Processes acting on the formation of subsurface flow

Distribution of the soil layers

The interflow or hypodermic flow is formed in the unsaturated soil layer and flows more or less directly through this soil layer to the river. It is differed in slow and fast interflow. While the slow interflow results from long flow paths in the soil layer the fast interflow occurs in areas with distinct gradient of the topography, short distance to rivers and in unsaturated soil zones with decreasing permeability in the vertical or a layered soil profile in which the permeability of the lower layer is much less than the upper one (by power of 2 to 3 for sandy soil and power of 1 for loamy soil(*1)). Zuidema (*2) showed that the interflow can occur in the network of macropores, soil pipes and cracks or through porous medium along an impervious layer (piston-flow).

Cross section GWR-river-Model approach for base flow



In steep regions (e.g. at hillsides) gravity can drive free soil water through the soil matrix, called matrix-throughflow(*3).

Interflow, which drains into wide flat valleys can be blocked by groundwater ridges. Here they will press the groundwater into the river by lifting the groundwater table(*4).

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Hydrology of Floods



*1 Peschke et al (1999)

*2 Zuidema (1985)

*3 Kirby/Chorly (1967)

*4 Blowes/Gillham (1988)



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