Innovative tidal inlet design

Abstract

Lagoons are connected to the sea by the presence of openings along their barriers. These openings, also known as tidal inlets, can either be natural or man-made and they highly determine the hydrodynamics within the lagoon system. Tidal inlet systems are found worldwide, and many of them are difficult to be understood due to their complex processes and lack of data. One of these systems is Lake Bardawil. Lake Bardawil, is located at the North coast of the Sinai Peninsula in Egypt and its ecological value is of great importance. Its existence mainly depends on the presence of three inlets which connect the lagoon with the Mediterranean Sea, called Boughaz 1, Boughaz 2 and Zaranik inlet. Boughaz 1 is located in the western side of the lake while Boughaz 2 and Zaranik are in the eastern side.
One of the recent researches that is carried out by the Dredging, Environmental and Marine Engineering (DEME), The Weather Makers (TWM) and Lanters (2016), studied how the ecosystem and the fish population of Lake Bardawil can be restored by new hydraulic interventions. This thesis is an extension of the aforementioned work, but current focus is put on the determination of an innovative design and associated methodology which is based on natural design elements and can improve the functionality of Boughaz 1 inlet.
Boughaz 1 was constructed in 1955 to allow the water exchange between the sea and the lagoon. Over the passing years, it has been subjected to a reduced tidal prism resulting in poor water quality in the lagoon, limited fish migration from the sea and sedimentation causes the need for dredging maintenance works. This led to the construction of breakwaters in 1985 until 1995 for the stabilization of the inlet and for the protection of the fish population in the lagoon. Although, the dredging works and constructed breakwaters minimized the abrupt sedimentation through the inlet and improved its stability in short term, the natural behavior of the system is gradually changed which worsen these conditions in longer term. For that reason, a design methodology is carried out to understand and improve the functionality of the Boughaz 1 inlet. The design methodology is based on the most important natural design elements, namely inlet cross sectional area, approach channel and inlet nourishment. Numerical models (Delft3D and Delft3D FM) are used to assess the influence of the different designs on the functionality of the system. A hydrodynamic analysis is carried out for each design element to define the final combined design of the initial phase of this design process. This final design is examined under hydrodynamics and the initial deposition and erosion patters. It is concluded that the functionality of the Boughaz 1 inlet can be optimized with the adapted design methodology. The tidal prism and flow velocities have been increased while the aim to mimic nature is validated with the initial deposition and erosion patterns.