Surface Hydrology: I—Explanation of Phenomena

Nonisotropic sloping soil leads to a horizontal flow component during rain and infiltration. Splashing of raindrops and flow in the transition zone between the soil bulk and the air also lead to lateral flow. The result is concentration of moisture in concave spots to the point of saturation and even seepage out of the soil. The same occurs at steep soil cuts. Such moisture concentration can explain the formation of runoff during rainfall at low rates that do not exceed infiltration capacity, partial area contribution to runoff, net recharge of groundwater by low-rate rainfall, the formation of rills and gullies in a relatively dry area, delay of runoff after a certain total amount of rain irrespective of rain intensity, variations in soil formation in different parts of the landscape, poor distribution of irrigation water in nonplane fields, and leaching of the soil surface by water that was assumed to run only above the surface.