Trees, gravel and compact communities guard against floods

At best, flooding is a hassle. Roadways close, basements become pools and shoes get wet. More severe runoff can destroy crops, displace entire populations and open the door to disease, starvation and war. Pakistan has already seen more than one thousand deaths following its recent flooding. By planning ahead and maintaining soil integrity, the threat of serious flooding and its side effects can be greatly reduced. A new study out of Purdue University has found that the most effective way to reduce water runoff is to reduce urban sprawl.

Urban sprawl replaces permeable surfaces like grasslands with impermeable surfaces like pavement and leaves water with no place to escape into the soil. Not only does excess water lead to flooding but, once trapped, the water can become saturated with contaminants such as fertilizers, pet waste and gasoline. Normally soil purifies water as it travels to underground aquifers, as the soil particles naturally filter out these impurities. Without this step, the polluted water can harm aquatic life as it seeps back into the rivers and streams. It can also harm the quality of our own drinking water.

In the Purdue study, researchers estimated the watershed runoff on Michigan's Muskegon River from the year 1900 through the present to 30 years in the future, and analyzed variables such as forest regrowth and urbanization to determine their impact on the landscape. The study found that adding permeable surfaces had the greatest positive impact on river ecosystems. It also found that urban areas are set to double in size in the next two decades at the current rate of growth, resulting in nearly double the watershed runoff.

Still, the Purdue study found that the Midwest presently has a better balance of urban and forested land than it did at the turn of the century, when the level of deforestation reached its peak.

"The past is the worst we'll ever see over a 140-year period. Even the worst-case scenarios show that the landscape won't be as bad as what we had in the 1890s and early 1900s," said researcher Bryan Pijanowski. "The lesson here is that with time and care, these systems can be restored. Recovery is possible."

If you're wondering how the rest of the world is faring, the Worldometer tracks our daily global energy use, remaining resources and mortality rate among other categories. The numbers can be eye-opening. As of this writing, the meter shows that approximately 9,380,000 acres of arable land has been lost due to soil erosion this year while 17,600,000 acres of forest has been lost. To put those numbers into perspective, that's about one acre of forest for every person in New York City, Los Angeles, Chicago and Houston. The combination of soil erosion and deforestation increases the risk of flooding.

Urban planners can take these factors into account by designing urban areas with more open spaces, smaller roads, fewer parking lots and permeable alteratives to pavement, like gravel or limestone paths. Even pre-existing developments can incorporate more soil-friendly structures, as Chicago has done in resurfacing its alleys with permeable materials. Permeable pavements may require more planning and expertise since they are not used as widely as conventional pavements. However, permeable pavement systems reduce the need for costly storm drainage systems and might even help motorists see road markers more clearly because of the material's reduced surface glare.

According to Purdue University's Safe Water program, the average yearly runoff in an area of solid pavement resulted in 19 inches of water.  Meanwhile, the average yearly runoff in a forest in Central Indiana was only 0.3 inches. Planting a tree may be one of the most basic yet meaningful ways to protect the soil and waterways, and it doesn't require a degree in urban planning.