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Hunkeler, Daniel
Nom
Hunkeler, Daniel
Affiliation principale
Fonction
Professeur ordinaire
Email
daniel.hunkeler@unine.ch
Identifiants
Résultat de la recherche
Voici les éléments 1 - 10 sur 18
- PublicationAccès libreCross-sphere modelling to evaluate impacts of climate and land management changes on groundwater resources(2021-8)
; ; ; - PublicationAccès libreA Framework for Untangling Transient Groundwater Mixing and Travel Times(2021-2)
; ; ; ; Kipfer, RolfUnderstanding the mixing between surface water and groundwater as well as groundwater travel times in vulnerable aquifers is crucial to sustaining a safe water supply. Age dating tracers used to infer apparent travel times typically refer to the entire groundwater sample. A groundwater sample, however, consists of a mixture of waters with a distribution of travel times. Age dating tracers only reflect the proportion of the water that is under the dating range of the used tracer, thus their interpretation is typically biased. Additionally, end-member mixing models are subject to various sources of uncertainties, which are typically neglected. In this study, we introduce a new framework that untangles groundwater mixing ratios and travel times using a novel combination of in-situ noble gas analyses. We applied this approach during a groundwater pumping test carried out in a pre-alpine Swiss valley. First, we calculated transient mixing ratios between recently infiltrated river water and regional groundwater present in a wellfield, using helium-4 concentrations combined with a Bayesian end-member mixing model. Having identified the groundwater fraction of recently infiltrated river water (Frw) consequently allowed us to infer the travel times from the river to the wellfield, estimated based on radon-222 activities of Frw. Furthermore, we compared tracer-based estimates of Frw with results from a calibrated numerical model. We demonstrate (i) that partitioning of major water sources enables a meaningful interpretation of an age dating tracer of the water fraction of interest and (ii) that the streambed has a major control on the estimated travel times. - PublicationAccès libreLow-flow behavior of alpine catchments with varying quaternary cover under current and future climatic conditions(2020-10)
; ; 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. - PublicationAccès libreLithological and tectonic control on groundwater contribution to stream discharge during low-flow conditions(2020-3-1)
; ; ; ; 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 - PublicationAccès libreAssessing the perturbations of the hydrogeological regime in sloping fens due to roads(2020-2-1)
; ; ; 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. - PublicationAccès libreCOMPEST, a PEST-COMSOL interface for inverse multiphysics modelling: Development and application to isotopic fractionation of groundwater contaminants(2019-5)
; ; In the geosciences, inverse problems, wherein observations corresponding to model outputs are known and model parameters are unknown, are commonplace. Many of these problems involve coupled physical, chemical, and other processes that can be modelled using forward finite-element models. Here, we present a novel interface, COMPEST, that connects the parameter estimation and uncertainty analysis package, PEST, with the finite-element modelling package, COMSOL Multiphysics. To demonstrate some of the capabilities of this approach, we also develop and present a novel model for the degradation and transport of chlorohydrocarbons in low-permeability units. This model integrates isotopic fractionation arising from degradation and diffusion. Three implementations of this model with increasing complexity are used to demonstrate the functionality of the developed interface. This linkage provides a means for parameter estimation, uncertainty analysis, and singular value decomposition to gain insight into the behaviour, identifiability, and interdependence of the various parameters in the model. COMPEST is written so as to be suited to a wide range of scientific and engineering applications and thus can be used to link any COMSOL model with PEST. This enables the use of advanced inverse modelling techniques previously unavailable to COMSOL users. - PublicationAccès libreExploring Geological and Topographical Controls on Low Flows with Hydrogeological Models(2019-1)
; ; ; ; 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. - PublicationAccès libreGeology controls streamflow dynamics(2018-8)
; ; ; ; 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. - PublicationAccès libreIntegrating hydrological modelling, data assimilation and cloud computing for real-time management of water resources(2017-7-1)
; ; ; ; ; ; - PublicationAccès libreInfiltration under snow cover: Modeling approaches and predictive uncertainty(2017)
; ; Groundwater recharge from snowmelt represents a temporal redistribution of precipitation. This is extremely important because the rate and timing of snowpack drainage has substantial consequences to aquifer recharge patterns, which in turn affect groundwater availability throughout the rest of the year. The modeling methods developed to estimate drainage from a snowpack, which typically rely on temporallydense point-measurements or temporally-limited spatially-dispersed calibration data, range in complexity from the simple degree-day method to more complex and physically-based energy balance approaches. While the gamut of snowmelt models are routinely used to aid in water resource management, a comparison of snowmelt models’ predictive uncertainties had previously not been done. Therefore, we established a snowmelt model calibration dataset that is both temporally dense and represents the integrated snowmelt infiltration signal for the Vers Chez le Brandt research catchment, which functions as a rather unique natural lysimeter. We then evaluated the uncertainty associated with the degree-day, a modified degree-day and energy balance snowmelt model predictions using the nullspace Monte Carlo approach. All three melt models underestimate total snowpack drainage, underestimate the rate of early and midwinter drainage and overestimate spring snowmelt rates. The actual rate of snowpack water loss is more constant over the course of the entire winter season than the snowmelt models would imply, indicating that mid-winter melt can contribute as significantly as springtime snowmelt to groundwater recharge in low alpine settings. Further, actual groundwater recharge could be between 2 and 31% greater than snowmelt models suggest, over the total winter season. This study shows that snowmelt model predictions can have considerable uncertainty, which may be reduced by the inclusion of more data that allows for the use of more complex approaches such as the energy balance method. Further, our study demonstrated that an uncertainty analysis of model predictions is easily accomplished due to the low computational demand of the models and efficient calibration software and is absolutely worth the additional investment. Lastly, development of a systematic instrumentation that evaluates the distributed, temporal evolution of snowpack drainage is vital for optimal understanding and management of cold-climate hydrologic systems.