Backwater occurs when a difficult-to-water-permeable body of silt or clay obstructs the downward movement of the seepage water in the ground. Backwater forms especially after heavy rainfall or after the snow has melted. In the event of prolonged drought and due to the water consumption of the vegetation ( evapotranspiration ), it usually disappears in the course of the vegetation period . The damming body is given the horizon designation Sd, the damming zone the horizon designation Sw.
The backwater can be viewed as a special form of groundwater. In contrast to groundwater , which is usually present permanently and also in deeper layers, backwater occurs only temporarily and only near the surface (reservoir bottom <130 cm below the surface); If the reservoir is deeper, the water is usually no longer completely consumed by the vegetation, so that it can be viewed as (permanently available) groundwater. The term backwater is only used in soil science . In geology, all water in the ground is understood as groundwater. In geotechnical engineering , the term stratified water is more commonly used.