Combining wetland restoration with artificial groundwater recharge in urban environments

Prof. Dr. P. Huggenberger, Dr. E. Zechner, R. Kirchhofer

Cooperation with: Christoph Wüthrich, Arnold Gurtner-Zimmermann, Urs Geissbühler, Jessica Kohl, <link de physiogeographieundumweltwandel external-link-new-window physiogeographie>Physiogeographie, Universität Basel, CH-4056 Basel

Artificial groundwater recharge is a commonly applied method to secure drinking water needs of densely populated areas. The artificial recharge process is typically realised with pre-filtered surface water in basins or fields with a more or less pre-defined size. The quality of the pumped drinking water, however, is not only linked to the surface water quality used for artificial recharge, but also to the active microbiological and hydrochemical processes during the passage of the components soil, unsaturated zone and saturated zone.

The presented experiment site is located in the alluvial plain of the Wiese River in Northwestern Switzerland. The Wiese River is, similarly to most rivers and streams of Central Europe, channeled for flood control purpose. Recent multidisciplinary efforts were directed towards reconnecting the Wiese River with its floodplain. We defined a set of goals: (1) creating an environment of partially flooded, wetland-type vegetation in the artificial recharge fields, (2) using river water for the artificial recharge which undergoes considerable fluctuations in discharge and water quality, and (3) maintaining a high quality drinking water from the production wells. In order to obtain the evaluation basis for the effects of the partial wetland restoration, we needed an improved understanding of the subsurface processes. Aquifer residence times of the infiltrated water or breakthrough behaviour of a persistent solute inside the aquifer were of key interest for judgement.

Flow-control structures, tensiometers, monitoring wells and geophysical methods are used to provide data of relevant water fluxes, distributions of hydraulic heads, surface water and pore water concentrations of different hydrochemical tracers (e.g. DOC, major ions, radon gas), and tomographies of the subsurface heterogeneities. A 3-D numerical flow and solute transport model is calibrated against different combinations of the available data. The presented modelling efforts will ultimately lead to a decision tool for larger-scale environmental restoration efforts in the alluvial plain.