 Such locks, each of which would only raise and lower boats through small height differences of a few feet, would not suffice when large height differences had to be tackled nor when water was in short supply.The caisson (or caisoon) was thought to be one solution, although it transpired that the technology of the day was not capable of achieving this type of construction economically.It was designed primarily as a water-saving measure, and also was an attempt to minimise construction costs compared with other engineering solutions of the time.