There must be many people in Brigg who are unaware that we are protected from flooding by the sluice arrangements at the lower end of the River Ancholme, where it runs into the mighty Humber - at South Ferriby.
The Ancholme has not been tidal for centuries and any flooding suffered in the Brigg area will be related to heavy rain being drained off the land, rather than a surge along the river.
That's why we did not end up suffering like North Lincolnshire villages along the Trent and Humber.
The Brigg area's last severe flooding came more than 30 years ago and was in the spring.
Maybe DN20 8XX postcode households should inform insurance companies of the fact that the River Ancholme is not tidal and see whether that has been taken into account when setting our premiums. Perhaps a few £s a year could be saved. Every little helps!
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Essentially, Nige, there are two potential causes of flooding in the North Lincs area.
For example, tidal flooding, as some parts of the area have recently experienced, can encroach onto low-lying land - this is sea-water flooding.
Secondly, there is fresh-water, excessive run-off overwhelming local water courses. Particularly vulnerable areas are those settlements which are low-lying and/or whose water-course (ie river) has an up-stream, extensive run-off catchment area. For instance, York is fairly low-lying and the River Ouse is channelled thro' a comparatively narrow vale, while the headstreams of the Ouse cover a widespread upland area where precipitation can be of very high volume - hence the frequent flooding of York.
The South-North course of the Ancholme is fairly level - ie there is comparatively little inclination and therefore, the River Ancholme (cannalised, or not)is inherently a slow flowing water course.(in the recent geological past, the Ancholme flowed in the opposite direction) However, it is a significant run-off area. Some excessive run-off can be held to a degree in dykes (often controlled by sluices), but periods of prolonged heavy precipitation can increase the river's volume.
Without the South Ferriby sluice, the Ancholme would be tidal with much of the Vale of Ancholme (as in the past)would flood twice daily - the extent depending on whether the tides were Spring or Neap.
The out-flow of the Ancholme can only be released when the tide level is below that of the River Ancholme.....and the period of release is also related to undulating range of Spring to Neap to Spring etc.
Consequently, potential flooding problems can occur when there has been a prolonged period of heavy rain and the Ferriby sluice is closed. (opening the sluice gates at periods of high tides in the Humber would be self-defeating and would serve only to exacerbate additional marine flooding of the Vale of Ancholme. Indeed, during the tidal monthly cycle between Sping/Neap tides, the periods in which the sluice gates can be open can be fairly narrow.
A third type of flooding, possibly experienced by the Trent-side villages, is a combination of marine and river flooding. For example, it is possible that the recent tidal surge up the Humber was channelled into the Trent, thus holding back the natural river flow of the Trent - hence a massive pooling of both marine and fresh water overflowing the river defences. (accepting that the Trent is normally tidal anyway to the point of Cromwell Lock in north Notts)
Just for info - Ancient geological history indicates that a tidal surge of circa 500BC dumped a massive sandbank across the Vale of Ancholme just to the north of Brigg.
This developed a dam and the valley around Brigg became a large lake - one of the few places to escape flooding was the area of slightly higher ground, now the Market Place.
This damming of the river seemed to have grossly affected the Late Bronze Age folk living about Brigg (at that time Early Iron Age) and they seemed to abandoned the area.
For further info - there are various pockets of silt, clay, sand, gravel in and along the Vale of Ancholme.....these resulted from the outflow carrying various material in suspension and depositing such from the melting glaciers of the receding Ice Age of 10k years ago. Hence the sites of gravel pits, clay works and etc in the valley.
In addition. there has been an stratum accumulation of vegetable matter - some very thick - during the period from the Ice Age. (ie the Ancholme Rowing club-house is built on piles some 10m deep thro' bog matter)
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