Ein Speicher-Durchfluss-Modell für die Abflussbildung im Oberjura-Karst der Schwäbischen Alb

Upper Jurassic karstified limestones in southern Germany are characterized by a dual-porosity system. Here we present a new model that describes the basic processes from recharge to discharge. While recharge is distributed to both main conduits and fractures, only minor amounts of the total runoff reach the karst system directly (direct runoff) while most water infiltrates into the fractured matrix. This mechanism expels pre-event water from the fissured matrix and into karst conduits. Additionally, matrix storage exponentially decreases during baseflow conditions. Altogether, direct runoff, pre-event water and baseflow fill the karst system and make up the spring discharge. Based on a time series of 40 years of recharge data, the model simulates daily changes of groundwater volumes within the two storage systems. Prerequisites are recession coefficients for baseflow and conduits. A distribution coefficient calculates the amount of direct runoff and a second coefficient the amount of pre-event water. Calculated discharges were in good agreement with the spring hydrograph.