Editing Lock (water navigation) (section)

===Drop locks===
[[File:Dalmuir drop lock.jpg|thumb|[[Dalmuir]] drop lock]]
A drop lock can consist of two conventional lock chambers leading to a sump pound, or a single long chamber incorporating the sump – although the term properly applies only to the second case. As the pounds at either end of the structure are at the same height, the lock can only be emptied either by allowing water to run to waste from the sump to a lower stream or drain, or (less wastefully) by pumping water back up to the canal. Particularly in the two-chamber type, there would be a need for a bypass culvert, to allow water to move along the interrupted pound and so supply locks further down the canal. In the case of the single-chamber type, this can be achieved by keeping the lock full and leaving the gates open while not in use.<ref>{{cite web|url=http://www.gentles.info/link/Drop_Lock/Drop_Lock.htm|title=Dalmuir Drop Lock| access-date =22 October 2007 }}</ref>

While the concept has been suggested in a number of cases, the only example in the world of a drop lock that has actually been constructed is at [[Dalmuir]] on the [[Forth and Clyde Canal]] in Scotland.<ref>{{cite web|url=http://www.voltimum.co.uk/news/496/infopro/Mitsubishi-helps-breath-new-life-into-important-canal-routes-.html|title=Mitsubishi helps breath new life into important canal routes|author=voltimum|date=11 December 2002| access-date =23 October 2007}}</ref> This lock, of the single-chamber type, was incorporated during the restoration of the canal, to allow the replacement of a swing bridge (on a busy A road) by a fixed bridge, and so answer criticisms that the restoration of the canal would cause frequent interruptions of the heavy road traffic. It can be emptied by pumping – but as this uses a lot of electricity the method used when water supplies are adequate is to drain the lock to a nearby [[Burn (landform)|burn]].<ref>{{cite web|url=http://www.gentles.info/link/Drop_Lock/Drop_Lock.htm |title=Clydebank Drop Lock |publisher=Gentles.info |access-date=2011-08-05}}</ref>