Towns downstream flood because water runs off the land upstream, rather than draining naturally into aquifers. Because of the lack of water in aquifers, water use must be restricted when there is low rainfall, even low rainfall within normal ranges. The problem is compaction of soil upstream, which could be ameliorated by restoring trees: rain passes down their roots into the soil below. When rivers are dredged, removing their habitat for wildlife, water flows more quickly: all the rain reaches the town at once, overwhelming the expensive flood barriers built on the riverbanks downstream. And that fast flowing water moves silt: dredging causes the need for more dredging. The answer is to allow rivers to meander and braid, holding the water back, filtering it and releasing it slowly.
I get all this from George Monbiot, in two Guardian articles, one more political, one in depth. Do read that second article, it explains the issues beautifully. The farmers of Pontbren, where the Severn rises, planted trees, to provide shelter and bedding for their hill-pastured sheep. One of the research papers estimates that – even though only 5% of the Pontbren land has been reforested – if all the farmers in the catchment did the same thing, flooding peaks downstream would be reduced by about 29%. Full reforestation would reduce the peaks by about 50%. For the residents of Shrewsbury, Gloucester and the other towns ravaged by endless Severn floods, that means – more or less – problem solved.
Monbiot explains that the Common Agricultural Policy is to blame: the Single Farm Payment, which pays the same for poor hillside pasture as for lowland pasture, will not be paid where there is “unwanted vegetation”. Farmers are paid to remove the trees which would prevent the flooding.
Monbiot quotes some of the ripostes. Rory Stewart, Conservative MP and now an Environment minister, attacked the National Trust because it “allows water to ruin the lowland pastures of small tenant farms, apparently on the advice of the Environment Agency”. Monbiot links Stewart’s article on the Green Alliance Blog. Small farms matter as a link to our traditional culture says Stewart, decrying rationalist “Whiggery” concerned with profit not people. Stewart supports the tradition of the legacy of more than a thousand years of small cultivation and also blames the CAP, which he says drives out small farmers. Land becomes either an industrial factory for the production of the maximum food at the cheapest price, or a national park almost devoid of human cultivation. His answer is to demand something impossible: that national parks should clarify not in the abstract but, specifically, valley by valley, what landscape they are seeking to create.
I am not rationalist. I am seduced by Stewart’s Yeats quote against whiggery: that levelling, rancorous, rational sort of mind that never looked out of the eye of saint or out of a drunkard’s eye. Yet I favour a collectivist response, balancing the interests of town dwellers downstream against those of farmers, small and large. It would reduce the need for public spending, £3.2bn, £500m more than in the last parliament, on flood defences downstream, which are failing.