Posted by Ken Humphries 1 on 18/04/2018 22:38:00:
… The "reens" I mentioned in the Somerset and Caldicot Levels, all contain NON RUNNING water, and act as drainage ditches to the agricultural land. The only time that water flowed out of them was when sluice gates are opened to release water into the Bristol Channel, which is seldom.
More to the ditches in these schemes than just drainage.
The area was once a salt-marsh refreshed with new sea-water every high-tide. Not good for crops!
To recover the land, stage one is to build a dyke fitted with sluices to keep the sea out.
Stage 2 is to open and close the sluices against the tide. Closed as the tide rises and opened to drain brackish water off the land at low tide. The area gradually loses salt and becomes rich agricultural land. At that point the sluices are managed to control wetness rather than to remove salt. In modern times the basic process is much expedited with pumps, originally windmills, then steam, now electric and largely automatic. So water in the Somerset Levels is moving, but perhaps not very much
It all looks rather benign and safe but Mother Nature occasionally bites back. The whole area is vulnerable to flooding; heavy rain, a spring-tide, and a storm-surge might combine and overcome the defences. Not a good idea to build houses there!
Dave
Edited By SillyOldDuffer on 19/04/2018 10:40:11