A storm surge arrives from the open ocean on the left and meets a line of coastal defenses. A mangrove belt (when enabled) dissipates wave energy through root drag and canopy friction before the water ever reaches engineered structures — a well-established coastal-engineering effect, not a decorative one. What remains hits the sea wall: if the surge exceeds the wall's crest, water overtops it and accumulates behind the wall as standing floodwater in the town. A drainage pump network continuously removes that floodwater, but only up to its rated capacity — beyond that, the flood level keeps climbing for as long as overtopping continues.
effective_wave = surge · (mangrove ? 0.55 : 1.0)
overtop_rate = max(0, effective_wave − wall_height) · k
d(flood)/dt = overtop_rate − min(flood, pump_capacity)
- Storm surge — the incoming wave/surge height at the shoreline, in metres above normal sea level.
- Sea wall height — the crest height of the engineered barrier; a taller wall raises the surge level needed before any overtopping occurs.
- Drainage pump capacity — how fast floodwater trapped behind the wall can be pumped back out to sea, in metres of level per second.
- Mangrove buffer — a natural, engineered-adjacent measure: attenuates incoming wave energy before it reaches the wall, reducing how tall (and expensive) the wall needs to be.
- Managed retreat — instead of resisting the water, the most exposed row of buildings is relocated inland, out of the flood's reach entirely — a genuinely different adaptation strategy from "build it higher."
Real-world relevance: coastal cities from Rotterdam to Ho Chi Minh City combine exactly these levers — hard infrastructure (walls, storm-surge barriers), nature-based buffers (mangroves, dunes), active drainage (pumps, canals) and, where defense is no longer economical, planned retreat — because no single measure covers every surge scenario alone.