Lower Bure Dredging

August 23, 2017

Vaughan suggested that something I mentioned on another thread was worth a thread of its own. I mentioned that the ebb and flood on the Lower Bure doesn't seem to be as great as it used to be, and suggested that this may be down to lack of dredging. I have long thought that lack of dredging on the Lower Bure is keeping the Northern rivers backed up and helping to play a part in the rising waters at Potter bridge.

It also seems that since the flood defence work on the Lower Bure they have created large lagoons between the set back bank and the original bank, with gaps for the water to pass in and out off. I can understand that on an incoming tide the water will fill these lagoons and dissipate from the river, thus creating less flow out on the main river, but are they really helping? After a series of high waters you need to drain the upper rivers as well as all these lagoons. Surely the deeper The Bure the more capacity it can carry back down to the sea once the tide turns?

It is a little known fact that the Thames Barrier has been raised more times to prevent fluvial flooding than it has to prevent flooding from the sea. Fluvial flooding is where the run off after a very heavy rain fall is met by an incoming tide that creates a watery dam, stopping the flood waters from escaping. When extremely heavy rain is forecast the Thames Barrier is raised at low water. This creates a huge void behind the barrier, holding back the incoming tide, for the flood water to drain into as it flows down from the upper reaches of the Thames. Once the high tide has past the barriers are gradually lowered to allow all the water to flow out. This is not of course the original design purpose of the barrier which was to stop storm surges and high incoming tides from the sea.

Based on the above I'm surprised that the lagoons on the Lower Bure weren't created in such a way that they are normally empty and with the original river bank slightly lower than the set back river bank. A high incoming tide would then over top the original bank into the lagoons which would have the capacity to take the water. The lagoons could then either be pumped dry, or drain via one way valves as the tide goes out. This idea would mean that for the majority of the time, the current would just ebb and flow on the main river without the lagoons slowing it's speed. Surely this would ultimately create more scour to help keep the lower reaches deeper?

Just my thoughts, will be interested to see what others think, and what their observations have been on the speed of the flood and ebb on the Lower Bure recently.

grendel · August 23, 2017

import a few more wherries and let then chain drag down the river, that would over time deepen the channel surely

LondonRascal · August 24, 2017

On the previous thread, Marshman said:

Quote

That is what they did on CrossRail - the trouble is that the size of the "squishing" bit was huge!!

Would you suggest an application to the Lottery to fund it? Or just the Navigation budget?

To which I m using this thread to reply:

Well, when I contacted the Broads Authority about this they were looking at innovative ways to tackle dredging - reading between the lines the cost of development and research might be EU funded. Since things have changed just a little with us and the EU that puts the kibosh on that.

But, the problem is the way the rivers are dredged at the moment is just pathetic. It is incredible basic, hit and miss approach of a hired excavator on a barge with the operator guessing through experience where the last scoop was taken from and how deep and thus where to take the next scoop from. After a bit of time the Barge alongside is full with both mud and water and has a long journey to a site to have the contents taken out by another excavator. Meantime engine off and feet up for the operator of the dredger.

Management of the navigation is above all other areas in my opinion top of the pyramid so far as funding and importance goes. So often there are complaints about shallow water, and silting of rivers causing everything and how 'things were not like this 40 years ago'.

You can rely on studies all you like but as the Somerset Levels flooding showed in 2013/2014 good old fashion deep wide channels and dredging is needed to increase capacity for water to flow and without it things soon back up and slow down. I say it is time to spend now in a single solution.

Nobody likes to be asked to spend more out - from rail fares to gas bills, you rarely get to see any actual tangible change. The other issue that the Broads Authority has is lack of trust - if they said we need to increase tolls for 5 years to fund this new dredging system, many toll payers would not believe that after 5 years the tolls would reduce from the additional percentage needed to fund the project once it was complete.

Despite this, if we collectively as toll payers had top pay more and then saw this machine slowly making its way up rivers day in and out I recon it would be seen as worthwhile in time. It would be something we funded doing something we could see helping our navigation. I also think it would work, the slow 'scoop and suck' would stop a great deal of disturbance compared to a bucket going in, grabbing mud and raising it out through he water spreading silt everywhere in the process.

It could be used not to just dredge a channel on Hickling but the entire Broad. It could be used on every river and every Broad to universally create a minimum agreed depth and it could do so being accurately guided by the same sort of GPS systems Combine Harvesters use to ensure smooth and even and complete dredging.

The only thing different to this and other suction based dredging is the the 'scoop' blade which would slide into the muddy river bottom at a set angle and feed the mud into the suction head, along with the high speed cyclonic separation of solids and heating of the mud/slurry to remove as much water from it as possible. Now this would need a lot of heat - electric or gas - and that is not going to be very 'green' but it would need fewer barges to go back and forth to a site to then be unloaded, make the resultant material easier to move and a damn sight lighter - it would be like a damp Peat basically and the more it dried out the lighter it became.

At least if the Broads Authority could work with or gain funding from somewhere and Norwich University study the viability of a system like this would be a step - hell put it on kick starter and then sell the system to others around the world and license it to have additional funds coming into their coffers.