A harbour that is designed to flood, on purpose
The seawall held. For eighty years it held, and in doing so it let the harbour silt up, the marsh behind it vanish, and the town's flood risk grow quietly until a single surge put water in a supermarket two streets from the water. Holding the line was never the cheap option.
Tidewater gives ground. A raised bund protects the working port. Behind it, 180 hectares of parkland and restored marsh are designed to flood on a fourteen-year return period, and the harbour basin is a designed storage volume with a tide gate rather than a barrier. On the day the sea comes in, the water goes somewhere we chose in advance, and it leaves the same way.
Tide gate
Problem
The basin could only be emptied by gravity, and the elevations on either side of the gate differed by 900 mm, which ruled out the obvious single-leaf arrangement.
Drawing
We made the gate asymmetric and drove it from the upstream water level rather than a clock, so the basin drains as fast as the tide allows instead of on a schedule that ignored the actual sea.
Marsh reconnection
Problem
The marsh had been drained and ploughed for sixty years, so there was no seed bank and no water level record to design against.
Drawing
We restored a partial record from historic charts and built the marsh to be cut and re-flooded, so the first season produced the data the second season was designed from.