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Geography in the News: Polder Salvation

By Neal Lineback and Mandy Lineback Gritzner, Geography in the NewsTM

Polder Salvation

The effects of global warming and accompanying sea level rise are threatening many of the world’s lowland areas. Although most such lands do not have the resources to protect themselves, the polder regions of the Netherlands are examples of such efforts.

Historically, the Netherlands, a European country built mostly on river deltas, has used river dikes and sea barriers to make its flood-prone and below sea level land usable. Now, with the increasing twin threats of river flooding from inland storms and higher ocean storm surges as the climate warms and sea levels rise, the Netherlands hopes to meet its future challenges with a variety of approaches.

The Netherlands (formerly called Holland) is located at the mouths of three rivers, the Waal (Rhine), Maas (Meuse) and Scheldt. For thousands of years, these rivers carried their sediment to the North Sea, spreading rich loamy clay on deltas and the shallow sea floor along the coast. A series of low barrier islands and sand dunes marked the outer edges of the shallow sea.

gitn_916_polders
Map by Geography in the News and Maps.com
Boundaries and names shown do not necessarily reflect the map policy of the National Geographic Society.

Land reclamation along the margins of the shallow sea began more than 2,000 years ago. The Frisians, the people who first settled the Netherlands, built terpen, low man-made hills upon which villages and farmhouses were built. Later, the terpen were connected to one another by dikes.

Once dikes were in place, the people began draining wetlands for agricultural use. By the 13th century, windmills were used to pump water out of the areas below sea level, creating the Netherlands’ famous polders.

A polder is a large tract of low-lying wetland or former sea floor partially or wholly encircled by dikes and drained mostly with pumps. Poldering is so important the Netherlands would barely exist without it. The problem with poldering is that, because the polders lie below the surrounding water levels, water invariably seeps back under the dikes. As a result, the water must be pumped by windmill or electricity more or less continuously into canals, which are found throughout poldered areas. The canals collect the water, which then flows or is pumped away to the sea.

The Netherlands, with a population of nearly 17 million, is about twice the size of New Jersey.  The Netherlands’ polderlands are home to more than 60 percent of the country’s population and generate 70 percent of the country’s gross domestic product.

Scientific predictions for global warming have the Dutch nervous about the future of their country. Globally, sea levels may rise up to a foot (0.3 m) during the early part of this century and up to nearly three feet (0.9 m) by century’s end. Sea level rise will also bring higher storm surges from the more intense coastal storms that scientists also predict may accompany global warming. These extreme events can over-top existing dikes, flooding polders with salt water, creating conditions similar to the flooding in New Orleans from Hurricane Katrina. Intense rainfall events expected inland also will create the risk of more frequent and severe river floods that may inundate polders.

The land of the Netherlands, however, is affected by other variables unrelated to global warming. The sea walls, drainage canals, levees and dikes themselves have impacted the country. River deltas in general tend to subside, or sink, naturally, increasing the impact of a rise in sea level. The Netherlands’ engineering projects also have limited the ability of streams to naturally add new sediments to the deltas.

Thankfully, the government of the Netherlands is well aware of its future challenges. Adaptation planning efforts range from major engineering feats to allowing Mother Nature work naturally once again.

One example is the Biesbosch, a small inland delta and national park, where the Dutch government has breached some dikes originally built to protect farmland and dug additional drainage channels. Such methods aim to reduce peak flood flows to cities downstream. No longer will the water be held captive by tightly constricted river and canal channels. Instead, big floods are allowed to spread across the Biesbosch delta to serve as a temporary reservoir. This tends to reduce the threat of water spilling over the top of levees that guard densely populated cities downstream.

Other ideas are to place newly built homes on stilts or design them to float. In the future entire villages might be built to float in place, linked by buoyant sidewalks and roads. With such forward-thinking ideas, its no wonder the Christian Science Monitor  (Nov. 15, 2007) once said“…nowhere are adaptation planning efforts to address rising sea levels and flooding more advanced than in the Netherlands.”

As sea levels rise during the next century, low-lying coastal areas will have to adjust. Officials in other sea-rise prone areas around the world, including southern Louisiana, are paying close attention to the Netherlands’ strategies and successes at keeping the ocean at bay. The question for these regions is whether there are enough resources available to stave off the rising ocean.

And that is Geography in the News.

Sources: GITN 916 “The Netherlands and Sea Level Rise,” Maps.com, Dec. 21, 2007; and Spotts, Peter. “How to Fight a Rising Sea,” Christian Science Monitor, Nov. 15, 2007.

Co-authors are Neal Lineback, Appalachian State University Professor Emeritus of Geography, and Geographer Mandy Lineback Gritzner. University News Director Jane Nicholson serves as technical editor. Geography in the NewsTM  is solely owned and operated by Neal Lineback for the purpose of providing geographic education to readers worldwide.