Zeitliche und räumliche Skalen der Fluss-Grundwasser-Interaktion : ein multidimensionaler hydrogeologischer Untersuchungsansatz

Die Prozesse der Fluss-Grundwasser-Interaktionen sind stark skalenabhängig und im Allgemeinen stark instationär. Einen für das Prozessverständnis wichtigen Aspekt betreffen die kleinräumigen Strömungsverhältnisse an der Grenzschicht zwischen Oberflächengewässer und Grundwasser im hyporheischen Interstitial. Dies betrifft insbesondere auch Fragestellungen zu Strömungsverhältnissen in Forellenlaichgruben kiesführender Flüsse. Exemplarisch für kleinere mit Sohlschwellen verbaute und kanalisierte Fließgewässer wurden am voralpinen Schweizer Fluss Enziwigger verschiedene Methoden entwickelt, getestet und kombiniert, die es erlauben die vier Dimensionen (drei räumliche und eine zeitliche) der Interaktion Oberflächengewässer-Interstitialraum-Grundwasser für einzelne Flussabschnitte zu erfassen. Der Aufbau eines Messnetzes sowie die Durchführung von Feldmessungen lieferten Grundlagen für eine Grundwasserströmungsmodellierung. Kontinuierliche Zeitreihen der Hydraulik, Temperatur und elektrischen Leitfähigkeit im Fließgewässer, an der Gewässersohle sowie im flussnahen Grundwasser dienten zudem der Identifizierung von Zonen mit signifikantem Fluss-Grundwasser-Austausch und von zeitlich instationären bevorzugten Fließpfaden im Grundwasser bei unterschiedlichen hydrologischen Randbedingungen. Die Resultate der Feldmessungen in Kombination mit der instationären Modellierung und Szenarienentwicklung illustrieren die Bedeutung von sich dynamisch verändernden Infiltrations- und Exfiltrationsmustern im Flussbett. Abstract River-groundwater interactions show strong scale-dependencies and are often strongly transient. In this regard, small-scale flow conditions in the hyporheic zone at the interface between surface- and groundwater can be important for process-understanding. This especially includes questions concerning flow conditions in salmonid redds of gravel-bed rivers. The Swiss subalpine river Enziwigger was chosen as an example for a small channelized river with artificial steps within the riverbed. Several methods were developed, tested and combined that capture the four dimensions (three spatial and one temporal) of the interactions between surface water, the hyporheic zone and groundwater, for individual river segments. The setup of a monitoring network as well as the realization of field-measurements provided data for groundwater flow models. Continuous time series of hydraulic data, temperature and electrical conductivity within the river and the riverbed, as well as within the riverine groundwater, allowed identifying zones with significant exchange of surface water and groundwater. Additionally, the data helped describe the transient character of groundwater flow-paths under various hydrological boundary conditions. Results of the field-measurements in combination with transient groundwater flow modeling and scenario analyses illustrate the relevance of dynamically changing infiltration and exfiltration patterns within the riverbed

Do SASS5 scores vary with season in the South African highveld? A case study on the Skeerpoort River, North West province, South Africa

Macroinvertebrate assemblages can vary with season as a result of changing environmental conditions and phenology of individual species. The objective of this study was to determine whether results from the South African Scoring System version 5 (SASS5) are affected by season. The standard SASS5 protocol was used to sample three sites on the Skeerpoort River, South Africa, in autumn, winter and spring 2013, and summer 2014. At each site, stream morphology was characterised and physicochemical variables were measured. Two-way analysis of variance (ANOVA) was used to compare SASS indices in relation to site and season, and a one-way ANOVA was used to test the effect of season using both current and historical data. Macroinvertebrate assemblage similarity of sites was determined using nonmetric multidimensional scaling ordination, followed by analysis of similarity. Whilst macroinvertebrate assemblages differed between seasons and sites, there was no seasonal variation in the values of SASS indices, but they did differ between sites. SASS5 appears to be robust to seasonal variation in macroinvertebrate assemblage and seems suitable for use throughout the year in a perennial river draining the South African highveld region.University of Pretoria through a Research Development Programme.http://www.tandfonline.com/loi/taas202015-12-30hb201

Adaptive groundwater management in urban areas Effect of surface water-groundwater interaction using the example of artificial groundwater recharge and in- and exfiltration of the river Birs (Switzerland)

Groundwater resources in urban areas are under increasing pressure. The purpose of this manuscript is to demonstrate how adaptive groundwater management techniques can establish conditions for sustainable use of groundwater resources. To illustrate this, a representative transient dataset from the Lower Birs Valley (Switzerland) was investigated. The main focus of this work was to evaluate effects of river-groundwater interaction and artificial groundwater recharge. Results showed that the evaluation of a hundred year flood significantly contributed to the understanding of the transient character of river-groundwater interaction. An extended period without artificial recharge in the study area provided insights into the impact of planned changes in groundwater management. This investigation contributes to the better understanding of recharge processes in the groundwater system and provides a framework for discussion of goals for regional management of urban water resources. Hydrogeologie der Nordwestschweiz, Grundwasse