally, beach nourishment on the western side of the river mouth will decrease the accumulated

of sediments at inlet. As shown in Figure 7. Also, it works as a sand engine where the sediment

bypasses from the western side to the eastern one as shown in “Fig.8a”. Moreover, this scenario keeps

a western part of the inlet valid for the navigation process compared to the no action case that nearly

close all the inlet resulting in hindering the navigation through the inlet as shown in “Fig. 8 b& 6c”.

The effect of beach nourishment increases with increase sand volume than 200,000 m3.

Figure 4. Model results of the morphological changes for different beach nourishment scenarios for ( 300

0000 m3 ) of sediments a) no action, b) at right side, c) at western side, d) at both eastern and western side,

the black line surround the nourishment area.

c

b

d

a


Figure 5. Model results of the different bed profile for the second scenario with different volumes ( 100

0000, 200 000, and 300 000 m3 )

Figure 6. Three subareas used to estimate sediment volume (accretion erosion and net volume).

Eastern

Western

Middle


Figure 7.Annual sediment volume of the second scenario for different nourishment volumes (100

0000, 200 000, and 300 000 m3); a) eastern area, b) middle area and c) western area.

Figure 8.a)Sediment concentration map at (10/11/2005) with 300 000 m3 sand nourishment west of the

promontory, b) bed evolution related to this scenario, and c) bed evolution with do nothing scenario

a

c

b


3.2 Nearshore nourishment

The morphological change after one year, for different scenarios of 100,000 m3, 200,000 m

3, and

300,000 m3

were simulated using the CMS . “Figure 9” shows a sample of the results for the

nourishment volume of 300,000 m3. From the results, it is clear that all scenarios almost have the same

trend at the accreted areas. To check deeply the effect of this technique on the bed changes in cross

shore direction, the bed profiles are plotted compared to the initial profile before adding the

nourishment material. It is clear that all scenarios showed a negligible effect compared to no action

scenario except scenario two which showed slight improvement at the eastern profile WBP 3.8 as

shown in “Figure 10”. Also, the total sediment transport rate decreases with increasing the

sediment volume, “Figure 11”.

Although the second set of scenarios with sand volume (300,000 m3) is slightly better than

other scenarios in comparison with no action scenario, it is clear that there is no significant

effect of the nearshore nourishment technique in decreasing the severe erosion in front of the

seawalls. It may be due to the interaction between the revetment and the hydrodynamic force

which guide the sediment outside the desirable area. On the other hand, it increases the

siltation problem inside the outlet.

Figure 9. Model results of the morphological changes of different near shore nourishment scenarios for

(300 0000 m3 of sediments a) no action, b) at right side of nodal point, c) at centered of the nodal point, d)

at both eastern and western side.

a b

c d


Figure 10.Annual sediment volume of the second scenario for different nourishment volumes (100 0000,

200 000, and 300 000 m3); a) eastern area, b) middle area and c) western area.

Figure 11. Sediment concentration map, and total sediment transport for the second scenario with

different volumes, a) do nothing scenario , b) 100, 0000, c) 200, 000, and d) 300, 000 m3 ).

From above discussion, it can be inferred that the beach nourishment at the western side of the

promontory can mitigate the accumulation of the sediment inside the outlet and keep the western part

a b

c d


of the outlet with suitable water depths for the navigation, "fig4-c". On the other hand, this scenario

shows a partial improvement regarding the erosion problem especially at the western side of the

promontory. For the second method of the near shore nourishment, the accumulation of the sediment

inside the outlet is continuous because the outlet is already exposed to the waves coming from NW

direction which generate strong eddy vortex inside the outlet that combined with the current diverted at

the nodal point towards the outlet. This eddy vortex pushes the sediment toward the outlet. In addition

to that, there is no significant effect on shoreline stability.

4 CONCLUSIONS AND RECOMMENDATION

Rosetta outlet experienced continuous erosion in front of the existing seawalls, and accretion inside

Rosetta outlet. To enhance the stability of the promontory, soft protection measures represented in sand

nourishment are proposed. Beach nourishment and nearshore nourishment are applied using a

calibrated Coastal Modeling System software. The sediment sizes are selected according to the

availability of the material, and the distance from the site. The suitable size based on the particle

tracking modeling is 0.32 mm come from El Khatatba 150 km south of the site.

For the two nourishment techniques, three scenarios were selected. For each scenario, three different

volumes are selected (100,000, 200,000, and 300,000 m3). For the beach nourishment technique, the

beach nourishment on the western headland decreases the accretion problem inside the outlet and

enhances the situation regarding the erosion problem particularly at the western side of the

promontory. The second technique of the nearshore nourishment has insignificant effect on the

promontory. This is due to hydrodynamic effect of the promontory with the revetment which transfers

the sediment outside the desired area.

Although, the beach nourishment shows a significant effect in mitigating the accretion problem and the

erosion one especially at the western side, but the eastern part of the promontory still suffer from

erosion. So, it is recommended to test a combination of two jetties which control the flow and sediment

from the outlet with beach nourishment east and west of the promontory to solve the erosion problem.

ACKNOWLEDGMENTS

The first author would like to thank Egyptian Ministry of Higher Education (MoHE) for granting

him the PhD scholarship. Appreciations also goes to Egypt-Japan University of Science and

Technology (E-JUST) and JICA for their support and for offering the tools needed for this research.

Sincere thanks are due to Dr. Lihwa Lin and Honghai Li, the developers of (CMS and PTM software),

Research Hydraulic Engineer, at Coastal and Hydraulics Laboratory, US Army Corps of Engineers for

their enormous and continuous technical support. All appreciation to Coastal Research Institute and

Hydraulic Research Institute for great support with field data. This work was partially supported by

JSPS "Core-to-Core Program, B.Asia-Africa Science Platforms".

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NEAR SHORE AND BEACH NOURISHMENT’S EFFECTS ON THE STABILITY OF ROSETTA PROMONTORY, EGYPT

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