More potential hazards loom even as waters slowly recede across the upper Plains: The pools of livestock manure that spilled waste and bacteria into the Mississippi and Missouri river basins; the threat that high waters made room for invasive carp to migrate north; the risk that nutrients washed from cropland will fuel larger algae blooms and contaminate drinking water wells.
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Not only are existing dams and other infrastructure not built for such extremes, it’s even hard to keep guidelines for new projects in line with future climate projections, said Christine Kirchhoff, an associate professor of engineering design and innovation at Penn State University.
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Dams considered to be “high hazard” — meaning their failure could cause significant death and destruction of homes — are typically designed for as much as 25 inches of rainfall within a 48-hour period, said Bill McCormick, a past president of the Association of State Dam Safety Officials. In the Blue Earth River watershed upstream of the Rapidan — which is considered to be of a slightly lower risk category, “significant hazard” — rainfall came mercifully short of that intensity.
But those risk calculations don’t consider how often heavy rains are falling, and how much more frequently a dam may now be hit with major or near-record storms. With some $3 billion in outstanding costs to rehabilitate dams around the country and heavier rainfall becoming more common, the stress on infrastructure could compound to create more crises like the one in Minnesota, said Lori Cannon Spragens, the dam safety association’s executive director.
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