Conventional flood water management often involves building pipes or drains to carry away water as swiftly as possible, or reinforcing river banks with concrete to ensure they do not overflow.
But a sponge city does the opposite, seeking instead to soak up rainfall and slow down surface run-off.
It tries to do it in three areas. At the source, where a city tries to contain water with many ponds; through the flow, where instead of trying to channel water away quickly in straight lines, meandering rivers with vegetation or wetlands slow water down and the third is the sink, where the water empties out to a river, lake or sea.
This is an interesting piece. It does have its critics however, with questions raised as to whether, in the face of more extreme floods linked to climate change, sponge cities can truly work.