Editing River Foss (section)

==River modifications==
[[File:River Foss - geograph.org.uk - 1553874.jpg|thumb|The River Foss in Central York]]
The Foss Barrier was built across the river near its mouth at Castle Mills. When closed, it prevents floodwater from the Ouse forcing the flow of the Foss back on itself.  When the Ouse reaches 7.4m above ordnance datum, the staff at the barrier are alerted. When the level reaches 7.8m AOD the barrier is lowered after running pumps for several minutes to clear silt and debris from the river bed to make a watertight fit. It takes four minutes to lower the barrier. 
[[File:Foss Locks and Sluice - geograph.org.uk - 1608387.jpg|thumb|York Foss Locks and Sluice in the late 1980s]]
To avoid the build-up of water behind the barrier causing the Foss to burst its banks, water is pumped around the barrier into the Ouse by eight pumps that pump water at 50 tonnes per second preventing the Foss flowing back on itself. The water pumped out should maintain a water level of 6.5m AOD behind the barrier. When both sides of the barrier are equalised, the barrier is raised.<ref>Protecting York From the Threat of Floods – The Environment Agency</ref>

Castle Mills Lock is 34 metres long and 6 metres wide. There are mooring points in the lock basin on the Ouse side and overnight mooring on the Foss is prohibited. Beyond Rowntree Wharf there are few opportunities for turning.<ref name="Foss">{{cite web|url=http://www.york.gov.uk/environment/Parks_and_open_spaces/rivers/foss/|title=River Foss & Castle Mills Lock|work=River Foss|publisher=City of York Council|access-date=13 November 2010|url-status=dead|archive-url=https://web.archive.org/web/20120314025739/http://www.york.gov.uk/environment/Parks_and_open_spaces/rivers/foss/|archive-date=14 March 2012}}</ref>