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Runoff Pathways

Runoff Pathways. Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001. Southern Sweden—much like NE US. (Grip and Rodhe, 1994). A different form of overland flow.

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Runoff Pathways

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  1. Runoff Pathways Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001

  2. Southern Sweden—much like NE US (Grip and Rodhe, 1994)

  3. A different form of overland flow

  4. Overland flow (infiltration excess+ saturation excess) emerging from a sugar cane paddock over Kasnozem (Oxisol) soils (originating from Basalt), South Johnstone near Innisfail during a monsoon event, March 1985. Photo courtesy of Brian Prove

  5. Experimental Design of Dunne and Black (1970)

  6. Seasonal Variations in VSA Dunne, 1969; 78

  7. The link to flow From Dunne and Leopold, 1978

  8. Direct Precipitation onto Saturated Areas and Return Flow • Expands and contracts during events • Expands and contracts seasonally • Key zone for partitioning fast and slow runoff • Key non-point source hot spot! Brooks et al., Fig 4.11 From the original diagram by Hewlett, 1982

  9. Where Saturation Occurs Ward, 1970 Relation to live streams

  10. Saturated areas: We can sometimes estimate based on topography Dave Tarboton, Utah State U.

  11. Seasonal or storm period fluctuations HOF vs SOF Generalised dependence of Runoff Coefficient and Style of Overland Flow on Arid-Humid scale and on Storm Rainfall Intensities Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001

  12. Runoff Pathways Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001

  13. The British Invasion Benchmark papers by Burt, 1970s and early 1980s and Weyman, Anderson, Kirkby, Chorley………. From Kirkby, 1978

  14. Topographic Convergence Anderson and Burt, 1978 Hornberger et al text

  15. Topographic Controls on Saturation Development Ruhe and Walker, 1968

  16. Subsurface Stormflow • At the start of an event, percolation occurs vertically • Soil moisture increases & some water bypasses to depth • Where percolation reaches a less permeable layer that will not accept the wetting front, saturation will develop • Saturation development controlled by permeability & available storage • The saturated “wedge” or perched water table contributes significantly during peak runoff Weyman 1973

  17. Whipkey’s work

  18. Data: Whipkey, 1965

  19. Highly preferential Sidle et al 2001 HP Tarboton web course

  20. What are the conditions necessary for lateral flow regardless of process?

  21. What are the conditions necessary for lateral flow regardless of process? • Gradient • Hydraulic Conductivity Contrast

  22. Hydraulic Conductivity Contrasts • Where do they occur? • Soil surface • IF Ksat< rainfall rate HOF

  23. Hydraulic Conductivity Contrasts • Where do they occur? • Soil surface • Wetting front • Even in uniform texture, character curves for a soil can be responsible for generating saturated layers under the right circumstances…HOW?

  24. Hydraulic Conductivity Contrasts • Where do they occur? • Soil surface • Wetting front • Grain anisotropy • Kx >> Ky • Can lead to ponding

  25. Hydraulic Conductivity Contrasts • Where do they occur? • Soil surface • Wetting front • Grain anisotropy • Capillary barrier • Pic is of snow, can happen in soil under what conditions?

  26. Hydraulic Conductivity Contrasts • Where do they occur? • Soil surface • Wetting front • Grain anisotropy • Capillary barrier • Layering in saturated soils • High K over low K can lead to ponding ON low K layer • Perched aquifers • Impermeable basement

  27. Hydraulic Conductivity Contrasts • Where do they occur? • Soil surface • Wetting front • Grain anisotropy • Capillary barrier • Layering in saturated soils • High K over low K can lead to ponding ON low K layer • Low K over high K

  28. Lateral Gradients • Where do lateral gradients occur? • Unsaturated soil? • When K contrasts lead to ponding on sloped surfaces • 3D perspective • Water balance in convergent zones

  29. Flow pathways • Must somehow mobilize stored water

  30. Not a new idea

  31. Pinder and Jones 1969 WRR

  32. Two component mixing model • Solve two simultaneous mass-balance equations for Qold and Qnew • Qstream = Qold + Qnew • CstreamQstream = ColdQold+ CnewQnew • To yield the proportion of old water Hooper (2001)

  33. Weiler et al. 2004, WRR Qpe/Qs = (Cs-Ce)/(Cpe-Ce)

  34. Groundwater Surface Water Interactions “Groundwater” is the main component of flood hydrographs Variations in stream discharge, dD, and electrical conductivity at M8 (Sklash et al., 1986 WRR)

  35. Runoff Pathways Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001

  36. How is old water mobilized? • Many theories including • Groundwater ridging • Pressure wave translation • Transmissivity feedback

  37. Groundwater Ridging

  38. The Soil-Water Interface and the Effect of Suction Abdul and Gillham, 1984

  39. Capillary Fringe Precipitation Seepage face Equipotential lines Flow Lines Groundwater Ridging

  40. ...a Swedish view on the subject Rodhe, 1987 Transmissivity feedback From Grip and Rodhe; Seibert et al. 2002 HP

  41. Rodhe, 1987 Transmissivity feedback

  42. Runoff PathwaysPutting it all together Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001

  43. Storm Precipitation Saturation Overland Flow Hortonian Overland Flow Channel Precip. + Overland Flow Soil Mantle Storage Baseflow Overland Flow Subsurface Stormflow Interflow Basin Hydrograph Re-drawn from Hewlett and Troendle, 1975

  44. Dominant processes of hillslope response to rainfall Thin soils; gentle concave footslopes; wide valley bottoms; soils of high to low permeability Direct precipitation and return flow dominate hydrograph; subsurface stormflow less important Horton overland flow dominates hydrograph; contributions from subsurface stormflow are less important Variable source concept Subsurface stormflow dominates hydrograph volumetrically; peaks produced by return flow and direct precipitation Topography and soils Steep, straight hillslopes; deep,very permeable soils; narrow valley bottoms Arid to sub-humid climate; thin vegetation or disturbed by humans Humid climate; dense vegetation Climate, vegetation and land use (Dunne and Leopold, 1978)

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