GeoGraph - photograph every grid square

Boom across the River Trent near Alrewas, Staffordshire

For about three hundred metres here the Trent and Mersey Canal follows the course of the river.
The barrier, more than a hundred metres long, is to prevent narrowboats navigating the canal on its left from being dragged down the river on to the weir (just visible on the right) which maintains the water level here for the canal users. The canal and the weir were built in the late 1760s or 1770s. The canal was opened fully by 1777, engineered by James Brindley. I know not for how long the barrier has been in place. The photograph was taken less than half an hour before the sun dipped to the horizon.