Topic 2.2.a Project4 SASME Book of Abstracts DUT 1 Equilibrium bays; stability and modelling Jan van de Graaff*, Koen Sweers**, Hanneke Keijer** and Dano Roelvink*** *Senior Scientific Officer, Delft University of Technology (DUT), Faculty of Civil Engineering and Geosciences, Section of Hydraulic Engineering. **MSc student, DUT. *** Specialist, Delft Hydraulics / DUT. Abstract Bay-shapes between natural headlands or behind man-made shore parallel offshore breakwaters are frequently found along coasts all over the world. For design purposes some empirical formulae are present which describe the position of the waterline in plan view. These empirical formulae are mainly based on careful fits of measured existing coastlines. The objective of this study is to investigate whether complex morphological computer models might be a helpful tool for design purposes of bay-shapes. Introduction Bay-shapes 'supported' by either natural headlands or artificial headlands like shore parallel breakwaters, are found all over the world. Fig.1 shows an artificial example. Figure 1. Bay-shapes supported by shore parallel offshore breakwaters. A series of shore parallel detached breakwaters is frequently used in coastal protection schemes. Sometimes tombolo's are formed at the end of the day. Tombolo's are also to be considered as equilibrium bay-shapes. Besides the application in schemes to protect coasts from structural erosion, series of breakwaters are also used to stabilize e.g. new beaches, like in the example of Fig.1. For design aims it is important to know what will the (or an?) equilibrium shape depending on the boundary conditions (like wave conditions, angles of approach, water levels, tidal currents, lay-outs of the series of