10 
Arterial Drainage 
as five-hundredfold. In the hills of Yorkshire, Lancashire, 
and Derbyshire, which constitute the backbone of England, the 
yield of the springs in dry weather varies from about 12 to 18^ 
cubic feet per minute for every square mile of contributing 
ground, whilst the flood-drainage varies from 4915 to 9830 
cubic feet per minute. In the more impervious granite districts 
and other igneous and metamorphic regions there is almost a 
total absence of springs, nearly the whole of the water flowing 
off in floods ; the quantity discharged amounting to 19,200 cubic 
feet per minute.* 
On the Devortian formation, from observations made on the 
small River Allen, which drains 1*76 square mile, it was found 
that, whereas in February when the ground had attained its 
maximum saturation, out of a rainfall of 5 • 13 inches, 96 per 
cent, was discharged by the river, the maximum flow being 295 
cubic feet per minute per square mile ; while in August, when 
evaporation and absorption had the greatest effect, out of a rain- 
fall of 4*88 inches, 8 per cent, flowed off by the river, the maxi- 
mum discharge then being 20 * 5 cubic feet per minute.f 
In the Fen districts of Lincolnshire and Cambridgeshire, 
where perhaps more attention has been devoted to the science of 
drainage than in any other part of England, it is usually calcu- 
lated, in estimating the amount of horse-power required for 
lifting the water into the main drains in winter, that provision 
should be made for a quantity equal to a quarter of an inch 
of rain falling over the whole district in twenty-four hours, or 
403 • 3 cubic feet per minute per square mile. The soil consists 
of a mixture of peat and alluvial matter resting on clay, the 
greater proportion is arable, highly cultivated, and thoroughly 
under-drained. 
The average daily discharge from the basin of the Thames 
above Teddington Weir, embracing an area of 3676 square 
miles, is given as varying from 17 to 22 cubic feet per minute, 
or, by different authorities, from 6*8 to 8 • 7 inches of rainfall 
out of a total average for the year of 26 inches. % 
Percolation, Absorption, and Evajwration. — The variation in 
the discharge of different streams is accounted for by the varying 
amount of percolation, absorption, and evaporation, which takes 
place in their drainage-areas ; each depending respectively upon 
♦ Beardmore, ' Manual of Hydrology ' ; '' Rise and Fall of the River Wandle," 
'Trans. Instit. Civil Engineers,' 18GI ; "Discharge from Under Drains." By B. 
Denton, idem., vol. sxi. ; " Fresh Water Floods of Rivers," idem, vol. xxvii. 
t ' Tl-.e Rainfall of Cornwall, witli ob.scrvations on the Flow of Streams.' Bv 
II. M. Whitley. Truro : Lake, 1876. 
X Grantham on "Arterial Drainage" (Hawkesly), 'Trans. Instit. Civil Engi- 
neers,' vol. six. ; Redman on ' the Thames ' (Taunton and ^ymoiis), idem., 
vol. xlLx. 
