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See detailCharacterization of a cavern conduit system in Vietnam by time series correlation, cross-spectrum and wavelet analyses
Tam, V. T.; De Smedt, F.; Batelaan, Okke et al

in Hydrological Sciences Journal = Journal des Sciences Hydrologiques (2004), 49(5), 879-900

Time series analyses are applied to characterize the transient flow regimes of the Nam La cavern conduit, northwest Vietnam. The conduit transforms the input signal to an output signal, and the degree of ... [more ▼]

Time series analyses are applied to characterize the transient flow regimes of the Nam La cavern conduit, northwest Vietnam. The conduit transforms the input signal to an output signal, and the degree of transformation provides information on the nature of the flow system. The input for the analysis is net precipitation and the flow hydrograph at the cave entrance, while the output series is the flow hydrograph at the resurgence. Cross-correlation and cross-spectrum analysis are used to investigate the stationarity and linearity of the input-output transformation of the system, resulting in hydrodynamic properties such as system memory, response time, and mean delay between input and output. It is shown that during high flow periods, the flow in the conduit is pressurized. Consequently, the linear input-output assumption holds only for low flows. To highlight the hydrodynamics of the cavern conduit for the high flow periods, wavelet spectrum and wavelet cross-spectrum analyses are applied. [less ▲]

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See detailThe Sahelian drought may have ended during the 1990s
Ozer, Pierre ULg; Erpicum, Michel ULg; Demarée, Gaston et al

in Hydrological Sciences Journal = Journal des Sciences Hydrologiques (2003), 48(3), 489-492

The severe drought that affects the Sahel since the late 1960s has been very closely studied and monitored during the last three decades. Recently, after several wet years, it was questioned from a ... [more ▼]

The severe drought that affects the Sahel since the late 1960s has been very closely studied and monitored during the last three decades. Recently, after several wet years, it was questioned from a statistical point of view whether the drought was over. The conclusions of a recent study were that the rainfall deficit was not over at the end of 2000 and that the drought continues. The analysis of the change points in the station rainfall time series suggests differentiating these findings. There is now growing evidence that there is a potential shift towards a more humid state. However, the present analysis shows that the assumption that a significant increase in rainfall may have occurred around the early 1990s could only be verified at the customary confidence level in about 10 years from now. [less ▲]

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See detailL'opération sources en Belgique : premières analyses statistiques des résultats et légitimité des cartes "nitrates".
Wattecamps, J. M.; Bernier, Jacques; De Backer, Louis et al

in Hydrological Sciences Journal = Journal des Sciences Hydrologiques (2000), 45(1), 43-60

L'opération sources du WWF (Worldwide Fund for Wildlife) est une action éducative de sensibilisation à la qualité des eaux souterraines. Elle implique principalement les élèves de cinquième et sixième ... [more ▼]

L'opération sources du WWF (Worldwide Fund for Wildlife) est une action éducative de sensibilisation à la qualité des eaux souterraines. Elle implique principalement les élèves de cinquième et sixième primaires de Belgique. Depuis 1994, des centaines de dosages des ions nitrates ont été effectués dans un grand nombre de sources et de puits à l'aide de bandelettes colorimétriques. A l'issue de chaque campagne, les points d'eau surveillés ont été reportés sur une carte de Belgique où leur couleur indique leur qualité eu égard à la concentration en nitrates. L'objectif pédagogique étant atteint, la validation de ces cartes en tant qu'image de la réalité pose le problème de la vérification du lien entre la concentration réelle (mg l-1) du point d'eau visité et sa couleur sur la carte. A cette fin, des vérifications ont été réalisées sur 308 points d'eau choisis au hasard dans l'ensemble des sources et puits visités. L'analyse statistique révèle que la relation entre le test colorimétrique et le contrôle réalisé en laboratoire est hautement significative. Ce résultat justifie des investigations ultérieures, notamment la mobilisation de l'information régionale pour la qualification d'un point d'eau peu surveillé et la comparaison des cartes dans le temps. [less ▲]

Detailed reference viewed: 48 (8 ULg)