Soil Regulates Circulation of Water on the Planet Earth - Soil: The Skin of the Planet Earth - page 137

Fig. 10.4 Soil water content profi les measured at increasing times in a homogeneous soil initially
at a soil water content θ i during a rain of constant intensity. Time t 1 is just after the start of infi ltra-
tion. The time t 4 equal to t p designates the ponding time when the soil surface becomes water satu-
rated θ S . For greater times like t 5 in our fi gure, the curve shows the water-saturated segment of the
profi le continually elongating roughly in a similar way like in fl ood infi ltration demonstrated in
Fig. 10.2
the terrain is ideally fl at. If there is a slope, the water fl ows down the surface with
the runoff increasing with time. The water fl owing on the surface starts to be con-
centrated in rills and fi nally it reaches a river or lake. If the rising water level reaches
and exceeds a critical geographical level, a fl ood covers the valley of the river.
Although the curves in Fig. 10.5 demonstrate that the ponding time comes earlier
when the rain intensity is increased, we must remember that the hydraulic