Several towns have flooded recently and these surveys may suggest the reasons why. This was obviously partly due to excessive rainfall, what is officially called a “one in two hundred year “ flood. The trouble is, with global warming, these floods seem to come every 5-10 years nowadays. As gravel and silt continue to be deposited, the banks continue to encroach and the river gets narrower, flooding will increase. The old stone bridges, built about 200 years ago, were usually built to replace an earlier bridge swept away by the previous big flood and would have been built, at great expense, to allow that amount of water to pass. Therefore the river channel will have to have a similar cross section to top of flood bank level or the banks will overtop causing flooding - see St Asaph. Some bridges have an ‘invert’ (a paved area underneath) as part of the original construction which should be kept clear to maximise flood capacity. Most bridges appear to have accumulated gravel over the invert, building up from downstream of the bridge, reducing the flow capacity.
By using Google Earth, Bing maps, Geograph.org.uk and ordinary photographs, it is possible to find the flood points and hopefully someone will be able, with a bit of digging, to reduce if not prevent future flooding. This work used to be carried out as a matter of river maintenance by the local councils or even angling clubs on a yearly basis and if not done experience showed which places flooded. With the advent of The Environment Agency in the 1996 this maintenance was centralised and promptly ceased, we are now reaping the rewards. The major problem is that no-one is allowed to “dredge” a river or clear banks because of disturbance to fish, wild life, trees and natural habitat, etc. This is a directive from ‘above’ and appears in all county and council plans. It would be nice to get this altered. The EA can only remove gravel near bridges in emergencies and the gravel is classed as waste and can only be tipped in designated land fill sites. Actually the gravel is a valuable resource and can be sold, the top soil and timber can be recycled.
All rivers move gravel and silt downstream as part of natural erosion and cannot be prevented, in flood conditions this will be thousands of tons. This causes the river bed itself to rise and the banks, usually the inside of a curve, to encroach on the river itself. Council road works, sports fields, building in flood plains, house gardens, commercial premises, etc. have also encroached on the river which seems perfectly feasible in dry weather but it all causes flooding in heavy rain. Rivers are now supposed to be allowed to find a natural course with meanders, swamps, tree corridors for wild life, etc. which is a commendable ideal, but life gets complicated when there is a town in the way. If the government is prepared to allow Cockermouth, Ripon, Morpeth, West Auckland, etc. to return to marshland, then so be it.
The common sense way to stop flooding is to start clearing a river from below a town to the same width and depth as the upstream bridge and maintain the same cross section through the protected area. The original banks (when the bridges were built) of a river can usually be determined - old walls, etc - on site and the river width should be maintained at this width and depth. A suitable weir upstream of the town (probably existing) could be selected to collect any gravel coming downstream and be regularly cleared as necessary. Obviously the banks are now consolidated with buildings etc - see Thirsk - but we must attempt to restore the rivers to their original capacity or suffer increased flooding.
Personally I am just a semi-retired builder of 40 years experience, with no qualifications, but with a bit of common sense and knowledge gained by asking local people. Of course I may be talking out of the back of my head - you will have to make up your own mind - but most of the people affected by the flooding agree that the gravel build up is getting worse and may contribute. As the gravel or silt accumulates, an unstoppable happening in all rivers, there will be more and more flooding in future years. This can be allowed in country areas, although the farmers will not be happy, but it gets rather expensive ( £250 million in Cockermouth, £6 Billion nationwide in 2007 ) in towns and we must try to to protect people’s property, lives and livelihoods. Restoring the river beds to their former states - quietly - cannot affect wild life and will provide suitable habitats for plants, animals and humans as they were 200 years ago.
Most measurements are approximate as they are taken from the Google Earth pictures but they are pretty good.