4-O Book of Engineering 



railway separated by this unfortunate 

 tunnel. 



Very similar trouble was experienced on 

 the much greater venture under the Severn. 

 This tunnel was not rendered necessary by 

 any obstinate landowners, rather was it 

 entered upon to improve the service of the 

 Great Western to the coalfields and large 

 towns of South Wales. 



The Severn is easily the greatest of our 

 English rivers, and it has a singularly wide 

 estuary, involving, with its approaches, a 

 tunnel under the water of no less than four 

 and a half miles. Unfortunately for the 

 engineers they found the Severn a singu- 

 larly fickle river; it overflowed its banks 

 at unexpected moments, it was subject to 

 a bore (a tidal wave), and the bottom of the 

 river was porous to an extent not guessed. 



From the outset it was necessary to install 

 pumps and in ordinary circumstances they 

 were sufficient to deal with the inflow and 

 also the flooding from high tides. But when 

 the Great Spring, as it came to be called, 

 was encountered there was consternation. 



