The OS map c.1900 shows the relationship of Cefn-y-Wrâch to Penarth Head. A channel has been cut to permit shipping to exit to the Severn Sea from Penarth Dock without the need of executing a sharp right-hand-down by the helmsman! The channel was first cut through the shoal in 1859 when the Cardiff Bute East Dock was opened. It was subsequently deepened and widened to keep abreast with the ever increasing tonnage of ships. It is recorded that the Penarth Dock authorities made the channel much safer in 1878. Constant dredging of this channel and all other approaches to the Ely Tidal Harbour and entrance to the Penarth Dock Basin was found to be necessary in order to maintain safe shipping routes. [010] [398]

A section of the 1920 edition OS map which clearly indicates 'The Patch' and 'Cefn y Wrâch'. The channel to the Seven Sea directly in-line with the entrance to Penarth Dock is no longer maintained but the main channel past Penarth Head is wider and dredged to suit the needs of shipping for both Cardiff and Penarth. [010]