Holding back the tide

Two weeks of high pressure were enough to flatten the surf into a murmur and usher some sand ashore again, soft as a fresh fall of snow on the hard slope of the strand. This is how the beach restores itself in the summer's long calms, reclaiming the sediment stripped away in winter and stored on that shadowy, underwater slope beyond the third wave.

The rhythm of the beach's erosion and repair is as much a part of the seasons as the growth and withering of plants. There are longer cycles, too, of exceptional storms, enduring calms, ruled by some mysterious sub-clause of chaos. The level of the strand falls and rises, exposing great whalebacks of bedrock and covering them again.

This apparently effortless production of sand, in vast quantities, has reassured the centuries of farmers who have carted it away for cattle bedding, or to dress the land. When carting was what they did - a slow, hard job with shovels and horses - the sheer effort involved kept the operation small. But for decades now, powerful tractors have come straining up the hill, their trailers heaped by mechanical shovel: sometimes, a dozen trips a day.

Three hundred loads a year, say, for 30 years, is 45,000 cubic metres. And still, the hole scooped in the strand is filled and filled again. Where does it all come from?

The answer is that the beach and the dunes behind it, the slope of underwater sand that lights up the waves in summer, add up to what scientists call a "cell" of coastal sediment, a self-contained system hemmed in by the rocky cliffs at each end. Part of the cell is more or less fixed in place but a lot of it is mobile, constantly moved around by wind and water. Even the mountain river, rushing out through the strand, helps the circulation of sand. All this movement seems to have a purpose - one of those weird, interlocking mechanisms which have got Gaia, Mother Earth, talked about as if she were a living organism. The purpose of a sandy beach is to absorb and dissipate the energy of waves, pounding the shore for much of the year like a line of runaway trucks. The beach is a natural line of defence that will keep on repairing itself - or trying to - right to the last grain of sand.

But very often it is working with a fixed amount of sand, a total "budget". And where, over decades, too much mobile sand is hauled off in tractors, the system has to cash in some assets. As the level of the beach falls and steepens, the winter waves seethe up to grab a few hundred tons of dunes, a few more metres off the bottom of sandy fields (also, in our case, the big burial mound, once a landmark in the strand).

In a coastal "cell" as big, wild and robust as Thallabawn, the net effect of the departing trailerloads can be absorbed, perhaps indefinitely, within the wider picture of natural erosion. There are no roads to undermine, no sea walls to fall; the first house is still a good way up the boreen.

Elsewhere around Ireland, the carting away of sand and shingle has had dramatic and regretted results. But it is still just one of a host of separate causes of erosion - more than 300, at current estimate - sent to plague the engineers of coastal county councils. Many of the causes are natural and part of dynamic cycles of change. Others are the work of particular storms.

Still more are man-made, often by engineers themselves. Piers, harbours and breakwaters have all interfered with the natural drift of sediment along the shore. This is specially true on the east coast, where harbour walls sticking out into the sea have had unlookedfor effects. At Rosslare Harbour, Co Wexford, for example, the building of a solid sea wall in the 1970s pushed the flow of sand offshore so that Rosslare Strand became denuded and erosion cut back into the coast. In a "beach nourishment" operation a few years ago, more than 275,000 cubic metres of sand was dredged from a site six kilometres offshore and pumped back on to the beach between rock groynes.

The Rosslare story is one of the case-studies in a fascinating document that really ought to be a widely-used book - in some respects, a coastal counterpart of the much-praised Atlas Of The Rural Irish Landscape. Instead, the code of practice for ECOPRO (Environmentally Friendly Coastal Protection) comes as a glossy, technical ring-binder, produced by Forbairt and costing £30 from Government Publications. In this form, undoubtedly, it sits well on the engineer's office shelf - a resource to help diagnose the causes of coastal erosion and what, if anything, could done about it. Here are all the "soft engineering" techniques of coastal repair and conservation, including some new to me. Marram planting, yes, and sand-trap fencing, rock-filled gabions and brushwood barriers, but artificial seaweed? Beds of kelp-sized plastic fronds can be anchored offshore to trap passing sand - unless, as happened off Cahore in Wexford, an easterly storm arrives to sweep them away.

Engineers have rarely been short of solutions. But even the best manual for King Canute needs a proper understanding of the problem. This one does an outstanding teaching job on the nature of Irish coasts and the forces that are shaping them: the workings of storms, waves and currents, the history and ecology of beaches and dunes, all made understandable and relevant. Understanding why things are happening is all the more important just now, as coastal erosion threatens to accelerate, and tourism and building development add to the pressures on the shoreline. Decisions that work against nature will end up costing money to no purpose. Sometimes, a managed retreat or even doing nothing will make the most sense.

Forbairt's code of practice has had inputs from universities and consultants, north and south, and its knowledge belongs to a wider audience. Coastal community groups, geography teachers and environmentalists should all make use of it.