Is the Corrib a tidal river?

bobbyss

Standing on the banks of the Corrib you can see the river flowing very strongly towards town, throw a stick in and off it goes downwards. Sometimes, when there is a wind you can see the river chopping around the place with no distinctive flow downwards. Is it only the wind causing this?

Or is it the tide coming in? Is it, in fact a tidal river? Is it influenced by the tide? What is a tidal river?

MadYaker

It depends on where you are. If you're upstream of the salmon weir then the river isn't tidal and is flowing towards town regardless of what the wind is doing. Below the salmon weir the river level is effected by the tide but it still always flowing downstream towards the sea.

bobbyss

MadYaker wrote: »

It depends on where you are. If you're upstream of the salmon weir then the river isn't tidal and is flowing towards town regardless of what the wind is doing. Below the salmon weir the river level is effected by the tide but it still always flowing downstream towards the sea.

How would you notice the effects of the tide on the river up to the weir? The weir acts as some kind of dam (I think) and no tide surely would make an impact on the strength of the river from the weir downwards?

Why are some parts of the weir opened and closed occasionaly? Sometimes you can see fishermen standing in the middle of the river there just at the cathedral and sometimes the river is too strong for them to be there. What is that all about?
Thanks for you reply

dubhthach

All rivers are tidal where they enter the sea. In case of the Corrib there is a drop of circa 6 metres within the city (from Weir to Claddagh). If you go look at the old navigation lock on Eglinton canal you can see how high a drop that is in one location. The bulk of the river of course is non tidal as it stretches from the weir to Loch Corrib.

dubhthach

As for operation of the weir. Loch Corrib is the second biggest lake on the island, it drains a fairly massive area, including Loch Mask in Mayo (which is connected via underground rivers in the Cong area). At different times of year there's gonna be different levels of waterflow, this is generally predicated on the level of rainfall within the catchment area

bobbyss

dubhthach wrote: »

All rivers are tidal where they enter the sea. In case of the Corrib there is a drop of circa 6 metres within the city (from Weir to Claddagh). If you go look at the old navigation lock on Eglinton canal you can see how high a drop that is in one location. The bulk of the river of course is non tidal as it stretches from the weir to Loch Corrib.

I see.
So when I don't see the strong flow downwards towards town that i see sometimes at Dangan, this is explained by the amount of rainfall that has occurred in days prior? Is the wind that sometimes lashes up the river a factor?

dubhthach

bobbyss wrote: »

I see.
So when I don't see the strong flow downwards towards town that i see sometimes at Dangan, this is explained by the amount of rainfall that has occurred in days prior? Is the wind that sometimes lashes up the river a factor?

It can be part of it, ye'd notice that in November/December that often the entire Salmon Weir is open (all gates) whereas in mid August you might only have one/two gates open.

If the event of heavy rainfall if the river can't drain fast enough into the sea you end up getting flooding in parts of it's catchment (for example the River Clare). There's obvioulsy a huge body of water sitting in the two Lakes alone.

bobbyss

dubhthach wrote: »

It can be part of it, ye'd notice that in November/December that often the entire Salmon Weir is open (all gates) whereas in mid August you might only have one/two gates open.

If the event of heavy rainfall if the river can't drain fast enough into the sea you end up getting flooding in parts of it's catchment (for example the River Clare). There's obviously a huge body of water sitting in the two Lakes alone.

I see. You seem to know quite a lot about this stuff. So...

What is the weir for? Why was it built? If there were no weir, what would happen? When was it built?

There is a big drop from the weir to next level -is that a natural drop or was it man made? If there was no drop, then presumably there would be no weir? Who is responsible for monitoring the flow and opening closing the gates? Is there a timetable for opening / closing? What about those fishermen-they'd want some notice? They couldn't be looking over their shoulder.

Thanks for you previous responses

Brad768

bobbyss wrote: »

I see. You seem to know quite a lot about this stuff. So...

What is the weir for? Why was it built? If there were no weir, what would happen? When was it built?

There is a big drop from the weir to next level -is that a natural drop or was it man made? If there was no drop, then presumably there would be no weir? Who is responsible for monitoring the flow and opening closing the gates? Is there a timetable for opening / closing? What about those fishermen-they'd want some notice? They couldn't be looking over their shoulder.

Thanks for you previous responses

Weirs alter the flow of a river. They can measure the speed at which the water passes through them and they help to prevent flooding.


There are 16 gates that can be opened and closed accordingly. The drop assists in measuring the flow rate. The water needs to be drawn away from the weir, creating that slanted drop allows that. As for who controls it, I'm not sure. There isn't a timetable as such, but you'd have a fairly good judgment that for most of the winter it'll be 8-16 gates and during the summer it'll be 2 gates or so.

It's a fairly big spot among fishermen, apparently people come from all over the world to fish there

McTigs

i think it's tidal up as far as between o'briens bridge and the salmon weir bridge.... any relative height of water further upstream is due to the lake emptying out and the extent to which the gates are open on the weir

Galwayps

bobbyss wrote: »

I see. You seem to know quite a lot about this stuff. So...

What is the weir for? Why was it built? If there were no weir, what would happen? When was it built?

There is a big drop from the weir to next level -is that a natural drop or was it man made? If there was no drop, then presumably there would be no weir? Who is responsible for monitoring the flow and opening closing the gates? Is there a timetable for opening / closing? What about those fishermen-they'd want some notice? They couldn't be looking over their shoulder.

Thanks for you previous responses

The answer to some of your questions.
The OPW control the gates but pass on info to the fisheries based at the Weir. The OPW have some small sheds over there as well.
There is loads of info about the development of the Fishery and then the waterways but the current levels are a result of dredging in the 1950s when a new weir was built.
Check out http://www.galway.net/galwayguide/history/waterways/ for more info or look for books by Maurice Semple