More development implementing Sustainable Urban Drainage would also assist (although the beavers would do a better job) and given that's a requirement for all new developments (including limiting water discharge to greenfield rates even when it's raining with a 1:100 year storms plus 40% of extra storage for climate change).
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Dawlish avoiding route?
- Thread starter Ashley Hill
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More development implementing Sustainable Urban Drainage would also assist (although the beavers would do a better job) and given that's a requirement for all new developments (including limiting water discharge to greenfield rates even when it's raining with a 1:100 year storms plus 40% of extra storage for climate change).
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Indeed. Upper flood plain management is an important action in all of this. Just having more trees will make it take longer for water to get to the river, which is what is needed.
How so ?
More extreme climactic events will mean more blockages, which will mean more occasions when you need to divert.
I responded to this comment:
Flooding is not the problem at Dawlish, but is the fundamental risk at Cowley Bridge. Logically, if you have a problem of flooding at the place that you are making fundamental to your contingency plan, there is a contradiction.
I agree with you that slowing the upland flow of water into the Exe and Creedy will be helpful. So have been the engineering projects near Cowley bridge. But, taking your view of increasing convection storms as given, they deal with the current problem - not the one that will come.
And, regardless of what you do with Dawlish, that risk remains and blocks travel west of Exeter.
But flash flooding can occur at all sorts of places, potentially West of Newton Abbot as well (even without the separate coastal issues that may affect Dawlish).
Cowley Bridge may be a bit of a hot spot for flooding, but that doesn't mean its the only place it can happen.
As I've said previously, the best option for resilience is not to be overly reliant on one route.
I don't know the Creedy, but the upper reaches of the Exe flow through bare moorland where there are essentially no trees beyond the very occasional stunted dwarf and are never going to be any. There is no "upper flood plain" - it's not like the rivers which accompany certain well-known stretches of railway in Scotland. Same goes for the Barle which is the major "upper reaches" tributary. The runoff into these rivers is moderated by the capacity of the moorland peat to absorb water, and what happens in the case of sudden peaks depends on how much rain there has been in general over the past month or two and how much of that capacity is already full. You don't get trees until you're beyond what could be described as the "upper reaches".
As for the beavers with any luck someone's dogs will find themselves a bit of entertainment.
The Cowley Bridge area has been prone to flooding ever since the railways were built, despite various measures being taken over the years on the basis of trying to get away with doing as little as possible. Surely the answer here is simply to do it properly for a change; raise it a bit more than the bare minimum and replace the embankments with low-altitude viaductlets (ie. like Langport).
It's also likely to be fairly short lived (at least compared to a sea wall breach) and so if there's (say) 24 hours of no trains it's not as significant as other failure points.
For that sort of disruption, buses are easy enough to arrange.
Whist we should be trying to limit significant single points of failure, without bypassing Exeter this point is likely to continue to be an issue.
Also, it's already an issue for the railways, it's not like we're adding something new which is a bit of an unknown. Therefore, whilst not ideal, could come across as someone thinking "I don't want X to happen, so will put forwards something which is a smallish issue in the grand scheme of things when generally the solution isn't terrible but we can make it sound worse than it actually is".
I'm not saying anyone is doing that here, just that sometimes it's something which can happen (for example this who cry about how much extra energy HS2 trains would use, when the extra cost on a discounted return ticket isn't even 5%).
I agree - but the argument you're making is that the resiliency should be delivered by focusing further on a single point of failure, which is generally causes a similar level of disruption to the sea wall closures
Even with moorland there's plenty which can be done to encourage water storage. Especially given that whilst climate change is altering rainfall, it's not necessarily resulting in the annual total being much different (for example longer periods of dry weather in the summer being offset by more intense rainfall when we do have summer rains).
Even planning for the winter (assuming it's wetter) there's the potential of creating basins which dry out during the summer and only have standing water in more extreme periods of wet weather, with the rest of the winter they are a bit boggy.
This is all stuff which nature had been doing (including beavers, there was a town somewhere, I think Canada, which was going to do some fancy engineering only the beavers got their first and saved the council a shed load of money and basically did what the engineers said should have been done) for a very long time.
Yes there's other factors, like where we build our stuff, and sometimes we don't help ourselves (even when we're trying to fix it), however if this bridge were to become a significant single point of failure over the 20 year timeline I've mentioned, that should be a small enough project (a few tens of millions maybe) that it's not a significant cost when looking at other options.
Finally, of the 3 options (Sea wall only, DAL, via Okehampton) none of them propose a solution for this bridge and so would need to be fixed anyway.
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