THE SEVERN TUNNEL. 61 



the tide was blown up to a height of eight inches above the 

 hio-hest tide he had recorded at the Pier, to whicli the waves 

 also did considerable damage. This tide was blown up to 

 a hei"-ht of within eight or ten inches of the top of the 

 marginal sea-banks of the Severn, as measured in a quiet 

 place in Chessel Pill, where there were no waves. 



Now, on referring to the tide-table, the writer observed 

 that the tide of this day, though the biggest in that set, 

 was still /oMr /eeflower than the hig springs just fourteen 

 days socnior or later. The (|iicstion then naturally occurred 

 to him, " What would have been the result had this same 

 gale occurred just fourteen days sooner or later ? " It 

 would undoubtedly have risen above the marginal sea- 

 banks, and have flooded the whole of the Severn marsh 

 lands to a depth of seven or eight feet ; and if the Severn 

 Tunnel cuttings arc never to bo flooded, it will bo neces- 

 sary that thoy should have sea-banhs around them of much 

 greater heiglit than the niai'giual sea-banks of the Severn. 



It then became necessary to decide what this height ought 

 to bo. 



The writer first tried to find out the greatest height to 

 which any tides, whether spring or neap, had ever been 

 known to have been blown up. After full inquiry, he came 

 to the conclusion that eight feet might be taken as the 

 extreme limit. Then, taking 3 feet 6 inches above the 

 alluvial level as the heiglit to which the biggest spring 

 tide would ever rise if it came in quietly in calm weather, 

 he obtained 11| feet above the alluvial lands at the New 

 Passage as the greatest possible height of the storm floods. 

 To this he added four feet more as a margin of safety 

 against the possible wash of the waves in such floods, and 

 made his sea-banks round the cuttings in these meadows 

 sixteen feet high. 



