Assessment of groundwater residence times in the pore aquifers of the River Elbe Basin

An area covering assessment of the groundwater residence times for the upper pore aquifers in the River Elbe Basin was performed. Residence times were determined by combining groundwater velocities and flow distances along each flow-path to the surface waters using a two-dimensional model approach. Groundwater velocity was calculated as a function of hydraulic conductivity, hydraulic gradient and effective yield of pore space. Flow paths were obtained by an analysis of the morphology of the groundwater table. The mean groundwater residence time in the pore aquifers of the River Elbe Basin was quantified to about 25 years. A strong temporal blurring in the different regions between less than one year and more than 250 years was obtained. For the regional groundwater management in the Elbe Basin the groundwater residence times are an important parameter, which helps to take into account the temporal dimension in the assessment of the impact of political measures aiming at the improvement of groundwater quality with regard to diffuse pollutants (e.g. nitrate).