wave climate and coastal structures in the nile delta coast of egypt

Emirates Journal for Engineering Research, 18 (1), 43-57 (2013) (Regular Paper)

43

WAVE CLIMATE AND COASTAL STRUCTURES IN THE NILE DELTA COAST OF EGYPT

Moheb M. Iskander

Coastal Research Institute, National Water Research Center, Egypt, 15 El-Pharaana St., El-Shallalat, postcode 21514, Alexandria, Phone +2 03 4844614, Fax +2 03 4844615, E-mail [email protected]

(Received August 2012 and Accepted February 2013)

آم على الساحل الجنوبي الشرقي للبحر المتوسط وتتعرض للعديد من المشاآل 240تمتد شواطئ دلتا وادى النيل بالزيادة السكانية وضعف التخطيط واالثار الجانبية الناتجة عن انشاء السد العالي باإلضافة الى التغيرات ةالمرتبطومن اهم . لمصرية المعرضة للخطر بتأثير التغيرات المناخيةوتصنف دلتا وادى النيل من اآثر المناطق ا. المناخية

التحديات التى تواجه التنمية بالمنطقة زيادة منسوب سطح البحر وتغلغل المياه المالحة في المناطق الساحلية .باإلضافة الى زيادة معدل حدوث النوات

مام دلتا وادى النيل ومدى تأثرها بالتغيرات واهتمت هذه الدراسة بالكشف عن الخواص الموجية بالمنطقة الساحلية االمناخية على المدى الطول ومدى تأثير ذلك على اتزان المنشآت الساحلية وقد تم االستعانة ببيانات االمواج المقاسة

للتعرف على خواص االمواج بالمنطقة ومعدل التغير فيها على المدى 2010الى 1977امام الدلتا خالل الفترة من لدراسة توزيع االمواج بالمنطقة ImSedTran-2Dيل آما تم االستعانة بالنموذج الرياضي ثنائى االبعاد الطو

وتحديد الطاقة الموجية المؤثرة على المنشآت الساحلية ومدى تغيرها مع الزمن ومدى تأثير ذلك على اتزان .المنشآت الساحلية

The Nile Delta coast lies in the south eastern Mediterranean and extends about 240 km alongshore. It suffers from many threats, due to population increase, uncontrolled development, construction of Aswan High-Dam, and climate change. The Nile Delta is considered one of Egypt’s most vulnerable areas to climate change. Sea level rise, salt-water intrusion and increase in storm frequency and effect are considered the main challenges of climate change to any development plans in the Nile Delta coastal zone. The historical measured wave data from 1977 to 2010 are examined to investigate the effects of climate change on wave climate in front of the Nile Delta coast. Also, the hydrodynamic numerical model ImSedTran-2D has been used to describe changes in wave energy from place to place and to check that existing coastal structures will remain effective. Results show that there is an increasing trend in the mean significant wave height during the period from 1985 to 2010 by a rate ranging from 2.6 to 2.9 cm/year. Increase in wave height coincides with a decrease in wave period ranging from 0.01 to 0.26 sec./year. Wave energy in front of the coastal structures within this area will increase by about 20% within high storms and decrease by about 1 % within the normal conditions in the next 50 years. Nevertheless, most of the Egyptian coastal structures are over designed and will not be affected by the increase in wave energy due to the climate change.

Keywords: Climate change, Egyptian wave climate, numerical model, design wave, coastal structures

1. INTRODUCTION Climate change will take place over the next century in spite of international efforts to reduce greenhouse gas emissions. This exacerbates existing environmental problems worldwide. As a result, climate change research is changing from understanding phenomena to impact assessment, mitigation and adaptation strategies for the future development of society. In general, the coastal zone is particularly vulnerable, with expected impacts of sea level rise, salt water intrusion and increasing storm events in addition to existing problems such as

coastal erosion, subsidence, pollution, land use pressures, and ecosystem deterioration. Ocean waves and storm surges are considered among the dynamic side issues of climate change. Long-term changes of storm waves and surges are important for coastal disaster prevention and reduction. Moreover, stability of the coastal zone depends on wave characteristics. Few researchers have conducted the future wave climate projection by using wind-wave models, in-situ measurements and satellite data[1,2,3,4]. These studies have shown that the averaged and extreme ocean wave climate changes have not a general trend on both global and regional

Moheb M. Iskander

44 Emirates Journal for Engineering Research, Vol. 18, No.1, 2013

scales[5]. Large wave events are increasing at a greater rate than mean wave heights[6].

The Mediterranean region is one of the sensitive areas on Earth in the context of global climate change, due to its position at the border of the climatologically determined Hadley cell and the consequent transition character between two very different climate regimes in the North and the South[7].

Mediterranean weather is highly seasonal in nature and is strongly related to large-scale pressure systems whose limits overstep the boundaries of the Mediterranean area and extend towards the North Atlantic, Eurasia and Africa[8]. The North Atlantic Oscillation influences Mediterranean wave climate with an instantaneous response[1]. In the Mediterranean sea, the future significant wave height (2071 to 2100) may be characterized by milder marine storms and wave conditions all over the year except in summer in some areas mean and extreme significant wave height are higher[9]. These influences may lead to great changes within coastal regions, especially in heavily populated mega delta regions such as the Nile Delta.

The Nile Delta coast of Egypt lies in the south eastern Mediterranean, (Figure 1). It is classified as one of the most vulnerable areas to climate change, as well as the most important part of the country from a socioeconomic viewpoint. While scarce research work covered the wave climate changes adjacent to North Africa and the Nile Delta coast. Abo Zed and Gewilli[10] showed that there is a slight change (of about 10 degrees) in the predominant wave direction from 1985 to 2003 in front of the Rosetta coast, Nile Delta, Egypt. There is a marked seasonality in the wave climate, with higher waves in the winter and lower waves in the non-winter period. The western coast of Egypt has a more energetic wave climate than the Nile Delta[11]. High-resolution wave hindcasts were performed for the period 1958–2001 over the Eastern Mediterranean by using WAM model within the HIPOCAS project.

The model results show that the 50th percentile of significant wave height has a decreasing trend in the range of 0.2–2.2 mm/year all over the region. While the 90th percentile shows a negative trend (less than 5 mm/year) in extreme wave regimes over the region, with some slightly positive trends (0.5 mm/year) in the Aegean Sea and along the coastline of Algeria, Libya and Egypt[3].This study is a test to check the effect of climate change on wave climate in front of the Nile Delta coast and to identify the areas vulnerable according to that. This target will be achieved by examining historical wave data along the Nile Delta coast to study changes in wave characteristics with time. The hydrodynamic numerical model ImSedTran-2D[13,14] will then be used to describe changes in wave energy from place to place. Existing protection works within these areas

will be monitored to identify the implications of this altered wave climate.

2. NILE DELTA COAST The coastal zones of Egypt extend for over 3,500 km in length along the Mediterranean and Red Sea coasts. The Mediterranean shoreline is the most vulnerable to climate change due to its relative low elevation especially within the Nile Delta coast[15]. The Nile Delta shoreline extends from Alexandria to Port-Said with a total length of about 240 km and is typically a smooth wide coast (Figure 1). It is the most fertile land of the country accommodating several millions of population with population densities up to 1600 inhabitants per square kilometer.

It includes centres of significant economic activity, hosts vital centres for summer tourism and recreation areas as well as archaeological sites from ancient civilization. It contributes 30–40% of agricultural production and 60% of fish catch. Half of Egypt’s industrial production comes from the Delta[16].

The Nile Delta coast suffers from a high rate of population growth, unplanned urbanization, land subsidence, excessive erosion rates, sea level rise, salt water intrusion, soil salinization, land use interference, ecosystem pollution and degradation and from a lack of appropriate institutional management systems[17,18].

Egypt has been suffering from increased severity and frequency of sand storms, dense haze and flooding. These extreme events have had negative socio-economic impacts on almost all sectors[19]. Statistical analysis of the tide measurements along the Egyptian North coast during the period from 1943 to 2000 indicated that the rate of sea level rise ranges between 1.6 mm and 5.3 mm included the land subsidence (Table 1),[18,16]. It is estimated that 11.75% of the low land Delta regions will be affected due to sea level rise by 2100. Increases in storm events within the Nile Delta coastal zone will complicate these problems and reduce the efficiency of mitigation and adaptation measures

Wave Climate and Coastal Structures in the Nile Delta Coast of Egypt

Emirates Journal for Engineering Research, Vol. 18, No.1, 2013 45

Table 1. Estimated average annual seal level rise (cm) relative to year 2000 sea level, after El Shinnawy et al., (2010).

City Year IPCC

Scenario 2025 2050 2075 2100

Alexandria A1F1

13.0 34.0 55.0 72.0 Burullus 14.75 37.5 60.3 79.0 Port Said 27.9 68.8 109.6 144.0

Coastal projects have been undertaken to protect some parts of the Nile Delta coast through hard structures as well as artificial nourishment that has been applied at some sectors. For instance, the Government of Egypt (GOE) spent about 170 million US dollar to protect the three promontories of the Nile Delta; Rosetta, Burullus and Damietta (Figure 1). It is unclear whether past approaches to managing coastal zones, through the construction of hard defences along the shoreline and through beach nourishment, will remain cost effective in the face of accelerated sea level rise and anticipated increases in extreme weather events. In addition, increase in the frequency and severity of storm surges will definitely impact coastal structures[19].

3. METHODOLOGY The directional wave climate obtained from a series of field campaigns during the last decades will be described and interpreted to find out the change in

wave climate with time. ImSedTran-2D numerical model is used to simulate the wave climate at the near shore zone for two scenarios. The first is for present conditions (existing sea level and wave climate). The second assumes a sea level rise over 50 years in line with IPCC and local estimates of sea level change with the 50 years return period wave characteristics. Also, stability of structures will be studied based on the Hudson stability criteria[20].

3.1 Wave Database

Actual measurements have been made along the Egyptian Mediterranean coast at nine stations by Coastal Research Institute (CoRI); El Hamra, El Dikheila harbor, Abu Quir Headland, Abu Quir bay (two locations), Burullus, Damietta harbor, and east & west of Ras El Bar, (Figure 1). Also, Israel’s measured wave data at Ashdod , at a depth of 20 m, is used to fill the gap in the seventies. Table 2 summarizes these wave monitoring campaigns.

Abu

Quir Ba

y

Rosetta

Abu

Quir

head

land

Burullu

s

Dam

ietta

Alexa

ndria

Ras El Bar

Port Said

El Dikhe

ila harbo

r

0 10 20 30 40 km

Wave gauges:

S4DW CAS system OSPOS Wave Rider

Model part 1

Model part 2

Model part 3

Mediterranean Sea

Nile Delta

El Ham

ra

Ash

dod

Nav

igat

ion

Cha

nnel

To RosettaTo Alexandria

Maa

dia V

illag

e

East

B. W

.

Wes

t B. W

.

Maadia Outlet

1

Rosetta Promontory

E. Protection Wall

W. P

rote

ctio

n W

all

2

Gro

ins

Groins

CityBorg El-Burullus

Groin

Burullus Lake Outlet and Burg El-Burullus

Concrete Wall

Village

Extension of W. Jetty

NewE. Jetty

New Harbour

3

Baltim Sea Resort

Detached Break Water4

Dam

ietta

Bra

nch

Ras El Bar Peninsula

Detached Break Water

Dam

ietta

Bra

nch Ea

ster

n Je

tty

Wes

tern

Jetty

El M

anza

lla O

utle

t

Concrete Wall

Wes

tern

Jetty

Eastern Jetty

New Damietta Harbour East Damietta

5 6 7

Figure 1. Map of the Egyptian Mediterranean coast showing the Nile Delta coast, wave measurement stations, selected areas for executing the numerical model and the coastal structures distribution along the area, modified from

Silem (2008)[12].

Moheb M. Iskander


Measurements were made using an Offshore Suspended Pressure System (OSPOS), a Wave Rider buoy, a Cassette Acquisition System (CAS) and an S4DW Current and Wave Meter. Frihy[21] concluded that there is a strong correlation (a coefficient of 0.82) between significant wave heights for wave records measured at Abu Quir bay and Damietta harbor. According to that wave data of each station was analyzed separately to get the change of wave climate within this station with time. These results are used to represent the changes in wave climate in the Nile Delta.

OSPOS wave data were collected at Abu Quir Headland, Burullus and east of Ras El Bar during the period from 1971 to 1983. OSPOS is essentially pressure meters which measure variations in pressure caused by the waves. The wave direction is assumed

to be the same as that of the wind. CoRI experienced many problems analyzing these records manually by using the zero up-crossing method[22,23]. The available OSPOS wave data only describe some storms, and are insufficient to enable any trend analysis. So, the Wave Rider data at Ashdod, which were installed by Israel Ports Authority during the period from 1977 to 1980, were used to represent the wave climate within the seventies. The Ashdod waves measured were analyzed by computer digitizing two pen-and-ink records per day, applying standard spectral analysis techniques and computing significant wave heights and periods[24]. Digitizing accuracy was determined to be ± 0.5 sec. and ± 5 cm for wave periods and heights, respectively[25].

Table 2. Wave data sources along the southeastern Mediterranean coast.

No. Location Position Instrument Depth Period Duration (month)

Meas. Interval

1 El Hamra Lat. 30o 55.9' N; Long. 28o 50.1' E S4DW 8.0 July 1998 to May 1999 11 20 minutes 2.0hr.

2 El Dikheila Harbor

Lat. 31o 08.326’ N; Long. 29o 48.826’ E S4DW 17.0 March 1992 to March

1995 40 20 minutes 4.0hr.

3 Abu Quir Headland --------- OSPOS 6-8 Some records during the

period from 1971 to 1977 ---- 20 minutes 6.0hr.

4 Abu Quir Bay

Lat. 31o 22.3273' N; Long. 30o 13.503' E CAS 18.5 Sep 1985 to Dec, 1990 64 34 minutes each

6.0hr.

5 Abu Quir Bay

Lat 31o 23.5667’ N; long 30o 15.5167’ E S4DW 14.1 Dec. 2003 to Nov. 2005 24 20 minutes 4.0

hr.

6 Burullus ---------- OSPOS 6-8 Some records during the period from 1972 to 1983 ----- 20 minutes 6.0hr.

7 Damietta Harbor

Lat. 31o 30.4316' N; Long. 31o 45.5994' E S4DW 12.0

Sep. 1997 to June 1999 June 2001 to March 2004 Nov. 2009 to Sep. 2010

22 33 10

20 minutes 4.0 hr.

8 West Ras El-Bar

Lat. 31o 31.4201' N; Long. 31o 49.1847' E CAS 7.0 May 1985 to Dec. 1990 68 34 minutes each

6.0hr.

9 East of Ras El-Bar ------------- OSPOS 6-8 Some records during the

period from 1972 to 1977 ---- 20 minutes 6.0 hr.

10 Ashdod, Israel -------------- Wave rider 20 Jan. 1977 to Des. 1980 30 3.0 hr.

The S4DW data of El Dikheila and El Hamra harbors were collected in the lee of a headland or breakwater, which means that these gauges represent local conditions, and did not give an unfiltered view of the wave climate within these periods. Also west of Ras El Bar wave data were collected in relatively shallow water which suffers from refraction, diffraction, shoaling and breaking and is not suitable to be used in this study. In Abu Quir bay, the CAS system data, which was moored at 18.5 m depth during the period from 1985 to 1990, is used to represent the wave climate within the eighties. CAS system consists of three pressure sensors which are fixed under the water level on the legs of a Gas Platform in Abu Quir bay about 18 km from the

shoreline. They are spaced 7 m apart in a triangular array and send their data to an encoder. A special program is used to analyze the row data to get wave characteristics by the use of Fourier transformation[26].

The wave climate within the last two decades is described by the S4DW wave data, which were collected in front of Damietta harbor at 12.0 m depth. The S4DW consists of an electro-magnetic current-meter with a pressure sensor. These are converted to wave measurements using a sampling frequency of 2 samples/sec. Wave direction is derived from the two components of the wave orbital currents. A wave program utilizes the measured pressure information at a point to compute the statistics of sea surface



elevation by the use of Fourier transformation. Information about the directional properties of the wave field is obtained from the phase differences observed between the surface elevation and the two components of velocity[27].

Data from each station is analyzed separately and used to get the change in wave characteristic with time for its specific duration. According to frihy et al., 2008 these results can be used to represent the change in wave characteristics along the Nile Delta.

3.2 ImSedTran-2D Model In the current study, the ImSedTran-2D model[13,14] is applied to determine wave distribution along the study area under the effect of changes in bed morphology and wave characteristics for the next 50 years, which corresponds to the coastal structures’ lifetime. Model input consists of wave characteristic, bed morphology, coastal structures and bed sediment characteristics. Expected changes in wave characteristics have been obtained related to the available data within the study area. Future morphology of the study area has been predicted according to the effect of sea level rise only using the A1F1 scenario as shown in table 1.

The governing equations used to determine wave direction and wave height distribution for refraction calculations are summarized as follows:

1 cossinsincos →∂

∂+

∂

∂−=

∂

∂+

∂

∂

y

K

yK

x

K

xK θ

θθθ

θθ

20) 8

2()

8

2( →=

∂

∂+

∂

∂θ

ρθ

ρCosGC

gH

ySinGC

gH

x

Whereas x and y axes are the alongshore and offshore directions, respectively, K is the wave number, is the angle between wave crest and the bed contour, ρ is water mass density, g is the gravity

acceleration, H is the wave height, and GC is the group velocity.

The wave diffraction calculation based on the Kraus[28] solution is used to simulate the wave condition in the vicinity of the coastal structures. The wave height at the location in question is simply the product of the specified partially refracted incident wave height and diffraction coefficient. The angle of the wave crest is computed assuming a circular wave front along any radial; this angle is then refracted using Snell’s law. Throughout the refraction and diffraction schemes, the local wave heights were limited by the value 0.78 of water depth. Calculations of the wave distributions are based on shoaling processing, refraction, diffraction, and depth limited breaking. Model is designed to take the actual wave data measurements at any point offshore of the breaking point.

4. RESULTS 4.1 Nile Delta Wave Climate

Wave action along the coast is seasonal in nature, with storm waves (winter) starting from mid October to March; the summer (swell) season covers the months from June to mid October. The spring season covers the months April and May. In general, there are sixteen storms per year, of which seven are fairly strong, with high winds and heavy rain[23,29].

Statistical analysis of the waves recorded in Abu Quir bay, at 18.5 m depth between 1985 and 1990, shows that waves had significant wave height of 1.91 m, average wave height of 1.12 m, and average peak wave period of 6.0 sec. originated from the NW (Table 3). Figure 2 shows the monthly wave characteristics in Abu Quir bay. It is clear that in more than 50% of the year, the wave heights range between 0.5 and 1.5 m and the wave periods range between 5 and 7.0 sec. In summer, about 50% of the waves come from the NW direction while in winter 50% of the waves oscillate between NNW and WNW. In spring and early summer, the predominant wave direction may be changed to NE direction.

In front of Damietta harbor at 12.0 m depth between 1997 and 2010, waves had significant wave height of 1.02 m, average wave height of 0.56 m, average peak wave period of 6.3 sec. originated from the NW (Table 3).

Figure 3 shows the monthly wave characteristics in front of Damietta harbor. It is clear that in more than 75% of the year, the wave heights are less than 1.0 m. More than 50% of the year, the wave periods range between 5.5 and 6.5 sec. and it rarely (less than 1% of the year) increases than 9.0 sec. In summer, about 50% of the waves oscillate between NNW and WNW directions, while in winter 50% of the waves oscillate between N and NW directions.

4.2 Change in Wave Climate

The spatial distribution between wave characteristics and time is used to identify the changes in wave climate, (Figures 4&5&6). Results show that there is a general increasing trend in the mean significant wave height during the period from 1985 to 2010 by using all Hs value ranging from 2.6 to 2.9 cm/year, (Figure 4). This trend follows a very small decreasing trend of the mean significant wave height by 0.29 cm/year during the seventies, (Figure 5-A)

θ

Moheb M. Iskander


Table 3. Wave characteristics along the Nile Delta coast.

Location Abu Quir Bay Damietta Harbor Duration 1985 – 1990 1997 - 2010

Measured Depth 18.5 m 12.0 m T

otal

per

iod

Hs 1.91 m 1.02 m Hav 1.12 m 0.56 m Tp av. 6.0 sec. 6.3 sec Direction NW NW Maximum wave condition Hs= 5.44, Tpc= 12.8 sec., WNW Hs= 4.47, Tsc= 5.6 sec., NW

Win

. Monthly Hs 1.24 – 3.18 m 0.5 – 2.16 m

Monthly Tp Av. 4.5 – 7.8 sec. 4.4 – 8.3 sec.

Sum

. Monthly Hs 1.15 – 2.12 m 0.43 – 1.12 m

Monthly Tp Av. 4.9 – 6.8 sec. 4.5 – 7.3 sec.

Figure 2. Wave characteristics in Abu Quir bay illustrating all the available observations during the period from

1985 to 1990 at 18.5 m depth .

0

1

2

3

4

5

6

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Monthes

Sign

ifica

nt w

ave

heig

ht (m

).

1%

m e a n-S t. Dv.

25%

M e dium

M e a n

75%

m e a n+S t. Dv.

99%

M a x.

2

4

6

8

10

12

14


Monthes

Peak

wav

e pe

riod

(sec

.)

1%

m e a n-S t. Dv.

25%

M e dium

M e a n

75%

m e a n+S t. Dv.

99%

M a x.

-100

-80

-60

-40

-20

0

20

40

60

80

100


Monthes

Wav

e di

rect

ion

from

Nor

th. 1%

m e a n-S t. Dv.

25%

M e dium

M e a n

75%

m e a n+S t. Dv.

99%



0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5


Monthes

Segn

ifica

nt w

ave

heig

ht (m

).1%

mean-St. Dv.

25%

Medium

Mean

75%

mean+St. Dv.

99%

Max.

3

4

5

6

7

8

9

10

11


Monthes

Sign

ifica

nt w

ave

peri

od (s

ec.)

1%

mean-St. Dv.

25%

Medium

Mean

75%

mean+St. Dv.

99%

Max.

-200

-150

-100

-50

0

50

100

150

200


Monthes

Wav

e di

rect

ion

from

Nor

th

1%

mean-St. Dv.

25%

Medium

Mean

75%

mean+St. Dv.

99%

Figure 3. Wave characteristics in front of Damietta harbor illustrating all the available observations during the period from 1997 to 2010 at 12.5 m depth.

Moheb M. Iskander


A Student t test has been used to assess the statistical significance of wave height trend[30]. The null hypothesis of zero-slope is rejected for the above cases at a 1%- level of significance. The monthly significant wave height (one monthly value) increases with a rate of 3.65 cm/year while the monthly maximum wave height increases within a wider range of 7.3 to 11 cm/year during the period from 1985 to 2010 (Figure 5-B&C).

Increase in wave height during the period from 1985 to 2010 coincides with a decrease in wave period ranging from 0.01 to 0.26 sec./year. The null hypothesis of zero-slope is rejected for the above cases at a 1%- level of significance. The decrease in wave height during the period from 1977 to 1980 coincides with an increase in wave period of 0.029 sec./year (Figure 6).

Check of seasonal effects shows that seasonal wave climate has insignificant effect on the general increase trend but affects only the increased value. In winter, mean significant wave height during the period from 1985 to 2010 increases by a rate ranging from 1.8 to 3.3 cm/year, (Figure 4), while the wave period decreases by a rate ranging from 0.01 to 0.37 sec./year (Figure 6-B&C). During summer, the

increase rate of wave height ranged from 1.1 to 2.6 cm/year and the decrease rate of wave period ranged from 0.037 to 0.22 sec./year (Figures 4&6).

Significant wave heights of 2.0 m were chosen to characterize storm and non storm waves. A similar wave height limit was used by Frihy[11]and Carmel[31] to characterize winter and non-winter wave climates on the Mediterranean coast of Egypt and Israel. Figure 7 illustrates the distribution of annual storm percentage of occurrence with time. The results show a normal distribution of the storms with time but the available data are not enough to identify any trends in storm frequency.

4.3 Design Wave Conditions

The long-term statistics of these measurements and the probability analyses provide useful information regarding design wave conditions for coastal engineers. The approach used here to calculate extreme wave height and associated return periods follows the methods discussed in Issacson and Mackenzie[32].

0

1

2

3

4

5

6

Jul-85 Feb-86 Aug-86 Mar-87 Sep-87 Apr-88 Nov-88 May-89 Dec-89 Jun-90 Jan-91

Sign

ifica

nt W

ave

heig

ht (m

).

Date & Time (day)

Linear (all data)

Linear (Winter)

Linear (summer)

Abu Quir Bay wave Gauge-18.0 m depth

00.5

11.5

22.5

33.5

44.5

5

Mar-97 Nov-98 Jun-00 Feb-02 Oct-03 May-05 Jan-07 Sep-08 May-10

Sign

ifica

nt w

ave

heig

ht (m

).

Date & Time (day)

Linear (All data)

Linear (Winter)

Linear (Summer)

Damietta wave gauge-12

Figure 4. Change in wave height with time at Abu Quir and Damietta stations during the period from 1985 to 2010.



Figure 5. Change in monthly average, significant and maximum wave height with time at the three measured stations during the period from 1977 to 2010.

0

1

2

3

4

5

6

Nov-84 Sep-85 Jul-86 May-87 Feb-88 Dec-88 Oct-89 Aug-90 Jun-91Date & Time (day)

Mon

thly

Wav

e H

eigh

t (m

)

Hmean (m)Hs (m)Hmax (m)

Abu Quir Bay wave Gauge-18.0 m depth

0

0.2

0.4

0.6

0.8

1

1.2

Aug-76 Mar-77 Oct-77 Apr-78 Nov-78 May-79 Dec-79 Jun-80 Jan-81 Aug-81Date & Time (day)

Mon

thly

Wav

e he

ight

(m).

Ashdod w ave gauge- 20.0 m depth.

0

1

2

3

4

5

Dec-96 Jul-98 Mar-00 Nov-01 Jun-03 Feb-05 Oct-06 Jun-08 Jan-10 Sep-11

Date & Time (day)

Mon

thly

Wav

e H

eigh

t (m

). Hmean (m)Hs (m)Hmax (m)

Damietta w ave gauge-12

Moheb M. Iskander


Figure 6. Change in wave period with time at the three measured stations during the period from 1977 to 2010.

0

2

4

6

8

10

12

14

Jul-85 Feb-86 Aug-86 Mar-87 Sep-87 Apr-88 Nov-88 May-89 Dec-89 Jun-90 Jan-91

Date & Time (Day)

Peak

Wav

e pe

riod

(sec

).

Linear (All data)

Linear (Winter)

Linear (Summer)

Abu Quir Bay w ave Gauge-18.0 m depth

5

5.5

6

6.5

7

7.5

8

Aug-76 Mar-77 Oct-77 Apr-78 Nov-78 May-79 Dec-79 Jun-80 Jan-81 Aug-81Date & Time (Day)

Segn

ifica

nt W

ave

peri

od (s

ec.)

Ashdod w ave gauge- 20.0 m depth.

0

2

4

6

8

10

12

Mar-97 Jul-98 Dec-99 Apr-01 Sep-02 Jan-04 May-05 Oct-06 Feb-08 Jul-09 Nov-10

Date & Time (Day)

Sign

ifica

nt W

ave

peri

od (s

ec.)

Linear (All data)

Linear (winter)

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Damietta w ave gauge-12 m



In Abu Quir bay, at 18.5 m depth, the results showed that a wave height of 7.60 m can be expected to occur once in fifty years with a maximum height of 8.10 m occurring at least once every 100 years. Since there was no single wave period associated with the extreme wave height, periods of the largest waves

recorded are associated with the estimated extreme wave heights (wave period 10.7 to 12.8 sec.). The predominant storm wave direction varies between NW and WNW. Estimates of extreme wave heights are summarized in table 4

Table 4. Estimated extreme wave heights related to the wave measurements at 18.5 m depth in Abu Quir bay during the period

from 1985 to 1990. Return periods (year) 1 2 5 10 20 30 40 50 100

Wave Height (m) 4.70 5.20 5.90 6.40 6.90 7.20 7.40 7.60 8.10

4.4 Wave and Coastal Structures

The ImSedTran-2D model is used to determine wave distribution in the nearshore zone and in front of the coastal structures along the study area. The Nile Delta bed morphology is taken from the bathymetric map of May 2010 which covered the area from the backshore zone to (-6.0 m depth) below the mean water level surveyed by Coastal Research Institute. The remaining contours to (-18.0) m depth are from the

most recently available full Delta survey, of May 1986, surveyed by Misr Offshore Services and Surveys. The characteristic wave conditions were obtained from the wave measurements in front of Nile Delta coast, (tables 3&4). The future morphology of the study area has been predicted according to the effect of sea level rise only for A1F1 scenario (Table 1).

To apply the model, the Nile Delta is divided into three parts; the western part Rosetta promontory, the middle part Burullus and the eastern part Damietta

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Figure 7: Yearly percentage of occurrence of storms getting from wave data collected at two stations during the period from 1985 to 2010.

Moheb M. Iskander


(Figure 1). For each part, the following modules are built: 1. Recent morphology with the average wave

condition (Hav= 1.12, T= 6.0 sec., NW direction, Depth= 18.0 m) (Table 3).

2. Recent morphology with the maximum wave condition in 50 years (Hmax= 7.60, T= 10.7 sec., NW direction, Depth= 18.0 m) (Table 4).

3. Future morphology (recent bathymetry + the sea level rise in 2050 (Table 1)) with the average significant wave condition.

4. Future morphology with the maximum wave condition in 50 years. Figure 8 is an example of the model results

which deduced that: • The effect of sea level rise for the case of average

wave condition is negligible except for the shoreward movement of the breaking point. The wave energy in front of the coastal structures within this area has a slight decrease with time, will reach 1% after 50 years.

• The sea level rise has a reasonable effect for the case of maximum wave condition. The wave energy in front of the coastal structures within this area will increase by about 20% after 50 years.

The stability checks for the Egyptian coastal structures are got from applying Hudson criteria and reviewing the physical model reports of the coastal projects. It can be concluded that most of the Egyptian coastal structures constructed between 3.0 to 4.0 m depth will be affected by 3.0 to 3.5 m wave height maximum. Obviously, these structures designed to face 5.0 to 6.0 m wave height and remain stable if water depth in front of the structure reaches 7.0 to 8.0 m. It means that most of the Egyptian coastal structures are over designed and will not be affected by the increase in wave energy due to climate change. However, the change in wave characteristics may affect the sediment transport, shoreline orientation and wave overtopping which will affect the efficiency of the coastal structures.

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Figure 8: Wave distribution across Rosetta promontory with: (A) the recent morphology for average wave conditions, (B) the 50 years sea level rise for average wave conditions, (C) the recent morphology due to a

maximum 50-year wave condition, and (D) the 50 year sea level rise due to maximum wave condition in 50 years. Wave height is denoted by the color scale in meters and wave direction by arrows.



5. DISCUSSION The available data show an increasing trend in the mean significant, monthly significant and monthly maximum wave height during the period from 1985 to 2010. The trend calculated from all the available data seems more reasonable than that from the monthly values for this case. The monthly significant and the monthly maximum wave height are calculated if more than 50% of the measurements are available, which affected the results and may be did not give fully confident results. The storm trends are not clear because the southeast Mediterranean is particularly susceptible to changes in the frequency of storms due to annual differences in time of the seasonal displacement of the subtropical zone, and variations in number of winter cyclones[33].

The above result is different from Musić and Nicković[3], who show that the median significant wave height has a decreasing trend in the range of 0.2–2.2 mm/year all over the east Mediterranean region. It may be due to the lack in simulation of the high storms and swell within the WAM model. In addition, his paper concludes that the model shows better performance for the buoy in the open sea compared to the coastal buoys. A possible underestimate of the wind speed components due to a lack of resolving small, sharp scale features in the wind pattern, may affect the WAM-computed values of wave height[34]. However, there are also problems with the data used in this study as these data are neither continuous nor representative of whole years. So, it is very important to compare the result of WAM model in HIPOCAS project with the actual measurements in front of the Egyptian coast to identify the reason of inconsistent results.

The increase in wave height during the period from 1985 to 2010 coincides with a decrease in wave period ranging from 0.01 to 0.26 sec./year. It means that there is a movement towards more local sea waves than the swell waves. The statistical significance of these negative trends has been shown at the 1%-level.

S4DW wave gauge takes the current direction near the bed as wave direction, while the CAS system calculates the wave direction from the phase difference between the signals of two sensors. It means that the S4DW wave gauge does not give the exact wave direction. So the changes in wave direction trend cannot give the real situation for this case.

6. CONCLUSIONS AND RECOMMENDATIONS This work is a step to study the effect of climate changes on wave climate within the Nile Delta coast. All the available data in Abu Quir bay, Damietta and Ashdod have been analyzed separately to understand

the change in wave climate with time. More investigations are required to assess the actual change rate or direction. Also, the ImSedTran-2D numerical model is used to check the effect of change in wave climate in the nearshore zone and in front of the coastal structures. The main results show that: • There is an increasing trend in the mean

significant wave height during the period from 1985 to 2010 by a rate ranging from 2.6 to 2.9 cm/year. The statistical significance of these positive trends has been proved at the 1%-level. This trend followed a very small decreasing trend of the mean significant wave height by 0.29 cm/year during the seventies.

• The increase in wave height during the period from 1985 to 2010 coincides with a decrease in wave period ranging from 0.01 to 0.26 sec./year. It may be due to increase in sea wave and decrease in the swell waves. The statistical significance of these negative trends has been proved at the 1%-level. The decrease in wave height during the period from 1977 to 1980 coincided with an increase in wave period of 0.029 sec./year.

• The predominant wave direction oscillated between NNW and WNW directions during the period from 1985 to 2010. The only exception is within the spring season and some times the early summer season. Within this period, the predominant wave direction may be changed to NE direction.

• Wave distribution obtained from ImSedTran-2D model after 50 years shows that the wave energy in front of the coastal structures within this area increases by about 20% within high storms. While it decreases by about 1% for the normal wave condition.

• Stability check within the coastal structures lifetime shows that nearly most of the Egyptian coastal structures are over designed and will not be affected by the increase in wave energy due to the climate change.

• Wave data should be collected in a consistent, operational manner, over tens of years with complete annual coverage to get the actual changes of wave characteristics with time but until that, the worst scenario should be taken into consideration in designing coastal structures.

• It is recommended to execute a comparative study between the result of this project and the result of HIPOCAS project[3] in front of the Nile Delta coast to unify the results.

• It is very important to study the combined effect of increase in sea level rise and wave energy on sediment transport and the resulting effect on coastal structures.

Moheb M. Iskander


ACKNOWLEDGEMENTS

This research is supported by Coastal Research Institute (CoRI), Swedish International Development Cooperation Agency (SIDA) and Swedish Metrological and Hydrological Institute (SMHI). I am deeply grateful to Dr. Philip Axe from SMHI for supervising, and revising this work. Also, thanks to Prof. Dr. Ibrahim El Shinnawy, Alfy Fanos and Abu Bakr Abu Zed from CoRI for providing me with wave observations in Egypt.

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