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.

Many of the available tracts were so narrow that the cost of embankment was very high in proportion to the area secured; and hurricanes from oceanward sometimes raised the streams until they over-topped the banks and broke them.

If these invading waters were briny the standing crop would be killed and the soil perhaps made useless for several years until fresh water had leached out the salt.