100 



THE BRITISH ISLES. 



suddenness is dungerous to small craft. Shouts of '* Flood ! flood O ! " herald 

 its approach, and warn boatmen to prepare to meet its shock. The tide-waves, 

 especially wlien a liigh wind blows up channel, frequently endanger the safety 

 of the coast lands, and miles of sea-wall have been constructed for their protec- 

 tion. 



Some of the sand-banlvs in the channel of the Severn are of considerable extent, 

 that known as the Welsh Grounds, for instance, covering an area of 10 square 

 miles. They have been utilised, in a few cases, for the construction of piers, 



Fig. 5;5.— K.ui.w.w Feuuy at Pohtskewet. 

 Scale 1 : 75,000. 



2-44 



1 Mile. 



as at Portskewet, where a railway ferry-boat crosses the river at regular intervals. 

 Until quite recently the first bridge met with on ascending the Severn was that of 

 Gloucester, but since 1879 a railway bridge has spanned the river at the Sharpness 

 Docks, above the entrance to the Gloucester and Berkeley Ship Canal. Including 

 a masonry approach, this bridge has a total length of 4,162 feet. It is composed 

 of bowstring girders, carried on cast-iron cylinders filled with concrete. Two of its 

 spans have a width of 327 feet each, with a headway of 70 feet above the 

 high-water level of ordinary spring tides. 



The basin of the Severn is designed by nature as a region of great commercial 



