Is the water in estuaries clearer at the moment and is this because of the drought?

[Kukri]

We have noticed that we could see the bottom several feet down in the Orwell in places where we would normally see pea soup.

We were wondering if that might be because less river water is entering the estuary?

 

[GrandadPig]

Very likely. There is a process called flocculation, that occurs (iirc) when sediment in fresh water mixes with saltwater. It causes clay particles to clump together and eventually settle out. I guess reduced freshwater flow could well lead to clearer water in estuaries. Also add in the reduced run-off from cultivated fields in the first place.

 

[Kukri]

Thank you!

 

[Tim Good]

Yeah I think the reduced run off is significant. We were cruising Cornwall last late March and April and it was unusually dry. Everywhere was super clear. Plymouth, Dartmouth, Fowey, Helford etc.

 

[Frogmogman]

I liked Nick Newman’s take on low river levels.

 

[sailorman]

We have noticed that we could see the bottom several feet down in the Orwell in places where we would normally see pea soup.

We were wondering if that might be because less river water is entering the estuary?

mlkmh gbcweatber lwinb sedkme t to drop ljt
To see the bottom with Yr sraughis going some ??
et

 

[sailorman]

mlkmh gbcweatber lwinb sedkme t to drop ljt
To see the bottom with Yr sraughis going some ??
et

calm weather allows the sediments to drop out
e

 

[sailorman]

Very likely. There is a process called flocculation, that occurs (iirc) when sediment in fresh water mixes with saltwater. It causes clay particles to clump together and eventually settle out. I guess reduced freshwater flow could well lead to clearer water in estuaries. Also add in the reduced run-off from cultivated fields in the first place.

Much as I was trying to yk say

 

[myquest]

Yeah I think the reduced run off is significant. We were cruising Cornwall last late March and April and it was unusually dry. Everywhere was super clear. Plymouth, Dartmouth, Fowey, Helford etc.

That's odd. I have never seen so much natural debris in the Dart in the pat 30 years. There are so many tree trunks and branches that I saw someone out collecting them, no doubt for winter heating fuel.

 

[LittleSister]

We have noticed that we could see the bottom several feet down in the Orwell

Us East Coast sailors will all be getting vertigo!

 

[LadyInBed]

I noticed that when I picked up my mooring lines yesterday. After a week away, they are normally covered in slime and gunge.

 

[johnalison]

There are often local differences too. Goldhanger creek was known for its clear water.

 

[AntarcticPilot]

Geologist hat on!

The ability of a river to carry sediment is strongly and non linearly dependent on the flow. It goes up as some power of the flow velocity; I forget what but certainly more than the square of the velocity.

Velocity depends on the amount of water, the slope, the cross-section of the channel and no doubt other things I've forgotten. But basically, rivers flow more slowly as they reach the sea - that's why estuaries are full of mud!

So, low river flow means that flow velocity is low, so sediment drops out of suspension further upstream than it would normally. It also means that tidal influences penetrate further inland in the absence of human flow management.

In other words, I wouldn't be at all surprised if coastal waters are clearer - less sediment will make it to the sea.

 

[Concerto]

It reminds me of back in May 1987, I was motoring along the shore off Hove and Brighton, and I could clearly see the bottom in about 12 to 15ft of water. It had been very settled for several weeks and all the small particles had dropped to the seabed and all the small air bubbles from wave action had risen to the surface. The further north and west I have travelled, I have noticed how much clearer the water is. Generally there are few areas that have as much sediment in the water as the Thames Esturary.

 

[fredrussell]

We have noticed that we could see the bottom several feet down in the Orwell in places where we would normally see pea soup.

We were wondering if that might be because less river water is entering the estuary?

But the only river water entering the Orwell is from the Gipping surely? And there’s very little or no flow from that river unless lock gates are open further upstream. And even then, it’s a tiny output compared to the tidal input to the Orwell estuary. I think the only thing that would affect clarity of river is amount of mud particles in suspension. Something to do with constant easterlies of late perhaps?

 

[Frogmogman]

This thread does remind me of how traumatised a Sardinian friend of mine was by the brown sea when she lived in Ramsgate for a couple of years.

“But why da sea, he is a-brown ?”

To be fair, this is what the sea looks like from her house in Sardinia…….