Hydrodynamic Simulation of Rip Currents Along Al-Nakheel Beach, Alexandria, Egypt: Case Study

Abstract

Al-Nakheel beach is located northwest of Alexandria city, Egypt, along the Mediterranean coast. During the period from 1998 to 2003, seven detached breakwaters were constructed along Al-Nakheel beach to create a sheltered area for swimming. Unfortunately, the structures amplify rip currents, shoreline accretions, and erosions. The aim of this research is to track the variations of the rip currents within the study area and show the effects of the breakwaters on the shoreline. The research is based on the hydrodynamic and morphological data of the study area and uses the Delft3D hydrodynamical model combined with other data analysis tools to serve the model input. The data include measured sea-level observations in 2013, the ERA-interim wave datasets from 2015 to 2018 and wind data in 2018, bed morphologies, and Google Earth satellite images from 2010 to 2020. The model is calibrated on the basis of the available current measurements within the nearshore zone. Results show that the shoreline eroded at an average rate of about 0.9 m/yr. Moreover, pairs of vortices are formed behind the breakwaters with an average current velocity of 0.6 m/s. The predominant northwest waves induce rip currents on the leeside of the structures with velocities reaching 1.2 m/s, associated with the rip pulsation that extends offshore. The problem solution decision recommends the removal of the sand deposition on the leeside of the breakwaters by an average amount of 100 000 m³/yr and the fencing of the safe area for swimming by a floating fence of 1 000 m length and 65 m average width.

Keywords

Nearshore process / Rip current / Al-Nakheel beach / Delft3D model

References

[1] Benassai G, Aucelli P, Budillon G, De Stefano M, Di Luccio D, Di Paola G, Montella R, Mucerino L, Sica M, Pennetta M. Rip current evidence by hydrodynamic simulations, bathymetric surveys and UAV observation. Natural Hazards and Earth System Sciences, 2017, 17(9): 1493-1503

[2] Booij N, Ris RC, Holthuijsen LH. A third-generation wave model for coastal regions: 1. Model description and validation. Journal of Geophysical Research: Oceans, 1999, 104(C4): 7649-7666

[3] Castelle B, Coco G. Surf zone flushing on embayed beaches. Geophysical Research Letters, 2013, 40: 1-5

[4] Castelle B, McCarroll RJ, Brander RW, Scott T, Dubarbier B. Modelling the alongshore variability of optimum rip current escape strategies on a multiple rip-channelled beach. Natural Hazards, 2016, 81(1): 663-686

[5] Ciarmiello M, Di Natale M. Coastal erosion control. In: Kennish M. J. (ed.) Encyclopedia of Estuaries, 2016, Dordrecht: Springer

[6] Dudkowska A, Boruń A, Malicki J, Schönhofer J, Gic-Grusza G. Rip currents in the non-tidal surf zone with sandbars: numerical analysis versus field measurements. Oceanologia, 2020, 62(3): 291-308

[7] Elkut AE, Taha MT, Zed ABEA, Eid FM, Abdallah AM. Windwave hindcast using modified ECMWF ERA-Interim wind field in the Mediterranean Sea. Estuarine, Coastal and Shelf Science, 2021, 252: 107267

[8] EPADP (2019) Ministry of water resources and irrigation. Public Authority for Drainage Projects

[9] Gallop SL, Bryan KR, Pitman SJ, Ranasinghe R, Sandwell DR, Harrison SR. Rip current circulation and surf zone retention on a double barred beach. Marine Geology, 2018, 405: 12-22

[10] Holthuijsen LH. Waves in oceanic and coastal waters, 2007, Cambridge, United Kingdom: Cambridge University Press, 24-29

[11] Iskander MM. Wave climate and coastal structures in the Nile Delta coast of Egypt. Emirates Journal for Engineering Research, 2013, 18(1): 43-57

[12] Iskander MM. Stability of the Northern coast of Egypt under the effect of urbanization and climate change. Water Science, 2021, 35(1): 1-10

[13] Iskander MM, Frihy OE, El Ansary AE, El Mooty MMA, Nagy HM. Beach impacts of shore-parallel breakwaters backing offshore submerged ridges, western Mediterranean coast of Egypt. Journal of Environmental Management, 2007, 85(4): 1109-1119

[14] Iskander PN. Sedimentological and morphological studies of the Northwestern Coast of Egypt (Alexandria-Abu Talat), 2008, Alexandria, Egypt: Faculty of Science, Alexandria University, 47-48

[15] Iskander MM, Hassan RM, Almaghraby MM, Abd-Almonem IM. Overpopulation and rip current mitigation plan for the Egyptian coasts, 2021, Cairo, Egypt: Cairo Water Week, 1-10

[16] Khedr AM. Sea level modeling and realization of lowest astronomical tide (LAT) for Alexandria Harbor, Egypt, 2019, Alexandria, Egypt: Arab Academy for Science, Technology and Maritime Transport, 27-53

[17] Leatherman SP (2012) Rip currents: types and identification. GSA Annual Meeting, Denver, USA, 5–10. DOI: https://doi.org/10.1130/abs/2016AM-278408

[18] Mosetti F, Purga N. Tides and sea level evolution at Alexandria, Egypt. Il Nuovo Cimento, 1990, 13(3): 647-651

[19] Moursy ZA. Sea temperature contribution to sea level at the South East sector of the Mediterranean. Oebalia, 1996, 22: 131-137

[20] Nelson EW. A simple and accurate method for calculation of the standard deviation of the horizontal wind direction. Journal of the Air Pollution Control Association, 1984, 34(11): 1139-1140

[21] Pitman S, Gallop SL, Haigh ID, Masselink G, Ranasinghe R. Wave breaking patterns control rip current flow regimes and surfzone retention. Marine Geology, 2016, 382: 176-190

[22] Roth G. Global burden of disease collaborative network. global burden of disease study 2017 (GBD 2017) results. Institute for Health Metrics and Evaluation (IHME), Seattle, USA. The Lancet, 2018, 392: 1736-1788

[23] Salama NM. Application of a hydrodynamic model for simulation of water movement and sediment transport between Agami Headland and Sidi Krir, Alexandria, Egypt, 2021, Alexandria, Egypt: Faculty of Science, Alexandria University, 60-62

[24] Short AD. Rip-current type, spacing and persistence, Narrabeen Beach, Australia. Marine Geology, 1985, 65(1–2): 47-71

[25] SPA (2018) Hydrodynamic study for el Nakhiel detached breakwater 21 km west of Alexandria. Shore Protection Authority, Alexandria, Egypt, National Water Research Institute Final technical report No. 20

[26] Williams JJ, Esteves LS. Guidance on setup, calibration, and validation of hydrodynamic, wave, and sediment models for shelf seas and estuaries. Advances in Civil Engineering, 2017, 2017: 1-25

[27] Wright LD, Short AD. Morphodynamic variability of surf zones and beaches: a synthesis. Marine Geology, 1984, 56(1–4): 93-118