The Thames - 'strong stream' red boards

[George94]

Thanks Par.

 

Useful, but doesn't address my initial question.

 

How does one assess the strength of the stream from the levels data? I'm particularly interested now as despite an 8" drop in level, the stream has only moderated slightly today at Goring, AND the red boards remain up. In particular, why do the EA chose to use the term "STRONG STREAM" on the red boards when they don't know what the rate stream is flowing at?

 

Rhetorical question really. I don't expect an answer

 

Mike

 

As somebody else has already pointed out, the river is not flowing at one speed. Both depth and breadth of the river will affect the flow, so whilst it might be 6 knots in one place, it could be 4 knots just a short distance away. Or vice-versa.

 

Furthermore, after heavy rain, the flow will not be stable. It may fluctuate considerably from hour to hour, so any speed given would have to be for a particular place at a particular time, and would be subject to frequent revision.

 

So you are asking for the impossible.

[RLWP]

Go the long way around, downstream first

 

Richard

[MtB]

Go the long way around, downstream first

 

Richard

 

I certainly thought about it, but the idea of going downstream at 30mph is just a bit too scary...

 

As somebody else has already pointed out, the river is not flowing at one speed. Both depth and breadth of the river will affect the flow, so whilst it might be 6 knots in one place, it could be 4 knots just a short distance away. Or vice-versa.

 

I disagree. Expressed in cubic metres per second, it IS a constant speed at any point along any given pound.

 

I can make my own allowances for changes in width/depth.

[RLWP]

I certainly thought about it, but the idea of going downstream at 30mph is just a bit too scary...

 

 

Don't worry. You get two goes to get off the Thames in London, and if you miss, there's not much to hit in the estuary

 

Richard

[oarfish]

We are currently moored on the upstream moorings of a lock till the weekend, when I approached the lock keeper wallet in hand to pay for my moorings he said that we can have safe haven whilst the river is on yellow / red boards which means no charge. Very decent.

 

That is our experience too. They have been very decent about it. We are over our 15 day visitor license as well.

[RichardN]

Don't worry. You get two goes to get off the Thames in London, and if you miss, there's not much to hit in the estuary

 

Richard

 

Ah you do have some extra chances including a quick pop up Barking Creek to visit top man Bill and the other exceedingly sociable residents in Barking Pool ....

[FadeToScarlet]

I certainly thought about it, but the idea of going downstream at 30mph is just a bit too scary...

 

 

 

I disagree. Expressed in cubic metres per second, it IS a constant speed at any point along any given pound.

 

I can make my own allowances for changes in width/depth.

 

I'm not sure that's right. Cubic metres per second (cumecs) is the discharge of the river and doesn't equate to speed.

 

I hope my maths is right here, it's a long time since I did A level Geography......

 

If the river has a cross section of 5 square metres, and is discharging 5 cumecs, the speed of the current is 1m/s.

 

If the cross section is 10 square metres, a discharge of 5 cumecs is a speed of 0.5 m/s.

 

I this k the most accurate statement is that in any given river reach (I think that's the river equivalent to a canal pound) the discharge of the river stays constant, but the speed of flow changes according to cross sectional area, moored boats, vegetation, etc.

[MtB]

I'm not sure that's right. Cubic metres per second (cumecs) is the discharge of the river and doesn't equate to speed.

 

I hope my maths is right here, it's a long time since I did A level Geography......

 

If the river has a cross section of 5 square metres, and is discharging 5 cumecs, the speed of the current is 1m/s.

 

If the cross section is 10 square metres, a discharge of 5 cumecs is a speed of 0.5 m/s.

 

I this k the most accurate statement is that in any given river reach (I think that's the river equivalent to a canal pound) the discharge of the river stays constant, but the speed of flow changes according to cross sectional area, moored boats, vegetation, etc.

 

I fully understand the arithmetic involved. A flow rate would be a start at least, and a helluvalot better info than the 'nothing' we are told at the moment.

 

The cross section of the Thames actually varies very little locally. We know this because the speed of the current varies very little when cruising any given reach.

[MoominPapa]

I'm not sure that's right. Cubic metres per second (cumecs) is the discharge of the river and doesn't equate to speed.

 

I hope my maths is right here, it's a long time since I did A level Geography......

 

If the river has a cross section of 5 square metres, and is discharging 5 cumecs, the speed of the current is 1m/s.

 

If the cross section is 10 square metres, a discharge of 5 cumecs is a speed of 0.5 m/s.

 

I this k the most accurate statement is that in any given river reach (I think that's the river equivalent to a canal pound) the discharge of the river stays constant, but the speed of flow changes according to cross sectional area, moored boats, vegetation, etc.

That's a start, but I think it would give a consistent under-estimation of the speed as seen by a boat. The reason is that river flow is not the same throughout the cross-section, it's more like a version of laminar-flow. Ie the speed is zero immediately next to the side or bottom and increases towards the middle. In a big river like the Thames there will be a lot of cross-section which is sufficiently far away from the banks that it doesn't feel this effect, but there will still be a lot that does. That reduces the speed close to the banks, and therefore to maintain your mass-flow equation, the speed in the centre (where the boats are) has to be higher.

 

In real life, of course, there are other effects from bends and eddies and changes in cross section to take into account.

 

 

MP.

[Timleech]

I fully understand the arithmetic involved. A flow rate would be a start at least, and a helluvalot better info than the 'nothing' we are told at the moment.

 

The cross section of the Thames actually varies very little locally. We know this because the speed of the current varies very little when cruising any given reach.

 

The speed generally increases as you go upstream towards a lock. This is quite logical, if you think of the river bed as following a natural gradient which is interrupted by the weirs, the river will be shallower below a weir than above it unless artificially altered. Of course there are lots of localised variations.

 

My understanding is that the decision to put up red or yellow boards is mainly determined by the amount of weir which is open.

 

Tim

[mark99]

"The cross section of the Thames actually varies very little locally"

 

I echo sounded a bit of the middle/lower Thames and the depth does vary in sections.

 

Deepest I found was 39 foot (and going deeper but could not get closer to weir to finalise) in Shepperton Weir (suspect severe scouring). Most was 11 - 13 foot with various obstructions and features. NB I've also ran aground mid stream below Hammersmith Bridge breaking the shear pin.

 

The three dimensional water speed profile starts at zero at the banks and the bottom and varies throughout cross section. So where do you measure speed at any given height and any given river width? ironically, on one river I observe, the lower the water the faster it flows. I assume because whe river channel cross sectional area reduction relative to water volume reduction is greater (so it's not a linear or obvious relationship).

 

You could imagine a scenario where the river becomes huge but the surface flow reduces as the water speads out.

 

The lock keepers also tend to alter sluices all the time hence varying flows.

 

All told it's a moving feast and \I would imagine that the actual level height and experience is the signal to water managers not the speed.

 

Mark

Edited October 10, 2012 by mark99

[Keeping Up]

On a river with fixed weis, the level gauges will give an accurate indication of the state of the flow in the river, but when they are variable weirs as on the Thames the level gauge will tell you nothing. If the lock keeper opens a new section of weir the level gauge will show a decrease in level but the flow rate will have increased.

[kremmen]

Although it may not help answer your original query I have observed that at sonning the state of boards is set by the number and position of the wiers . There is an indicator in the lock office and at sonning they were all up when I left on Saturday .

 

Paul

[OldGoat]

"The cross section of the Thames actually varies very little locally"

 

I echo sounded a bit of the middle/lower Thames and the depth does vary in sections.

 

Deepest I found was 39 foot (and going deeper but could not get closer to weir to finalise) in Shepperton Weir (suspect severe scouring). Most was 11 - 13 foot with various obstructions and features. NB I've also ran aground mid stream below Hammersmith Bridge breaking the shear pin.

 

The lock keepers also tend to alter sluices all the time hence varying flows.

 

All told it's a moving feast and \I would imagine that the actual level height and experience is the signal to water managers not the speed.

 

Mark

 

The depth at Shepperton House Weir is an anomaly - as you say due to scouring from the Wey and the main weir stream. Apparently there's a large Thames barge at the bottom which was sunksome years ago and they can't retrieve it.

 

 

Managing the flow is a bit of an art and the gates are pulled in a specific order and then managed gently as the flow subsides.

Most of the weirs are still mechanically operated and even with some being completely electric (not a lot of fun when the power goes off), it's not possible to automate them (without EA spending very large amounts of money). That's one of the main reasons why the locks are still manned, and that adds to the character of the River.

 

If CART do take over in 2015 as targeted, I suspect that the lockies will be amongst the first to go, which is not good for the boating community, or for flow management.

 

 

As others have said the Red and Yellow boards are governed by the state of the weirs. When you get to Reds all weirs in a particular section have been pulled (open) and nothing more can be done. The flow can range from "nasty" to "OMG" and at that latter stage nothing more can be done to prevent flooding.

 

 

EA's advice is based on the types of boats that were on the River many years ago (mostly underpowered petrol launches) before any serious MB traffic had started. BUT it still has relevance because of increased flotsam and difficulty for any vessel to navigate safely through narrow channels and bridge 'oles.

 

It's great to see a thread on the Thames as it's a great place to cruise, but it has conditions, rules and practices that should be understood by visitors (and residents alike)

[Steilsteven]

Thanks Par.

 

Useful, but doesn't address my initial question.

 

How does one assess the strength of the stream from the levels data? I'm particularly interested now as despite an 8" drop in level, the stream has only moderated slightly today at Goring, AND the red boards remain up. In particular, why do the EA chose to use the term "STRONG STREAM" on the red boards when they don't know what the rate stream is flowing at?

 

Rhetorical question really. I don't expect an answer

 

Mike

 

You can't, is the answer, levels don't give any clues as to the strength of the stream.

The volume per second is the only way to gauge the flow and, I think, that's what E.A. uses to select the appropriate boards.

The difference in level but little reduction in flow at Goring, is probably because Goring has shut in a bit but Whitchurch hasn't yet, which may be due to having more land water to disperse for instance.

 

There is a volume meter by Reading Bridge, I'd imagine there are others along the river.

 

Keith

[Paringa]

Apparently Red boards come out when the weir is open to half or more of it's capacity...

[The Lockie]

Apparently Red boards come out when the weir is open to half or more of it's capacity... :-) Spot on Paringa!! Although some specific reaches go red at less than 50℅ the rate of flow is academic when it gets to red boards its fast and dangerous! Best to stay moored up.

 

The comment about Lock keepers going when CART takes over is speculation ,but you won't find many lock keepers who disagree!! They have was Trying to get rid of lock staff for years, the opportunity to do so seems to have presented itself with the proposed CART amalgamation

[OldGoat]

Apparently Red boards come out when the weir is open to half or more of it's capacity... :-) Spot on Paringa!! Although some specific reaches go red at less than 50℅ the rate of flow is academic when it gets to red boards its fast and dangerous! Best to stay moored up.

 

The comment about Lock keepers going when CART takes over is speculation ,but you won't find many lock keepers who disagree!! They have was Trying to get rid of lock staff for years, the opportunity to do so seems to have presented itself with the proposed CART amalgamation

 

 

Apologies, guys,

I do try to get it right before I post on here.

 

Trybig to find a logical explanation in a quantifiable way for something that's only intended to be advice to users (they can't stop you navigating - but are trying to save you from disaster).

 

Lockies- oh, yes it is speculation but the rumour has it that some years ago it was put about that BW said they could run the River with "8 lockies"; ignoring the boaters' services just concentrating on level management. On top of the then recent lock house problem it made an awful lot of folks very unhappy NOT just the staff. It's one of the many reasons why I and other users are totally opposed to CART taking over. I've waffled on here before so I won't bore you all again.

[X~Pat]

http://www.mwronline.net/mrc/default.aspx

 

As someone has mentioned this link is useful

Maidenhead Rowing Club river flows , combined with the EA boards site help . There is a history on the flow page so you can esttimate when the the boards/flows may come down.

 

Yellows decreasing may be OK but it seems you will always get caught out somewhere so best to moor up.

 

Any hint of boards has me moored up especially if single handed. With strong flows you sometimes need the whole river width to ferry glide a bridge or lock entrance and there will always be someone else coming the other way. As you don't know what they are doing its a no go so I moor up zzzzzzzzzz !

Edited October 10, 2012 by X~Pat

[Steilsteven]

Apologies, guys,

I do try to get it right before I post on here.

 

Trybig to find a logical explanation in a quantifiable way for something that's only intended to be advice to users (they can't stop you navigating - but are trying to save you from disaster).

 

Lockies- oh, yes it is speculation but the rumour has it that some years ago it was put about that BW said they could run the River with "8 lockies"; ignoring the boaters' services just concentrating on level management. On top of the then recent lock house problem it made an awful lot of folks very unhappy NOT just the staff. It's one of the many reasons why I and other users are totally opposed to CART taking over. I've waffled on here before so I won't bore you all again.

 

Are there no lock keepers on the Severn anymore?

If there are, does CaRT have plans to get rid of them?

 

Keith

[OldGoat]

Are there no lock keepers on the Severn anymore?

If there are, does CaRT have plans to get rid of them?

 

Keith

 

 

1. I don't know we haven't been up there for many years

2. I wouldn't know and I don't suppose CART does either.

 

It's not really a valid point - The few Severn locks were build for substantial sea going craft and IIRC are quite deep with poor / no access from the river for DIY.

 

The Thames locks are smaller and have been designed / modified for user operation. NB owners will be pleased with the operation of the locks above Oxford - they are a dream. Thames lockies act as an information centre (!) to all and sundry - even if it's not part of their job. There are myriads of users who prefer not to operate the locks and the lockies go, I suspect the traffic will decline to the detriment of all.

[The Lockie]

1. I don't know we haven't been up there for many years

2. I wouldn't know and I don't suppose CART does either.

 

It's not really a valid point - The few Severn locks were build for substantial sea going craft and IIRC are quite deep with poor / no access from the river for DIY.

 

The Thames locks are smaller and have been designed / modified for user operation. NB owners will be pleased with the operation of the locks above Oxford - they are a dream. Thames lockies act as an information centre (!) to all and sundry - even if it's not part of their job. There are myriads of users who prefer not to operate the locks and the lockies go, I suspect the traffic will decline to the detriment of all.

 

Salient point here is that whilst known as ."lock keepers" that is the second most important aspect of the role. They are WEIRKEEPERS first and foremost. That's the bit that keeps the levels right for boating and prevents unneccesary flooding. A resident lockkeeper can be on their weir within 15 mins day or night, no other way of operating the weirs can produce such a fast response time

[Martin Megson]

Having travelled up the Thames against red boards in May I would advise much caution. As others have said the flow varies with width and depth of river. I set off in what seemed like a 4mph flow in a 55ft boat with 35hp which was able to move it along at a reasonable rate - I estimate i was doing about 2 mph past the bank so about 6mph overall. There were a couple of times going through narrows where the boat slowed to a crawl and it took 5 minutes to get under Windsor bridge where the water was piling up in front of the pillars.

 

I did find the lock keepers very helpful. Initially they advised me to stay put but once I decided to press on I asked for any tips and most offered advice on spots to avoid and stretches where a particlar side of the river would be easier to navigate.

 

One final but important point is to check your insurance. I found afterwards that mine includes a clause which states that.. "I must not do anything which would endanger the craft". It is likley that they insurance company would consider ignoring red boards breached this.

[Timleech]

"The cross section of the Thames actually varies very little locally"

 

I echo sounded a bit of the middle/lower Thames and the depth does vary in sections.

 

Deepest I found was 39 foot (and going deeper but could not get closer to weir to finalise) in Shepperton Weir (suspect severe scouring). Most was 11 - 13 foot with various obstructions and features. NB I've also ran aground mid stream below Hammersmith Bridge breaking the shear pin.

 

 

 

Mark

 

The tide must have been out!

We rode over a lump in the middle of the river just below King's lock last week.

 

Tim

[OldGoat]

Salient point here is that whilst known as ."lock keepers" that is the second most important aspect of the role. They are WEIRKEEPERS first and foremost. That's the bit that keeps the levels right for boating and prevents unneccesary flooding. A resident lockkeeper can be on their weir within 15 mins day or night, no other way of operating the weirs can produce such a fast response time

 

 

I agree absolutely, the challenge is getting Management and other interested parties to accept that it is a necessary function. Perhaps this year's rainfall pattern will show them the sense of having local operation available.