What to do with 4.5m tons of soil

The biggest man-made nature reserve in Europe is to be constructed from the vast quantity of earth excavated for Crossrail. Charlie Cooper reports

Everyone knows that when a dog digs a hole, it throws up a big pile of dirt behind itself. Replace the dog with a 1,000-tonne drill and the pile of dirt with Europe's largest man-made nature reserve, and you have the principle behind the Wallasea Island project.

Dreamed up four years ago by the Royal Society for the Protection of Birds (RSPB), the scheme will see 4.5 million tonnes of earth – dug out from under London by the Crossrail tunnelling machines – transported to the Essex coastline to create a nature reserve twice the size of the City of London. The first shipment of London clay arrived at Wallasea Island yesterday. Over the next seven years, 670 hectares of arable farmland will be transformed into a thriving wetland habitat of mudflats, salt marshes and lagoons – the landscape that last existed here 400 years ago.

The excavated earth will create areas of high ground, before engineers breach the levees that currently protect the farmland, flooding the plain.

Rare wetland birds like the avocet, dunlin, redshank and lapwing are expected to flock to the reserve to breed, following centuries in which their intertidal habitat has been in retreat along the British coast. The spoonbill and the Kentish plover, which no longer, or rarely, breed in this country, could also return.

The project, which will be completed by 2019, has been held up by the Government as "the gold standard" of how to marry economic growth with environmental protection. Crossrail is Europe's largest construction project, at a cost of £14.8bn. It will link Maidenhead to the west of the capital with Shenfield to the east.

But what to do with the six million tonnes of material displaced by eight huge tunnelling machines boring a 21km twin tunnel under London was a dilemma for planners whose contract was granted on the condition of meeting environmental targets.

The answer, from the RSPB, was the culmination of their long fight for threatened wetland habitats. Four hundred years ago there were 30,000 hectares of intertidal salt marsh along the Essex coast, home to a wide variety of wading birds as well as mammals such as otters and seals.

Over the centuries more and more of this type of landscape has been drained, or protected from rivers and the sea by levees to produce more arable or grazing land. Today there are just 2,500 hectares of salt marsh in Essex – a decline that has been mirrored all along the coast.

Climate change has also taken its toll. The south-east of England is particularly susceptible to drought and during the long spell of dry weather that finally ended in spring, it was wading birds that suffered the most among Britain's wildlife. Another threat comes from rising sea levels caused by the Arctic sea ice melt, threatening the lowlands of the east coast. The RSPB predicts 1,000 more hectares of wetland could be lost in the next decade – either for a want of water, or a catastrophic flood of it.

What the Wallasea Project proposes is to manage a middle way between the two scenarios, where a controlled landscaping will recreate the ideal habitat that once existed before man began meddling with the coastlines and the climate.

Dr Mike Clark, chief executive of the RSPB, said the project demonstrated how environmental concerns could go hand-in-hand with development. "This is about a vision for a world in which you can have a first-class economy, but also a world rich in nature."

The new Environment Minister, Owen Paterson, also backs the scheme, although admitted at yesterday's launch that he is "no expert" on coastal erosion. Mr Paterson's appointment to Defra raised eyebrows. He has a record of opposing wind energy as a local MP and has been called a climate-sceptic.

Yesterday, confronted with the rising waters at Wallasea, he said that climate change was happening and that there was a "man-made contribution", but he declined to say whether or not he believed human activity was the main cause, or whether Britain should be cutting back on carbon emissions.

"We shouldn't be frightened of big infrastructure, of doing things that really enhance the economy," he said of the project. "You can turn what is a problem into a huge environmental gain."