Why so low ?

J

John Pleasance

Guest
Many of you will be sharing the experience of very low rivers,but why,when there are several weirs in the length of a river does this need to be the case.

Why can't the weirs be set higher to hold more water back in times of low rainfall?

Is it ignorance or indifference or what?

Is there one body who controls the weirs throughout the length of a river,or does this vary depending on land ownership etc?
 
T

Tony Carter

Guest
Hi John,

I have to admit I don't recall seeing a weir that wasn't letting water through. Mind you at least the water immediatley below gets oxygenated - perhaphs the weirs nearest the outfall into the sea should hold the level back in the summer (or in drout conditions) but i guess it just might be too much like hard work for those who control them ?? who knows?
 
D

Dave Slater

Guest
It seems to be policy these days to run water off as soon as possible to prevent flooding. Personally I think this causes more problems than it solves.
 
A

Andrew Macfarlane

Guest
I think you would actually be starving other parts of the River if you backup water. The upper reaches of most Rivers have little or no economic value. As long as there is enough water to maintain fish stocks, the upper reaches will only get as much as is needed.
The lower stretches of Rivers rely on water for industry and tourism on a larger scale. Damming up Rivers would have a serious knock on effect downstream. I think if you travel into a city centre, you will find weirs are in fact raised for longer peiods of time in order to keep central activities functional.
 
A

Andrew Macfarlane

Guest
By the way. I'm not saying I,m happy about it, being an Angler. My fishing suffers as much as anyone elses but I realise water is needed for the greater good and fishing is after all, a hobby...or something like that.
 
R

Richard Drayson

Guest
We're talking about flow and depth.
Temporarily restricting flow, (as opposed to current speed which is different) to increase depth could starve other (lower) parts of the river temporarily, until the depth of water overcomes the weir or sluice. The flow lower down would then increase.
If done is a sensible and controlled manner (gradually), there is no reason that I can see why it's not possible to increase the depth whilst maintaining much of the flow.
 
D

Dave Slater

Guest
Eddie,
I think the pic is a carp angler after a long session.
 
D

Dave Slater

Guest
Yes Nigel, you get a gold star. Perhaps you should have a go at the Always a Crack thread.
 
C

Chris Bishop

Guest
Abstraction. Zillions of gallons of water extracted to irrigate farmlands during tims of drought, esp in SW Midlands, Thames Valley, Hants/Berks, E Anglia etc.
 
S

Stuart Bullard

Guest
I guess you sort of hit a point Chris, but abstraction is not just from rivers of course.

Going back to weirs and their use, I think you will find that controlling the water by weirs and "holding it back" is only a part of flow in a river. One issue is the water table and the height of this at any given time. Remember the majority of water accesses a river by throughflow (i.e. into the river via "underground" water). Rivers also assist in re-charging underground resources.

As such what ever you do in terms of restricting water it can have dramatic affects further down the chain. No easy answer and one thing is for sure, someone, somewhere will not be happy!
 
S

Stuart Bullard

Guest
......whcih leads onto another interesting point. Because we have had such a dry spell, if we have any heavy rain initially little will seep down in some areas (compaction) so its possible heavy rain could lead to some rivers swelling really quickly.

What we need is a gradual increase in rain, not lashings of it!
 
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