HOW TO FIGHT A RISING SEA

The Dutch enjoy a hard-earned reputation for building river dikes and sea barriers....

  The Dutch enjoy a hard-earned reputation for building river dikes and sea barriers. Over centuries, they have transformed a flood-prone river delta into a wealthy nation roughly twice the size of New Jersey. If scientific projections for global warming are right, however, that success will be sorely tested. Globally, sea levels may rise up to a foot during the early part of this century, and up to nearly three feet by century's end. This would bring higher tidal surges from the more-intense coastal storms that scientists also project, along with the risk of more frequent and more severe river floods from intense rainfall inland. Nowhere does this aquatic vise squeeze more tightly than on the world's densely populated river deltas.So why is one of the most famous deltas – the Netherlands – breaching some river dikes and digging up some of the rare land in this part of the country that rises (barely) above sea level? In the Biesbosch, a small inland delta near the city of Dordrecht, ecologist Alphons van Winden looks out his car window at a lone excavator filling a dump truck with soil. He considers the question and laughs. "We do have a hard time explaining this to foreigners," he says. The work here represents a keystone in the country's ­climate-adaptation plans, Mr. van Winden says. Indeed, nowhere are adaptation planning efforts to address rising sea levels and flooding more advanced than in the Netherlands? To be sure, the country's economic wealth and long experience dealing with threats from seas and rivers give it an advantage over other low countries that face rising waters, such as Bangladesh, Vietnam, and the tiny tropical island nation of Tuvalu in the South Pacific. But many of the approaches the Netherlands is taking can and are being slowly adopted even in countries far poorer, specialists say. The excavation work here is one example of what van Winden calls "soft approaches" to flooding in this small nation where competing interests jostle for every square foot of land. By buying out the few farmers remaining in this region, breaching the dikes they built to protect their land, and digging additional water channels, the Dutch government aims to reduce peak flood flows at Dordrecht and other cities downstream. No longer will tightly constricted river and canal channels hold high water captive. Big floods will overspread the Biesbosch, reducing the threat of water spilling over the top of levees that guard densely populated cities to the west. The Biesbosch may also be critical to the future of farming on the productive southwest coast. There, most of the area's fresh water sources are close to the coast – and vulnerable to salt-water contamination from a rising North Sea. This could make farming difficult, if not impossible. The Biesbosch, however, hosts three large reservoirs, each surrounded by a 20-foot-high dike. Fresh water piped from these reservoirs, some 50 miles inland, could keep coastal areas supplied. Globally, some 21 percent of the world's 6.6 billion people live within 20 miles of a seacoast – and nearly 40 percent within 60 miles, says Robert Nich­­olls, a professor of civil and environmental engineering at the University of Southampton in England. Seacoast populations who face the greatest risk from floods, storms, and sea-level rise live on river deltas, says the UN-sponsored Inter­governmental Panel on Climate Change. In the IPCC's latest set of reports on the impact of global warming, released earlier this year, scientists looked at data from 40 of the globe's river deltas, home to 300 million people. If current trends continue through 2050, flooding in the Nile, Mekong, and Ganges-Brahmaputra river deltas could each displace more than 1 million people. Up to a million more may be forced to head for higher ground in each of another nine deltas, including the Mississippi River delta. Up to 50,000 could be forced to relocate in each of 12 other deltas, including the Rhine River delta – an area known more widely as the Netherlands. Besides global warming, scientists say the challenges these regions face have other causes as well. Levees, sea walls, drainage canals, dams, and other land-use patterns have taken a toll. Deltas tend to subside (sink) naturally, accentuating the rise in sea level. Past engineering projects can actually limit the ability of natural processes to replenish the land mass of deltas.