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)