The
stream, in its normal state of flow, would have generated insufficient force or
consequently head of water to drive a normal mill wheel. It has been suggested
that the Saxons used an undershot mill in the first instance. With an undershot
mill, the water wheel either lies horizontally (see Tamworth Mill below) or vertically
in the water. The shaft rotates the grinding wheel at the other end.
The
mill stones were often no more than eighteen inches in diameter and ground very
slowly. One revolution of the water wheel only produced one revolution of the
stone.
This type of mill was only for use in minor streams.
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Picture left- Example
of undershot mill. This was excavated at Tamworth in 1971 and radiocarbon
dates it back to the mid eight century. |
Later
they may have tried damming the water to increase its head and force to drive
a more efficient wheel.
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This evidence
is "damming" still visible, the remains of a mill dam
are still apparent.
On the photograph, look directly above the railings.
There you will see a long, low, tree covered mound which was the
embankment.
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The
Colchester Archaeological Group cut a section through this mound and concluded
from their findings that "the mound was built as a dam across the valley
of the brook in order to hold back sufficient water to drive a small mill"
Once a dam had been constructed, a large embankment wall would have been required
to hold back sufficient head of water to drive a normal milling wheel.
The
picture below indicates the position of this possible storage lake and undershot
wheel, now using a storage lake and dam
The level of the water in the mill pond was maintained
by wooden hatches fitted in two separate channels. When the wheel was stopped
the water was diverted into the brook via a `spillway`. The overflow hatch (D)
was lifted to achieve this. Well, in advance of starting work, the miller replaced
the spillway hatch to build up a good head of water and thus store power for the
mill. The sluice gate (C) was then raised allowing water to turn the wheel.
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Artists impression
of what the Mill may have looked like.
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Unfortunately,
no mills survive which is not surprising when you consider the hazards
they were exposed to. Many stood on marshy ground which provided very
poor foundations. Timber piles rotted away in water logged soils.
Rivers in flood also posed another danger. Vibration of the machinery
tended to weaken the complete structure. Friction between the grinding
wheels could at any time spark of a fire.
As
time progressed two changes may have happened:-
With
more productive farming methods there would have been a greater need for milling,
Secondly the mill pond and dam walls may have been extended so that a more efficient
overshot wheel could be used. This is the type we see today, instead of the water
going under the wheel it pours over the top.
The dam wall would have to be
in the region of 10 feet high, to allow water to pour over the top of the wheel.
This height, gave a more efficient use of power, some 68% against 35% because
it now utilised the weight of the water, not just its flow.
Ref to:-
The Watermill in the Manor of Mount Bures at 1086 by S Walker (1991)
NB:-
Back to more modern times, during the 1950 and 60`s, Cambridge Brook
was used extensively for the extraction of water for local farms.
Click
here for link about hydraulic water pumps in Bures
