Erosion and Sediment Control Tip #95

I often hear the statement that “It’s flooding like I have NEVER seen it flood before”.  Sometimes it is easy to blame this on Climate Change, but it can be caused by land use changes.  For example, a watershed that changes from a Runoff Curve Number of 70 (a lot of woods and green space) to 95 (urbanized) can experience flooding more often. In this scenario, the runoff from a 2-year, 24-hour (50% chance of occurrence) event in the urbanized watershed can resemble the runoff from a 25-year, 24-hour (4% chance of occurring) event in the green watershed. So, it floods more frequently.  Something to think about!

 

Perry L Oakes, PE

Alabama’s Erosion and Sediment Control Program Manager

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