in lincoln, the river flows into brayford pool and exits along a narrow channel that passes under the medieval high bridge. the bridge not only restricts navigation due to its small size, but the volume of water that can pass through the gap is limited in times of flood. this is alleviated by the sincil dyke, which leaves the main channel at bargate weir and runs for through the industrial areas to the south of the main city centre. it used to rejoin the main channel at stamp end, but was re-routed into the south delph, a drainage ditch constructed by john rennie in the early 19th century that joins the main channel below bardney lock. the origins of the sincil dyke are unknown, but it is known to have been used as a drainage channel in the mid-13th century and is thought to be pre-medieval or even roman. parts of it were culverted in 1847 to allow the construction of lincoln central railway station.