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Streamflow Processes in Watershed Areas

Explore the mechanisms of streamflow generation, including Hortonian overland flow, subsurface flow, and saturation overland flow. Learn about the factors influencing streamflow and its hydrograph.

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Streamflow Processes in Watershed Areas

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  1. Streamflow Processes • 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.

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

  3. 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

  4. 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.

  5. 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

  6. Soil macropores

  7. 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

  8. 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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