Stretching coasts

June's fretful seas have quite dragged back the soft, fluffy terrace of fresh sand that lapped ashore in the long calms of May: we are back to a firmer footing a few thousand tonnes further down.

The rise and fall of the strand is measured at reefs of rock that stretch out from the base of the dunes, their every crack and crevice wedged with broken shells. There was a time when the very emergence of rock surprised us; now it makes a perennial rampart in our path, a greater or lesser scramble, depending on the season.

Above the rock the dunes are faced with a raw sand-cliff, almost sheer but zig-zagged with the tracks of ascending otters. It retreats in a steady succession of collapses: the one irreparable constant in this whole shifting scene.

The millions now to be spent in resisting coastal erosion are indeed a drop in the ocean, but a dignified retreat from rising sea-levels makes both financial and ecological sense. We can also, perhaps, expect a tougher line on sand-removal, now we know how the sea insists on balancing its books between one piece of shore and another.

I have been staggered to learn recently of the rate of sand-extraction in pre-Famine Ireland, when, as a slow-release form of lime, shell-sand was used along with seaweed to fertilise crops and grass on acid land. In Munster alone, the amount dredged from the sea into boats and dug from strands in coves and bays in "an almost feverish activity" was estimated conservatively in 1844 at one million tons a year.

The "red" sand to the east of Galley Head and at Clonakilty, coloured by its dense shell-content, was specially sought after and attracted horses and carts, hundreds at a time, at low tide. They hauled the sand far inland, where the most distant farmers scattered it thinly by hand from bowls, like precious seed.

What such intensive extraction did to the shoreline can only be guessed at, but it does qualify my surprise to find that Cork has the greatest length of mud along its coast of any county in Ireland: 236.3 km in all.

The precision is new - part of a digital overhaul of our coastline data that labels every kilometre of the high-tide mark with its dominant kind of sea-bed. It is the work of Brigitte Neilson at Trinity's Environmental Sciences Unit and Mark Costello of EcoServe, the marine ecological consultancy, and provides an island-wide geographical information system for managing the coast, especially for nature conservation.

Grist to their computers were the Ordnance Survey's half-inch maps and the 50odd British Admiralty Charts, drawn at many different scales but rich in description of the shore of mainland and islands. By the time all the wiggly bits had been straightened out digitally, like measuring something with a piece of string, Ireland had gained an extra 1,024 km of coast.

The new figures are a total Irish coastline of 7,524 km, including 1,653 km of islands. Clare has the greatest length of marsh (think of the Shannon), Donegal of gravel, Galway of rock, Kerry of cliff and Mayo the greatest length of sandy shores - 593.6 km, no less.

The study was part of the EU-backed BioMar project which has produced such a wealth of detailed information on the habitats of the sea-bed and their animal and plant communities. This is now being used to select the areas of prime conservation importance, protected by SAC orders or even to become marine national parks.

If putting our coastline under the microscope like this will help care for its marvellous diversity, one can only be pleased. But I expect Tim Robinson, my favourite metaphysical cartographer of Aran, Burren and Connemara, will be wryly amused by the latest digital presumptions.

No one could know better than he how the Irish coastline lends itself to the infinite regressions (or extensions) of fractal geometry: how the wiggly line describing a sea inlet on a map can rhyme with the wiggly line that is just one of the inlet's coves and the perhaps even wigglier line of just one gap between the rocks.

It was this mocking continuum of scale that led him into mapping - on foot - the coast of south Connemara, one of the most convoluted shorelines of the world. Between Roundstone and Ros a' Mhil, villages about 30km apart, he found at least 400km of coastline: more, perhaps, if he had looked

under every tuft of seaweed. The new coastline of Ireland purports to follow the line of Mean High Water, but not, one suspects, on a track that dances around every wave.

The new attention to our shores can have its downside. Clean water and tidelines, yes, but I felt more than a ripple of unease about decisions to take Blue Flags away from some of our beaches because they hadn't enough signs to give "environmental information" or some such rubbish. Surely, what makes our strands special is the raw, unmediated rapture they offer; every unnecessary word in the landscape becomes a redundant human slogan.

Meanwhile, more maps, and a lot of information one would actually be very pleased to have. The Mournes, by Paddy Dillon, (O'Brien, £5.99) describes 32 walks in or around a range of granite mountains that invite some heroic peak-to-peak marathons but also reward a simple day out. The Mourne Wall Walk once grew so popular that it attracted some 4,000 people on a single day - a mass event never repeated. Dillon gives it here, with due caution about fitness, but his routes are generally more humane and exploratory.

Tipperary, the official touring guide by locals Donal and Nancy Murphy takes a splendidly thorough approach, with something engaging to say about almost everything along the road. Folkfarms, forest walks, heritage trails in three languages, the finest collection of decorated gravestones in North Tipperary - there really is an awful lot going on.

The BioMar-Viewer compact disc includes a map-linked database of habitats and marine species, with photographs and descriptions, and is available for £12, inc p&p, from EcoServe, 17 Rathfarnham Road, Terenure, Dublin 6W. It needs ideally 32 Mb RAM, Windows 95 and Internet Explorer 4.0 or later.