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Flood Relief - Problems and Solutions

  • 21-09-2015 10:57pm
    #1
    Registered Users Posts: 205 ✭✭ random_guy


    ...And in several pages of posts, no one has commented on the suggestion that there is a plan to put €1Bn into Flood defences. In terms of the specifics, I for one welcome that, as in direct terms, dealing with flooding issues will benefit many more people that will a Dublin Underground. Having suffered first hand the devastation of flooding, I know exactly how important it is to remedy the massive lack of adequate investment in the proper planning and structure in relation to flood issues.
    ...


    This follows on from something that was raised in the Dart Underground Thread and is also an interesting topic.

    What are the realistic flood relief schemes that can be put in place?

    I'm not sure of the current or past rules that are/were in place in Ireland but I do have some experience with Scottish Water* and their system.

    For all green and brownfield sites the post-development outflow has to match the pre-development outflow. Normally following an application they will push for a very restricted outflow (ca. 40-50% of the pre-development outflow) but this can usually be negotiated up to matching the post to pre.

    What are the rules in Ireland?

    And what are the solutions to fixing what is not already in place? In Scotland taking into account all the restrictions needed on mechanical and biological treatment proper attenuation can usually be achieved with a mixture of porous paving + a wrapped stone filled trench + a throttled outlet.

    Instead of spending money on installing new flood defenses which is quite reactive, is it not worth investing the money at the source and where possible introduce appropriate attenuation in the green spaces that exist in already constructed estates**

    The Scottish system actually results in pretty large stone-filled trenches but that also takes into account the treatment issues that are required. Going back at this stage, attenuation could be introduced with the likes of Wavin's Aquacell at a fraction of the space (they have something over 90% porespace).

    Most flooding in Ireland is as a result of the uninterrupted outflow of runoff into the various water courses. Reducing these peaks at the source will have a massive benefit to reducing the overall flooding.

    What are other peoples thoughts?

    *My experience is a bit old and maybe a bit out of date.
    ** When technically feasible
    *** I don't work for Wavin or any such manufacturer :D


Comments

  • Registered Users Posts: 3,612 ✭✭✭ Dardania


    They cite SUDS quite a bit on planning permission lately, which is similar to what you describe:

    http://www.dublincity.ie/main-menu-services-water-waste-and-environment-water-projects/sustainable-drainage-systems-suds-and

    The ultimate in sustainability is to not build in flood plains in the first place, I feel. But I do agree - attenuating where it hits the ground makes sense


  • Registered Users Posts: 930 ✭✭✭ Brian CivilEng


    The Greater Dublin Strategic Drainage Study in 2005 is a good read, part of it sets sets out exactly what you are describing. SuDS and good attenuation go without saying for any project I've worked on in the last decade (mostly commercial or infrastructure).

    http://www.greaterdublindrainage.com/

    As a victim of flooding myself however, I do think residential areas are where the problem is. Swales and balancing ponds work well in new developments but over time knowledge of their purpose is lost and they can be removed by occupants. Simple livability reasons, more car parking required, cutting down on household maintenance, extensions etc. Nothing major, people living their life long after the developers have moved on.


  • Registered Users Posts: 6,699 ✭✭✭ plodder


    I'm pretty sure attenuation tanks etc have been part of residential developments here going back several years. I certainly know of one development around 15 years old that has it. The difficulty of course is flood events that overwhelm the attenuation measures. I don't work in this area, but it always struck me that there should be some property tax incentive for houses/properties that have porous (garden & driveway) surfaces that don't runoff directly into drains etc.


  • Registered Users Posts: 205 ✭✭ random_guy


    Thanks for the responses.


    Dardania wrote: »
    They cite SUDS quite a bit on planning permission lately, which is similar to what you describe:

    The ultimate in sustainability is to not build in flood plains in the first place, I feel. But I do agree - attenuating where it hits the ground makes sense

    SUDS, i had completely forgotten that word. Building in flood plains is in my opinion complete madness, however the damage is already done. The problem now is to how to go back and rectify it?


    As a victim of flooding myself however, I do think residential areas are where the problem is. Swales and balancing ponds work well in new developments but over time knowledge of their purpose is lost and they can be removed by occupants. Simple livability reasons, more car parking required, cutting down on household maintenance, extensions etc. Nothing major, people living their life long after the developers have moved on.

    This strikes me as strange. In a Scottish example all drainage infrastructure whether it be above of below ground will be taken in charge by the roads authority or Scottish Water, depending on the circumstances. It's certainly not left to the whims of the resident as to whether they want to fill them in or not.
    plodder wrote: »
    I'm pretty sure attenuation tanks etc have been part of residential developments here going back several years. I certainly know of one development around 15 years old that has it. The difficulty of course is flood events that overwhelm the attenuation measures. I don't work in this area, but it always struck me that there should be some property tax incentive for houses/properties that have porous (garden & driveway) surfaces that don't runoff directly into drains etc.

    Are these not designed to account for large events? While attenuation systems can be described simply as a hole in the going the design that is (should) be carried out is not exactly that.

    I can remember that attenuation tanks or basins needed to be designed to completely contain a 1in 30 year event and checked for a 1in50 year event to ensure that no houses were flooded.

    As for tax incentives, I would say that it should be mandatory on new developments to have a proper system in place.

    As for flood defences, they do work and when done properly can be quite unobtrusive, but the investment and disruption needed to install them is crazy when other options exist.


  • Registered Users Posts: 8,781 ✭✭✭ Carawaystick


    sher we had about 4 1in50 year floods in Dublin in the last 6 or so years...

    I guess the point about residents was that people install hard surface areas many years after construction. The initial construction may have made assumptions for the attenuation of an estate which assumed x amount of grass cover.
    These assumptions are no longer valid.


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  • Moderators, Motoring & Transport Moderators Posts: 6,364 Mod ✭✭✭✭ Irish Steve


    The issues with flooding are massive, some are down to fundamentally corrupt planning decisions that allowed housing to be put where it never should have been, but some is down to the (criminal) underfunding of local authorities over decades, which resulted in a complete lack of supervision and oversight of developers, and no resources on the ground to make sure that things were done in accordance with regulations and approvals.

    That meant that they got away with putting storm water into sewers, saving themselves on the cost of a second water movement system, or things like ground levels were not correctly enforced, or bridges, pipes and culverts were undersized, or small streams that pass through residential estates were not piped at all, and now get used as a quick, cheap and easy way to get rid of grass cuttings, tree prunings and other inappropriate domestic waste that then causes massive problems further downstream when it becomes jammed or lodged in a grid or pipe, and causes massive local issues.

    Then there are significant issues with the bad and inadequate design of the infrastructure that deals with storm water in residential and commercial areas, and we've seen plenty of examples of this in recent times at places like Dundrum, among others.

    Then there is the incredible problem of responsibility and accountability, which doesn't exist in local authorities, no matter how badly they deal with infrastructure issues, no one has every been fired or removed from post for these failings, despite the massive human cost and trauma that is the result of such incompetence and inadequacies. The usual way that incompetents are dealt with in public service is by promoting them sideways into a "new" department, and we've seen the result of that over the last few decades, and it's not pretty!

    I will put this very clearly into the public domain, I have nothing but total contempt for a significant number of the full time administrators of Meath County Council, who have repeatedly refused to adequately engage with me to deal with a problem of a sewer that crosses the line of a river, and acts as a dam, the issue has existed since the early 1990's, so over 20 years on, the problem is still there, and has now resulted in our house being flooded on 3 occasions, 2000, 2002 and 2014. The sewer did NOT conform to the requirements laid down by OPW in 1987, but despite regular letters, meetings and pressure through local councillors, they have done NOTHING. It's now even more complex, as Irish Water are now in the loop, as they are "responsible" for sewers, but getting them to respond is even more difficult that getting Meath County Council to respond.

    Now, we're also facing into changes in the climate, with more frequent and significantly heavier rainfall that causes surges and rapid rises in levels.

    There are some flooding issues that cannot be easily dealt with, no matter how much money is thrown at the problem, and there are many others that could be relatively easily dealt with if the funding was put in place, and the right decisions were made about how water courses in urban areas were dealt with. Be under no illusions, the deficit in spending goes back decades, and there is then the fundamental issue that dealing with issues like flooding is not on the agenda for most politicians, as the results of such massive spending will most likely not gain them any political advantage in the polls and at the next election, so it's completely off their radar, the only thing that might change that will be the pressures from EU legislators, as they seem to be more aware and proactive in facing up to flooding problems.

    There are then other issues, which will have to be faced fair and full on, there are things like ancient bridges that are now not fit for purpose due to changes that have happened upstream, and they cause problems when high volumes of water can't get through, and it is no longer acceptable to have people's lives disrupted or their houses damaged because An Taisce or similar want to preserve "our heritage".

    Yes, I'm vocal on this issue, when you've sat on the stairs in your house, and seen a brand new carpet destroyed before it had even been walked on, and realised that the problem could have been solved by the local authority, that tends to generate some very strong emotions. The psychological stress and trauma of dealing with flooding cannot be described, and no matter how long you spend trying to deal with it, those pressures don't go away, every time there's heavy rain, a decent night's sleep becomes difficult, as there's always that doubt in the back of your mind that no matter how good the protections that you've put in place are, they might not be enough.

    We've spent thousands of Euro trying to ensure that we don't get yet more damage going forward, in the absence of action from the people that should have been dealing with it, the ONLY redeeming feature is that after the most recent flood in our area last year, MCC have been forced to get consultants in to review "our" river, as it caused more widespread damage to houses and business premises, so they can no longer hope the problem will go away. What's sickening is that they were clearly warned in 2003 that if they allowed development downstream from us, it would make the problems worse, and 12 years down the line, that was exactly what happened.

    The big issues with this are that there are too many agencies involved. Irish Water, the local authorities and OPW are all implicated, and in some cases, there are then others, like ESB or specific drainage management authorities, and getting them to coordinate action is a bit like herding cats, it doesn't happen.

    Then there are "issues" with things like maintenance of water courses. Small channels used to be cleared by a group of staff walking the line, but that's no longer permitted, so they are supposed to use machines to do the work, but there are many places where it's not possible to get machines in to the channel to clear it, and as time goes on, they are becoming increasingly overgrown and obstructed, making the problem worse than it already is. and in a lot of cases the only solution will be to completely pipe such channels so that they no longer require any maintenance, but getting funding for that type of work is going to be a nightmare.

    I'm under no illusions, the issues of flood management are going to be a very large item on the agenda going forward, and it will be a brave politician or party that faces up to the cost and implications of properly dealing with it, I suspect it might not happen in my lifetime, given how much of a hot potato this issue is.

    Shore, if it was easy, everybody would be doin it.😁



  • Registered Users Posts: 6,699 ✭✭✭ plodder


    sher we had about 4 1in50 year floods in Dublin in the last 6 or so years...
    Exactly. It sounds like a joke, but there is truth to it, which I think shows there is a touch of voodoo around the estimation of these events.
    I guess the point about residents was that people install hard surface areas many years after construction. The initial construction may have made assumptions for the attenuation of an estate which assumed x amount of grass cover.
    These assumptions are no longer valid.
    It doesn't seem right though that someone should be able to do that without any consequence for the extra loading it puts on public drainage. When I lived in Munich 20 years ago, it was common to put down concrete lattice on driveways that allows grass to grow through it. Apart from being nicer to look at, it allows much more natural drainage to occur. I don't think I've ever seen it here.


  • Registered Users Posts: 205 ✭✭ random_guy


    plodder wrote: »
    Exactly. It sounds like a joke, but there is truth to it, which I think shows there is a touch of voodoo around the estimation of these events.

    It doesn't seem right though that someone should be able to do that without any consequence for the extra loading it puts on public drainage. When I lived in Munich 20 years ago, it was common to put down concrete lattice on driveways that allows grass to grow through it. Apart from being nicer to look at, it allows much more natural drainage to occur. I don't think I've ever seen it here.

    Regardless of how severe am event is, the effects of that would be reduced if proper measures are implemented.

    I would be very interested in seeing some models of these types of scenarios. It's a shame that none have probably ever been carried out.

    I've seen similar to the concrete lattice you mention but made of some form of hard plastic. Probably more effective than the concrete as the surface area of the lattice is reduced in the plastic version. That said it seemed pretty effective as it was used in a heavily utilised carpark and none showed any sign of deformation.


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