the impact of erosion from water runoff
Post on 22-Feb-2016
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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??
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