Floods, and what the town does about them
A flood is what happens when the valley delivers more water than the channel holds. The town refuses to build below the flood line, ditches its wet streets, banks the river, and grows uphill.
A flood is not a dice roll. Every month the water model reports the river’s stage; when it runs over bank-full by more than the town’s defence, the town rolls against how far over it is, and the river rises one to four courses into the low ground. Buildings in the water lose condition, more the deeper it stands, less where the ground was ditched; a share of the stored grain is lost; and the chronicle records how many paces and how many buildings went under.
The defence is one number the tuning page can turn: the natural bank, plus what an embankment adds, plus what the flood works policy adds. After a flood the town will not build below the flood line, which is how a flooded town grows uphill. It ditches and culverts its wet streets to win that ground back, a parish budget of columns a year; it raises an embankment along both banks once the treasury and the age allow; it loses a working to the water table and stops driving the next one that deep; from the industrial era it pumps the drowned ones out for a fee. None of it is free and all of it stays in the ground.
What to look for. The water lens during the flood, then era a few decades on: the houses that came down and were rebuilt higher are a different colour from their neighbours, and the ground between them has been made up.
In the code: crates/sim/src/city/water.rs crates/sim/src/events.rs