Jan., 1889 . 
MIDDLE LIAS OF NORTHAMPTONSHIRE. 
13 
fifty times as much water as is represented by its ordinary 
summer discharge, much less with some of the larger falls; 
for it is evident that so long as restricted channels exist, such 
as locks, sluices, waste-weirs, bridges, and narrow parts in 
the river itself, the discharging power of the river above 
them is only equal to their discharging power, whatever 
may be its capacity as a reservoir, and the locks and flood¬ 
gates at the various mills along the Nen would always be 
used in such a manner as to keep the river as nearly bank- 
full as now, until just before a flood was expected. For these 
reasons I have attached less value to the blocking-up of the 
Nen as a cause, and its cleaning out as a remedy for floods 
than many people, though it is a factor that should not be 
lost sight of, particularly in connection with certain other 
remedial causes. 
Cleaning out and widening of a river anywhere does bring 
certain advantages, for it increases its storage capacity, and, 
therefore, the volume of water available for doing useful work 
in the dryer parts of the year, though alone it would not 
materially diminish floods. 
The expense connected with a really efficient cleaning out 
of the river, and other works, would be very great at first, 
and for the cleaning out recurrent. The increased scour 
and consequent self-cleansing supposed, by some, as likely to 
result from a freer discharge of water, would not be per¬ 
ceptible eastward of Northampton because of the many 
impediments already referred to. The total fall of the Nen 
between Northampton and Peterborough is about 177 feet, 
but owing to the sinuous course of the stream, the average 
inclination is only 38-7 inches per mile ; this, however, would 
allow of considerable scour but for the impediments. 
According to a survey made by Messrs. Siddons, in 
December, 1848, when from 10 to 30 inches of water was 
running over the sills of the different overshots, the total 
fall at the eleven staunches and thirty-three mills between 
Northampton and Peterborough amounted to 163J feet, so 
that the actual inclination of the water between these various 
obstacles only amounted to 13J feet, or an average of about 
three inches per mile, whilst at least 4in. per mile is needed 
to prevent silting up. As a matter of fact, when the over- 
shots are not running, the motion of the water is only just 
perceptible, because held up in successive flats; and when 
they are running, owing to the perpendicular descent, the 
main body of water is not much accelerated. Under such a 
condition of things, weeds and other aquatic plants grow 
rapidly, and I anticipate it would be necessary to cut them 
twice a year to keep the stream in really good condition. 
