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02/23/2006. Runoff Processes. Slides from Venkatesh Merwade and Suzanne Anderson Reading: Applied Hydrology Sections 5.1 and 5.2. 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

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runoff processes

02/23/2006

Runoff Processes

Slides from Venkatesh Merwade and Suzanne Anderson

Reading: Applied Hydrology Sections 5.1 and 5.2

surface water
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.
sources of streamflow
Sources of streamflow

http://uregina.ca/~sauchyn/geog327/outline.html

streamflow generation
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
slide6

Denudation

Erosion and weathering control the extent of critical zone development

Weathering front advance

slide7

Sediment

Water, solutes and nutrients

Critical zone architecture influences sediment sources, hydrology, water chemistry and ecology

slide8

Fort Collins

The Colorado Front Range

Boulder

Golden

slide9

Fort Collins

The Boulder Creek watershed

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

Boulder

Limits of glacial

and fluvial rejuvenation

Golden

boulder creek critical zone observatory
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.

slide12

Three experiments in one:

the geomorphic context of Boulder Creek

Upper: glaciated

Middle: steady, old

Lower: rejuvenated

slide15

Oregon Coast Range- Coos Bay

Channel head

Anderson et al., 1997, WRR.

Montgomery et al., 1997, WRR

Torres et al., 1998, WRR

hortonian flow
Hortonian Flow
  • Sheet flow described by Horton in 1930s
  • When i<f, all i is absorbed
  • When i > 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 > q

Infiltration, f

Later studies showed that Hortonian flow rarely occurs on vegetated surfaces in humid regions.

subsurface flow
Subsurface flow
  • Lateral movement of water occurring through the soil above the water table
  • primary mechanism for stream flow generation when f>i
    • 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
saturation overland flow
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
streamflow hydrograph
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