Mapping the mysterious submarine terrain

Another Life:No one can live beside the sea and not wonder at times, with a child's curiosity, how the view to the horizon would look with all the water gone. There are plenty of inshore seabed maps, but few that offer the detail the imagination craves: the sculpture and relief of hidden heights, valleys and plains.

So many are the product of painstaking guesswork, their contours sketched in between Victorian soundings made with lead, line and sextant. Global positioning, multibeam sonar and airborne lasers do a rather more thorough job.

For those who live along the northern slopes of the Dingle Peninsula, for example, it must add a few mental pictures to know that, a few hundred metres out from the tideline and well beyond paddling distance, there's an enormous, wide trench, parallel with the shore and 40km long - the "Brendan Trench", as it's been dubbed. And beyond that, a 10km ridge in the seabed - another glacial moraine to add to the dozens that flowed off the island around 13,000 years ago.

One by one, the significant bays of Ireland are being mapped by the €12 million Infomar project, led by the Geological Survey of Ireland (GSI) and the Marine Institute. It is a follow-up to the deep-water mapping of the National Seabed Survey and continues to use the Institute's high-tech vessels, the big MV Celtic Explorer and her smaller sister, MV Celtic Voyager, but also boats as small as Ribs. And for the really rugged or complicated bays, the measurements are made by Lidar, using pulses of light from laser-fitted aircraft to measure water depth: I shall be watching for the high-winged de Havilland this year, arriving to fill in the last wiggly bits of Killary Harbour.

The Infomar programme is covering 26 "priority" bays and other coastal areas totalling 125,000sq km. The product will be three kinds of maps: the hydrographic, showing in 3-D relief all the sandbars, reefs, canyons and cliffs; the sedimentary, showing the make-up of the seabed; and biological maps of habitats rich in marine flora and fauna. Since the summer of 2006, it has covered many of the valuable fishing and fish-farming bays, such as Bantry, Dunmanus and Waterford, and big biologically sensitive and fish-spawning areas off Dingle and Galway.

This year the mappers will be pinging inshore in - or buzzing over - Dublin Bay, Carlingford Lough, Donegal Bay and Sligo Bay. And in a separate, cross-border contract, the Marine Institute will complete coverage of key inshore waters from Donegal round to Dundalk Bay.

Dramatic discoveries of cold-water coral reefs on the deep slopes of Rockall and Porcupine gave the far-flung explorations of the National Seabed Survey a certain glamour these more domestic exercises may lack.

But inshore Ireland is becoming a busy arena, as aquaculture expands; as wind-farms, marinas and wave-energy machines seek new moorings; and inshore fishing itself is brought into better balance with resources. In judging where things can be done and where they can't, the first thing needed is maps that tell the whole story.

One sector eager to see them will be the aggregates industry, quarriers of sand and gravel for construction. So far in the building boom, the material has all been quarried onshore, often from ice-age eskers and moraines, but previous sonar reconnaissance by the GSI, out to 20m depth of sea, promised several million cubic metres of gravel and perhaps 100 times as much sand.

The greatest volumes are in the Irish Sea and off the southeastern and northwestern coasts, with more in a few western bays, such as Tralee and at the mouth of the Shannon. Some big deposits fill deep "palaeochannels" carved out in the ice age and drowned as sea level rose.

Built into Infomar's handy acronym are the words "sustainable" and "marine resources", and one objective was to map deep drifts of sediment that could be dredged without harming seabed ecosystems, fish spawning beds or flows of sand to the shore.

But the great sand and gravel resources of the southern Irish Sea have become a special case. A study by the Irish Sea Marine Aggregates Initiative (Imagin), led by an Irish/Welsh scientific consortium, has been funded by the EU's regional development programme.

Juggling nature conservation, fishing, navigation and coastal protection, together with costs and benefits, Imagin will deliver this year "a strategic framework and scientific rationale" to guide government licensing of extraction. Within its territory is the chain of huge banks of sand and gravel that lie off Ireland's southeast coast, feeding its beaches with sediment and holding back erosion.

Offshore wind turbines have claimed their first swathe of the Arklow Bank. Whelk fishermen and dredgers-up of seed mussels have been expressing their worries at Imagin's consultative workshops. The aggregates industry hovers expectantly, ready with plans that have been hanging fire for years.