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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. 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

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  1. 02/23/2006 Runoff Processes Slides from Venkatesh Merwade and Suzanne Anderson Reading: Applied Hydrology Sections 5.1 and 5.2

  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 • Affected by climate, land cover, soil type, etc.

  3. Sources of streamflow http://uregina.ca/~sauchyn/geog327/outline.html

  4. 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

  5. Welcome to the Critical Zone

  6. Denudation Erosion and weathering control the extent of critical zone development Weathering front advance

  7. Sediment Water, solutes and nutrients Critical zone architecture influences sediment sources, hydrology, water chemistry and ecology

  8. Fort Collins The Colorado Front Range Boulder Golden

  9. Fort Collins The Boulder Creek watershed • Precambrian crystalline bedrock • Uniform climate history • Three erosional states Boulder Limits of glacial and fluvial rejuvenation Golden

  10. 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.

  11. Three experiments in one: the geomorphic context of Boulder Creek Upper: glaciated Middle: steady, old Lower: rejuvenated

  12. Front Range ‘Rocky mountain surface’

  13. Lower: Boulder Canyon-Betasso

  14. Oregon Coast Range- Coos Bay Channel head Anderson et al., 1997, WRR. Montgomery et al., 1997, WRR Torres et al., 1998, WRR

  15. 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.

  16. 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

  17. Soil macropores

  18. 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

  19. 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

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