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Jeannin, Pierre-Yves

Nom
Jeannin, Pierre-Yves
Affiliation principale
Email
pierre-yves.jeannin@unine.ch
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https://libra.unine.ch/handle/123456789/809

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  • Publication
    Accès libre
    Hydraulics and Turbidity Generation in the Milandre Cave (Switzerland)
    (2021)
    Vuilleumier, Cécile 
    ;
    Jeannin, Pierre-Yves 
    ;
    Marc Hessenauer
    ;
    Perrochet, Pierre 
    AbstractKarst aquifers may convey significant sediment fluxes, as displayed by the intense turbidity peaks commonly observed at karst springs. The understanding of the origin of the suspended solids discharged at springs is key in assessing spring vulnerability and securing drinking water quality. The mechanisms for turbidity generation and sediment transport in karst are however difficult to investigate because of the general lack of access to the karst conduits. These processes have been examined in the Milandre Cave, which hosts a karst drain of regional importance, for more than 10 years by means of turbidity monitoring both inside and at the outlets of this karst system. Additionally, the composition of the suspended load (particle‐size distribution and Escherichia coli content) has been monitored over the course of a flood event. These data are compared against a numerical simulation of the mean boundary shear stress inside the conduit network. The following conceptual model for sediment transport through the system is derived: during minor flood events, most of the turbidity comes from underground sediment remobilization, while during medium to intense flood events, soil‐derived turbidity also reaches the spring. Hydraulics in the epiphreatic zone is tightly linked with autochthonous turbidity generation (mostly during the flooding and the flushing of conduits). In comparison, allochthonous turbidity is associated with finer particles, higher E. coli, and higher UV fluorescence. This improves the overall understanding of turbidity generation and could help the monitoring and forecast of pollution events at drinking water supplies.
  • Publication
    Accès libre
    The role of tributary mixing in chemical variations at a karst spring, Milandre, Switzerland
    (2007-01-01)
    Perrin, J.
    ;
    Jeannin, Pierre-Yves 
    ;
    Cornaton, Fabien 
    Solute concentration variations during flood events were investigated in a karst aquifer of the Swiss Jura. Observations were made at the spring, and at the three main subterraneous tributaries feeding the spring. A simple transient flow and transport numerical model was able to reproduce chemographs and hydrographs observed at the spring, as a result of a mixing of the concentration and discharge of the respective tributaries. Sensitivity analysis carried out with the model showed that it is possible to produce chemical variations at the spring even if all tributaries have constant (but different for each of them) solute concentrations. This process is called tributary mixing. The good match between observed and modelled curves indicate that, in the phreatic zone, tributary mixing is probably an important process that shapes spring chemographs. Chemical reactions and other mixing components (e.g. from low permeability volumes) have a limited influence.
    Dissolution-related (calcium, bicarbonate, specific conductance) and pollution-related parameters (nitrate, chloride, potassium) displayed slightly different behaviours: during moderate flood events, the former showed limited variations compared to the latter. During large flood events, both presented chemographs with significant changes. No significant event water participates in moderate flood events and tributary mixing will be the major process shaping chemographs. Variations are greater for parameters with higher spatial variability (e.g. pollution-related). Whereas for large flood events, the contribution of event water becomes significant and influences the chemographs of all the parameters. As a result, spring water vulnerability to an accidental pollution is low during moderate flood events and under base flow conditions. It strongly increases during large flood events, because event water contributes to the spring discharge.
  • Publication
    Accès libre
    A quantitative method for the characterisation of karst aquifers based on spring hydrograph analysis
    (2005)
    Kovacs, Attila 
    ;
    Perrochet, Pierre 
    ;
    Kiraly, Laszlo 
    ;
    Jeannin, Pierre-Yves 
    This paper presents a method for characterizing flow systems in karst aquifers by acquiring quantitative information about the geometric and hydraulic aquifer parameters from spring hydrograph analysis. Numerical sensitivity analyses identified two fundamentally different flow domains, depending on the overall configuration of aquifer parameters. These two domains have been quantitatively characterized by deducing analytical solutions for the global hydraulic response of simple two-dimensional model geometries.

    During the baseflow recession of mature karst systems, the hydraulic parameters of karst conduits do not influence the drainage of the low-permeability matrix. In this case the drainage process is influenced by the size and hydraulic parameters of the low-permeability blocks alone. This flow condition has been defined as matrix-restrained flow regime (MRFR). During the baseflow recession of early karst systems and fissured systems, as well as the flood recession of mature systems, the recession process depends on the hydraulic parameters and the size of the low-permeability blocks, conduit conductivity and the total extent of the aquifer. This flow condition has been defined as conduit-influenced flow regime (CIFR).

    Analytical formulae demonstrated the limitations of equivalent models. While equivalent discrete-continuum models of early karst systems may reflect their real hydraulic response, there is only one adequate parameter configuration for mature systems that yields appropriate recession coefficient. Consequently, equivalent discrete-continuum models are inadequate for simulating global response of mature karst systems. The recession coefficient of equivalent porous medium models corresponds to the transition between matrix-restrained and conduit-influenced flow. Consequently, equivalent porous medium models yield corrupted hydrographs both in mature and early systems, and this approach is basically inadequate for modelling global response of karst aquifers.
  • Publication
    Accès libre
    L’eau, sculptrice sur pierre
    (2004-08-25)
    Huber, Nicolas
    ;
    Jeannin, Pierre-Yves 
    Non, l’intérêt géologique du canton de Neuchâtel ne se limite pas au Creux-du-Van ! Nouvelle preuve avec le quatrième volet de nos cinq découvertes aux côtés d’un spécialiste. Aujourd’hui, sur les traces de l’eau avec l’hydrogéologue Pierre-Yves Jeannin, directeur de l’Institut suisse de spéléologie et de karstologie (Isska).
  • Publication
    Accès libre
    Vulnerability assessment in karstic areas: validation by field experiments
    (2004)
    Perrin, J.
    ;
    Pochon, Alain
    ;
    Jeannin, Pierre-Yves 
    ;
    Zwahlen, François 
    Several methods have been developed for vulnerability mapping in karstic areas. These methods need additional validation by field experiments. Several tests have been carried out in the Swiss Jura with natural and artificial tracers. The protective role of some intrinsic properties of the system, such as glacial deposits covering karst, epikarst storage and system dilution effect, have been clearly demonstrated. Use of three tracers in parallel showed the reactivity of the epikarst: all tracers arrived at the same time, but their relative concentration stayed clearly different. A classification of contamination scenarios into four classes is proposed. It is shown that the relevance of some intrinsic properties depends on the considered scenario class. The hydrodynamic state of the aquifer influences greatly flow velocities and can strongly modify contaminant concentrations at the output of the system. The spatial repartition (point vs diffuse) and the quantity of contaminant entering the system will also influence the output response. Hence, results from tracing experiments cannot be used straightforward for obtaining a representative value of flow velocity, dispersion or recovery rate.
  • Publication
    Métadonnées seulement
    A deterministic approach to the coupled analysis of karst springs' hydrographs and chemographs
    (2003)
    Grasso, D Alessandro
    ;
    Jeannin, Pierre-Yves 
    ;
    Zwahlen, François 
    During the chemically based recession flow phase of karstic springs the carbonate (dissolved limestone) concentration can be expressed as negative power of the flow rate. The empirically determined Conc/Q relationship allows two parameters (alpha and A) to be defined, of which one (alpha) depends on the geometric dimensions of the saturated (submerged) karstic network. In this paper we present a deterministic model which simulates the concentration of carbonate at the outlet of a network of circular rectilinear conduits as a function of flow rate. This model, based on hydraulic principles and the calcite dissolution kinetics, allows the sensitivity of the alpha and A parameters to be studied under different chemical, physical and geometric scenarios. Simulation results show that A is a function of the calcite saturation concentration, whereas alpha depends on the spatial dimensions of the karstic network (void length and aperture). The deterministic model results were applied to real karstic systems to evaluate the geometric dimensions of submerged karstic networks. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Publication
    Accès libre
    Implications of the spatial variability of infiltration-water chemistry for the investigation of a karst aquifer: a field study at Milandre test site, Swiss Jura
    (2003)
    Perrin, J.
    ;
    Jeannin, Pierre-Yves 
    ;
    Zwahlen, François 
    Le site test de Milandre est un aquifère karstique idéal pour étudier lhétérogénéité spatiale des éléments chimiques majeurs car de nombreux points dobservation sont accessibles : source, rivière souterraine et affluents, forages à différentes profondeurs. Les principales causes de la variabilité spatiale des paramètres chimiques sont : nature et localisation des intrants, la structure de la zone dinfiltration, la réactivité des paramètres (temps de transit vs. cinétique de réaction) et le mélange des eaux. Les chimiogrammes observés à la source du système karstique représentent la somme de cette hétérogénéité spatiale. Il est de fait difficile, pour un tel aquifère, dinterpréter la réponse chimique globale en termes de mélanges deau des différents sous-systèmes de laquifère (ruissellement, réservoir matriciel, épikarst). Les éléments chimiques correspondant aux intrants agricoles montrent des variations saisonnières relativement importantes (Coefficient de variation denviron 15%) alors que les paramètres liés à la pluie (δ18O) et à laquifère (Ca2+, HCO3–) présentent des variations de quelques pour cents. Un tel résultat indique un stockage deau dau minimum quelques mois dans lépikarst., The Milandre test site is an ideal karstic aquifer for studying the spatial heterogeneity of groundwater chemistry. Numerous observation points can be sampled: the spring, the underground river and its tributaries, and boreholes at different depths. The main causes of the spatial variability of the chemical parameters are: nature and localisation of the input, the structure of the infiltration zone, chemical reactions (transit time vs. reaction kinetics) and mixing of different waters. Physico-chemical data on springs discharging from the karstic system represent the sum of this spatial heterogeneity. Therefore, it is difficult to interpret the global-chemical response with a simple mixing model of the aquifer subsystems (runoff, matrix reservoir, epikarst). Chemical constituents related to agricultural inputs show important seasonal variations (coefficient of variation approximately 15%) and parameters linked to rainfall (δ18O) and to the aquifer (Ca2+, HCO3–) present variations of less than 5%. This result indicates the importance of water storage in the epikarstic aquifer for periods of a few months., La zona de ensayos de Milandre (Suiza) es un acuífero kárstico ideal para estudiar la heterogeneidad especial de la química de las aguas subterráneas. Se puede muestrear numerosos puntos de observación, incluyendo manantiales, ríos subterráneos y sus tributarios, y sondeos a diferentes profundidades. Las causas principales de la variabilidad espacial de los parámetros químicos son las siguientes: naturaleza y localización de la entrada, estructura de la zona de infiltración, reacciones químicas (tiempo de tránsito versus la cinética de las reacciones), y mezcla de aguas diferentes. Los gráficos hidroquímicos de los manantiales en el sistema kárstico representan la suma de esta heterogeneidad espacial. Por tanto, es difícil interpretar la respuesta química global con un modelo de mezcla simple de los subsistemas acuíferos (escorrentía, reservorio de la matriz, epikarst). Los parámetros asociados a aportaciones de origen agrícola muestran variaciones estacionales importantes, con un coeficiente de variación en torno al 5%, mientras que los parámetros vinculados a la precipitación (δ18O) y al acuífero (calcio, bicarbonato) presentan variaciones inferiores al 5%. Este resultado indica que se produce un almacenamiento importante de agua durante un par de meses en el acuífero epikárstico.
  • Publication
    Métadonnées seulement
    Epikarst storage in a karst aquifer: a conceptual model based on isotopic data, Milandre test site, Switzerland
    (2003)
    Perrin, Jérôme
    ;
    Jeannin, Pierre-Yves 
    ;
    Zwahlen, François 
    The Milandre test site is a karst aquifer characterized by diffuse infiltration, a well developed conduit network, and several tributaries feeding an underground river. Field data include discharge rate measurements, stable isotopes, weekly rainfall and spring-water isotope sampling, and detailed isotope sampling during three flood events. Flood sampling was carried out at several tributaries corresponding to conduit flow, vadose flow and seepage flow. Weekly sampling showed a strong buffering of the rainfall isotopic signal at the spring. This attenuation suggests an important mixing reservoir in the system. Flood events showed highly peaking hydraulic responses but buffered rain isotope responses. These results indicate that the soil and epikarst sub-systems have an important storage capacity. A conceptual model of flow and transport in the soil and epikarst zone is proposed: Soil plays an important role in mixing due to the presence of capillary water storage. Consequently dampened concentrations reach the epikarst despite a rapid hydraulic response. The epikarst acts as the storage element and distributes water as either a base flow component or a quick flow component. When recharge exceeds a given threshold, excess infiltrated water bypasses the soil and epikarst and reaches the saturated zone as fresh flow. Based on this model, the significance of phreatic storage is thought to be limited, at least in Milandre test site. Hence the saturated zone is seen mainly as a transmissive zone through its well developed conduit network. (C) 2003 Elsevier B.V. All rights reserved.
  • Publication
    Accès libre
    Water vulnerability assessment in karst environments: a new method of defining protection areas using a multi-attribute approach and GIS tools (EPIK method)
    (1999)
    Doerfliger, N.
    ;
    Jeannin, Pierre-Yves 
    ;
    Zwahlen, François 
    Groundwater resources from karst aquifers play a major role in the water supply in karst areas in the world, such as in Switzerland. Defining groundwater protection zones in karst environment is frequently not founded on a solid hydrogeological basis. Protection zones are often inadequate and as a result they may be ineffective. In order to improve this situation, the Federal Office for Environment, Forests and Landscape with the Swiss National Hydrological and Geological Survey contracted the Centre of Hydrogeology of the Neuchâtel University to develop a new groundwater protection-zones strategy in karst environment. This approach is based on the vulnerability mapping of the catchment areas of water supplies provided by springs or boreholes. Vulnerability is here defined as the intrinsic geological and hydrogeological characteristics which determine the sensitivity of groundwater to contamination by human activities. The EPIK method is a multi-attribute method for vulnerability mapping which takes into consideration the specific hydrogeological behaviour of karst aquifers. EPIK is based on a conceptual model of karst hydrological systems, which suggests considering four karst aquifer attributes: (1) Epikarst, (2) Protective cover, (3) Infiltration conditions and (4) Karst network development. Each of these four attributes is subdivided into classes which are mapped over the whole water catchment. The attributes and their classes are then weighted. Attribute maps are overlain in order to obtain a final vulnerability map. From the vulnerability map, the groundwater protection zones are defined precisely. This method was applied at several sites in Switzerland where agriculture contamination problems have frequently occurred. These applications resulted in recommend new boundaries for the karst water supplies protection-zones.