File:Foss Flood Barrier - Geograph.org.uk - 1608297.jpg
The Foss Barrier was built in 1989 as part of a flood alleviation scheme following the 1982 floods. It is located at St Georges Field in York where the River Foss meets the River Ouse. The barrier is a 16 tonne gate which is lowered into the River Foss to stop the Foss levels from rising flood waters on the River Ouse.
It also has eight pumps capable of pumping 32 cubic metres of water per second - which is 32 tonnes of water every second.
for more details see: http://www.environment-agency.gov.uk/news/57552.aspx (I think the mathematics are slightly incorrect as one cubic metre weighs one tonne)
http://www.kirklees-ednet.org.uk/subjects/geog/resources/ks34/flooding/info-packs/group-B-%28EA%29/EA-York-flood-protection-8-pages.pdf(required by the license)