Lack of dredging contributing to the floods

We've dinged our props on the Severn several times, even when the depth log shows 7+ feet. There is all sorts of sh!te washing slowly down. When I took Rafiki from Tewkesbury to Upton a couple of weeks ago, there was a huge ammount of debris snagged under trees, just waiting for an opportunity to get washed down, and lurk beneath the surface, ready to attack my props!
 
Mad Pad said:
A few years ago we were based in Chiswick Quay Marina in London for a few months having work done.The owners wanted to dredge it ie,PUT THE SILT BACK IN THE THAMES WERE IT CAME FROM,but oh no that wasn't allowed......................
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Exactly the same situation in Liverpool Marina and Victoria Dock Marina in Caernarfon.
Completely barmy because the silt is from the River/Menai Strait and is a tiny mount of material compared to the tidal water volumes.
 
Mad Pad said:
A few years ago we were based in Chiswick Quay Marina in London for a few months having work done.The owners wanted to dredge it ie,PUT THE SILT BACK IN THE THAMES WHERE IT CAME FROM,but ON NO that wasn't allowed.I lost interest...
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I can see that dumping it straight back in the river would be good business for dredging firms - they then get paid to dredge again half mile downstream the very same material they've only just dredged and dumped once, and so on alll the way down to the sea!:rolleyes:
 
OK ,so why not take an action against the River Authority,in the case of Chiswick Quay,I think the PLA,for illegally dumping thier silt in a private dock..unless they remove it forthwith!!!!!!HOW ABOUT THAT THEN??I believe Chelsea Harbour has the same problem.Maybe someone with IT skills could move this post to the Thames Forum just to throw another log on the fire.Thanks in anticipation.
 
Dredging will in many places have very little permanent effect. LittleSister has rightly mentioned that farming practices have a significant effect on silting up. I have studied soils and farming for many years and I have seen the degradation of soils over my lifetime, aggressive soil tillage and large amounts of nitrogen fertilisers have led to a loss of soil bacteria and earthworms. This reduces the soils ability to soak up water and transfer it to lower ground reserves, increasing run off and silting. This then fills ditches/streams and reduces run off into rivers and hence increases flooding. Others have mentioned hedge and tree removal, paved gardens and other factors all of which add to the problems. But farmland takes up nearly all the available space that water would naturally be able to filter through so is therefore the place to concentrate drainage improvements. It would take a change in agricultural policy to achieve but would lead to less flooding, better water and food quality and increase food yields. And of course allow more clean and deeper water for sailing!
 
penfold said:
There's a good low impact way of doing it; build training walls on the river and the river will scour itself. That's how the Clyde and many other ports on rivers were persuaded by man to shape themselves from the landscape before the advent of steam powered dredgers. Without training walls on the Clyde Glasgow would not exist, as it would not have become a major port and centre for trade and ship building.
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Yes

Was reading about flooding on the river Ouse in 2000.

Apparently after the floods subsided the depth had increased by 2m - more in some places.
 
Are our rivers so badly polluted? With what? Sewage from combined system overflows?

tolhurstorganic said:
Dredging will in many places have very little permanent effect. LittleSister has rightly mentioned that farming practices have a significant effect on silting up. I have studied soils and farming for many years and I have seen the degradation of soils over my lifetime, aggressive soil tillage and large amounts of nitrogen fertilisers have led to a loss of soil bacteria and earthworms. This reduces the soils ability to soak up water and transfer it to lower ground reserves, increasing run off and silting. This then fills ditches/streams and reduces run off into rivers and hence increases flooding. Others have mentioned hedge and tree removal, paved gardens and other factors all of which add to the problems. But farmland takes up nearly all the available space that water would naturally be able to filter through so is therefore the place to concentrate drainage improvements. It would take a change in agricultural policy to achieve but would lead to less flooding, better water and food quality and increase food yields. And of course allow more clean and deeper water for sailing!
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Dredging to be effective must be carried out sufficiently frequently that the natural process of silt production and deposit doesn't cause flooding where the reduction in channel capacity causes out of channel flow.

Equally well for navigation reasons dredging is necessary to maintain our ports.

'Environmental' reasons are used to evade spending money on watercourse maintenance.

Is it really the case that our rivers are so polluted that silt cannot be recovered for use as soil?

Do we no longer need gravel?
 
Beadle said:
Yes

Was reading about flooding on the river Ouse in 2000.

Apparently after the floods subsided the depth had increased by 2m - more in some places.
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Yes. It is worth bearing in mind that the majority of river erosion takes place during extreme events (i.e. floods). This is when the energy available to transport sediment is at its highest.
 
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