1,721,061 research outputs found
L'hydrologie : Porteuse de Surprises Dans Le Vallon de Nant
No full textLa réserve naturelle du Vallon de Nant, située dans les Alpes vaudoises sur la commune de Bex, est un joyau de biodiversité préservée en Suisse. C’est également un terrain d’étude privilégié de l’Université de Lausanne, en particulier autour des thématiques de la climatologie, de l’hydrologie, de la géomorphologie, du transport sédimentaire, de la géologie, de la pédologie et de l'écologie alpine.
Des chercheuses et chercheurs des universités de Lausanne, Neuchâtel et Berne emmènent le grand public à la découverte de leurs travaux de recherche in situ et in vivo durant une série de visites avec des activités ludiques et interactives accessibles à tous les âges.
Le 27 septembre, découvrez l'hydrologie du Vallon de Nant.
Durant cette après-midi, nous parlerons des changements des flux hydrologiques au cours d'une année et d'une année à l'autre. Nous parlerons des fluctuations du débit, de l'expansion et de la contraction du réseau hydrologique, du stockage de l'eau, de la fonte des glaciers, des conséquences des conditions changeantes sur la neige et la végétation et de l'effet des changements de végétation sur l'hydrologie. Nous présentons comment nous, hydrologues, utilisons des traceurs naturels (isotopes, eDNA) et nous vous convainquons que l'hydrologie est liée à tout le reste, apportant toutes les surprises.
La visite sera guidée par Dr. Natalie Ceperley et les étudiantes en master Anna Meier et Martine Helfer qui effectuent leurs recherches dans le Vallon de Nant. Elles travaillent toutes à l'Université de Berne dans le département de géographie.
La présentation sera en français avec possibilité de traduction en anglais et en allemand.
La visite débutera à 13h00 et durera environ 4 heures (dont 3 heure de marche)
L'activité est gratuite, sur inscription (le nombre de places est limité).
Informations pratiques
Rendez-vous au Pont de Nant devant l'auberge.
Prévoir des habits adaptés.
Contact [email protected]
Towards a conceptualization of the hydrological processes behind changes of young water fraction with elevation: a focus on mountainous alpine catchments
Full text linkThe young water fraction (F*yw), defined as the fraction of catchment outflow with transit times of less than 2-3 months, is increasingly used in hydrological studies that exploit the potential of isotope tracers. The use of this new metric in catchment intercomparison studies is helpful to understand and conceptualize the relevant processes controlling catchment functioning. Previous studies have shown surprising evidence that mountainous catchments worldwide yield low F*yw. These low values have been partially explained by isolated hydrological processes, including deep vertical infiltration and long groundwater flow paths. However, a thorough framework illustrating the relevant mechanisms leading to a low F*yw in mountainous catchments is missing.
The main aim of this paper is to give an overview of what drives F*yw variations according to elevation, thus clarifying why it generally decreases at high elevation. For this purpose, we assembled a data set of 27 study catchments, located in both Switzerland and Italy, for which we calculate F*yw. We assume that this decrease can be explained by the groundwater storage potential, quantified by the areal extent of Quaternary deposits over a catchment (Fqd), and the low-flow duration (LFD) throughout the period of isotope sampling (PoS). In snow-dominated systems, LFD is strictly related to the snowpack persistence, quantified through the mean fractional snow cover area (FSCA). The drivers are related to the catchment storage contribution to the stream, that we quantify by applying a cutting-edge baseflow separation method to the discharge time series of the study sites and by estimating the mean baseflow fraction (Fbf) over the PoS.
Our results suggest that Quaternary deposits could play a role in modulating F*yw elevation gradients via their capacity to store groundwater, but subsequent confirmation with further, more detailed geological information is necessary. LFD indicates the proportion of PoS in which the stream is sustained and dominated by stored water coming from the catchment storage. Accordingly, our results reveal that the increase of LFD at high elevations, to a large extent driven by the persistence of winter snowpacks and the simultaneous lack of a liquid water input to the catchments, results in lower F*yw. In our data set, Fbf reveals a strong complementarity with F*yw, suggesting that the latter could be estimated as F*yw ≃ 1 - Fbf for catchments without stable water isotopes measurements.
As a conclusion, we develop a perceptual model that integrates all the results of our analysis into a framework for how hydrological processes control F*yw according to elevation. This lays the foundations for an improvement of the theory-driven models
Storage-Discharge Characteristics of Headwaters by Tracer Analysis: A Case Study in the Vallon de Nant over the Recession Period 2022
No full textIsotopic analysis of extracted water from a larch (Larix decidua) stand in a high mountain watershed (Vallon de Nant - Switzerland)
No full textA total of 185 samples of soil and trees were taken from a stand of larch (Larix decidua) spanning from 1500 to 1600 m.a.s.l. in the Vallon de Nant in the Swiss canton of Vaud. Twenty individual trees and soil were sampled along two transects perpendicular to the main river channel of the Avançon de Nant at approximately midday on seven days in the foliage season between July 2017 and June 2018.
The data consists of two data (csv) and one document (pdf) files. The sample data file includes the date and estimated time of sampling, the type of sample (vegetation or soil), the transect and tree ID for look-up in the tree metadata file, the soil depth in centimeters, and the determined mean and standard deviation of deuterium, oxygen-18, and oxygen-17. The tree metadata file includes the transect (north or south), the tree ID number, the latitude, longitude, elevation (meters above sea level), and tree height and diameter at breast height in centimeters. Finally, a document describing the methods in more detail is included
When snow and ice are gone: beyond hydrological regime changes, what are the nuts and bolts of future streamflow generation processes?
Full text link- …
