level in the pound is normally controlled by a bywash weir at the lower lock, some of the water from the upper lock may be lost over it, and if the lower lock has a deeper fall, there is a net loss of level when a boat passes through the pound. Side pound A side pound is a particular type of extremely short lock pound, which is extended sideways to make up for the short distance between locks so as to avoid excessive level fluctuations. An example of this is the Caen Hill locks on the Kennet and Avon Canal. Climbing the hill that leads to Devizes requires 29 locks. The first seven and the last six have conventional pounds, but the middle sixteen have large side pounds, enabling all 16 to be fitted into a distance of around . Serving a similar function are the side ponds on lock flights such as the Foxton flight. The ten locks are organised as two staircases of five chambers each, where each lock can discharge water into the pond below it and receive water from the one above it. Although connected to the locks by sluices, they are still often called side pounds, as they are maintained at the level at which an intermediate pound would be if one were present. The term side pond is also used to refer to a water saving basin, which is maintained at a level between the upper and lower level of a single lock. Most of the locks on the Grand Union Canal between Whilton Locks and lock 45 at Bulbourne, the junction with the Wendover Arm, were built with two such side ponds, although they are currently disused. Regulating water level Canals have several devices used to keep the water level from rising too high in the pounds, causing floods, washouts, and other damage. Waste weirs Waste weirs are used to regulate the height of the water in the canal. Any water higher than the highest board in the waste weir would flow over the board, and out of the canal pound. Boards could be added or taken out to adjust the height of water. Waste weirs often had paddle valves at the bottom, allowing the canal to be completely drained for repairs, emergencies, or at the end of the boating season for winter. On some canals (e.g. the Chesapeake and Ohio Canal) with