Water Flow in Soils
Water movement in soils is a key process that a¦ects water quantity and quality in the environment. Since the transport of solutes is closely linked with the soil water ¥ux, any quantitative analysis of solute transport must rst evaluate water ¥uxes into and through soil. Water typically enters the soil surface in the form of precipitation or irrigation or by means of industrial and municipal spills (Figure 5.1). Some of the rainfall or irrigation water may be intercepted by the plant canopy. If the rainfall or irrigation intensity is larger than the inltration capacity of the soil, water will be removed by surface runo¦ or will accumulate at the soil surface until it evaporates back to the atmosphere or inltrates into the soil. Part of the water that inltrates is returned back to the atmosphere by evaporation. Water that inltrates into the soil prole may also be taken up by plant roots and eventually returned to the atmosphere by plant transpiration. ¤e processes of evaporation and transpiration are oen combined into
the single process of evapotranspiration. Only water that is not returned to the atmosphere by evapotranspiration may percolate to the deeper soil zone and eventually reach the groundwater. If the water table is close enough to the soil surface, the process of capillary rise may move water from the water table through the capillary fringe toward the root zone and the soil surface.