USING FLOOD WATER FOR ARTIFICIAL GROUNDWATER RECHARGE TO DAMPEN FLOOD PEAKS AND DROUGHTS - INVESTIGATIONS IN THE THUR CATCHMENT (SWITZERLAND)

The Thur catchment, located in NE Switzerland, includes high altitude groundwater flow systems that play an important role for drinking water supply and groundwater flow systems in the alluvial plains. The mainly channelized Thur River is draining the front ranges of the Swiss Limestone Alps into the Rhine River and it is the largest river without retention areas in Switzerland. River discharge is very dynamic from 3 to up to 1100 m³/s (average discharge around 53 m³/s). Numerous abstraction wells along the Thur River and in the Thur valley are used for drinking water supply. However, some of the wells fall dry after long and dry summers, whereas periodic flooding can cause substantial damages during the snow-melt period in late spring.

Within the multidisciplinary RECORD Catchment Project, a follow-up project of the RECORD Project (RECORD – Restored Corridor Dynamics), we investigate what measures are most effective to influence the river corridor in a way, that river restoration and groundwater flow systems can be designed to help mitigate the effects of floods and droughts. Furthermore, we want to deduce general key indicators, which can help to give recommendations for future river restoration projects, not only along the Thur River.

With strategic combinations of ecologically and economically sustainable water harvesting, storage and supply, water in a catchment can be spatially and temporally distributed in such a way that peak flow can be significantly dampened. This is achievable through a combination of restoring river sections, holding back and redirecting water flows in subcatchments, creation of retention areas and by artificial groundwater recharge. We furthermore hypothesize that restored river sections will help to improve river water quality through enhanced hyporheic exchange and through water exchange in the riparian zone. In addition, the orders-of-magnitude slower water flow velocities in the subsurface (in comparison to rivers) will help to “retard”, store and purify the water, which also enhances water quality in the entire Thur catchment.

At the GSA, we present an overview on the background, applied methods and results of the RECORD project as well as of the RECORD Catchment Project.