The upper end, where a hard drawdown changes what a lift is sitting in.
Shallower water at this end means the winter drawdown has consequences that deeper properties never see. Cradles that clear the bottom comfortably in summer can be resting on it in a low January.
That produces a specific seasonal category of damage, and it means a lift can develop a fault purely because of an unusually low winter rather than through any wear at all.
Seasonal damage from a hard drawdown rather than accumulated wear.