Modeling of groundwater flow velocity and aquifer recharge in a Cenozoic multi-aquifer system – a case study from Eastern Brandenburg (Germany)

In recent years, deep aquifers (> 50 m below ground level) have become increasingly interesting for the supply of drinking and irrigation water or geothermal use. Understanding the regional flow processes between near-surface and deep aquifer systems is an important criterion for the sustainable management of deep groundwater resources. However, hydrogeological conditions, regional flow rates and aquifer recharge in deep aquifers are largely unknown in many cases. The aims of the present study are therefore to determine (i) groundwater flow velocities in a Cenozoic multi-aquifer system, and (ii) proportion of aquifer recharge into the individual Cenozoic aquifers and timescales to completely replace water in the Cenozoic aquifers (turnover time).  

The numerical study was carried out in three adjacent groundwater catchment areas in the region of Eastern Brandenburg. In a first step, a hydrogeological 3D model of the entire Cenozoic aquifer system (85 km × 73 km and down to a depth of 0.5 km) was developed, which comprises up to 12 unconsolidated sandy aquifers and 10 confining units (glacial tills, silts and clays). In a second step, a steady-state flow modelling was performed including calibration using natural hydraulic head data from both regional main and deep aquifers.

The modeling results show that the average groundwater flow velocities decrease from 20-50 m/a in the near-surface Pleistocene main aquifers to 1-2 m/a in the deep Oligocene aquifers. At the same time, the aquifer recharge in the aquifer system decreases substantially with increasing depth. Depending on the catchment geology, the Pleistocene main aquifers are recharged by 65-70 % of infiltration water, while the aquifer recharge of the deep Oligocene aquifers is only 4.5-9.5 %. The calculations of turnover time indicate that the time periods to completely flush the deep aquifers are very long (approx. between 90 and 4600 years). The results thus allow a first quantification of the flow processes between near-surface and deep aquifers as well as the identification of flow paths to develop a utilization concept for deep groundwater resources in the region of Eastern Brandenburg.