HISTORY OF COLCHESTER CORPORATION WATER WORKS, 31
form a small stream or tributary of the Colne, and had from
time immemorial been the only motive power for driving
Lexden Corn Mill; after passing through the mill the stream
discharged into the main river. (See Plan of the Lexden
Springs. Plate II.)
The source or gathering ground is a large plateau of gravel
and sand to the south west, extending to Stanway in the west,
to the limits of the Roman river in the south, which river runs
in an easterly direction around the plateau to a junction with the
river Colne nearly opposite Wivenhoe. The area of this enormous
bed of sand and gravel is about 13 square miles, and the bed
falls both towards the main valley of the Colne and the Roman
river. The plateau rises to a maximum altitude of about
130 feet above O.D. The springs rise or show themselves at
an elevation varying from 40 to 50 feet above O.D. to the
south-west of the Malting Farm. From the left of the springs
the gravel rises rapidly, the 100 feet contour being only a
short distance away. The water escapes from four or five well
defined springs, and yields considerable quantity, even after
abnormal dry periods; in fact the discharge has been looked upon
in the neighbourhood for ages past as practically constant,
but such is not quite the case, as it varies with wet and dry
periods. The beds are of a porous nature, and of considerable
thickness, and due to their porosity a considerable portion of the
rainfall percolates into the soil, and ultimately finds its way
in the shape of springs into the valleys before mentioned,
especially at Lexden. The beds undoubtedly form a most efficient
natural filter, as at the points of collection the formation is
practically all clean sand, and even after heavy rain the water
always comes away perfectly bright and clear; there is very
little doubt that the beds form an underground reservoir of no
mean capacity. The water is collected by cutting a trench in
the water-bearing bed at right angles to the direction of the flow
of the water, well at the back of each spring and below the level
of the natural discharge or lip, and laying therein special per-
forated stoneware pipes, around which is packed shingle. The
trench is then refilled with the material in the order it was taken
out. The collecting pipes are then led to a pit common to each
spring, and each pit is connected by an iron pipe controlled by a
valve to the main gravity aqueduct. By this means each spring