Modélisation déterministe de la crue extrême d'un bassin versant de montagne avec application de la description géomorphologique du réseau hydrographique

Les méthodes de calcul des crues de projet pour des grands barrages sont de type statistique ou de type déterministe (PMP/PMF). Ce dernier type de méthodes est principalement utilisé dans le monde anglo-saxon (États-Unis, Australie), mais peut offrir une alternative intéressante aux méthodes statistiques, qui présentent des lacunes pouvant être importantes.Une application des méthodes PMP/PMF sur des bassins suisses a mis en évidence l'intérêt de ces méthodes, mais aussi leurs faiblesses. Une adaptation des outils déterministes est nécessaire pour prendre en compte les particularités des bassins de montagne. Il s'agit principalement de mieux tenir compte des propriétés physiques des bassins versants et des phénomènes de non linéarité. Dans ce but, un concept de modélisation utilisant la description géomorphologique du bassin versant a été utilisé et amélioré. Le premier modèle utilisé est l'hydrogramme unitaire géomorphologique, qui existe depuis 1979. Le deuxième modèle utilise le concept de cascade de réservoirs hydrologiques à vidange non linéaire, dont les éléments sont issus de la description géomorphologique du bassin. C'est là une modélisation nouvelle qui est particulièrement adaptée au contexte des crues extrêmes dans les Alpes. Un travail de calibration et validation du modèle a montré que ce modèle a un bon potentiel d'utilisation. La principale difficulté revient à identifier la signification physique des paramètres du modèle, qui pourrait s'appuyer sur les résultats d'un autre type de modélisation couplant la géomorphologie du bassin aux equations de l'onde cinématique. Ce modèle est en cours de test à l'IATE.Design floods for large dams are computed either with statistical or deterministic methods (Probable maximum precipitation, PMP/probable maximum flood, PMF). The latter presents an interesting alternative to statistical rnethods, whose drawbacks may be significant, especially when hydrometeorological data are deficient.PMP/PMF methods are based on assumption of the existence of an upper limit of the hydrometeorological processes. The prevalent method for PMP estimation is the maximization - transposition technique. Simpler methods, such as the statististically based technique, also exist. However, the most accurate method may well be the use of a meteorological model, but this aspect is still in the research domain.PMF is derived from a PMP using a simplified loss function and a transfer function for which parameters are maximized. The prevalent transfer function is the unit hydrograph model.Application of traditional PMP/PMF method on alpine catchments showed important weaknesses due to the transfer function. Alpine catchments are characterized by steep slopes, thin soil cover, poor vegetation, and large floods are due to heavy, short thunderstorms. Consequently, hydrological response is very sensitive to the topography of the catchment. Nonlinearity must be taken into account in many cases. However, experience showed that a model cannot take into account a detailed description of the catchment.In order to take into account the characteristcs of alpine catchments while staying as simple as possible, we have used the geomorphologic description of the catchment as a modeling basis. This representation is based on the Strahler ordering scheme, and defines all possible path types that a surface runoff dropret may follow to reach the outlet. This description has been used since 1979 in the geomorphologic unit hydrograph (GUH) formulation.We developed a geomorphorogic nonlinear cascade (GNC) in order to take into account nonlinear processes. The GNC model uses the geomorphologic description of the catchment to define the reservoirs of hydrological cascades. A cascade represents a path type; the first reservoir ofa cascade is an overland element and subsequent reservoirs are channels with increasing Strahler's order. Outflow from a reservoir is the inflow of the downstream reservoir. Outflows from all cascades are combined to produce the global catchment response. The two equations used in the GNC model are a global continuity equation: I - O = dV/dt, and a nonlinear outflow equation: O = k Vx, where I is an input term, that is precipitation for the first reservoir, and outflow from the upstream element for channel reservoirs, V is the volume of water stored in a reservoir at time t, k is a consfant, and x an exponent. The parameter k varies with each reservoir as a function of surface area (for overland erements) or rength (for channel elements). The exponent x should be between 1 and 2.The two models, GUH and GNC, have been calibrated with an automatic optimization procedure, and tested on the Vogelbach catchment. This catchment is located in the swiss alps (Arptar, canton of schwytz); it is a third order catchment, and its area is 1,55 km2. Both models gave good results, although the GUH model had a tendency to smooth the dischage.Inorder to improve the physical meaning of the moder parameters, we are testing a third model linking the geomorphologic description with the kinematic wave equations. Results are promising, but are not shorm in this paper.The hydrologic modeling based on the geomorphologic description of the catchment seems to be a good compromise between lumped modeb and detailed distributed models, which are difficult to apply

Circadian variation in the circumstances of delivery in a population at low obstetric risk

While circadian variations in birth and perinatal mortality rates have previously been described in the literature, the reasons behind these observed rhythms remain unclear. The principal hypothetical causes include variations in obstetric practices and an association between the time of birth and biological parameters. In order to explore this issue we analysed the distribution patterns for time and day of birth, as well as circadian variations in maternal characteristics, obstetric practices and neonatal risk in a population at low obstetric risk. The study population included 685 low-risk pregnant women consecutively admitted at an early stage of labour to six maternity units. The results showed hourly variations in the birth rate and circadian variations in obstetric practices that might explain the hourly pattern observed for the birth rate. By contrast, the frequency of a positive neonatal risk indicator was uniform across all time categories in this population at low obstetric ris

Intergovernmental cooperation for hydrometry – what, why and how?

Two thirds of hydrological observation networks in developing countries are reported to be in poor or declining condition. At the same time innovation in sensor technologies and data processing are presenting opportunities for enhancing observation networks that are not being realized. The World Meteorological Organization’s Global Hydrometry Support Facility, or WMO HydroHub, was launched in 2016 to transform assistance to operational water monitoring agencies around the world. If successful, the initiative will increase the amount of hydrometric data available to researchers, catchment managers and water policy makers. To those unfamiliar with UN organizations, however, the nature of such initiatives, the reasoning behind the decisions taken to establish them and the mechanisms by which they try to deliver benefits for society, can be opaque. This paper adopts a novel dialogue-style format to explore the set-up of the WMO HydroHub and build awareness amongst those who ultimately may benefit from its approaches

Citizens AND HYdrology (CANDHY): conceptualizing a transdisciplinary framework for citizen science addressing hydrological challenges

Widely available digital technologies are empowering citizens who are increasingly well informed and involved in numerous water, climate, and environmental challenges. Citizen science can serve many different purposes, from the "pleasure of doing science" to complementing observations, increasing scientific literacy, and supporting collaborative behaviour to solve specific water management problems. Still, procedures on how to incorporate citizens' knowledge effectively to inform policy and decision-making are lagging behind. Moreover, general conceptual frameworks are unavailable, preventing the widespread uptake of citizen science approaches for more participatory cross-sectorial water governance. In this work, we identify the shared constituents, interfaces, and interlinkages between hydrological sciences and other academic and non-academic disciplines in addressing water issues. Our goal is to conceptualize a transdisciplinary framework for valuing citizen science and advancing the hydrological sciences. Joint efforts between hydrological, computer, and social sciences are envisaged for integrating human sensing and behavioural mechanisms into the framework. Expanding opportunities of online communities complement the fundamental value of on-site surveying and indigenous knowledge. This work is promoted by the Citizens AND HYdrology (CANDHY) Working Group established by the International Association of Hydrological Sciences (IAHS)

Sialic acid-modified antigens impose tolerance via inhibition of T-cell proliferation and de novo induction of regulatory T cells

Sialic acids are negatively charged nine-carbon carboxylated monosaccharides that often cap glycans on glycosylated proteins and lipids. Because of their strategic location at the cell surface, sialic acids contribute to interactions that are critical for immune homeostasis via interactions with sialic acid-binding Ig-type lectins (siglecs). In particular, these interactions may be of importance in cases where sialic acids may be overexpressed, such as on certain pathogens and tumors. We now demonstrate that modification of antigens with sialic acids (Sia-antigens) regulates the generation of antigen-specific regulatory T (Treg) cells via dendritic cells (DCs). Additionally, DCs that take up Sia-antigen prevent formation of effector CD4+ and CD8+ T cells. Importantly, the regulatory properties endowed on DCs upon Sia-antigen uptake are antigen-specific: only T cells responsive to the sialylated antigen become tolerized. In vivo, injection of Sia-antigen–loaded DCs increased de novo Treg-cell numbers and dampened effector T-cell expansion and IFN-γ production. The dual tolerogenic features that Sia-antigen imposed on DCs are Siglec-E–mediated and maintained under inflammatory conditions. Moreover, loading DCs with Sia-antigens not only inhibited the function of in vitro–established Th1 and Th17 effector T cells but also significantly dampened ex vivo myelin-reactive T cells, present in the circulation of mice with experimental autoimmune encephalomyelitis. These data indicate that sialic acid-modified antigens instruct DCs in an antigen-specific tolerogenic programming, enhancing Treg cells and reducing the generation and propagation of inflammatory T cells. Our data suggest that sialylation of antigens provides an attractive way to induce antigen-specific immune tolerance

A solitary bronchial papilloma with unusual endoscopic presentation: case study and literature review

<p>Abstract</p> <p>Background</p> <p>Solitary endobronchial papillomas (SEP) are rare tumors and most of them are described by case report. A misdiagnosis is common with viral related papillomas. A histopathological classification has recently permitted a major advancement in the understanding of the disease.</p> <p>Case Presentation</p> <p>We report a case of a mixed bronchial papilloma with an unusual endoscopic presentation. The literature was extensively reviewed to ascertain the unusual characteristics of the current case. A 39-year of age male was referred to our institution for the investigation of a slight hemoptysis. Routine examination was normal. A fibroscopy revealed an unusual feature of the right main bronchus. The lesion was a plane, non-bleeding, non-glistering sub-mucosal proliferation. No enhanced coloration was noticed. Biopsies revealed a mixed solitary bronchial papilloma. In situ HPV hybridization was negative. Endoscopic treatment (electrocautery) was effective with no relapse.</p> <p>Conclusion</p> <p>This lesion contrasts with the data of the literature where papilloma were described as wart-like lesions or cauliflower tumors, with symptoms generally related to bronchial obstruction. We advise chest physicians to be cautious with unusually small swollen lesions of the bronchi that may reveal a solitary bronchial papilloma. Endoscopic imaging can significantly contribute to the difficult diagnosis of SEP by pulmonary physicians and endoscopists.</p