Climate change affecting dikes and levees
Research from Hungary indicates a changing climate can weaken levees
In a recent survey of Hungary’s levees, two scientists, Zsombor Illés and László Nagy, found that climate change is weakening their country’s flood control structures. Their results were published in the the journal Geoenvironmental Disasters.
People have been building levees since the earliest days of human settlement. Indeed, levees are a natural part of the environment. As a river floods its banks, the receding waters leave sediment. Over time, this sediment builds up, creating embankments along the river—natural levees. When people build levees, they imitate nature, just building up the earth alongside a river or other body of water. No special materials are used. Brick or stone walls are not built up. The earth usually does a pretty good job.
The Carpathian Basin has almost 7,000 miles of levees and flood control embankments, of which more than 3,000 miles lie within Hungarian borders. The levees were mostly constructed during the 1800s and are made of layers of locally obtained clay, peat, silt, and sand.
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Newly built levees are often add-ons to existing levee material laid down decades or even hundreds of years ago. Some of the engineering decisions made that long ago did not include the best materials for this kind of construction. For example, the Hungarian researchers noted that most of their country’s levees are made of clay as this is a locally common material. However, clay expands when it’s wet; it shrinks and cracks when it dries, which can lead to levee failure.
Rain and the occasional high waters of a flood keep the earth of a levee in a naturally semi-moist state. The water content of the soil helps to hold it together. You might think of it this way. Try making a sand castle from moist sand. You can make ramparts, turrets, and towers all you want. Now try to make a castle with dry sand. You can’t do it because the dry sand won’t hold together. Soil is the same way. Having adequate—but not too much—moisture helps the soil to remain solid. Soils that are depleted of water can break apart or become brittle.
Because of higher temperatures worldwide, more water is evaporating from soil, including the soil used to build levees. The Hungarian scientists, Illés and Nagy, examined almost 800 miles of levees to see if this increased evaporation leads to desiccation and fissuring of levees. They found that levees in areas of higher drought were more likely to be plagued with cracks and fissures, and the drier the area, the larger the cracks and fissures.
Hungary is particularly vulnerable to climate change. The Carpathian Basin, which lies mostly within the borders of Hungary, is experiencing slightly more warming than the rest of the world. Hungary has also been hard hit by drought, and the number of heatwaves has increased. It is thought that Hungary’s moderate continental climate is shifting toward being more Mediterranean. Summers are longer, warmer, and drier; winters are milder, with more precipitation than before.
Memphis Minnie singing “When the Levee Breaks”
Of course, Illés and Nagy’s findings have implications for the rest of the world. Throughout the United States there are almost 7,000 levee systems containing nearly 25,000 miles of levees. If you put all the levees in the U.S. end-to-end they would easily circle the Earth. At least 17 million Americans live or work in levee-protected lands, and the levees protect $2.3 trillion dollars in property.
In reviewing recent scientific publications and newspaper articles for this post, almost every article included the word “aging.” Many of America’s levees were built during the postwar prosperity of the 1940s and 1950s, so they are 60 years old or older, and construction standards back then weren’t as high as they are now. A 2021 report from the American Society of Civil Engineers gave America’s dams and levees an overall grade of “D.”
Zep performing “When the Levee Breaks”
A good deal of the concern for climate change is the increased flooding that a warmer world is expected to bring, putting the levees to the test more frequently than they were designed for. Heavy rains in the spring of 2019 brought severe flooding to the U.S. Midwest. More than 80 levees managed by the Army Corps of Engineers were overtopped or breached. The floods damaged more than 700 miles of levees, with repairs estimated at $1 billion.
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