variable source area concept
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Variable source area concept
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John Hewlett
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from Hewlett:
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Simultaneous recognition on 3 continents of a Variable Source Area
à la Hewlett-san and Hibbert-san (1967)
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Runoff Pathways
InfiltrationCapacity
R a i n f a l l
Saturation OF
BedrockAquifer
Percolation
RegolithRegolith Subsurface Flow
Saturation
Aquifer Subsurface Flow
Hortonian OF
Percolation
Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001
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Hewlett on the hillslope scale
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from Hewlett
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Runoff Pathways
InfiltrationCapacity
R a i n f a l l
Saturation OF
BedrockAquifer
Percolation
RegolithRegolith Subsurface Flow
Saturation
Aquifer Subsurface Flow
Hortonian OF
Percolation
Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001
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(Grip and Rodhe, 1994)
Southern Sweden—much like NE US
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A different form of overland flow
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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
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Experimental Design of Dunne and Black (1970)
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Seasonal Variations in VSADunne, 1969; 78
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The link to flowFrom Dunne and Leopold, 1978
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From the original diagram by Hewlett, 1982
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
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Saturation Overland Flow
Dunne andBlack, 1970
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Where Saturation Occurs
Relation to live streamsWard, 1970
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Saturated areas: We can sometimes estimate based on topography
Dave Tarboton, Utah State U.
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0 M o r e I n t e ns e % R a in D ay s L e s s I n t e ns e 10 0
10 0
M o r eH um id
E T A C TE T PO T
%
M o r eA r i d
0
7 5 %
5 0 %
2 5 %T o t a l R uno ff
0 %
M ainlyH or t onianO ver land F low
M ainlyS at ur at ion
O ver land F low
Generalised dependenceof Runoff Coefficientand Style of Overland Flow on Arid-Humid scale and on Storm Rainfall Intensities
Seasonal or storm period fluctuations
Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001
HOF vs SOF
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Runoff Pathways
InfiltrationCapacity
R a i n f a l l
Saturation OF
BedrockAquifer
Percolation
RegolithRegolith Subsurface Flow
Saturation
Aquifer Subsurface Flow
Hortonian OF
Percolation
Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001
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The British Invasion
Benchmark papers by Burt, 1970s and early 1980sand Weyman, Anderson, Kirkby, Chorley……….
From Kirkby, 1978
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Topographic Convergence
Anderson andBurt, 1978
Hornberger et al text
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Topographic Controls on Saturation Development
Ruhe and Walker, 1968
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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
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Whipkey’s work
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Whipkey, 1965
Data:
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Highly preferential
Tarboton web course
Sidle et al 2001 HP
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Stable isotopes reveal the importance of stored water
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Not a new idea
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Pinder and Jones 1969 WRR
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Two component mixing model
Solve two simultaneous mass-balance equations for Qold and Qnew
Qstream = Qold + QnewCstreamQstream = ColdQold+ CnewQnew
To yield the proportion of old water
pold Qold
Qstream
Cstream Cnew
Cold Cnew
Hooper (2001)
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Qpe/Qs = (Cs-Ce)/(Cpe-Ce)
Weiler et al. 2004, WRR
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Variations in stream discharge, dD, and electrical conductivity at M8
(Sklash et al., 1986 WRR)
Groundwater Surface WaterInteractions
“Groundwater” is the main
component of flood
hydrographs
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Runoff Pathways
InfiltrationCapacity
R a i n f a l l
Saturation OF
BedrockAquifer
Percolation
RegolithRegolith Subsurface Flow
Saturation
Aquifer Subsurface Flow
Hortonian OF
Percolation
Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001
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Groundwater Ridging
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Abdul and Gillham, 1984
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The Soil-Water Interface and the Effect of Suction
Abdul and Gillham, 1984
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Abdul and Gillham, 1984
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Groundwater Ridging
Flow Lines
Precipitation
Seepageface
Equipotentiallines
Capillary Fringe
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...a Swedish view on the subject
From Grip and Rodhe; Seibert et al. 2002 HP
Rodhe, 1987 Transmissivity feedback
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Rodhe, 1987 Transmissivity feedback
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Runoff PathwaysPutting it all together
InfiltrationCapacity
R a i n f a l l
Saturation OF
BedrockAquifer
Percolation
RegolithRegolith Subsurface Flow
Saturation
Aquifer Subsurface Flow
Hortonian OF
Percolation
Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001
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Storm Precipitation
Soil Mantle Storage
Baseflow
Channel Precip.+
Overland Flow
Overland Flow
InterflowSubsurfaceStormflow
Saturation Overland Flow Hortonian Overland Flow
Basin Hydrograph
Re-drawn from Hewlett and Troendle, 1975
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Dominant processes of hillslope response to rainfall
Horton overland flow dominates hydrograph; contributions from subsurface stormflow are less important
Direct precipitation and return flow dominate hydrograph; subsurface stormflow less important
Subsurface stormflow dominates hydrograph volumetrically; peaks produced by return flow and direct precipitation
Arid to sub-humid climate; thin vegetation or disturbed by humans
Humid climate; dense vegetation
Steep, straight hillslopes; deep,very permeable soils; narrow valley bottoms
Thin soils; gentle concave footslopes; wide valley bottoms; soils of high to low permeability
Climate, vegetation and land use
Topography and soils
Variable source concept
(Dunne and Leopold, 1978)