2013 marks the 75th anniversary of the work of WTSWW in the west of its patch. This month is the last of our celebratory features from the magazine archive, re-visiting a chatty piece about work on Cors Goch nature reserve in Carmarthenshire.
West Wales Trust for Nature Conservation Bulletin No. 45 December 1987
A Dam Good Show
Cors Goch- the East Carmarthenshire MSC team “On the Bog”
He was gazing- admiringly, as we all were- at our newly completed dam. This was the first time we had been in a position to take a proper look at it, in all its glory. We had finished it on a Friday afternoon; and then for a week we had been at work in one of our other reserves.
It had rained heavily in the meantime, and now the dam was doing its thing in the most gratifying way. The water on the upstream side of it was twelve inches higher than it had been- we dipped with a stick- and a placid pool spread wide where before there had been nothing but a weed-choked ditch that you could jump across.
The site of our great engineering scheme was the Trust’s reserve at Cors Goch, which lies south of the A40 near Carmarthen, and west of the county showground. Cors Goch is a raised bog which has been designated as a SSSI; and it took years of fighting by dedicated naturalists, including one of the Honorary Wardens, Mrs Margaret Dunn, to save it from being buried under a mountain of rubbish. The local council wanted to use it as a municipal dump, but now that it has attained SSSI status, that risk is over. In any case, the Trust bought part of the bog a few years ago, and is negotiating for the rest of it; so attention can now be switched from its mere survival to a management plan which will conserve its most interesting features.
A raised bog is, in effect, a lens-shaped covering of peat which forms over a geological saucer of impermeable material. The rim of the saucer prevents the rainfall running off, so it accumulates; and in the strongly acid conditions of this area, vegetation growing over the top of this water rots only partially so it accumulates too. In the course of time, a skin of peat strong enough to walk on develops, although you can feel the quaking water underneath. Here and there ‘slop-holes’, irregular depressions covered with bright green sphagnum moss, show places where the peat has not joined up. Interesting plants such as sundew, white beaked sedge and the yellow water lily grow in the slop-holes; much of the rest of the bog is pink with heather.
Unfortunately the bog at Cors Goch is not now entirely as nature left it. Attempts were made to drain it- probably in the nineteenth century- and although the eastern end is still as we like it, the drainers have achieved a partial success in the west. This success is what we are now trying to reverse.
In any bog there is a risk of change. Over the centuries plants grow and die, leaving their detritus behind them; and as this accumulates, the land slowly rises above the water surface. Water-loving trees like willow, birch and alder colonise it, and what was once a swamp becomes a sort of intermediate terrain known as carr. With the trees drawing up large amounts of water and shedding great numbers of leaves every year, the process is accelerated, and eventually the carr turns into ordinary deciduous woodland- all very well in its way, but supporting a much less exciting population than the bog that it all started from.
The westernmost edge of our bog has virtually become birch carr. Thickets of small birches, up to about 20 feet tall, are encroaching, and their outliers, springing up here and there, show what would have happened had help not been at hand. A fringe of alders along the south-western edge of the reserve has grown to fifty feet or so; and several acres are covered in a really dense four-foot scrub of sweet gale, which look curiously like pictures I have seen of tea plantations!
But the most disagreeable invader of the Cors Goch bog is Molinia. This tussock-forming grass, with tough, sharp-edged leaves that will cut you as soon as look at you, has taken over a considerable area in the Trust’s original piece of bog; and where it is successful, the more delicate and interesting bog plants are choked out. Shoulder-high, the Molinia covers the ground so thickly that it becomes a weary business to push your way through it , and you skip, slide, stumble and swear as you alternately trip on its tussocks and disappear into the little drainage ditches that its rampant growth conceals. The Molinia is definitely public enemy number one, but there is no easy way to dislodge it. Cut it laboriously down and it springs up again, refreshed; poisoning and burning are not methods that a conservation trust lightly turns to. One obvious thing remains- to alter its environment. It seems to like the drier, western end of our bog; so what we are trying to do is to raise the water table, and drown it out.
Hence the dam. As well as a series of relatively shallow ditches in its main area, the bog has a large ditch which runs some way inside its southern boundary and joins an even larger one which forms the western edge. Damming the western ditch would raise the water table not only in our land, but in the neighbouring farmer’s field as well, which would not be acceptable. The dam we have built in the southern ditch affects nobody but ourselves.
Access was the first problem. Armed with strimmers, slashers, mattocks- even chainsaws- the team hacked a way through to the ditch and surveyed the banks for the best site. The track had to be a good one, for there was no way we could get our Land Rover anywhere near the proposed dam, everything had to be carried in by hand, and some of the component parts were very heavy indeed.
I particularly admired the way the team handled the main beam into position, this was an alder trunk some twenty two feet long and fifteen inches across the butt- and, being fresh-felled and full of sap, it must have weighed a ton. A long rope was laid out on the ground beside it in a zig-zag pattern, and the log was rolled onto it. Then eight people, four each side, grasped the sticking-out loops, lifted, and tottered forward. With much panting and blowing it was manoeuvred into position above the smaller log which had been dropped into two deep slots cut into the bank. Four-foot stakes six inches thick were driven into the ground to hold it in position- and we had our framework.
The actual dam itself is made of sleepers. It was sunny the day they were driven in, and I have some splendid photographs of Paul balancing on the cross-beam, thumping them into the mud with a mell. The Van Goch-like look of the dam, rising towards the sluice at the middle, decided itself at this stage, because for some reason the outer sleepers on both sides went down further before they came to a firm footing. But Brian, our supervisor, who was responsible for the whole design, was not slow to take advantage of this serendipity; and the pleasing symmetry of the finished creation is much to his credit.
A lighter log on the upstream side of the sleepers makes part of the housing for the sluice gate, and also provides the anchorage for that edge of the bridge. This, like everything except the dam itself, is made from alder thinnings, and is floored in the handsome and practical style that out team always uses. Split lengths of wood are arranged alternately round side up and flat side up; butted tightly together, they overlap considerably to support each other; and the alternating surfaces give a good grip to the foot to avoid slipperiness. The raw alder wood soon oxidised to a brilliant orange which looks lovely alongside the lovat-green lichened bark.
Taking it in turn to wear The Waders, people slithered gingerly into the upstream pool and shovelled out the debris. Black stinking mud came first, to be followed by dark, fibrous peat as we extended the area of open water to a pleasing curved shape. Jeff spent an uncomfortable couple of hours crouching under the bridge caulking the cracks between the sleepers with peat- and luckily it was only after he finished that we saw a four-inch-long leech squirming slowly across the surface of the water! Cors Goch is well known for its dragonfly and damselfly populations, and we saw a number of species, including one pair in the tandem mating posture which seemed to set the seal of approval on our new pool by laying eggs in it.
We have not yet finished our work on the Cors Goch reserve. A track, waymarked with the silhouette of a dragonfly, is being cut, the advance guard of the birch scrub is being extinguished and a tremendous fencing job down the whole south edge remains in prospect. But what we have done so far can already be seen to be raising the water table to some extent; and we are hoping that with a return to wetter conditions, the invasive Molinia will be discouraged, and the bog’s specialities, like the white beaked sedge and the lovely crimson marsh cinquefoil will be given a new lease of life.
Elizabeth Cragoe, Field Officer