charles rangeley-wilson – writing about fishing, travel, rivers, conservation

If it’s here, it ain’t there.

Yesterday I wrote a slightly barbed critique of what I felt were unnecessarily vague and conditional comments on the recent floods by an expert on hydrology, Professor Alan Jenkins. I did allow for the fact that the windy blog post I’d satirised was not quite finished. Clarity might follow, I wrote. And to be fair, it has. Kind of. Here is the elaboration of that seven point summary: What Difference Could Natural Flood-Management Techniques Make?

There’s more detail, but it’s still all so conditional. This problem of clarity seems in part to hang on the problem of evidence. For example, there is little evidence that alternative forms of upland management would have made a difference in recent floods. But the panel very specifically mean published, documented evidence. There is some, they say and that which exists suggests that attenuation of flow is possible at the local scale. But even then, we’re told, you can’t confidently extrapolate the same impact to larger scales of landscape or against larger scales of flooding. Basically, not enough research has been done.

And this was more or less all that could be said about the other potential forms of ‘natural flood-management’ cited in the discussion: debris-dams and trees on uplands. They might well have an impact, but what scale of impact, who could say? Not enough research. More science is needed.

My problem with this position is that the practices of land-management which I would argue exacerbate flooding have not been / are not enacted with anything like the same published, scientific evidence-base that is being required of a ‘natural’ alternative.

Does the farmer or drainage board look for published, scientific evidence before dredging a ditch? The empirical evidence that informs the dredging is simply that if you cut and maintain a deep ditch, the land either side of it drains and dries and holds less water and therefore the land is better for crops. That’s why they do it. Could that observation of drainage on a local scale be safely extrapolated to imply a similar impact on a larger scale? Basically, yes.

But of course, if the enquiry to a given expert was urgent and critical: ‘will these results replicate elsewhere? and will that save us from damnation?’ the expert might well be inclined to caveat their reply with the same caution: it really depends on soil type and bed-rock and time of year and ambient rainfall and pre-saturation levels etc. etc. I can’t say. More science is needed.

The conclusion of this more detailed What Difference Could Natural Flood-Management Techniques Make? is marginally less conditional. These natural schemes will probably have some beneficial impact and are unlikely to make things worse: so what to lose? Enact them where you can.

But sadly, the chances of funding schemes like this or getting all the heads together needed to enable the scale of demonstration that we so clearly need are hardly improved by such luke-warm endorsements.

Do we really have to sit so firmly on the fence?

For a start there is a ton of published, scientific evidence and established knowledge, that demonstrates how rivers work and how there is a given point of discharge for every river and every flow regime, beyond which the river will naturally overflow onto its floodplain. If we dredge rivers and ‘ditches’, lower their beds relative to the floodplain, not only will that damage the channel with unforeseen and unwanted knock-on consequences of erosion and deposition, but it becomes that much harder to get the excess flow on to the floodplain where you want it – the open land upstream of our cities and towns – as opposed to where you don’t – the towns themselves. The floodplain is a massive unused storage space that isn’t already full at the point when it is needed. It is the natural flood-management technique and yet the floodplain wasn’t mentioned in the Centre for Ecology and Hydrology briefing.

London Underground has just offered half-price fares before 7.30 am for exactly the logic we can very confidently apply on a landscape scale against any rainfall event. If you want to mitigate and manage congestion (floods) you have to slow and stagger traffic (water flow). Surely we can know, in that way a farmer knows why he digs a drainage ditch, that a fully realised, catchment-scale enactment of every trick in the flood-management book is likely to have a much better chance of lessening the impact on a downstream town-centre by the simple logic of “if it’s still up here, it’s not down there “?






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