Lockhouse, Guard Lock 5

This lock provides access to the pool behind Dam 5 which was used by canal boats for a distance of about half a mile until the canal resumed beyond a rocky cliff that had blocked it. These locks behind dams were often called “inlet locks” as well as “guard locks.” The term “inlet lock” emphasizes that they let water into the canal from the river and the term “guard lock” emphasized that they were built into a guard, allowing the canal to pass through it. Such guard walls extend from the dam abutment to the adjacent hillside. Because inlet or guard locks were right at river level, the locks and the canal below them were very vulnerable to high water. The guard walls helped hold back the typical flood waters and this protected the line of the canal below the guard gate from being damaged by the high water. The upstream gate in a guard (or inlet) lock was always as high as the guard wall, although the lock itself would not need to be so high. Guard walls were of little use in the event of the great floods where the water rose above the height of such protective berms and overtopped or even sometimes completely covered them.