Beginning about 1783 there was accordingly a general replacement of the
reservoir system by the new one of tide-flowing.[4] For this method tracts
were chosen on the flood-plains of streams whose water was fresh but whose
height was controlled by the tide. The land lying between the levels of
high and low tide was cleared, banked along the river front and on the
sides, elaborately ditched for drainage, and equipped with "trunks" or
sluices piercing the front embankment. On a frame above either end of each
trunk a door was hung on a horizontal pivot and provided with a ratchet.
When the outer door was raised above the mouth of the trunk and the inner
door was lowered, the water in the stream at high tide would sluice through
and flood the field, whereas at low tide the water pressure from the land
side would shut the door and keep the flood in. But when the elevation of
the doors was reversed the tide would be kept out and at low tide any water
collected in the ditches from rain or seepage was automatically drained
into the river. Occasional cross embankments divided the fields for greater
convenience of control. The tide-flow system had its own limitations and
handicaps.
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