The Basingstoke Canal is owned by Surrey and Hampshire County Councils and managed on their behalf by the Basingstoke Canal Authority. As Canal Manager, I recently met the Ash Vale Flood Forum who felt some information about how and why we manage the Canal would be helpful to parishioners in the area.
A Canal is very much a man-made and managed waterway. Consider it like a big bath tub, the taps are like the land drains and rainfall, over which we have no control. Our two main points of control are the bath plug (our sluices), and the overflow hole (our weirs). We try to optimise our comfortable bath by keeping it at a good level where our rubber ducks (boats) can float along and we don’t spill over and make the bathroom floor all wet. This is our ideal water level and we call it design water level or level zero. When the Canal has extra water in it we then say it is plus, by however many millimetres (mm), or minus by however many mm. We then have actions that are triggered by these readings which can vary along the Canal.
We actively watch the weather forecasts and are on the warning alerts from the Met office, warning us of an impending bath time! Before substantial rainfall we let some water out of the bath to pre-empt a sudden influx. The water we let out is either encouraged to flow quicker down the Canal (via the use of lock bypass weirs and lock gates) and/or out of our sluices such as at Ash Vale, allowing large rainfall to easily be accommodated when it hits. This also means our main loading of local rivers is before any major rainfall and thus when they can comfortably cope with it. We have many large sluices on the canal, several of these are upstream of Ash and help to remove storm water before it even reaches this area. Overseeing all this is a Canal ranger, who we have on duty 24/7, 365 days a year to manage the Canal levels. The ranger works alongside other staff who are on-call as back up during periods of bad weather.
Where possible, we want to keep water in the Canal to feed our flights of locks which are mainly downstream of Ash. The Canal actually has a water shortage issue and has done for the last 200 years. Most Canals have a river feed, however our main feed of water comes from springs under the Greywell tunnel and a feeder stream at Broadoak, Hampshire. In the summer months when we have lots of lock use, we can easily run out of enough water and find that we have to close lock flights to boats.
The Canal is far from just a ditch, but with many houses being built up around it for the last 200 years it is now very much an integral part of the water drainage system. It also supports a host of wildlife (it’s nationally renowned for plant life) and recreation for powered boats from all over the country and also three canoe clubs, charity trip and hire boats and commercial boat businesses and an angling club. It is a highly valued recreational resource, with over a million people using it for informal recreation and commuting every year.
Glossary
Weir – a low dam built across a river to raise the level of water upstream or regulate its flow.
Sluice – an artificial channel for conducting water, often fitted with a gate (sluice gate) at the upper end for regulating the flow
Flight of Locks – sequence of locks by which a canal ascends/descends an incline.
Fiona Shipp, Canal Manager, Basingstoke Canal Authority (01252)370073