THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
118 
A deduction of 10 inches of. the rainfall over an area of 
150 square miles would amount to about 21,779 millions of 
gallons. 
A second loss is to be considered in the average flow of 
the river. According to Mr. Beardmore,* the Nen, at Peter¬ 
borough, has drained 620 square miles, and its ordinary 
summer discharge at this place is 5,000 cubic feet per minute, 
which is equal to 8*06 cubic feet per minute for each square 
mile of area drained. This represents 1*82 inches of the 
rainfall, and so the contribution for the area under considera¬ 
tion is equal to 3,964 millions of gallons per annum. 
The water which sinks into the ground and is not evapo¬ 
rated again need not be considered as a loss, because it all 
reappears as springs, feeders of the river, or accumulates in 
the Middle Lias, that being the lowest water-bearing bed of 
the district, where, of course, it is still available. 
The remainder then, after deducting loss by evaporation 
and ordinary flow of the river, may be regarded as flood 
water, which is disposed of by the river, or along the river 
valley. So great is the discharge sometimes, that according 
to Mr. Slielford, C.E., the amount of water passing through 
Peterborough Bridge was on one occasion increased from the 
ordinary flow of 5,000 cubic feet per minute to 480,000 cubic 
feet per minute. All this water is to spare, and would be 
better disposed of in another way. 
The quantity of water to spare, therefore, from the drain¬ 
age of 150 square miles would be about as below :— 
Millions of Gallons. 
Bainfall (23T inches per annum) ... ... 50,810 
Loss by evaporation 21,779 millions 
,, ,, flow of river 3,964 ,, 
Total loss ... ... ... 25,743 
24,567 
—i ■ I J 
That is, a quantity of water equal to a daily supply of 
over 67 millions of gallons is to be had if we can only take 
it. 
Of course I do not pretend that this amount could be 
impounded ; indeed, a fraction of it would be ample, but the 
great magnitude of the surplus water must be evident to 
everyone. 
* “ Hydraulic Tables,” by Nathaniel Beardmore, M. Inst. C.E. 
Weall, 1852. Quoted from Water Supply of England and Wales, by 
C. E. de llance, Assoc. Inst. C.E., F.G.S. 
(To be continued.) 
