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Variable source area concept

Variable source area concept. John Hewlett. from Hewlett:. Simultaneous recognition on 3 continents of a Variable Source Area. à la Hewlett-san and Hibbert-san (1967). Runoff Pathways. Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001.

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Variable source area concept

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  1. Variable source area concept

  2. John Hewlett

  3. from Hewlett:

  4. Simultaneous recognition on 3 continents of a Variable Source Area à la Hewlett-san and Hibbert-san (1967)

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

  6. Hewlett on the hillslope scale

  7. from Hewlett

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

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

  10. A different form of overland flow

  11. 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

  12. Experimental Design of Dunne and Black (1970)

  13. Seasonal Variations in VSA Dunne, 1969; 78

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

  15. 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

  16. Saturation Overland Flow Dunne and Black, 1970

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

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

  19. 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

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

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

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

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

  24. 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

  25. Whipkey’s work

  26. Data: Whipkey, 1965

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

  28. Stable isotopes reveal the importance of stored water

  29. Not a new idea

  30. Pinder and Jones 1969 WRR

  31. 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)

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

  33. 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)

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

  35. Groundwater Ridging

  36. Abdul and Gillham, 1984

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

  38. 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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