Spatiotemporal scales of river-groundwater interaction - The role of local interaction processes and regional groundwater regimes

Abstract

Drinking water production in the vicinity of rivers not only requires the consideration of different spatiotemporal scales and settings of river-groundwater interaction processes, but also of local and regional scale groundwater regimes. Selected case studies in combination with field-experiments and the setup of high-resolution groundwater flow models enabled the investigation of the spatiotemporal development of microbial (classical fecal indicator bacteria and total cell counts) and selected organic micropollutants in riverine and regional groundwater for different hydrological settings, including low and high flow conditions. Proxy indicators suitable as surrogates for the diverse contaminations in alluvial aquifers with different settings could be identified. Based on the study results, the basic elements for both groundwater management and river restoration concepts are derived, which include the: (1) compilation and evaluation of the "current state" concerning hydrogeology, microbiology and contamination by organic micropollutants, (2) definition of field-experiments to qualitatively assess variability related to the "current state", and (3) quantitative assessment of groundwater regimes, including variability of groundwater components and inflow areas, by application of high-resolution groundwater flow models. The validity and transferability of the concept and inferred controls (specifically drivers and controls of river-groundwater interaction) are tested by evaluations derived from hydraulic relationships to river sections with comparable settings and regional groundwater flow regimes in general. The results of our investigations illustrate the influence of dynamic hydrologic boundary conditions on river-groundwater interaction and of regional scale groundwater flow regimes on the water composition of riverine groundwater systems. It is demonstrated how to identify river sections and their variations with intensified river-groundwater exchange processes and how to quantify the transient character of the different groundwater components that constitute the raw water quality of drinking water wells near rivers.

Keywords: Filter-efficiency; Microbiology; Organic micropollutants; River sections; Spatiotemporal scales and settings; Variability of groundwater components and inflow areas.