A Decadal Sea Level Analysis Off Alexandria,

EgyptTarek M. El-Geziry* & Ahmed A. Radwan

Laboratory of Physical Oceanography

Division of Marine Environment

National Institute of Oceanography & Fisheries (NIOF), Alexandria, Egypt* tarekelgeziry@yahoo.com

Outlines Introduction Aim of the work Data & Methods of Analysis Results Conclusions

Astronomical Tides

-Minor Importance

-±20cm amplitudes

Surges

-More Important

-~ 1 m amplitudes or even more

Figure shows the amplitudes of tides in cm from Legos via Aviso Altimetry

Introduction

Aim of the owrk

The present work aims at:1. Getting the tidal astronomical constituents along

Alexandria coastline2. Calculating the surge elevations and its frequency of

occurrence3. Calculating the rate of sea level rise over the study period

Mean Daily Sea-level

Records

Data &

Methods of

Analysis

Sea Level

Astronomical Constituents Storm Surge

T_Tide Program(Pawlowicz et al.2002)

Sea Level – Astronomical elevations

ResultsThe Mean Daily Sea Level records over the period of investigation

ResultsThe Mean Annual Sea Level records (1996-2005)

50.67

cm

ResultsThe Astronomical Elevations over the period of investigation

ResultsThe Calculated Surge Elevations over the period of investigation

ResultsThe frequency of occurrence of different surge heights

0

200

400

600

800

1000

1200

20 30 40 50 60 70 80 90

Amplitude ranges (cm)

Freq

uenc

y of

occ

urre

nce

ResultsThe trend of Sea Level rise over the period of investigation

1.46 mm/yr

Conclusions In the present study, both the Mm (Lunar

monthly) and the Msf (Lunisolar synodic fortnightly) constituents have the largest constituent amplitudes, being 2.03 cm for the former and 7.06 cm for the later. This is in contrast to the outcome of Mosetti and Purga (1990) and Tayel (2008) who showed that the M2 (Lunar component) is the largest constituent with 6.7 cm amplitude.

Conclusions 35 tidal harmonic constituents have been

constructed using the T_TIDE program. The minimum annual Mean Sea Level (MSL)

was 48.62cm (1997), while the maximum was 52.96cm (1996). The MSL over the study period is 50.67cm.

The surge height over the study period varied between 14.64cm and 87.15cm, with an average of 50.66cm.

The 51-60 cm surge height is the most frequent to occur (1187 events) over the investigated period, while the 81-90 cm is the lowest (6 events).

Over one decade (1996-2005), the sea level rise off Alexandria had a rate of 1.46 mm/year. This is in good agreement with the rate previously calculated for the same area by El-Sayed (1.2 mm/year; 1988), Frihy (2 mm/year; 1992) and Frihy (1.6 mm/year, 2003).

Conclusions

The results of the present research show that while astronomical tide contributes with 0.005-37.63% in the observed sea level, surge contributes with 62.37 - 99.995%. This might refer to the meteorological and climatic effects, which are very developed at Alexandria region.

Moreover, the developed local seiches may have some impact on the observed surge elevation.

The greater contribution of surge over tidal elevation assures the nature of low astronomical tides at Alexandria, as in the whole Levantine Basin.

Conclusions