a guillotine gate in a wooden frame was used from the early seventeenth century onwards. The gate was opened by operating a large spoked wheel, connected by chains to a toothed drum.

The pound lock holds water between two gates, and is considerably easier to navigate. Pound locks have been built in China since 983, in the Netherlands from 1065 and in Britain from the 1560s. Nevertheless, a few flash locks remained after the introduction