Runoff Pathways Slide from Mike Kirkby, University of Leeds, AGU Chapman Conference on Hillslope Hydrology, October 2001 Infiltration Capacity R a i n f a l l Saturation O F B edrock A quifer Percolation Regolith Regolith Subsurface Flow Saturation A quiferSubsurface Flow H ortonian O F Percolation
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. - PowerPoint PPT Presentation
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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
(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
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
What are the conditions necessary for lateral flow regardless of process?
What are the conditions necessary for lateral flow regardless of process?
• Gradient• Hydraulic Conductivity Contrast
Hydraulic Conductivity Contrasts
• Where do they occur?– Soil surface
• IF Ksat< rainfall rate HOF
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?
Hydraulic Conductivity Contrasts
• Where do they occur?– Soil surface– Wetting front– Grain anisotropy
• Kx >> Ky
• Can lead to ponding
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?
Hydraulic Conductivity Contrasts• Where do they occur?