Graduation of Philipp Bangen
The Effects of Annual Extreme Weather Conditions on the Exchange Flows between Lake Bardawil and the Mediterranean Sea
Professor of graduation: Prof. dr. ir. S.G.J. (Stefan) Aarninkhof
Supervisors: Dr. ir. J. (Judith) Bosboom (TU Delft), Prof. dr. P.M.J. (Peter) Herman (TU Delft), ir. R. (Rick) van Bentem (The Weather Makers), ir. M. (Merel) Kroeders (DEME Group)
Lake Bardawil is a hypersaline, shallow coastal lagoon located along the coast of the norther Sinai Peninsula in Egypt. When talking about hypersaline systems, in general it means that throughout the year the salinity exceeds values of 30 parts-per-thousand (ppt).
Being located in the arid climate region of North Africa the lagoon is subject to year-round extreme weather conditions which are dominated by high air temperatures (Mean Annual Temperature (MAT) = 21°C), extreme evaporation rates and limited precipitation. All the above in combination with the lagoon’s shallow bathymetry and restricted freshwater input causes Lake Bardawil to inhibit hypersaline conditions throughout the whole year. For Lake Bardawil this means average salinity values in the order of 42 – 51 ppt.
Forming the transitional zone between land and water is a vital area for bird migration and home to unique species. The hypersaline conditions and restricted exchange flows with the Mediterranean Sea, however, cause the ecosystem to be in decline and call for action to restore an independently functioning ecosystem. In order to be able to provide holistic and sustainable solutions the system needs to be understood thoroughly.
The here conducted study is the first in the line of five successive studies focusing on the three-dimensional hydrodynamics. By making use of the three-dimensional hydrodynamics, the movement of water and salt through the lagoon is investigated in order to properly assess the effect on the overall ecological value of the system. Here the response of the system to the extreme meteorological conditions around Lake Bardawil is investigated. Meteorological forcing causes subtidal flows in coastal waters which are responsible for the propagation of waterborne characteristics such as salt and pollutants.
The here presented results show that during periods of extreme meteorological forcing the response of the lagoon and its inlets is in line with expectations from literatures. During periods and events of high evaporation the lagoon shows an overall increase in top and bottom layer salinity. While the lagoon waters act rather inert as shown for the average conditions during the month of April, it is the wind that initiates the motion. Successively the phenomenon of gravitational circulation in the deeper areas around the inlets can be observed with more saline waters propagating towards the inlets along the bottom layer. At times, these processes cause for subtidal velocities up to 0.15 m/s, which were computed in the inlets. Furthermore, it is shown that the complex geometry of Lake Bardawil is of major importance when considering subtidal flows and circulation patterns in the lagoon. Here the tidal divide, a location where very calm flow conditions are present, on the verge of the western bottleneck to the eastern basin was found to be of crucial importance. The eastern basin with its vast areal extent is susceptible to wind-driven circulations, while the western bottleneck is bound by its narrowness and the tide dominance.
The application of system adaptations as proposed by The Weather Makers (TWM) proves to increase the exchange flow with the Mediterranean Sea. A more dynamic system is established where the inner lagoon connectivity is significantly enhanced. This is evident by the wide-spread presence of Mediterranean waters and the decreased salinity in a broad stretch along the barrier island. However, the lagoon waters in remote locations along the fringes of the eastern basin and in isolated ponds remain of high salinity and show still little interaction with the tidal flow.