Just stepping on to the Aqueduct, the structure is quite larg, so it does not hold back the flood water of the river Aire. The CaRT has this to say about the structure:
Dowley Gap Aqueduct, also known as the Severn Arches aqueduct, was designed by the famous engineer James Brindley and constructed by John Longbotham who designed the Bingley Locks.
It carries the canal 9 metres (30 ft) over the river Aire.
The river started life around 10,000 years ago as an overflow channel from a melting glacier. The mounds of gravel and boulders (moraine) at Hirst Wood were dropped by this glacier.
The overflow channel flowed round them and over the years cut down through the moraine to form the current course of the River Aire.
The pitched stones beneath the aqueduct were laid to protect the foundations of the aqueduct when the river floods.