Presentation on theme: "Erosion of the Seminary Fen Boundary Ditch in 2013 Sam Wetterlin October 24, 2013."— Presentation transcript:
Erosion of the Seminary Fen Boundary Ditch in 2013 Sam Wetterlin October 24, 2013
Boundary Ditch, Falls and Seepage The ditch at the north boundary of the SNA provides overflow drainage for the seepage area, and areas well west. It also drains precipitation runoff from a considerable area. Heavy runoff is likely the cause of the erosion of the ditch discussed below. View to northwest
Waterfall in April, 2013 This shows the flow of the boundary ditch stream where it joins the main flow coming from the Prime Fen waterfall. April, 2013. Note that the boundary stream falls several feet when it hits the edge of the ravine.
Eroded Boundary Ditch Boundary ditch stream enters ravine from upper left. On 5/9/13 (left), this created the waterfall shown in the previous slide. On 10/24/13 (right) the entry point was so eroded that the boundary stream entered the ravine at the level of the ravine bottom, eliminating the waterfall. The deep erosion extends to the upper left (west) a considerable distance toward the seepage area. This erosion occurred in less than six months, and most likely occurred in the rainy period from mid-May to mid-July.
Eroded Boundary Ditch From Above View of the junction of the boundary ditch and ravine from above, showing that the erosion is broad and deep.
Water Parsnip in Seepage Area The erosion of the boundary ditch is proceeding west toward the seepage area, shown in April and October, 2013. The principal vegetation in the wet area is cut-leaf water parsnip (right), which is listed as threatened in Minnesota. If the erosion reaches this seepage area, it will be quickly drained.