12 
MIDDLE LIAS OF NORTHAMPTONSHIRE. 
Jan., 1889 . 
THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
BY BEEBY THOMPSON, F.C.S., F.Gr.S. 
(Continued from Vol. XI., page 294.) 
3. —Blocking up of Streams.— Perhaps no one cause of 
floods has been more considered of late years than this, 
because it so readily suggests the remedy—cleaning out. 
The growth of weeds and accumulation of silt in the Nen, 
particularly since the diversion of traffic to the Northampton 
and Peterborough Railway, has greatly reduced the water¬ 
carrying power of its bed, and so, to some extent, been 
a cause of floods. The following remarks are intended to 
indicate, somewhat, the extent of responsibility this cause 
must bear. 
The drainage area of the Nen above Peterborough is 
estimated at 620 square miles, and the ordinary summer 
flow of water through Peterborough Bridge at 5,000 cubic 
feet per minute, or 45,000,000 gallons per day. This is only 
about 70,000 gallons for each square mile of area drained, 
or *005 inch of rain over the same area per day. The flood 
discharge through the same bridge has, however, amounted 
to 480,000 cubic feet per minute,* a quantity, it will be seen, 
ninety-six times the ordinary summer flow, and equal to 
about ‘5 inch of rain over the drainage area in twenty-four 
hours. This is, no doubt, an exceptional amount, but in 
the Fen Districts of Lincolnshire and Cambridgeshire pump¬ 
ing power is usually provided for lifting half this amount, or 
•25 inch of rain in twenty-four hours over the drainage area, 
into the main drains. A little consideration will show that, 
to prevent floods, a much greater provision would have to be 
made in the Nen Valley than in the Fens, for the “ Upper 
Valley,” that is the part above Peterborough particularly 
subject to floods, has an area of about 16,000 acres, 
which at times constitutes one vast reservoir, whilst the area 
draining into it is about 400,000 acres; so the Nen Valley 
has to receive the drainage of a district twenty-five times its 
size, whereas the Fen lands are only burdened with the 
drainage of a district about six times their own size. 
Now, supposing the river were thoroughly dredged, and 
other improvements in the river bed effected, so as to reduce 
friction by one half, and double its capacity, these alone 
would not enable it to cope with the ordinary winter rains, 
which would deliver into the valley often from twenty to 
* “ Hydraulic Tables,” by Nathaniel Beardmore, M.Inst.C.E. 
