North of the city of York is a large area of summer pasture land which forms part of the city's flood defences. Flood banks encircle this area, with sluice gates at the upstream and downstream ends allow water in and out. Measuring devices upstream measure water volumes flowing towards York and allow the height of the approaching flood to be predicted. To reduce the maximum flood height water can be diverted into this storage area, and released again as the flooding drops.
Ian