Delft3D Model of Nature-Based Solutions: Comparing a Sand Engine, Living Shoreline, and Reef at Sand Point and Keller Bay, Texas

Abstract Nature, nature-based features, and nature-based solutions (NbS) are increasingly used for coastal shoreline protection, and in practice, managers often evaluate multiple engineering and design alternatives at a single site. Yet few studies compare distinct NbS categories in consistent hydrodynamic terms within a single field-anchored, process-based model for wind-wave-dominated shallow bays. We addressed this gap by using a Delft3D-FM (version 2023.02) model to evaluate shoreline-protection alternatives intended to reduce the risk of breach at the Sand Point Peninsula, Texas. Waves and currents were measured with an instrumented tripod 180 m offshore, and model performance was evaluated against water level, significant wave height ( H s ), and current velocities at the tripod site. We then simulated a baseline and four NbS alternatives representing distinct design approaches: a sand engine, a staggered living shoreline with gaps, a continuous living shoreline, and a spit protection reef. All alternatives were evaluated under the same forcing using H s and cross-shore and alongshore current velocities extracted at fixed observation points. Living-shoreline alternatives produced the strongest immediate reductions in H s and current velocities along the breach-prone reach, consistent with wave sheltering and weaker wave-driven circulation. The spit protection reef reduced waves and currents in its lee but produced localized acceleration near the reef tip, indicating where scour screening and adaptive monitoring are important. The sand engine had its strongest short-term hydrodynamic effect near the placement area, with limited immediate change near the targeted breach location, consistent with a sediment-supply intervention whose main benefits are expected to emerge through redistribution over longer time scales. Together, the results support a portfolio strategy that combines nearshore wave attenuation for near-term stress reduction, reef-type features for localized protection, and beneficial-use sediment placement for longer-term resilience in the sediment budget.