Water retention capacity of Bavaria’s soil function map 1:25,000 (BFK25) for three project areas

Soils fulfil important functions in the natural environment. The Federal Soil Protection Act protects these valuable soil functions. Soil function maps evaluate the performance of soils in the natural environment. The assessment is based on soil maps (mostly overview soil maps i.M. 1:25,000) and other information on the environment and location. The area information is implemented by means of linking rules to assessments. The soil has the important balancing function in the water cycle to absorb precipitation water, to store and to provide water delaying the vegetation, rivers and streams or the groundwater reservoir. The assessment of the soil as a balancing body in the water cycle is carried out on the basis of the criterion ‘water retention capacity of the soil’. This refers to the ability of the soil to store precipitation water in the pore room or to pass it on to deeper layers by leaching, thus removing the superficial drainage. Based on the saturated water conductivity, the usable field capacity and — in a flat or drain carrier location — the air capacity is estimated how much precipitation water a soil can absorb before surface drainage occurs. Soil hydromorphy, slope inclination and hydrogeological conditions are used as differentiation criteria. The maps can be used to take into account the balancing and protective effect of the soil on the water balance in terms of decentralised flood protection and water purification during planning and to be able to identify important water retention rooms. The soil function map “Compensation body in the water cycle” represents a soil protection evaluation of the soil map. Since the basic data of the soil function map are partly based on different topographical foundations, overlapping inaccuracies occur when comparing with current usage maps, especially at usage limits. In some cases, the evaluated areas in the soil function map are very inhomogeneous, so that in addition to the evaluation stage shown, different evaluations are also subordinated. Areas of less than 5 000 m² were added to neighbouring areas.