Hydrodynamic and safety-based optimization of detached breakwaters for sustainable shoreline stabilization

Conceptual infographic illustrating the use of Delft3D numerical modelling to compare two coastal protection scenarios. The upper section shows a computer screen labeled “Delft3D” connected to two offshore breakwater configurations (Scenario 1 and Scenario 2), with colored arrows representing wave and current circulation patterns. A risk legend indicates swimmer hazard levels from low to high. The middle section highlights three evaluated parameters: wave heights, current velocities, and swimmer hazard. The lower section presents expected coastal outcomes, including reduced erosion, gradual beach stabilization, and maintained sediment continuity, illustrated with simplified beach profiles. Downward arrows indicate reductions in wave heights and current velocities, culminating in improved swimmer safety, represented by a swimmer icon with a green check mark. Coastal protection structures profoundly reshape nearshore hydrodynamics, yet their design rarely integrates shoreline stability with human safety. Along the Baltim coast (Nile Delta, Egypt), recent groin construction has triggered severe downdrift erosion exceeding 700 m, exposing critical infrastructure and amplifying coastal risk. Here, we develop a coupled hydro-safety optimization framework to identify breakwater configurations that simultaneously reduce erosion drivers and swimmer hazards. High-resolution Delft3D simulations are used to quantify wave transformation, current redistribution, and hazard rate (HR) under dominant northwest forcing (Hs = 1.8 m, Tp = 8 s). Across four engineering scenarios, structural geometry emerges as a primary control on coastal dynamics. A continuous emerged breakwater maximizes wave attenuation (0.01–0.09 m) but induces localized current intensification at structure edges. A submerged configuration minimizes central flow velocities (down to 0.05 m/s) while redistributing hydrodynamic energy downdrift. In contrast, segmented breakwaters provide the most balanced performance: reduced gap width yields uniform wave attenuation, moderates circulation, and eliminates moderate-risk zones across all observation points. These findings demonstrate that neglecting hydrodynamic hazard can shift, rather than resolve coastal risk, and establish a transferable multi-criteria design paradigm for resilient shoreline protection.