Trunk Drainage. 
53 
open, is thorefore In a very bad condition. It can undoubtedly 
be so improved as to carry any uniform quantity of water that 
can be sent down from above ; and the effect of improving the 
Upper Valley will be to deliver the floods sooner in time, but 
more uniform in quantity. As Peterborough may be regarded as 
the outfall of the Upper Valley, the portion of the river below 
that point must be improved before the works can be commenced 
in the Upper Valley ; and we shall therefore notice first the state 
of this part of the channel, and the measures adopted to perfect 
it. Instead of 3^ feet per mile, the fall from the ordinary surface 
of the water at Peterborough to low-water mark at the river 
mouth is only 7 inches per mile. This fall is very irregularly 
distributed ; but, by the removal of obstructions between Peter- 
borough and a point just below the town of Wisbech, the river may 
be brought to an uniform inclination under ordinary circumstances 
of 4 inches per mile, which would be sufficient for the stream to 
act ; and this would lower the water-level at Vt^isbech Bridge 5 ft. 
8 in., at Guyhirn 9 ft. 8 in., and at Northey Gravel, three miles 
below Peterborough, 10 ft. 8 in. This shows that an ample fall 
exists and is attainable for the waters of the Upper Valley dis- 
charging as it were at Peterborough. The 3750 acres of Wash 
Lanils lying between the barrier-banks, and open to the river from 
Peterborough to Guyhirn— intended by Vermuyden, who directed 
tlie general drainage in the seventeenth century, as an imitation 
of the upland meadows, or a sort of reservoir to hold the floods 
until the imperfect outfall could pass them off — are 3 or 4 feet 
higher than the adjacent fens, having never been dried and con- 
solidated like the other peat land, and having received continual 
additions from the expanding floods. The waters now frequently 
overwhelm this long tract with G feet depth of water, but, with 
tlie river channel perfected, there would be a fall of 3 or 4 feet 
from the surface of the land, or, in other words, a means of 
secure drainage. It must be borne in mind that this is only 
when the tide is at low-tcater mark ; the levels differ every minute 
during the day, the tide rising twice a-day and stopping the 
outflow of the drain-water, rising at the higher points of its 
swell far above the level of the land and causing the surface of 
the river to incline from the sea towards Peterborougfh. Thus 
the high-water mark at Cross-Keys Bridge, near the river mouth, 
is about 4^ feet higher than at Peterborough in ordinary springs, 
that is, there is a fall of It inch per mile backwards. An unu- 
sually high spring tide which rose 24 feet at Cross-Keys Bridge, 
and 7 feet above the level of the adjoining land, was 12 feet above 
adjoining land at Guyhirn ; at the " Dog-and-Doublet," 12^ feet 
above adjoining land in the North Level, and 9 feet above the 
surface of the Wash Land ; and at Peterborough Bridge, 6 feet 
