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  • Publication
    Accès libre
    Cross-sphere modelling to evaluate impacts of climate and land management changes on groundwater resources
    (2021-8) ; ; ;
    Rössler, Ale
    ;
    Holzkämper, Annelie
    Climate change affects both water resources and agricultural production.With rising temperatures and decreasing summer precipitation, it is expected that agricultural production will be increasingly limited by drought. Where surface- or groundwater resources are available for irrigation, an increase inwaterwithdrawals for irrigation is to be expected. Therefore, quantitative approaches are required to anticipate and manage the expected conflicts related to increased water abstraction for irrigation. This project aims to investigate how agricultural production,water demand for irrigation, runoff and groundwater dynamics are affected by future climate change and howclimate change impacts combinedwith changes in agriculturalwater use affect groundwater dynamics. To answer these research questions, a comprehensive, loosely coupled model approach was developed, combining models from three disciplines: an agricultural plant growth model, a hydrological model and a hydrogeological model. The model coupling was implemented and tested for an agricultural area located in Switzerland inwhich groundwater plays a significant role in providing irrigationwater. Our suggested modelling approach can be easily adapted to other areas. The model results show that yield changes are driven by drought limitations and rising temperatures. However, an increase in yieldmay be realized with an increase in irrigation. Simulation results showthat thewater requirement for irrigation without climate protection (RCP8.5) could increase by 40% by the end of the century with an unchanged growing season and by up to 80%with varietal adaptations. With climate changemitigation (RCP2.6) the increase inwater demand for irrigationwould be limited to 7%. The increase in irrigation (+12mm) and the summer decrease in recharge rates (~20mm/month)with decreasing summer precipitation causes a lowering of groundwater levels (40 mm) in the area in the late summer and autumn. This impact may be accentuated by an intensification of irrigation and reduced by extensification.
  • Publication
    Accès libre
    Low-flow behavior of alpine catchments with varying quaternary cover under current and future climatic conditions
    (2020-10)
    Arnoux, Marie
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    Schlaefli, Bettina
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    Mott, Rebecca
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    ;
    Alpine environments are particularly vulnerable to climatic warming, and long term observations suggest a shift of snow-influenced river discharge towards earlier periods of the year. For water resources management, the seasonal patterns of discharge in alpine areas are particularly relevant, as the shift to lower flows in summer and autumn combined with increased water demand could lead to water shortage in downstream catchments. The storage of groundwater in alpine catchments could significantly modulate how changing climatic conditions influence the annual streamflow regime. However, groundwater storage and its buffering capacity in alpine areas remain poorly understood. Moreover, studies on how climate change will impact water resources in alpine areas rarely consider the influence of geology. In this paper, catchment geology is used as a basis for the classification of future summer low flows behavior of several alpine catchments in Switzerland. Based on the analysis of the relationship between low-flow indicators and geology, the role of unconsolidated quaternary deposits is explored. We show that quaternary deposits play a critical role in the seasonal storage of groundwater, which can contribute to rivers during lowflow periods. Three climate change simulations based on extreme RCP 8.5 scenarios are fed into a conceptual hydrological model to illustrate the buffering role of groundwater. Past and future low flows normalized by mean past and future streamflows appear correlated with the percentage of unconsolidated quaternary deposits. These results highlight that catchments with high groundwater contribution to streamflow relative to precipitation will have a slower decrease in future summer discharge. Therefore, we propose two indicators that can be used to anticipate the response of future summers low flows in alpine areas to climate change: the current winter low flows and the percentage of unconsolidated quaternary deposits of the catchments.
  • Publication
    Accès libre
    Lithological and tectonic control on groundwater contribution to stream discharge during low-flow conditions
    Knowing how stream discharge in an ungauged catchment reacts to dry spells is a major challenge for managing water resources. The role of geology on these dynamics is poorly understood. For the Swiss Molasse basin, we therefore explored how the geology influences the groundwater contribution to stream flow during low-flow conditions. Using existing data from geological reports and maps as well as from deep boreholes, we constructed a basin-wide overview of the hydrogeological quality of the bedrock and investigated five catchments in 3D. We found that catchments with the most permeable sedimentary bedrock are least sensitive to low flows (marine sandstone, K = 10−4 to 10−5 m/s, Peff = 5–10%). In contrast, if bedrock K is low (K < 10−6 m/s), the presence of a productive Quaternary volume becomes decisive for groundwater contribution to stream flow. Limitations exist due to a restricted database for K and Peff values of the Molasse and limited information on continuation of lithologies with depth. This emphasizes the need for more hydrogeologically relevant data for the future management of water resources. Our results highlighting what lithotypes favor groundwater contribution to stream flow are valid also in other regions for the assessment of a catchment’s sensitivity to low flows
  • Publication
    Accès libre
    Assessing the perturbations of the hydrogeological regime in sloping fens due to roads
    Roads in sloping fens constitute a hydraulic barrier for surface and subsurface flow. This can lead to the drying out of downslope areas of the sloping fen as well as gully erosion. Different types of road construction have been proposed to limit the negative implications of roads on flow dynamics. However, so far, no systematic analysis of their effectiveness has been carried out. This study presents an assessment of the hydrogeological impact of three types of road structures in semi-alpine, sloping fens in Switzerland. Our analysis is based on a combination of field measurements and fully integrated, physically based modeling. In the field approach, the influence of roads was examined using tracer tests in which the area upslope of the road was sprinkled with a saline solution. The spatial distribution of electrical conductivity downslope provided a qualitative assessment of the flow paths and, thus, the implications of the road structures on subsurface flow. A quantitative albeit not site-specific assessment was carried out using fully coupled numerical models jointly simulating surface and subsurface flow processes. The different road types were implemented and their influence on flow dynamics was assessed for a wide range of slopes and different hydraulic conductivities of the soil. The models are based on homogenous soil conditions, allowing for a relative ranking of the impact of the road types. For all cases analyzed in the field and simulated using the numerical models, roads designed with an L drain (i.e., collecting water upslope and releasing it in a concentrated manner downslope) constitute the largest perturbations in terms of flow dynamics. The other road structures investigated were found to have less impact. The developed methodologies and results can be used for the planning of future road projects in sloping fens.
  • Publication
    Accès libre
    Your work is my boundary condition!: Challenges and approaches for a closer collaboration between hydrologists and hydrogeologists
    (2019-4)
    Maria, Staudinger
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    Michael, Stoelzle
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    Jan, Seibert
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    Markus, Weiler
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    Hydrologists and hydrogeologists both study the flux and storage of water with the numerous interactions and feedback mechanisms of surface water and groundwater. Traditionally however, focus, models and scales of the studies differ. In this commentary, situations are illustrated where boundary conditions that each discipline assumes, preserves and actively uses, can and have to be overcome. These situations occur when the domain of one discipline cannot be separated from the other one because of existing interaction and feedback mechanisms at the boundaries. Highlighted are especially these boundary conditions, where closer collaboration between catchment hydrologists and hydrogeologists would be most useful. Often such collaborations would be relatively straight-forward and rather requiring an increased awareness than novel methods.
  • Publication
    Accès libre
    Exploring Geological and Topographical Controls on Low Flows with Hydrogeological Models
    This study investigates how catchment properties influence low-flow dynamics. With 496 synthetic models composed of a bedrock and an alluvial aquifer, we systematically assess the impact of the hydraulic conductivity of both lithologies, of the hillslope and of the river slope on catchment dynamics. The physically based hydrogeological simulator HydroGeoSphere is employed, which allows obtaining a range of low-flow indicators. The hydraulic conductivity of the bedrock K bedrock , a proxy for transmissivity, is the only catchment property exerting an overall control on low flows and explains 60% of the variance of Q95/Q50. The difference in dynamics of catchments with same K bedrock depends on hillslope gradients and the alluvial aquifer properties. The buffering capacity of the bedrock is mainly related to K bedrock and the hillslope gradient. We thus propose the dimensionless bedrock productivity index (BPI) that combines these characteristics with the mean net precipitation. For bedrock only models, the BPI explains 82% of the variance of the ratio of Q95 to mean net precipitation. The alluvial aquifer can significantly influence low flows when the bedrock productivity is limited. Although our synthetic catchment setup is simple, it is far more complex than the available analytical approaches or conceptual hydrological models. The direct application of the results to existing catchments requires nevertheless careful consideration of the local geological topographic and climatic conditions. This study provides quantitative insight into the complex interrelations between geology, topography and low-flow dynamics and challenges previous studies which neglect or oversimplify geological characteristics in the assessment of low flows. © 2018, National Ground Water Association.
  • Publication
    Accès libre
    Geology controls streamflow dynamics
    Relating stream dynamics to catchment properties is essential to anticipate the influence of changing environ-mental conditions and to predict flows of ungauged rivers. Although the importance of subsurface processes incatchment hydrology is widely acknowledged, geological characteristics are rarely explicitly included in studiesassessing physiographic controls on catchment dynamics. In this investigation of 22 catchments of the SwissPlateau and Prealpes, we use a simple linear regression approach to analyze the relationship between streamflowindicators and various geological and hydrogeological properties of the bedrock and quaternary deposits, alongwith meteorological, soil, land use and topographical characteristics. We use long-term discharge percentiles, aswell as dimensionless flow duration curves (FDC, standardized by long-term mean discharge) that allow toevaluate the catchment response to climate forcing. While climate conditions dominate the high to mediumdischarge percentiles (Q5–Q50), the capacity of the catchments to buffer the meteorological forcing can only beattributed to geological characteristics. The sandstone proportion in the catchments explains 54% of the varianceof both extremities of the dimensionless FDC (Q5/Qmean and Q95/Qmean) and productive quaternary depositsare responsible of 55% resp. 58% of the variance of the two ratios. Examining the hydrogeological characteristicsof both bedrock and quaternary lithologies considerably improves the understanding of catchment dynamics.