Lec 14: Runoff Generation I Flashcards
How does most water reach stream channels?
via hillslopes
How do flow pathways vary?
What do they determine?
What are they controlled by?
- vary spatially and temporally
- determine quality of water
- controlled by climate, topography, soils and vegetation
Define overland flow (surface runoff)
water reaching the stream while traveling
above ground
Define subsurface flow (subsurface runoff)
What does it include?
water reaching the stream through
shallow soil and underlying rock layers.
It includes:
‒ Throughflow, interflow or shallow subsurface flow (SSSF) in upper soil
layers
‒ Groundwater flow (GWF) in deeper soil layers and rock layers
Hortonian Overland Flow is also known as …
When does it occur?
Infiltration excess overflow
occurs when
the precipitation rate exceeds the soil infiltration rate
Define infiltration
Define infiltration rate
Define infiltration capacity
Infiltration is the flow of water into the ground through the earth surface
rate of water entering the soil surface
maximum rate at which a soil can absorb water through its surface
Define excess rainfall
What is a graph of excess rainfall versus time called?
Rainfall that is neither retained on the land surface nor infiltrated into the soil
an excess rainfall hyetograph
Where does hortonian overland flow occur?
- On road surfaces and other impermeable or compacted areas (Bedrock outcrops, city parks, lawns, roads, trails)
- On hydrophobic soils (fire and seasonality will influence their presence)
- On trampled and crusted soils (especially in semi-arid areas where soil surface crusts and intense rainfall events are common)
- On frozen ground (e.g., Northern Canada and Siberia)
- On low-permeability soils (Silt-clay soils without macropores)
When does saturation-excess overland flow occur?
occurs when the soil is fully saturated
(“soaked”) and there is no space for additional water to infiltrate
What is return flow?
Where does it mainly occur?
How does it occur?
subsurface water from saturated areas is “pushed” towards the
surface (exfiltrated)
SOF occurs mainly in topographic lows and near stream channels
Direct rainfall on saturated surfaces –> Excess water in soil is pushed upward –> water exfiltrate at the surface (return
flow)
What must occur in order for saturated areas to form?
- there must be places where upslope water converges and the soil storage capacity is exceeded
- i.e., the water table reaches the surface
Define the Variable Source Area concept
Why are there temporal values in VSA dynamics?
Saturated areas expand and
contract during precipitation
events and seasonal
In which conditions is HOF most likely to occur?
In which conditions is saturation OF most likely to occur?
HOF: more intense rain, more arid
SOF: less intense rain, more humid
