Complex sentence: Normally the level of the river is several feet below the level of the canal, and the river is carried in a tunnel under the Castlefield canal basin, reappearing at Potato Wharf, where it is supplemented by excess canal water draining into a circular weir.
Split into simpler sentences: Normally the level of the river is several feet below the level of the canal. The river is carried in a tunnel under the Castlefield canal basin, reappearing at Potato Wharf, where it is supplemented by excess canal water draining into a circular weir.