The Impact of Erosion from Water RunoffBy: Nicolas Wieland and Tony Nixon

Overview• Farm in Scott County, Minnesota• Erosion occurs on a cattle pasture• Drain tile directs water flow • Additional surface water flow• All water drains to a wetland

Contributing Area

Erosion• Erosion - is the process by which soil and rock are removed

from the Earth's surface by natural processes such as wind or water flow, and then transported and deposited in other locations

• Most noticeable source of erosion: water runoff/drainage• Influencing factors to erosion: vegetation cover, topography,

soil structure, and quantity of water

Agricultural Practices• Livestock Grazing• Tillage• Hillside Farming• Drain Tile

Materials• Total Station• Prism Rod• Global Positioning System• Geographic Information System• Microsoft Excel• Field Notebook• Pitchfork• Knee Boots

Methods: Data Collection• Visual inspection of site• Revealed slight long-term erosion and very severe erosion

• Total Station for collecting elevation information• Recorded Horizontal Angle, Horizontal Distance, Vertical

Distance, and sufficient notes• Benchmark set as 100 feet• 4 groups of foreshots: undisturbed terrain, slightly eroded

terrain, 2 sets to define the aggressive erosion

Four Groups of Foreshots

Methods: ArcMap Analysis• IDW interpolation of digital elevation models (DEM) • Predicted • Actual

• Use break lines in interpolation for increased accuracy• Gully edge for actual elevation model• Gully centerline for predicted elevation model

• Predicted elevation model excluded the points from the bottom of the gully

• Raster calculator subtracting cell values of the DEMs• Surface volume calculation

• Contributing area determination and calculation

From Tile Exit to Bottom• 430 feet long• 16.5 vertical feet• 5 vertical feet from south edge to tile exit

Results• 8,659.7 cubic feet removed• 2.9 cubic feet not removed• 94 acres contributing to runoff

Analysis• IDW vs. Spline interpolation• Dirt 'not' eroded• Non-erodable materials

Implications• 12 inches of snow + 0.5 inch of rain = 683,000 cubic feet (5.1 million gallons)• Melt and drain in 5 days• Impermeable frost layer or saturated ground = 1.5 cubic feet per second (average)• Reasonably double, or more, at times

Geeky Stuff• 2 feet high column of water exerts 1 psi.• Assume water flows at 2 feet/second = 1.5+ feet cross section of water = 216+ square inches• Pressure adds up quickly

Questions??