"Parks' and greenways should be designed to facilitate those processes that contribute to the efficient functioning of cities: surface water detention and infiltration, waste management, air cooling and cleansing, urban agriculture and others.
Some of the money that is spent on building drains and channelizing rivers could be saved by giving parks a role in surface water management. Park owners could then charge drainage authorities for this service. In times of heavy rainfall, these parks would be subject to controlled flooding. Luckily, floods are beautiful phenomena. Drainage engineers reckon the size of a flood by the frequency with which it is likely to return. They speak of a 1-year flood, a 10-year flood and a 100-year flood. Grassed and semi-natural areas in parks could be designed to flood. After a night of exceptionally heavy rainfall, people would enjoy the sight of flood park as much as they enjoy seeing a blanket of snow.