Sands of time start to run out: what our building frenzy is doing to seas and lakes

Michael Viney: We are extracting aggregates faster than the planet can replace them

Mweelrea: the first autumn flood in the mountain river snatches at sand on its curve to the waves, mixing old grains with freshly worn ones. Illustration: Michael Viney

Mweelrea: the first autumn flood in the mountain river snatches at sand on its curve to the waves, mixing old grains with freshly worn ones. Illustration: Michael Viney

 

The first spring tide of September wipes off the last footprints of summer to leave its own rippled imprint on the strand. And the first autumn flood in the mountain river snatches at sand on its curve to the waves, mixing old grains with new ones worn freshly from Mweelrea.

Connacht’s highest summit is a stump of unimaginably old mountains. Its sandstone was pressed into rock beneath ancient tropical seas, then folded up to be worn down all over again. Most, indeed, of all the sand on the shores of the world and in the seas has been ground down from mountains.

So you could think, about sand, that there’s always plenty more.

In “the sands of time”, however, the millions of years are what count. In our effort to concrete over the world, we are now mining sand and gravel much faster than the natural erosion of the planet can replace them.

China’s largest source of sand is its biggest freshwater lake, Poyang, from which it has been extracting some 236 million cubic metres a year

A conservative estimate of the world consumption of aggregates, in a report from the United Nations, is more than 40 billion tonnes a year – twice the amount of sediment carried by all the rivers of the world. Each tonne of cement takes about six or seven times more tonnes of sand and gravel to produce, and the report even calculates the size of the wall just one year’s production would build around the equator: 27m high by 27m wide.

China, which has one big wall already, is singled out for its current, enormous consumption of sand for new dams, concrete roads and cities. There’s always the Gobi Desert, one might suppose, but the wind-blown grains of desert sand are too rounded to lock together.

China’s largest source of sand is its biggest freshwater lake, Poyang, from which it has been extracting some 236 million cubic metres a year. Poyang is also a wetland of international conservation importance, and although it is naturally prone to winter droughts, sand mining has now helped to shrink it catastrophically.

Nothing like that has happened yet to Lough Neagh, the largest freshwater lake in Ireland. But this year should see the end of long-standing commercial dredging of up to 2 million tonnes of sand a year. The lake is EU-protected for its rich winter birdlife, and Friends of the Earth has now secured a legal judgment that challenges extraction.

When lakes, rivers and land quarries have reached their limits, sand from seashores can be tempting. It is not a good choice for building, as the chloride rusts steel reinforcement, but it can be washed and blended with other sand.

In Morocco, a whole shore was scooped to the rock by illegal sand miners to build hotels for tourists – with swimming pools, of course, as the beach had disappeared

In Morocco, a whole shore was scooped to the rock by illegal sand miners to build hotels for tourists (with swimming pools, of course, as the beach had disappeared).

In Ireland, sandy beaches are generally well protected, no longer even losing farm-trailer loads for liming land or bedding cattle. Quarrying sand and gravel for the building boom of the Tiger years chewed hard instead into the huge humps of sediment – drumlins and eskers – left by the glaciers of the Ice Age.

By 2005, the Irish demand for aggregates to make concrete had reached some 130 million tonnes a year. That’s 30 tonnes per person, or four times the per-capita average in Europe. Although land-based sources, including crushed rock, would meet the industry’s short-term needs, the option of mining sandbanks in the Irish Sea was reckoned worth national inquiry.

In a joint project by Irish and Welsh authorities, the Irish Sea Marine Aggregates Initiative (Imagin), a team of scientists from University College Cork’s coastal and marine centre were among the researchers. The work had support from aggregate companies and the use of survey vessels from the Marine Institute (Marine Environment & Health series, no 32 and no 36, 2008).

Imagin was concerned both with resources of sand for dredging and its impact on seabed ecosystems, notably the spawning and nursery areas vital to fish and shellfish. It also considered the wider marine-conservation measures now slowly taking shape within the European Union.

The huge sandbanks off the Irish coast may have fixed names on the map – Kish, Arklow and so on – but are, in parts, naturally mobile and dynamic

Marine sands off the eastern shore of the Irish Sea are relatively stable and have been dredged industrially for decades. The huge sandbanks off the Irish coast on the other hand, from Dublin Bay to Carnsore Point, may have fixed names on the map (Kish, Arklow and so on) but are, in parts, naturally mobile and dynamic.

Sucking sand from such unstable zones “would have a minimal biological impact in the long term”, and much of the surveyed area off Dublin Bay, for example, would largely recover within one to two years.

All this, of course, lost some immediate point as Tiger construction crashed. But now the concrete mixers are churning again, and a big new suburb is planned for Dublin. It could well leave some rather empty avenues beneath the sea.

  • Michael Viney’s Reflections on Another Life, a selection of columns from the past four decades, is available from irishtimes.com/irishtimesbooks; viney@anu.ie
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