Impact of river reconstruction on groundwater flow during bank filtration assessed by transient three-dimensional modelling of flow and heat transport

• Published in: Hydrogeology journal Vol. 28; no. 2; pp. 723 - 743
• Main Authors: Wang, Wei-shi, Oswald, Sascha E., Gräff, Thomas, Lensing, Hermann-Josef, Liu, Tie, Strasser, Daniel, Munz, Matthias
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.03.2020; Springer Nature B.V
• Subjects: Aquatic Pollution; Aquifers; Biodegradability; Canals; Computer simulation; Earth and Environmental Science; Earth Sciences; Filtration; Flow paths; Geology; Geophysics/Geodesy; Groundwater; Groundwater flow; Heat transport; Hydrogeology; Hydrology; Hydrology/Water Resources; Mixing ratio; Oxidoreductions; Permeability; Reconstruction; River beds; River water; Riverbeds; Rivers; Surface water; Temperature; Temperature effects; Temperature patterns; Temporal distribution; Temporal variations; Three dimensional flow; Three dimensional models; Travel; Travel time; Unsteady flow; Waste Water Technology; Water infiltration; Water Management; Water Pollution Control; Water purification; Water quality; Water Quality/Water Pollution; Water utilities; Waterworks; Winter temperatures; Zonation; Bank filtration; Groundwater modelling; Groundwater/surface-water relations
• ISSN: 1431-2174; 1435-0157
• DOI: 10.1007/s10040-019-02063-3

Bank filtration (BF) is an established indirect water-treatment technology. The quality of water gained via BF depends on the subsurface capture zone, the mixing ratio (river water versus ambient groundwater), spatial and temporal distribution of subsurface travel times, and subsurface temperature patterns. Surface-water infiltration into the adjacent aquifer is determined by the local hydraulic gradient and riverbed permeability, which could be altered by natural clogging, scouring and artificial decolmation processes. The seasonal behaviour of a BF system in Germany, and its development during and about 6 months after decolmation (canal reconstruction), was observed with a long-term monitoring programme. To quantify the spatial and temporal variation in the BF system, a transient flow and heat transport model was implemented and two model scenarios, ‘with’ and ‘without’ canal reconstruction, were generated. Overall, the simulated water heads and temperatures matched those observed. Increased hydraulic connection between the canal and aquifer caused by the canal reconstruction led to an increase of ~23% in the already high share of BF water abstracted by the nearby waterworks. Subsurface travel-time distribution substantially shifted towards shorter travel times. Flow paths with travel times <200 days increased by ~10% and those with <300 days by 15%. Generally, the periodic temperature signal, and the summer and winter temperature extrema, increased and penetrated deeper into the aquifer. The joint hydrological and thermal effects caused by the canal reconstruction might increase the potential of biodegradable compounds to further penetrate into the aquifer, also by potentially affecting the redox zonation in the aquifer.