One look at the topography of Duluth, Minn., and you understand the challenges facing the city’s stormwater management team.Developed as a long, narrow strip against a ridge overlooking Lake Superior, Duluth features a steep drop of more than 880 feet from the top of Thompson Hill, its highest point, to the water’s edge. The velocity of stormwater as it rushes downhill, plus the area’s clay soil, can result in serious erosion, according to Chris Kleist, stormwater project coordinator.And then there’s winter. Temp-eratures can plummet to 40 degrees F below zero, and frost depths of 6 to 8 feet or more
