That Dredging Question?

[Timbo]

As usual, posts on the NBN have had me poking about various documents on the Broads Authority server, as well as actually reading the research cited in those documents. As you've probably guessed it's a dredging question, well, dredging and an old post of Griffs concerning staining on Broad Ambition's hull.

I'm currently only a quarter of my way through most of those documents but, there appears to be a trend appearing. I had to chuckle at various stages in Broad Authority reports regarding the Upper Thurne Management Plan where conclusions are drawn from references that are not so much 'vague' as 'catatonic'. I'm told that the Upper Thurne Management Plan is "a technical document to guide the site managers and is available to download on the Broads Authority website", however it isn't available to download. The brief outline Upper Thurne Management Plan for public consumption is your typical BA document both short on fact and heavily biased.

I was quite amused to find that according to the document that algal blooms have been on the decrease in the Upper Thurne. Ya reckon? Boating activities seem to be 'tacked' onto wildlife considerations and totally missing from the '20 year vision' for the area. What really caught my attention was references to 'sediment' management. I'm still wading my way through it all...probably because there's so much of it, sediment and documentation.

I did find an interesting monograph on 'The Effects of Boat Activity on Turbidity on a Small Broadland River'. In this instance, they are talking of the Ant from Hunsett Mill to Irstead. What I found really interesting about this was that boats don't have any effect above that of algal turbidity. In other words, it's all the algae that are fouling the rivers not the boat traffic. Of course, I'm trying to correlate this information with the Upper Thurne Management Plan that stipulates that rooted aquatic plants stabilizing sediment is the reason for the 'gin clear' waters of the Upper Thurne.

I'm still reading but the Upper Thurne Plan, and it's lack of input regarding boating in the next twenty years, is driving the lack of dredging around the system. I'll keep reading!

[ranworthbreeze]

Hi Tim,

Well done so far, I guess it is like wadding through treacle

Regards

Alan

[Vaughan]

I think it was Homer who said that the waters of the Aegean were "wine dark". I have also been told, by experts, that just because water is "gin clear" doesn't mean it is not polluted and is often quite the opposite.

One thing I do know - clear water will allow the sun onto the bottom, which will allow the growth of weed, which will encourage fish, which will encourage bird life, which will encourage bird watchers with a lot of money to spend.

If they spend some of that on dredging, they will find it protects their investment.

 

[ranworthbreeze]

I can not see bird watchers contributing much to the local economy. 

Regards

Alan

[Vaughan]

1 minute ago, ranworthbreeze said:

I can not see bird watchers contributing much to the local economy.

But they are buying the bloody place, aren't they?

[JennyMorgan]

6 hours ago, ranworthbreeze said:

I can not see bird watchers contributing much to the local economy. 

Regards

Alan

My wife and I often visit Minsmere, not that I am anything of a fan of the RSPB, but I have to admit it's a lovely place and it obviously brings in a great deal of money to the local community. Packed pubs and tea-rooms for one thing

[Timbo]

Here's a thought, surely an organisation that can scrat together a couple of million in such a short space of time can stick their hand in their pocket and cough up a Broads Toll. Especially considering the amount of the BA's budget taken up on the project? With the amount damage caused to the rest of the system, prymnesium blooms killing off the fish, restrictions to public use of the water and land I'd put them in the same bracket as a motorboat, even though it's wind-powered...of sorts. So with Hickling at 5.9 square kilometers, I make that £257 + £75,558 = a total of £75, 815 a year Now let's back-date that a few years... . Oh and yes I am a paying member of the Trust, so I have no objection to them making a contribution...they can afford it!

[Vaughan]

There is a discussion on the thread about Whisper Emblem which I thought I would talk about here, rather than hi - jacking poor Moosey's thread about a holiday! As a fairly new member he must wonder what we're like. Mind you, he'll soon find out!

Timbo mentions my dislike of the deep draining of marshes for arable crops, but I would like to explain why, as the problem is complex.

Growing arable crops is nothing new on the Broads and was done extensively during WW1, out of necessity. The problem for the farmer is that, whilst land used as grazing meadows will rapidly recover from brackish water flooding, if a ploughed wheat field gets flooded, you cannot use the land for arable again for around 5 or 6 years. In the 70s, the economy was turning away from dairy farming, due to the Common Market Milk Lake and farmers, who had a strong political lobby at the time, were not prepared to take the risk of going arable unless their land was protected from flooding, by building up the river banks and digging deep dykes which could maintain the water in the fields at a lower level.

This policy is completely contrary to the hydraulic management of the river basin, where the grazing meadows were deliberately used as "washlands" to accept the North Sea surge tides (there are always 2 at a time) and so protect other parts of the valleys from flooding. The building of these high banks beside the fields cut off the washlands and lo and behold - the flood water had to go somewhere else, so it flooded Beccles, St Olaves, Reedham, Stokesby, Norwich and even Wroxham. Oh dear, what do we do now? We will have to protect these places by building high flood banks!

Nowadays, thankfully, the economy has turned round and these fields are going back to the grazing marshes that they used to be. But they are still deep drained and the high river banks are still there. This will be one of the reasons, in my view, why salt water incursion on spring tides is going much further up the rivers.

The other reason is simply hydraulic. The principle of hydraulics is that you can't compress water. A volume of water will always be the same volume, wherever you shift it to. So if you dredge a mile of the lower Bure, you will almost double the volume of water that that mile can hold, so the salt water coming through Yarmouth Haven can be contained lower down and will not reach too far. On the other hand, if the river is shallow, the salt water coming in will flow over the bottom and must go further upstream as it must have somewhere to go. We are talking of the same volume of water in both cases.

It's not rocket science!

[BroadAmbition]

Cracking post, written in Yorkshire speak too, and for what it’s worth I agree. Well done. 

To add to it. For years n years the port commissioners had the lower Bure dredged both sides year on year, especially the corners / bends. There were two grab an chuck it cranes on station all year round. Resulting in PHB being easily navigable most of the times at LW. We used to take Broom Admirals through regular.

Older  Broadsmen have told me many times again and again that since the regular dredging stopped, the result has been  increased water levels at LW.  There were no increased salt surges above the ‘Norm’ either.  They should know, they live and work here.

The cynic in me thinks the BA won’t dredge it properly or even tackle the shoaled corners for fear of craft grounding elsewhere at LW forcing them to admit they are not holding their end up and maintaining levels they inherited.

Rocket science?  Indeed it is not.

Griff 

[Cheesey]

More birdwatchers, more people visit with knitted vests made out of shredded wheat, more they want to freeze The Broads in time and more the boating community gets pushed out.

[Guest]

2 hours ago, Cheesey said:

More birdwatchers, more people visit with knitted vests made out of shredded wheat, more they want to freeze The Broads in time and more the boating community gets pushed out.

Boat owners pay an annual toll based on boat size to contribute towards the maintenance of the broads for all to enjoy, maybe bird watchers should also pay a toll based on their height or body weight as their contribution.

[dnks34]

Ive said this before but fisherman who turn up and park themselves on a BA 24hr mooring, what do they contribute? 

Its happenss at Beccles, about this time of year when the holiday makers go home the 24hr moorings before the bridge are generally used by fisherman who come by car and park in the layby.

A sailing boat has been on there atleast 3 days now but thats for another thread! 

[Guest]

Fishermen; you've just given me another idea since they pay a rod licence, why not apply  apply the same principle to bird watchers based on equipment. A single bird watcher licence entitles you to one pair of binoculars and two thermos flasks  

[TheQ]

The rod Licence goes to the EA not the BA, although I believe the EA does some of the work around the Broads.

Trying to get the Money out of the RSPB, for the maintenance of the broads might be more dificult.

Ah.... do they pay council tax on their lands?

[Malanka]

"The other reason is simply hydraulic. The principle of hydraulics is that you can't compress water. A volume of water will always be the same volume, wherever you shift it to"

Unfortunately this whilst totally true is not totally accurate. Almost but not quite the full banana. 

Water has a density coefficient which changes with temperature and salinity. So water of one temperature profile of a particular salinity will have one density whilst water of a different temperature and salinity will have another. This profile is the reason that life exists on our planet pure and simple. Water is at peak density at 4 degrees centigrade, all water of the same salinity of different temperature profiles will be less dense. Thus complete mixing which is where the compressability issue sits is not 100% in play. Water of different salinity and temperature is stratified not fully mixed at all so allowing diffent layers to flow over and arround or under water of higher or lower density.

 

That's how submarines hide using thermoclines in the oceans. (sonar will not penetrate between layers too well)

 

Sorry to be a pedant.

 

M

[quo vadis]

31 minutes ago, Malanka said:

"The other reason is simply hydraulic. The principle of hydraulics is that you can't compress water. A volume of water will always be the same volume, wherever you shift it to"

Unfortunately this whilst totally true is not totally accurate. Almost but not quite the full banana. 

Water has a density coefficient which changes with temperature and salinity. So water of one temperature profile of a particular salinity will have one density whilst water of a different temperature and salinity will have another. This profile is the reason that life exists on our planet pure and simple. Water is at peak density at 4 degrees centigrade, all water of the same salinity of different temperature profiles will be less dense. Thus complete mixing which is where the compressability issue sits is not 100% in play. Water of different salinity and temperature is stratified not fully mixed at all so allowing diffent layers to flow over and arround or under water of higher or lower density.

 

That's how submarines hide using thermoclines in the oceans. (sonar will not penetrate between layers too well)

 

Sorry to be a pedant.

 

M

I knew that