Monday, 10 February 2014

Mr Pickles kicks the Environment Agency

 9 February 2014

The more I hear Ministers talking about how they should have ignored Environment Agency advice, the more I get irate. I thought that it would be worth talking a look at what is available on the extent of flooding and where the pinch points are along both the Tone and the Parrett. Interestingly, the Tone goes straight through the most flooded areas on the only map I could find, and joins the Parrett at Stanmore Bridge. So, dredging the Tone means that at low tide rather more water will enter the Parrett, which for many kilometres downstream is effectively a tidal canal. Dredging the Parrett upstream of the confluence will only lead to faster egress of water onto the flatlands of the Levels; all of which are upstream of Bridgwater. A sizeable part of each of these sections below Ham Bridge (ST285251) on the Tone, and Oath Lock (ST383278) on the Parrett is tidal. Thus in both cases even if dredged, there will be limited extra capacity at high tide and especially on spring tides. Thus, in as extreme a situation as this one, the likelihood is that flooding would still have occurred.

Now, moving on a step. The Parrett remains narrow and tidal as far downstream as Bridgwater where there are several apparent pinch points (according to maps). These pinchpoints are bridges and tightly constrained urbanised sections of river, so it is highly likely that over a single tidal cycle coincident with a major fluvial event such as this one, it might be expected that there would either be structural damage to bridges or, as likely as not, over-topping of defences and flooding of Bridgwater. Looking at Black & Veatch's assessment of tidal flood defences it appears as though Bridgwater is protected against a 1:200 return period tidal event (not once every 200 years). The defences appear to be primarily designed to deal with a tidal event rather than a fluvial event in which the upstream defences have been designed to ensure that the levels remain unflooded.

So, all this talk that dredging would have saved the day is as likely as not completely unsubstantiated and the advice the EA gave to Ministers is correct. In this sort of situation, with or without dredging, flooding would have ensued.

This leaves me hugely uneasy because it is highly likely that severe events of the sort we have just seen are pretty likely to return in a not too distant time-frame. If so, it seems to me that there is a pretty strong risk that dredging the Tone and Parrett may actually mean that in modest events farmland may not flood, but that in a major event Bridgwater would be inundated and then farmland would follow as water is held back by key urban pinchpoints.

It will be interesting to watch the coming years - one must hope for the sake of the residents of Bridgwater that there are no further major events! Clearly the big question then arises as to whether there is a case for a tidal surge barrier similar to that used at Barking or at Hull. That would certainly provide some relief against tidal impacts, but I wonder how it would perform in the face of the sort of fluvial events we have witnessed? I therefore cannot see how any strategic solution can proceed without some use of realignment or spillways to make use of parts of the Levels as containment space for major fluvial events. If such measures are not used, it is pretty inevitable that extra money will have to be used to raise banks considerably higher than they are today in order to accommodate extreme events of the sort we have recently seen.

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