immediately it became clear that the river was kicking back at the abuse it was receiving. In the winter of 1979–80 the Trannon careered off on a course of its own. Fencing, which had been set well back from the bank, now dangled over the gulf created by the all-swallowing river. As more and more stone-filled gabions were built in to reduce the erosion which the scheme had set in train, it became apparent that Pandora’s box had been opened, and that what might have worked as a piece of traditional river canalization in the cohesive sediments found downstream had proved a recipe for disaster when applied in the unstable gravels of this upland brook. At one point, the original river bank, shored up by wire and stone, remained the only still point, actually down the centre of the fast-moving Trannon, so that it was a job to guess whether the buckling gabions had belonged originally to the left or to the right. Seven years later, remedial works were still being carried out; the raised flood-banks set far too close to the watercourse were being eroded away; the stability of the downstream bridge was threatened; and the real cost to the public purse of what was a relatively small scheme originally has yet to be clearly counted. In 1982 the Institute of Hydrology carried out trials on the Trannon, and in 1986 was able to come up with a number of constructive lessons to be learned from this sorry story. Relatively cheap methods of testing local ground conditions which have been researched by geomorphologists can act as useful warnings to engineers as to whether they are risking the kind of problems which now make the Trannon scheme, with hindsight, a questionable one to have undertaken in the first place.6
Working with nature is clearly practical, as well as ecologically sound. In 1985 dredgers were busily raking up gravel from the shoals in the river to put into more gabions for bank reinforcement beside the Trannon. As part of the normal processes of a river, the stones in these shoals are neatly sorted and graded by the flowing water into an overlapping fish-scale pattern known as ‘armouring’, which makes them relatively stable. By dredging up gravel, therefore, river managers were actually de-stabilizing the river bed, thereby contributing to the erosion which they were supposedly trying to prevent. Riverside trees, whose roots increase the tensional strength of the bank material, are the best protection against erosion, especially if they are well established and are properly maintained. They also reduce land loss, since it is estimated that channels with 50 per cent tree and shrub cover on both banks require only approximately half the width for a given volume of bankfull flood-water speeding through the channel, compared to treeless brooks which erode out into the adjacent fields.7 If trees are felled in the hope of gaining extra land, a river is likely to move out to take that land, and on certain types of river a great deal more besides. One has only to stand on the bridge over the Trannon at Trefeglwys and look upstream to see the stable narrow river coursing elegantly between its magnificent borders of ash and sycamore, and compare this with the immediate downstream reach, which wanders amidst a waste of gravel.fn4
An engineered river moves out of control. After the trees had been removed, the stone and wire were set to reinforce the bank. The stream then split, turning the old bank into an island. River Trannon, Powys. © Malcolm Newson
NITRATES
Additional benefits of tree-lined streams, in reducing the effects of nitrates and phosphates in the water and in shading out the choking growth of summer weed in a river bed, which may otherwise necessitate further expensive dredging, have been recognized by Dutch and German scientists for over a decade.8 The only green thing about many of our English rivers nowadays is profuse algal growth in the water, which results from an excess of fertilizer leaching off arable fields straight into the stream. Traditional drainage has accelerated this problem in two ways: by promoting farming methods which require high levels of fertilizer, and by stripping out the buffer of vegetation between the riverside and the fields. It is not uncommon for tractors to slide into a stream as they attempt to cultivate every last scrap of land beside a watercourse. This approach has led to overexploitation of stream systems. Until 1986, the steeply graded banks of one river in arable country were regularly sprayed with the approved chemical 2-4-D amine, in order to reduce the nettles, which were less good at holding the banks than slow-growing grasses, but for which perfect conditions had been established by abundant nitrogen leaching off the fields. As is so often the case in operations which go wrong, over-heavy management went hand in hand with a haphazard lack of supervision. The spraying boat, affectionately known as the ‘Black Pig’, would set off on its regular journey up the river without any adjustment on the spraying nozzle. Consequently, once the motor was started, the spray was meted out indiscriminately to riverside walls, fishermen, lovers on the bank, and nettles alike.
It is estimated that for every pound farmers spend on fertilizer on their fields, they can expect the rain to wash away a good fifty pence-worth. But the real cost of such waste is not only monetary. Water is extracted for drinking purposes from many of our lowland rivers, and high nitrate levels in drinking water can lead to illness in bottle-fed babies. Thus, while land-drainage departments promote agricultural intensification, other departments in the same water authority have to spend more public money in expensive plant to treat the water, in order to comply with EEC regulations on nitrate levels. Further expense to the water authority in cleaning up river pollution caused by silage effluent is yet another consequence of high-gear monocultural farming, encouraged by land drainage.fn5
Peat shrinkage. The Holme Post, Cambridgeshire, showing levels of shrinkage between 1848 and 1932. © Cambridgeshire Libraries
PEAT SHRINKAGE FROM DRAINAGE
So much for the rivers themselves. Enthusiastic attempts to drain wetlands throughout the 1970s and early 1980s have in many cases failed to produce the high-quality farmland which was the object of these expensive exercises. It has now become increasingly clear that one of the real harvests of wetland drainage can be the physical ruin of the land. The most familiar example of such degradation is peat wastage. Peat wastes as a result of shrinkage, oxidation, and bacterial action, all triggered by the drying effect of drainage upon peat. A ten-year trial by the Ministry of Agriculture, started in 1980 on the Norfolk peat marshes near Acle, is indicating a fall in ground level of an inch each year. The level of the peat fenland in Cambridgeshire has fallen by up to 15 feet in many places since Vermuyden’s initial scheme was completed in the 1650s. The Holme Post, recording a drop of nearly 13 feet since 1850, presents an unrealistically optimistic picture of the problem, since it now stands in a damp nature reserve.
More convincing estimates of wastage can be made by assessing the height at which roads and even some wartime pillboxes stand proudly above the adjacent level of the fens. As the peat wastes, drainage of the land deteriorates, and so the drains are deepened, thus triggering further wastage. The lowest deposits of peat are also the most acid and so least valuable to the farmer. The Fens now resemble a gigantic and very profitable grow-bag. Like a grow-bag, however, they cannot go on producing their rich harvests of vegetable crops such as celery and carrots for ever, since once the peat has all wasted away, poor acid subsoils, especially clays, are often all that remain beneath. It is estimated that by the first decade of next century, only 20 per cent of the peat soils now present on the 138,600 acres marked by the soil map of the Ely district will remain.fn6 Once the peat has gone in such places, some land may be insufficiently fertile even for growing potatoes, and the very best land in the country will have been reduced to mineral soils of only average quality. Such downgraded land will still have to be pumped and embanked, since it will have dropped even futher below sea level,10 a situation worsened both by the fact that, due to the tilt of the land, eastern England is steadily falling in relation to the level of the North Sea, and by a possible rise in sea level due to the greenhouse effect.fn7
EROSION
Land
