crossroads powerpt 2015final
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Transcript of crossroads powerpt 2015final
Investigating recent rill erosion at a site approaching geomorphic equilibrium
Ryan WellsLittle 5 Week 2015
Outline• Hortonian theory of overland flow• Field site• Derivation process for model formulas• Data collection• Results
Ref: Horton (1945)
Hortonian Theory
Past Studies:Disagreement
Ref: W.J. ElliotRef: Gyssels 2005
Opportunity: Geomorphic Reclamation at AML Site
Post Reclamation
Rill incising the cap material … generating an alluvial fan
Derivation Process• What’s controlling rill and gully formation?
Derivation Process: Dependent Variables
• τ
•ω = τ (2)
• τ = shear stress (Pa)• = unit weight of water (N/)• = depth of flow (m)• = hillslope (degrees)• ω = stream power (W/• = specific discharge (m/s)
Derivation Process:Predicting Specific Discharge
• (6)
• (7)• = discharge ()• = Cross sectional area of flow ()• = Mannings’s coefficient (s/)• = hydraulic radius (m)• = Slope (degrees)• = depth of flow (cm)• = width of flow (m)
Derivation Process:Predicting Depth
• (3)
• (4)
• (5)
• = discharge ()• = depth of flow (cm)• = width of flow (m)• = specific discharge (m/s)• = runoff coefficient (unitless)• = Catchment area ()• = Precipitation rate (cm/s)
Constraining Independent Variables
Precip. Rates• Rain gage installed
on site• Literature for
extreme rain events
Ref: Huff and Angel (1992)
www.soilmoisture.com
Runoff Coefficient
Hillslope
*Note 5x vertical exaggeration
Model Results
Shear Stress Model : 4 cm Rain/hr
Stream Power Model : 4 cm Rain/hr
Stream Power Model : 8 cm Rain/hr
Conclusions• Stream power appears to be the better variable
controlling rill/gully formation at Minnehaha
Future Work• Drones!• Identify additional gullies• Make a few more measurements about rill
dimensions• Play with critical resistance values more• Investigate other variables