Trunk Drainage. 
41 
the rights of mill-ovmers and irrigators requiring to be held 
inviolable ; and it being desirable that the compulsory power 
possessed by the company of obtaining outfalls through inter- 
vening properties should be used with great precaution ! the 
following conditions became indispensable, viz., ^Hhat the icorhs 
to he executed shall ho altogether independent of existing streams, 
whether rivers, river branches, tributary watercourses, main 
water-carriers, or arterial surface drains ; by passing under 
them, where not diverted, with impermeable conduits of iron, 
brickwork, or earthenware ; and that the service of the works 
shall be confined to the discharge of the rain-water falling upon, 
or the under-water I'ising up within, or oozing through, the 
lands to which the operations extend." In determining the 
direction of the main outfall drains, " care has been taken," says 
the report, " to follow as straight a course as the lowest ground 
within the area and its local features will admit." Their depth 
was fixed according to the system of subordinate drainage 
necessary to secure the utmost economical depth of dry-working 
soil, and reduce the level of the water in the soil to a point at 
Avhich injurious evaporation would be cut off. In the present 
saturated condition of the soil the loss of water by evaporation 
is almost incredible. In the adjacent naturally dry chalk 
district the water evaporated is 57"6 per cent. The evaporation 
from the peat soil of the valleys is considered to exceed this by 
at least one half ; and this loss, to the miller for potcer and the 
irrigator for loater, amounts to " 750 tons from every contri- 
buting acre of land." A portion of the rain-water is also lost, 
as regards its motive power, by overflow, — the water not finding 
its way back again into the stream ; and from these two sources 
" 12 inches of water, over the whole surface of the valley, are lost 
in every year," — this is 1200 tons per acre, and multiplying this 
by 12,163 (the number of acres in the valleys), considering, at 
the same time, the extraordinary declivity of the valley, viz., 
9^ feet per mile, some idea may be formed of the magnitude of 
the present waste of motive power. The depth of the main 
outfall drains — portions of which will be open cuts, some 
covered, some of circular socket pipes — is fixed at 5 feet, — 
allowing for .4-feet subsoil drains. 
" In determining the capacity of the main outfall drains, which 
are intended gradually to lessen in dimension as they rise from 
the outfall, and the contributory area becomes less, we have 
considered that a capaljility of discharging 7 inches fall per 
month will be quite adequate to any service that can be required. 
In the lens of Cambridgeshire and Lincolnshire, where the 
annual fall of rain is less than 26 inches, the maximum quantity 
of water lifted by steam power per month is 2 inches. Now 
