AFTERMATH OF A STORM – Page 1

On May 27, 2010, EWG staff and a cameraman climbed into a helicopter in Ames, Iowa, to look for signs of soil erosion and water runoff caused by a rainstorm two days earlier. We didn’t have to fly far or long to find them. Everywhere we looked, recently planted fields of corn and soybeans were etched with dark gullies. Indeed, this telltale signature of erosion and runoff was evident even before we got to our original destination — an area of Marshall County (just 40 miles east of Ames) where rain had fallen two days earlier.

The May 25 rainstorm was not unusually heavy for Iowa in the spring. According to rainfall data collected by the Iowa Environmental Mesonet, the rainfall that day ranged from 0.25 to 1.65 inches in the area surveyed.9 A heavier storm two weeks earlier (May 12) produced an average of 1.45 to 1.93 inches in the area and may also have contributed to the obvious signs of erosion, runoff and gullying.

Figure 5: EWG’s Aerial Survey

On May 27, 2010, EWG staff flew over a small area of Marshall County, Iowa, looking for telltale signs of severe erosion two days after rain fell on newly planted crop fields. Red dots in this 2009 aerial photo show the locations where video photography documented what we saw.

Storms that produce two inches or more of rain are common. Six occurred somewhere in Iowa in April of 2010, three in May, 14 in June, 15 in July, 10 in August, six in September, one in October and one in November. The year 2010 proved to be a stormy one, with serious consequences for Iowa’s soil and water resources and for its citizens, whose lives and property have been repeatedly threatened by flooding. The heaviest downpours occurred after EWG’s May 27 aerial survey.

What we saw was very disturbing:

Figure 6: Gullies Everywhere


Gullies cut into crop fields like those in these photos scarred most of the fields EWG surveyed, visible evidence of serious erosion that is likely far in excess of rates considered “sustainable.” Gullies form when rainwater flowing over a field concentrates into narrow channels that strip away soil and even newly emerged plants. Farmers till up the soil each year to fill in the gullies, but this practice just makes them more vulnerable to erosion the next spring.

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