Master’s Dissertation TVVR 08/5010 Hydrodynamic modelling and estimation of exchange rates for Bardawil Lagoon, Egypt. An investigation of governing forces and physical processes using numerical models. ___________________________________________________________________ Jonas Linnersund Erik Mårtensson Division of Water Resources Engineering Department of Building and Environmental Technology Lund Institute of Technology Lund University Division of Water Resources Engineering ISRN LUTVDG/TVVR-08/5010+88p ISSN-1101-9824 Hydrodynamic modelling and estimation of exchange rates for Bardawil Lagoon, Egypt. An investigation of governing forces and physical processes using numerical models. Jonas Linnersund Erik Mårtensson Supervisor 1 Magnus Larson Division of Water Resources Engineering Department of Building and Environmental Technology Lund Institute of Technology Lund University November 2008 Printed in Sweden 1 Professor, Division of Water Resources Engineering, Lund Institute of Technology i ii Lund University Faculty of Engineering, LTH Departments of Earth and Water Engineering This study has been carried out within the framework of the Minor Field Studies (MFS) Scholarship Programme, which is funded by the Swedish International Development Cooperation Agency, Sida. The MFS Scholarship Programme offers Swedish university students an opportunity to carry out two months’ field work in a developing country resulting in a graduation thesis work, a Master’s dissertation or a similar in-depth study. These studies are primarily conducted within subject areas that are important from an international development perspective and in a country supported by Swedish international development assistance. The main purpose of the MFS Programme is to enhance Swedish university students’ knowledge and understanding of developing countries and their problems. An MFS should provide the student with initial experience of conditions in such a country. A further purpose is to widen the human resource base for recruitment into international co-operation. Further information can be reached at the following internet address: http://www.tg.lth.se , click at “MFS-stipendier”. The responsibility for the accuracy of the information presented in this MFS report rests entirely with the authors and their supervisors. Gerhard Barmen Local MFS Programme Officer Postadress Box 118, 221 00 Lund Besöksadress John Ericssons väg 1Telefon dir 046-222 9657, växel 046-222 00 00 Telefax 046-2229127 E-post [email protected] iii Hydrodynamic modelling and estimation of exchange rates for Bardawil Lagoon, Egypt. Abstract Bardawil Lagoon, a natural lagoon located on the northern coast of the Sinai Peninsula, Egypt, there are three inlets of which two are man-made connecting the lagoon with the Mediterranean Sea. The inlets are subjected to changes in morphology, due to sediment transport, over time and this may lead to degrees of closure of either inlet. The sediment transport is governed by longshore currents and the sediments originate from the eroding Nile delta. Inlet closure adversely affects the lagoon water quality which will have a detrimental effect on the ecosystem. In this dissertation the dominant coastal processes governing the water exchange between the lagoon and the Mediterranean are studied. Finite element conceptual computer models are applied to simulate and investigate the hydrodynamics of the inlets and the lagoon itself. Two types of models are applied within the Surface Modelling System (SMS) software; ADCIRC, a regional tidal model and CMS-Flow, a local circulation model. In order to estimate the exchange rate of the lagoon two methods are utilized; based on net intertidal volume and cross sectional flow through the inlets. The methods show a high degree of correlation. The renewal time was estimated to 9.0 days, which is equivalent to a daily replaced volume of 53·106 m3. Tidal forcing governs the water exchange while wind is responsible for the internal circulation. Keywords: ADCIRC, Bardawil Lagoon, CMS-Flow, finite element, internal circulation, net intertidal volume, renewal time, salt balance, sediment transport, tide, water balance, wind iv Hydrodynamic modelling and estimation of exchange rates for Bardawil Lagoon, Egypt. Preface This Master’s Dissertation report is the result of a combined field study and computer modelling of the hydrodynamics of Bardawil Lagoon, Egypt. The project was carried out in order to gain a further understanding of the coastal processes affecting the inlets and how manage them to preserve the clean environment and lagoon water quality. The project was a joint venture between Lund University, Division of Water Resources Engineering and Suez Canal University. Despite persistent attempts to obtain permission to visit the lagoon and conduct field measurements we failed to receive a permit. However, thanks to Coastal Research Institute in Alexandria, we managed to acquire necessary measurements from earlier studies. Acknowledgements We would like to express our gratitude to SIDA, Ångpanneföreningen's Foundation for Research and Development and Swedish Association of Graduate Engineers for financial support of our Master’s Dissertation which includes a two month field study in Egypt. Dr. Yasser Hamed at Suez Canal University, Port Said, for practical help in Port Said and the endless efforts in trying to obtain permission to visit the site. Prof. Ibrahim El-Shinnawy and Dr. Madhat Mohamed at Coastal Research Institute (CoRI) in Alexandria, for their hospitality and most importantly providing invaluable field data. Prof. Hans Hanson at the Division of Water Resources Engineering, Lund, and Dr. Ahmed Ahmed at Hydraulics Research Institute, Cairo, for guidance on theory and computer modelling. AB Teknoplan in Stockholm for digitizing field data and maps obtained in Egypt. Special thanks to Prof. Omran Frihy for his continuous interest in our work and its progress and providing us with interesting ideas throughout our stay in Egypt. During the course of constructing the 2D-finite element models within the Surface Modelling System software, several difficulties arose and without the help and technical support from both Adele Buttolph at Coastal Analysis, LLC Oregon, and Mitchell Brown at US Army Corps of Engineers the modelling would have been impossible. Also special thanks to US Army Corps of Engineers for providing us with licence to the software suite and the models. Finally our deepest appreciation to our supervisor Prof. Magnus Larson at the Division of Water Resources Engineering, Lund, for extraordinary expertise and assistance throughout the dissertation. v Hydrodynamic modelling and estimation of exchange rates for Bardawil Lagoon, Egypt. Table of contents Abstract ........................................................................................................................ iv Preface........................................................................................................................... v Acknowledgements ....................................................................................................... v 1 Introduction ........................................................................................................... 1 1.1 Background ................................................................................................... 1 1.2 Objectives ..................................................................................................... 2 1.3 Procedure ...................................................................................................... 2 2 Area description .................................................................................................... 5 2.1 Physical characteristics ................................................................................. 5 2.2 Climate .......................................................................................................... 7 2.3 Human activities ........................................................................................... 8 3 Coastal Processes at Bardawil Lagoon ................................................................. 9 3.1 Wind climate ................................................................................................. 9 3.2 Wave climate............................................................................................... 11 3.3 Water level fluctuations .............................................................................. 12 3.4 Sediment transport patterns ......................................................................... 13 3.5 Inlet morphology changes ........................................................................... 15 4 Physical processes in lagoons ............................................................................. 19 4.1 Water circulation ......................................................................................... 19 4.1.1 Water balance ...................................................................................... 20 4.1.2 Lagoon flushing .................................................................................. 21 4.1.3 Hydraulic-flushing replacement time .................................................. 23 4.1.4 Renewal time ....................................................................................... 23 4.2 Salt balance ................................................................................................. 24 4.2.1 Box model with