The earliest form of shutter weir, known as a bear-trap, introduced in the United States in 1818, and subsequently erected across the Marne in France, consists of two wooden gates, each turning on a horizontal axis laid across the apron, inclined towards one another and abutting together at an angle in the centre when the weir is closed; the up-stream one serves as the weir, and the down-stream one forms its support, and both fall flat upon the apron for opening the weir.'
This old form of bear-trap has been used for closing an opening 52 ft.
Of interest, during these cleaning activities he unearthed what appeared to be a bear trap wedged in a crack.
