variable source area concept
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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
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
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
Hewlett on the hillslope scale
from Hewlett
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
(Grip and Rodhe, 1994)
Southern Sweden—much like NE US
A different form of overland flow
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
Experimental Design of Dunne and Black (1970)
Seasonal Variations in VSADunne, 1969; 78
The link to flowFrom Dunne and Leopold, 1978
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
Saturation Overland Flow
Dunne andBlack, 1970
Where Saturation Occurs
Relation to live streamsWard, 1970
Saturated areas: We can sometimes estimate based on topography
Dave Tarboton, Utah State U.
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
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
The British Invasion
Benchmark papers by Burt, 1970s and early 1980sand Weyman, Anderson, Kirkby, Chorley……….
From Kirkby, 1978
Topographic Convergence
Anderson andBurt, 1978
Hornberger et al text
Topographic Controls on Saturation Development
Ruhe and Walker, 1968
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
Whipkey’s work
Whipkey, 1965
Data:
Highly preferential
Tarboton web course
Sidle et al 2001 HP
Stable isotopes reveal the importance of stored water
Not a new idea
Pinder and Jones 1969 WRR
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)
Qpe/Qs = (Cs-Ce)/(Cpe-Ce)
Weiler et al. 2004, WRR
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
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
Groundwater Ridging
Abdul and Gillham, 1984
The Soil-Water Interface and the Effect of Suction
Abdul and Gillham, 1984
Abdul and Gillham, 1984
Groundwater Ridging
Flow Lines
Precipitation
Seepageface
Equipotentiallines
Capillary Fringe
...a Swedish view on the subject
From Grip and Rodhe; Seibert et al. 2002 HP
Rodhe, 1987 Transmissivity feedback
Rodhe, 1987 Transmissivity feedback
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
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
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)