Indigo Dreaming

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Archive for February 28th, 2009

Environment Agency & River Conditions

Posted by indigodream on 28 February, 2009

Last year we found it hard to work out what the Thames was doing. Yes, there is a number that you can ring but it is all a bit of a process. Not this year. The EA have sharpened their act up and look there is a web site here which gives you river conditions. Wonderful. Closures incidentally are here. Web site design is a bit convoluted – you need to do a lot of clicks to get to the right place but worth having a go.

So that should make planning easier. Well, actually we have not really started yet other than knowing that we leave at the end of March and want to be in Birmingham at the end of May. We need to work in between weekends, we may also try to fit in the Falkirk wheel and some rugby in May so it is all a bit tight. Thereafter we will probably head north but who knows? And do we bring the boat back near London or over winter up north and get some work done on the boat? Decisions, decisions …

The EA seem to have generally sharpened their act up. I am working on a project not far from the tidal Thames where it would be terribly useful if the ground floor never ever flooded. Well never ever is not achievable but lets see how close we can get. First issue was the ground level locally was about +4.2m as reckoned by the Ordnance Survey. Now Sue on her perambulations into London has been scrutinising high tide levels in Lambeth and has been reporting just how high the river is (yes I know you thought she might go into London to do some work but actually she just subsidises Starbucks). Tide tables are available here but they use their own set of levels to chart datum, not those used by the Ordnance Survey. You can get a translation to ordnance survey levels here. Work that through and you get a high tide level of +4.3m AOD Wednesday before last. Not much good on the never ever scale as that is higher than street level locally – so that is why the Thames has high walls!

In the past getting flood information out of the EA was oh so difficult. Not now, it is fantastic. You have to pay but within days you get an answer telling you heights of local flood defences and expected flood levels for various probabilities up to 1:1000 years and for dates of now, 2055 and 2107. Many thanks to the customer services team in Hatfield.

For the anoraks among you: 0.00 m used to be 100′ below a bolt on St Johns Church in Liverpool. Then it changed, I am not sure why perhaps the bolt rusted? Anyway between 1915 and 1922 they measured mean sea level at Newlyn and they used that as 0.00m or feet on all Ordnance Survey maps. But obviously sea levels have changed since 1921 so what is our datum nowadays? I tried looking it up but gave up when I started reading about differences between orthometric heights and ellipsoid heights. Hmm I always thought that water in canals does not look flat.

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