30 ypical Waste Weir - Public Domain image, National Parks Gallery

This photograph shows a boat immediately after leaving the aqueduct. The large bend in the outside the aqueduct allowed the boats to be turned for the rest of their voyage east (or west depending on their destination.) The narrow water way adjacent to the bend is a waste weir and allowed excess water to flow downstream of the lock. It was the lock tenders duty to keep adequate water levels in the canal below his lock.