Lethal Salt Surge

[Meantime]

3 minutes ago, grendel said:

when i was coming downstream earlier this year i did encounter a shallow section, i was a good 12 foot from the bank, and suddenly slowed, I got off again and carried on round the  corner where there were yellow posts about 10 feet off the bank, so there are some shallow spots along that lower section.

The problem is that section also has green posts a good way into the river marking out shallows on the other side. So if you know where the unmarked shallows are and stay wide to avoid them it almost puts you on a collision course with anything coming up river that is giving the Green posts a wide berth.

[andyg]

Can someone please explain the barrier at herbert woods?? Why isn't there one at NBN in Wroxham or richardsons at Stalham?? I assume the fish try and avoid the salt surge in the basins. Apologies if that's a daft question. 

[Meantime]

19 minutes ago, andyg said:

Can someone please explain the barrier at herbert woods?? Why isn't there one at NBN in Wroxham or richardsons at Stalham??

2 hours ago, Meantime said:

I believe that the barrier at Herbert Woods has two purposes. When a salt surge event occurs normally the fish swim upriver to get away from the incoming salt. As the HW basin is a large dead end pool of water off the main river the fish can tend to swim into there in large numbers and become trapped and eventually lack of oxygen becomes an issue. So I believe the first purpose is to encourage fish to swim past and further up river to escape the salt surge, and secondly to protect any fish already in the basin before the salt surge occurred. 

I'm guessing there is no barrier at NBD or Richardsons because they are much further away from Yarmouth than Herbert Woods. 

[rightsaidfred]

21 minutes ago, andyg said:

Can someone please explain the barrier at herbert woods?? Why isn't there one at NBN in Wroxham or richardsons at Stalham?? I assume the fish try and avoid the salt surge in the basins. Apologies if that's a daft question. 

Both of those locations are so far upstream they are irrelevant.

Fred

[andyg]

31 minutes ago, rightsaidfred said:

Both of those locations are so far upstream they are irrelevant.

Fred

Cheers Fred, so there's a limit to how far upstream the salt water travels ?? I assumed it affected the whole network.

[rightsaidfred]

33 minutes ago, andyg said:

Cheers Fred, so there's a limit to how far upstream the salt water travels ?? I assumed it affected the whole network.

I am no expert just years of observation, the simple logic is about volumes, there is a finite volume of freshwater which the surge of varying strengths pushes against, as the upper limits on the North are a dead end there is only so far it can push it without over topping lower down ie flooding, this is why some myself  included think a barrier at GY is impracticable as the volume of incoming water has to go somewhere.

Fred

[Meantime]

1 hour ago, andyg said:

so there's a limit to how far upstream the salt water travels ?? I assumed it affected the whole network.

Fresh water continually drains into the sources of the rivers and runs downstream until it meets the incoming tide where it becomes brackish and eventually salt water. The amount of freshwater entering the rivers depends upon the recent rainfall, but will continue for many months after no rain, just at a severely depleted rate.

Recent lack of any significant rain and the direction of the wind combined with higher tides will have pushed the point at which it becomes brackish further and further upstream.

When you go to Coltishall, one of the reasons why you can often see the bottom is because of the amount of freshwater running off the land and downstream. Also it is rare that you see the current change direction there and head upstream.

[annv]

It stays in the north sea and goes down to Dover .John

[Smoggy]

6 minutes ago, annv said:

It stays in the north sea and goes down to Dover .John

As I understand it normally only goes as far as harwich where it meets the same tide coming the other way round the UK then ebbs back up the North Sea, if heading south down the coast if you aim for hw around harwich you can keep the tide mostly with you as the flood takes you there then the ebb takes you further south while the flood you arrived on ebbs the opposite way.

Direction of buoyant also changes around there but that's probably more to do with trinity house being based there.

[andyg]

Thanks guys I learned something today. Much appreciated 🙏 

[marshman]

Far from being dead ends, the upper limits on the North actually drain a large area of north east Norfolk - the river up to Aylsham was very important and carried a lot of water downstream, the Ant less so I admit but Meantime is of course correct and I may have alluded to earlier, in suggesting the dry summer may have limited the amount of freshwater coming downstream allowing the salt incursion to come further inland than previously.

About 15 years ago a big surge came up as far as Horning Waterworks and according to BASG map, this one actually reached Swan Corner although to be honest I doubt it "officially" got that far! Never tasted it, but I think it is wrong to assume it actually tastes like the sea - my guess humans probably may not even detect it but freshwater fish are quite sensitive to it. Probably more likely to be a mildly brackish solution hugging the bottom!

Going back to HW basin, it was always my understanding that it was used because a) it was there and b) fish coming upstream in front of the "salt" water went into the basin, simply because the bridge itself was a barrier of sorts and they just "dived" left!!!! Seems pretty plausible to me, a simple minded chap!!

 

[andyg]

Cheers marshman, I assumed again that's what happened at potter. Really quite interesting tbh. 

[FlyingFortress]

buoyant 

Bouyage

 

 

 

[rightsaidfred]

38 minutes ago, marshman said:

Far from being dead ends, the upper limits on the North actually drain a large area of north east Norfolk - the river up to Aylsham was very important and carried a lot of water downstream, the Ant less so I admit but Meantime is of course correct and I may have alluded to earlier, in suggesting the dry summer may have limited the amount of freshwater coming downstream allowing the salt incursion to come further inland than previously.

About 15 years ago a big surge came up as far as Horning Waterworks and according to BASG map, this one actually reached Swan Corner although to be honest I doubt it "officially" got that far! Never tasted it, but I think it is wrong to assume it actually tastes like the sea - my guess humans probably may not even detect it but freshwater fish are quite sensitive to it. Probably more likely to be a mildly brackish solution hugging the bottom!

Going back to HW basin, it was always my understanding that it was used because a) it was there and b) fish coming upstream in front of the "salt" water went into the basin, simply because the bridge itself was a barrier of sorts and they just "dived" left!!!! Seems pretty plausible to me, a simple minded chap!!

 

By dead end I was referring to the flood surge which has a limited reach not to freshwater entering the system.

Fred

[Smoggy]

11 hours ago, FlyingFortress said:

buoyant 

Bouyage

 

 

 

Sodding auto correct! Like wot he said.

[CeePee1952]

Barrier at HW still raised as at 0825 hrs this morning, I did notice yesterday that there are a few boats in the marina with people on board, I hope that their holiday hasn't been too badly affected!

Chris

[Mouldy]

25 minutes ago, CeePee1952 said:

Barrier at HW still raised as at 0825 hrs this morning, I did notice yesterday that there are a few boats in the marina with people on board, I hope that their holiday hasn't been too badly affected!

Chris

Just think how many visits to The Temple of Tat that could be achieved if you were locked in their basin for a few day!  Just think of the potential damage to your wallet!!

[YnysMon]

No where to go but Latham's for the day? That would be a complete nightmare!

[Meantime]

24 minutes ago, YnysMon said:

No where to go but Latham's for the day? That would be a complete nightmare!

Think I'd be inclined to take the X6 bus to North Walsham and either take the train to the coast, or Norwich, or even explore North Walsham. I do hope the staff at HW issue anyone stuck in the basin with some sensible tourist information and travel guidance. Actually thinking more about that, a little pack with local bus and train time tables as well as some local walks would be a good idea. 

If only the BA had a tourist information office in Potter! 

[BroadAmbition]

I can report that there was evidence of salt / brackish water past Ranworth Dam.
 

Horning into Wroxham is clear. 
 

Griff

[CeePee1952]

2 hours ago, CeePee1952 said:

Barrier at HW still raised as at 0825 hrs this morning, I did notice yesterday that there are a few boats in the marina with people on board, I hope that their holiday hasn't been too badly affected!

Chris

Barrier now lowered 

Chris

[Hylander]

Saw this just now ...   Breaks your heart.

 

[Mouldy]

22 hours ago, andyg said:

Cheers Fred, so there's a limit to how far upstream the salt water travels ?? I assumed it affected the whole network.

Found this on Faceache.  Shows the extent of the saline incursion.  According to the accompanying details, this only shows where the salt level reached lethal levels.  

[Ray]

As I moor at Herbert Woods (for 2 more days) I signed up to the EA email notifications re the barrier. As you can see from this example on the 26th it can and does open for boats at pre-arranged times. How this affects the fish I don't know.

 

"" Saline Barrier at Potter Heigham

Due to the continuing north westerly winds causing tide locking, we are expecting to see increasing salt levels in the River Thurne again over the next day or so.

This email is to inform you that due to these weather conditions, the saline barrier at Herbert Woods Boat Yard, Potter Heigham will need to be closed today, Monday 26th, at around 5pm to protect the fish in the basin.  

We will review the situation tomorrow but looking at the forecast currently, it is expected that the barrier may need to remain in place for up to 36 hours. We will email you again once we know when it can be opened. We will however have staff on site at 8am on Tuesday to allow boats in and out of the basin. Please make yourself known to them if you would like to take your boat through. 

Kind Regards,

Norfolk Land and Water team  | East Anglia Area Environment Agency ""

[Paul]

Salt surges are nothing new, and from what I have seen yet and reading Marshman's very enlightening posts this one seems nothing more than an average "ten-year" event. I think the reason it becomes more of an issue, seemingly with every salt incursion is the rising number of people on social media who make it such.  Salt comes, fish die, salt goes, fish recover. It has been happening since time began. Nature - red in tooth and claw, and fin on this occasion. 

Many people mistakenly believe that it is the salt that kills fish, and whilst this might be true for small numbers that become trapped in increasingly brackish water most die of suffocation, they swim upstream in front of the salt until they become so congested that the already over warm and oxygen low water becomes critically depleted of that oxygen and fish die. The strongest and the luckiest survive and will recover the population. You could take the view that our attempts to disturb this natural process are very arrogant. Nobody does it because they are worried for the FISH, they do it because they are worried about the FISHING.

So what to do about it? Should we do anything? It was happening long before the oldest of us ever saw the light of day and it will still happen long after our youngest shuffles off this mortal coil. 

Before deciding what to do we must understand why it happens. Marshman makes the point that the head of the northern rivers is not a dead end but drains a large part of North East Norfolk, but for rivers the size of the Bure, Ant and Thurne that is a woefully inadequate catchment, especially in a part of the UK known for having the lowest rainfall. There is simply too little downstream flow of fresh water to protect against these surges. It was the inadequate downstream flow remember which closed the locks on the NW&DC. We never see this issue on the Waveney which has much healthier DSF and rarely on the Yare.

Now we can't do anything about how much fresh water comes down the rivers, so can we stop the amount of salt going up? Yes, we can, and quite easily by erecting a barrier at Great Yarmouth but this would be a major engineering project with a huge cost. We are not talking a few planks and slots. It would have to be somewhere upstream of Haven Bridge and downstream of Bure Mouth a wide stretch of river. Who pays? Who benefits? What would be the justification? What would be the drawbacks? Everyone I have heard arguing that something must be done has a vested interest in the angling sector such as John Currie who has been very outspoken on the use, or rather lack of use of the HW barrier and happens to be chair of the Norwich Pike Assoc. 

Searching this forum alone for "salt surge" returns results from 2015, 2017, 2019, and 2020 and I recall the surge which Marshman refers to which IIRC was 2008 when angling societies across the Northern Rivers told us that fish stocks had been decimated for "generations to come". An EA hydrographywhatsitsname survey in 2014 showed volumes of fish in the Broads were higher than ever before. Forgive me if I am sounding blase but cry wolf comes to mind here.

So we return to the question what should we do if anything? I think it is likely that serious salt surges become more frequent, and so do we build the barrier. What if we do and the broads become overstocked with weak, disease-ridden fish due to the lack of this natural selection caused by the salt? What could we do other than a barrier? We could artificially aerate key parts of the upper reaches. Not difficult, you only need a big pump. It would not save every fish but it would help. Should we address the Bure bump as Griff calls it? People try and deny its existence and point to river depths in the lower Bure but I don't recall the huge mud shoals on those stretches that we see today being there in the 70s and 80s. Would this allow better ebb flow and the quicker and more effective release of salt water? Would it affect river levels upstream? I believe it should be looked at if only as a demonstration. I would like to see the whole width dredged from the Yacht Sta. to Five Mile House. Look at Google maps and switch to satellite view and look at the river colour, the thin blue line edged by brown shallow water all the way to Stracey almost.

Of course, what lets the salt out faster also lets it in faster, if indeed dredging that sector does improve flow, which I think we should accept that it should, would this be beneficial?

Or should we leave well alone and let nature take it's course?