Storm flow generation

Question 1

Horton, 1993:

Infiltration-limited overland flow

Answer 1

• high intensity rainfall
• reduced infiltration capacity
• sparse vegetation, soil crust, urbanisation etc.
• usually associated with semi-arid/arid regions
• water never enters subsurface
• fastest pathway to channel
• timing of overland flow generation is closely linked to timing of rainfall

Question 2

Hewlett, 1991

Saturation excess overland flow

Answer 2

• antecedant soil moisture
• topography
• variations in soil properties and vertical and lateral hydraulic conductivity
• enters subsurface so slower pathway to channel
• delay between overland flow and precipitation

Question 3

Subsurface storm flow

Answer 3

• not overland flow
• downslope flow through soil
• no saturation and soil is very permeable
• above seasonal average water table

Question 4

preferential flow

Answer 4

• created by roots, burrowing and activity
• flow may be more turbulent = erosion
• macro pores, fissures and piping
• higher velocities than flow through soil matrix
• macropore flow dominates during storm events
• flow effects soil water distribution and groundwater recharge

Question 5

Piston effect

Answer 5

• importance of old water

- new water pushes old water out

Question 6

Thomas Dunne:

Variable (or partial) contributing area

Answer 6

• suggesting that zones of runoff generation expand and contract with time
• as storm continues, saturation zone rises and area expands

Question 7

Catchment characteristics

Answer 7

• climate (precip, evap, and temp)
• vegetation
• soil type and structure (porosity and permeability)
• soil moisture (saturation etc.)
• geology (impermeable upland areas)
• topography

Question 8

Infiltration limited overland flow example

Answer 8

• area of low vegetation
• arid climate
• low infiltration
• exposed system
• rain impact soil surface, soil dries, bakes and hardens

Question 9

Summary

Answer 9

• 4 main mechanisms
• these are reflected in hydrograph shape
• surface topography exerts a strong control on the spatial location of surface runoff generation zones
• during a storm, the zones contributing surface runoff may expand spatially sure to progressive saturation