Mean Annual Rate of Percolation from the Soil in Germany

The mean annual rate of percolation from the soil is defined as the amount of water that leaves the soil after consideration of capillary rise. It is expressed in mm/a. Precipitation water infiltrated into the soil after deduction of surface runoff, first stands for the water supply of the vegetation available. Exceeds the water content in the root zone, the field capacity, the water infiltrated force of gravity moved following down and leaves the root zone. Movement of water in the unsaturated zone is affected by infiltration of precipitation and irrigation water, evaporation, absorption of water by plant roots, and ascent of water from the groundwater table by capillary action. The percolating water leaves the soil as interflow, discharging into surface water bodies, or via the groundwater table, recharging the groundwater. Percolating water affects soil formation and the migration and leaching of plant nutrients and contaminants. Knowledge of the rate of percolation is of particular importance for protecting groundwater quality. The mean annual rate of percolation is the balance of precipitation, evapotranspiration and surface runoff.