page_title: Bosley Lock Flight
section_title: Features
hierarchical_section_title: Bosley Lock Flight / Features
caption_attribution_description: English: Animation of lock with side pond filling and emptying
context_page_description: Bosley Lock Flight is a flight of twelve canal locks, situated on the Macclesfield Canal at Bosley, near Macclesfield, Cheshire, England. The locks are substantially built with stone blocks, and unusually for narrow locks have mitre gates at both ends. They were each built with a side pond, which enabled some of the water to be re-used during a filling and emptying cycle. The side ponds have been disused for many years, but there are plans to reinstate one of them for demonstration purposes.
context_section_description: The locks are unusual for narrow canals, in that they are fitted with mitre gates at both top and bottom, as opposed to the more usual clapper top gate. The chambers are constructed from large blocks of stone, with mason's marks visible on many of them. The locks were equipped with side ponds to save water, but these were taken out of use many years ago, although they still function as overflow channels. The frames for the paddle gear are still visible at four of them.
  Lock ponds are ponds which are maintained at an intermediate level between the upper pound and the lower pound. When a lock is emptying, water from the top of the lock fills the pond, and the rest is discharged to the lower pound. When the lock is filling, water from the pond fills the bottom of the lock, and the rest is then drawn from the top pound. By careful design of the size and level of the ponds, those at Bosley managed to re-use about 40 per cent of the water in this way. The bottom of each lock was connected by a culvert to the bottom of its pond, and a paddle controlled the flow of water through the culvert. The paddle had to be capable of sealing the culvert against flow in either direction, since when closed it had to prevent the lock from emptying when it is full, and from filling when it is empty.
  British Waterways, in conjunction with the Macclesfield Canal Society, are hoping to restore one of the side ponds to enable its operation to be demonstrated, although it is likely that it will only be used for demonstrations, rather than in normal operation of the lock. In 2008 the side pond adjacent to lock 4 was cleared and investigated. Although the paddle gear was beyond repair, enough of it was left to see that it included a counterbalance mechanism, and the stonework of the pond was still in good condition. The culverts are currently bricked up, and the brickwork will have to be removed if the side pond is returned to service.
  Each of the locks has a stone overflow weir on its towpath side, just above the top gates. A stone culvert runs under the towpath to feed the water into the side pond, which also has an overflow weir at its lower end. Another culvert feeds excess water back into the canal below the bottom gates of the lock.
caption: How a lock with a side pond works