How to implement flood defences on rivers.

MJohnston

OPW won't change their approach while there are maniacs like this in power:
https://twitter.com/SenatorMarkDaly/status/1361607870631059457

Thargor

He chooses that picture?

The OPW have destroyed nearly all natural river environments and done immeasurable damage to river ecosystems with their "improvements"

hans aus dtschl

I sometimes feel like maybe I'm incorrect about the OPW plans for Cork city.
It's really refreshing to see the outcry on that Senator's twitter page. There's at least a few people thinking the same way.
It looks like OPW are repeating the same mistake over and over and hoping it'll have a different effect.

Anyway, it's a topic for a different thread, but in general we don't make good use of our rivers in Ireland.

wakka12

MJohnston wrote: »

OPW won't change their approach while there are maniacs like this in power:
https://twitter.com/SenatorMarkDaly/status/1361607870631059457

That picture looks beautiful even if untamed. I can't believe money is being spent to the change that, like it just says clearing vegeatation, not even necessairily path improvements or facility upgrades. Find something more worthwhile to piss it away on pleaseee

Thelonious Monk

In fairness he's just doing what his constituents want. I think in a couple of decades there'll be very few riverbanks left, certainly none in urban areas. Look what they did in Skibbereen, depressing.

https://twitter.com/fergalrte/status/1116013014321438720

Sam Russell

Thelonious Monk wrote: »

In fairness he's just doing what his constituents want. I think in a couple of decades there'll be very few riverbanks left, certainly none in urban areas. Look what they did in Skibbereen, depressing.

https://twitter.com/fergalrte/status/1116013014321438720

Look what they did to the Poddle in Dublin. It is culverted over its entire length.

Flooding is a very expensive disaster, and very distressing for those affected. However, solving the problem in one town only to make the problem much worse further down river is not a good result.

Simple solutions do not always work as planned or at all.

Pete_Cavan

The need for, and type of, flood defenses are specific to each location. Its not a case of putting concrete walls along every river, where walls are used they are generally clad with stone.

The flood defenses in Bray look great and has created some excellent public realm, images and video here;

https://www.bray.ie/town-river/

Sam Russell

Sam Russell wrote: »

Look what they did to the Poddle in Dublin. It is culverted over its entire length.

Flooding is a very expensive disaster, and very distressing for those affected. However, solving the problem in one town only to make the problem much worse further down river is not a good result.

Simple solutions do not always work as planned or at all.

In the midlands, a better solution would be to restore as much bogland as possible to act as a sponge for the run off water, I know with the ending of BNM commercial operations that some land will be restored, but only a small proportion can be fully restored.


But even these small areas will slow the flood surges sufficiently yo slow down flooding.


I will also add (just to be on topic) , flooding a street is a sure-fire way to reduce traffic.

magicbastarder

Sam Russell wrote: »

Look what they did to the Poddle in Dublin. It is culverted over its entire length.

skib would have been much better off if they'd done the same.
though i don't know if you'd compare the two; the poddle wasn't culverted because of flooding, was it?

Sam Russell

magicbastarder wrote: »

skib would have been much better off if they'd done the same.
though i don't know if you'd compare the two; the poddle wasn't culverted because of flooding, was it?

Before my time I'm afraid. It was done before the founding of the state, I believe.

[skib?]

MJohnston

Sam Russell wrote: »

Before my time I'm afraid. It was done before the founding of the state, I believe.

[skib?]

Skibbereen

hans aus dtschl

Pete_Cavan wrote: »

The need for, and type of, flood defenses are specific to each location. Its not a case of putting concrete walls along every river, where walls are used they are generally clad with stone.

The flood defenses in Bray look great and has created some excellent public realm, images and video here;

https://www.bray.ie/town-river/

Proper river walls definitely have their place.

But the OPW solution to date has primarily been "concrete walls along every river", that's kind of the problem.

Skib: high concrete walls around the river
Clon: high concrete walls around the river
Cork: high concrete walls around the river
Fermoy: high concrete walls around the river

All different types of flooding, all with the same solution.
There's definitely room for more than one solution.

In most of the completed schemes, any idea of using the river as an amenity is lost forever. It's just a concrete bunker with water in the middle.
In Fermoy, at least they can still get to the river, but even that is far from ideal

Pete_Cavan

hans aus dtschl wrote: »

Proper river walls definitely have their place.

But the OPW solution to date has primarily been "concrete walls along every river", that's kind of the problem.

Skib: high concrete walls around the river
Clon: high concrete walls around the river
Cork: high concrete walls around the river
Fermoy: high concrete walls around the river

All different types of flooding, all with the same solution.
There's definitely room for more than one solution.

In most of the completed schemes, any idea of using the river as an amenity is lost forever. It's just a concrete bunker with water in the middle.
In Fermoy, at least they can still get to the river, but even that is far from ideal

"High concrete walls around the river" isn't the only solution, there are also earth berms plus demountable barriers and pumped systems (although these two require human intervention which can and has failed, leading to flooding). These images of Skib show stone clad walls not much higher than the original ground level;





"Using the river as an amenity is lost forever" is a bit dramatic, walls are only used in certain locations. Access can still be obtained elsewhere and the works have increased the amenity value in areas, see here. In the images above, it is clear that buildings along that stretch have had their backs turned to the river for more than a century. With the flood defenses there now, it is more likely that they will open up to and interact with the river more going forward given it is now safer and more pleasant.

I'd have more faith in the hydrologist designed solutions based on data and modelling being the right ones than "shur they shuda just done x".

magicbastarder

locked or locked up?

BonnieSituation

hans aus dtschl wrote: »

I sometimes feel like maybe I'm incorrect about the OPW plans for Cork city.
It's really refreshing to see the outcry on that Senator's twitter page. There's at least a few people thinking the same way.
It looks like OPW are repeating the same mistake over and over and hoping it'll have a different effect.

Anyway, it's a topic for a different thread, but in general we don't make good use of our rivers in Ireland.

That's putting it mildly

hans aus dtschl

Pete_Cavan wrote: »

"High concrete walls around the river" isn't the only solution, there are also earth berms plus demountable barriers and pumped systems (although these two require human intervention which can and has failed, leading to flooding). These images of Skib show stone clad walls not much higher than the original ground level;

"Using the river as an amenity is lost forever" is a bit dramatic, walls are only used in certain locations. Access can still be obtained elsewhere and the works have increased the amenity value in areas,

We're discussing two different rivers.
I have no issues with the one you're discussing.

magicbastarder

who does the work anyway? i assume it's not the OPW themselves. whoever they've been paying to do the work in Bandon have been on the gravy train for years now.
i'm sure if you ask a private company to do work to alleviate flooding, they're not going to want to deliver something cheap and cheerful.

Pete_Cavan

hans aus dtschl wrote: »

We're discussing two different rivers.
I have no issues with the one you're discussing.

Well you did mention several towns and claimed "All different types of flooding, all with the same solution", referring to high concrete walls which isn't really true (I'm also not sure that "All different types of flooding" is necessarily accurate either if you are narrowing it down to particular sections of flood defense in the towns mentioned, as opposed to the wider overall flood defense strategy for each).

The section of river shown in the tweets earlier also has pumps too, as can be seen here. Obviously a better solution here than simply creating extra space for the river to extend vertically within the same footprint, would have been to remove parking and landscape the area in such a way to allow the water to also expand horizontally into that space. I suspect that it was more local politics that prevented such options being implemented, rather than a desire to put "concrete walls along every river", as was claimed.

magicbastarder

being a tree hugger, i would argue for the 'replant the uplands so the water doesn't sheet off it' approach.

Pete_Cavan

magicbastarder wrote: »

who does the work anyway? i assume it's not the OPW themselves. whoever they've been paying to do the work in Bandon have been on the gravy train for years now.
i'm sure if you ask a private company to do work to alleviate flooding, they're not going to want to deliver something cheap and cheerful.

Its a mix of both. OPW direct staff would do smaller schemes and also repairs and maintenance type works, dredging rivers, cutting back, etc. Large schemes would be designed and then tendered to private contractors who build what was designed in the same way most public construction works are done. It doesn't matter what the private company wants to deliver, thats not for them to decide.

Sam Russell

Houses are being built on the flood plains which used to take the excess water when the river was in spate.

Also farm land expects to not be flooded and so measures are taken to make rivers able to pass water quicker which has detrimental effects down river.

Pete_Cavan

magicbastarder wrote: »

being a tree hugger, i would argue for the 'replant the uplands so the water doesn't sheet off it' approach.

The flooding issues in most places are far more complex than that. The towns themselves also contribute hugely to the problems, we have now far more hard impervious surfaces than years ago, all of which directs water into drainage systems at the same time when previously in would have soaked into the ground and slowly dispersed.

hans aus dtschl

Pete_Cavan wrote: »

Well you did mention several towns and claimed "All different types of flooding, all with the same solution", referring to high concrete walls which isn't really true (I'm also not sure that "All different types of flooding" is necessarily accurate either if you are narrowing it down to particular sections of flood defense in the towns mentioned, as opposed to the wider overall flood defense strategy for each).

The section of river shown in the tweets earlier also has pumps too, as can be seen here. Obviously a better solution here than simply creating extra space for the river to extend vertically within the same footprint, would have been to remove parking and landscape the area in such a way to allow the water to also expand horizontally into that space. I suspect that it was more local politics that prevented such options being implemented, rather than a desire to put "concrete walls along every river", as was claimed.

Cork City: Harbour tidal flooding - concrete wall around the city centre, and leave the rest of the harbour flood
Fermoy: downstream flooding - concrete wall around the town centre, and leave the rest of the area flood
Clon: direct tidal flooding and river flooding - concrete wall at the tidal side
Skib: tributary river flooding - concrete walls around two of the rivers and ignore the other sources of flooding

Look at the photos of Skib posted by others earlier, there are indeed high concrete walls. Feel free to browse for yourself here: https://www.google.ie/maps/@51.5483118,-9.2665097,3a,75y,112.33h,85.07t/data=!3m6!1e1!3m4!1sFJJeKa3dC0DRaC5UzMcz_g!2e0!7i16384!8i8192

Each has had exactly the same solution: build a concrete wall around it. As I have said previously, this can be an appropriate solution, but it seems to be the primary solution proposed by the OPW across most schemes: concrete walls, demountable barriers and earthen banks.

I don't have an emotional investment in this, I've just passed a few of these schemes and they have looked fairly ugly. Fermoy had the best I've seen, west of the bridge, but it's still a shame that the river has been totally disconnected from the town's street.
https://www.google.ie/maps/@52.1386949,-8.2754,3a,56y,227.93h,88.65t/data=!3m7!1e1!3m5!1sjOYG44jT7CMYM9TfihRFVw!2e0!6s%2F%2Fgeo1.ggpht.com%2Fcbk%3Fpanoid%3DjOYG44jT7CMYM9TfihRFVw%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D18.755028%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192

magicbastarder

in what way? if woodlands could act as a buffer, slowing the release of water into the river system, surely that would help?

if flooding is 'water arriving at X faster than it can leave X', slowing the pace at which it arrives can only be beneficial?

hans aus dtschl

Pete_Cavan wrote: »

The flooding issues in most places are far more complex than that. The towns themselves also contribute hugely to the problems, we have now far more hard impervious surfaces than years ago, all of which directs water into drainage systems at the same time when previously in would have soaked into the ground and slowly dispersed.

Yep that's it but certainly damage of the river catchment upstream is a very big factor.
In Cork we allowed huge development on traditional flood plains. Those fields flooded for many decades at least, and were all built on.
In Kenmare, there was significant land clearance upstream of the Roughty and serious town centre flooding followed a few months later.

Just bad overall river management in both cases.

Pete_Cavan

hans aus dtschl wrote: »

Cork City: Harbour tidal flooding - concrete wall around the city centre, and leave the rest of the harbour flood
Fermoy: downstream flooding - concrete wall around the town centre, and leave the rest of the area flood
Clon: direct tidal flooding and river flooding - concrete wall at the tidal side
Skib: tributary river flooding - concrete walls around two of the rivers and ignore the other sources of flooding

Look at the photos of Skib posted by others earlier, there are indeed high concrete walls. Feel free to browse for yourself here: https://www.google.ie/maps/@51.5483118,-9.2665097,3a,75y,112.33h,85.07t/data=!3m6!1e1!3m4!1sFJJeKa3dC0DRaC5UzMcz_g!2e0!7i16384!8i8192

Each has had exactly the same solution: build a concrete wall around it. As I have said previously, this can be an appropriate solution, but it seems to be the primary solution proposed by the OPW across most schemes: concrete walls, demountable barriers and earthen banks.

I don't have an emotional investment in this, I've just passed a few of these schemes and they have looked fairly ugly. Fermoy had the best I've seen, west of the bridge, but it's still a shame that the river has been totally disconnected from the town's street.
https://www.google.ie/maps/@52.1386949,-8.2754,3a,56y,227.93h,88.65t/data=!3m7!1e1!3m5!1sjOYG44jT7CMYM9TfihRFVw!2e0!6s%2F%2Fgeo1.ggpht.com%2Fcbk%3Fpanoid%3DjOYG44jT7CMYM9TfihRFVw%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D18.755028%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192

Concrete walls may be part of the solution but it is not true to say that they are the only solution.

In town centres, there is usually limited space to accommodate the volume of water so that volume has to expand vertically as there isn't the physical space to accommodate it horizontally. Where used, concrete walls are often clad with stone and look better than what was there before (which in a town centre certainly wasn't natural).

In most cases, there was already a barrier (old walls, fences or railings) for people to the water but it was permeable hence flooding. The barrier is now impermeable to prevent the flooding. For people, the new barrier does much the same as the old one, prevents them falling in. The river in Fermoy looks to be equally disconnected from the town's street post flood defenses as it was before it.

Thelonious Monk

magicbastarder wrote: »

being a tree hugger, i would argue for the 'replant the uplands so the water doesn't sheet off it' approach.

The problem is, uplands with any growth on them are seen as untidy and farmers want to burn everything and have them grazed. Having no vegetation and sheep on the uplands means water races to the land below and can't be soaked up or slowed down.
Padraig Fogarty was on Radio Kerry the other day discussing this, after the Kenmare tweet, as well as some local counselor.
Padraig was explaining how there are natural solutions to flooding but the counselor couldn't even fathom the idea of having things grow on the uplands and was giving out that they were only given one day to set fires last year.
This is what you're up against.
For some reason the podcasted interview has been taken down by Radio Kerry but I'll post it here again if it comes back.

hans aus dtschl

Pete_Cavan wrote: »

Concrete walls may be part of the solution but it is not true to say that they are the only solution.

In town centres, there is usually limited space to accommodate the volume of water so that volume has to expand vertically as there isn't the physical space to accommodate it horizontally. Where used, concrete walls are often clad with stone and look better than what was there before (which in a town centre certainly wasn't natural).

In most cases, there was already a barrier (old walls, fences or railings) for people to the water but it was permeable hence flooding. The barrier is now impermeable to prevent the flooding. For people, the new barrier does much the same as the old one, prevents them falling in. The river in Fermoy looks to be equally disconnected from the town's street post flood defenses as it was before it.

Agreed, but that was where this whole thread came from in the very first place.

We were discussing the fact that we don't make use of our rivers in Ireland and I said that changing that mindset will require a rethink of building high walls around the rivers: that was my sole point to be totally honest!

Pete_Cavan

hans aus dtschl wrote: »

Agreed, but that was where this whole thread came from in the very first place.

We were discussing the fact that we don't make use of our rivers in Ireland and I said that changing that mindset will require a rethink of building high walls around the rivers: that was my sole point to be totally honest!

I generally agree with you but, like I said, in town centres it is a case of creating enough space to accommodate the volume of water. As I pointed out, there was more space

The real genesis for this whole thread actually a post from me an article about a town in England looking to demolish a shopping centre in order to create more public space. I then posted about the river through Cavan which is hardly seen in the town and how we should be looking to do something similar and open up the river. Then came posts about putting concrete walls along every river which isn't accurate even where there are flood defenses and plenty of rivers do not have or need modern flood defenses so concrete walls do not automatically apply. Even if flood defenses were required, I would hope that more space could be created by widening horizontally rather than just going vertically.

I also think that there is a lot of over-simplification of flooding issues here. We are literally dealing with forces of nature and we can't just make these volumes of water just not happen. These defenses are designed to deal with once a century type floods as well as the effects of climate change (sea level rise, etc.). Planting trees in upland areas will only do so much, proper flood defenses are also needed.

Thelonious Monk

Yeah I would imagine it will have to be a mix of concrete and natural solutions.

Accidentally

Athlone is another wonderful example. Concrete over your floodplain with a shopping center and housing developments, and then complain when they flood. Who'd have guessed.

Sam Russell

Enniscorthy is another example.