Runoff Processes - ce.utexas.edu

Runoff Processes 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 Affected by climate, land cover, soil type, etc. Streamflow generation Streamflow is generated by three mechanisms 1. Hortonian overland flow

2. Subsurface flow 3. Saturation overland flow Some texts mention groundwater ridging as an additional mechanism contributing to streamflow Welcome to the Critical Zone Denudation

Erosion and weathering control the extent of critical zone development Weathering front advance Sediment Water, solutes and nutrients

Critical zone architecture influences sediment sources, hydrology, water chemistry and ecology Oregon Coast Range- Coos Bay soil

Channel head weathered rock water flow path fracture zone bedding 5m 5m

Anderson et al., 1997, WRR. Montgomery et al., 1997, WRR Torres et al., 1998, WRR Hortonian Flow Sheet flow described by Horton in 1930s 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 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 Soil macropores 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 Graph of stream discharge as a function of time at a given location on the stream Ephemeral river

Direct runoff Baseflow Perennial river Snow-fed River