Captain Yuna logged the harbor basin every morning. The tide came in from the west, filling the grid one column at a time — a dependable rhythm she'd tracked for twenty years. By the third morning the western three columns were full. Then the southerly surge arrived, pushing water up through the drainage channel along the bottom of the basin. The entire bottom row flooded at once, even the eastern cells that the regular tide hadn't reached yet. The result was an L-shape: three full columns on the left, plus the full bottom row. By the next survey the surge had receded and the normal tide pattern resumed.