Runoff Processes

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Runoff Processes
02/23/2006

• Slides from Venkatesh Merwade and Suzanne
  Anderson
• Reading Applied Hydrology Sections 5.1 and 5.2

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Surface water

• Watershed area of land draining into a stream
  at a given location
• Streamflow gravity movement of water in
  channels
• Surface and subsurface flow
• Affected by climate, land cover, soil type, etc.

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Sources of streamflow
http//uregina.ca/sauchyn/geog327/outline.html
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Streamflow generation

• Streamflow is generated by three mechanisms
• Hortonian overland flow
• Subsurface flow
• Saturation overland flow
• Some texts mention groundwater ridging as an
  additional mechanism contributing to streamflow

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Welcome to the Critical Zone
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Critical zone architecture influences sediment
sources, hydrology, water chemistry and ecology
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Fort Collins
The Colorado Front Range
Boulder
Golden
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Fort Collins
The Boulder Creek watershed

• Precambrian crystalline bedrock
• Uniform climate history
• Three erosional states

Boulder
Limits of glacial and fluvial rejuvenation
Golden
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Boulder Creek Critical Zone Observatory

• How do weathering and transport processes control
  the structure of the CZ?
• What is the impact of CZ structure on
  hydrological, geochemical and biological
  functions?

Glacial limits
Slope map draped over shaded relief.
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Three experiments in one the geomorphic context
of Boulder Creek
Upper glaciated Middle steady, old Lower
rejuvenated
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Front Range Rocky mountain surface
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Lower Boulder Canyon-Betasso
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Oregon Coast Range- Coos Bay
Channel head
Anderson et al., 1997, WRR. Montgomery et al.,
1997, WRR Torres et al., 1998, WRR
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Hortonian Flow

• Sheet flow described by Horton in 1930s
• When iltf, all i is absorbed
• When i gt f, (i-f) results in rainfall excess
• Applicable in
• impervious surfaces (urban areas)
• Steep slopes with thin soil
• hydrophobic or compacted soil with low
  infiltration

Rainfall, i
i gt q
Infiltration, f
Later studies showed that Hortonian flow rarely
occurs on vegetated surfaces in humid regions.
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Subsurface flow

• Lateral movement of water occurring through the
  soil above the water table
• primary mechanism for stream flow generation when
  fgti
• Matrix/translatory flow
• Lateral flow of old water displaced by
  precipitation inputs
• Near surface lateral conductivity is greater than
  overall vertical conductivity
• Porosity and permeability higher near the ground
• Macropore flow
• Movement of water through large conduits in the
  soil

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Soil macropores
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Saturation overland flow

• Soil is saturated from below by subsurface flow
• Any precipitation occurring over a saturated
  surface becomes overland flow
• Occurs mainly at the bottom of hill slopes and
  near stream banks

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Streamflow hydrograph
Direct runoff

• Graph of stream discharge as a function of time
  at a given location on the stream

Baseflow
Perennial river
Snow-fed River
Ephemeral river