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The aim is to build a seasonal flood frequency analysis model and estimate seasonal design floods. The importance of seasonal flood frequency analysis and the advantages of considering seasonal design floods in the derivation of reservoir planning and operating rules are discussed, recognising that seasonal flood frequency models have been in use for over 30 years. A set of non-identical models with non-constant parameters is proposed and developed to describe flows that reflect seasonal flood variation. The peak-over-threshold (POT) sampling method was used, as it is considered to provide significantly more information on flood seasonality than annual maximum (AM) sampling and has better performance in flood seasonality estimation. The number of exceedences is assumed to follow the Poisson distribution (Po), while the peak exceedences are described by the exponential (Ex) and generalized Pareto (GP) distributions and a combination of both, resulting in three models, viz. Po-Ex, Po-GP and Po-Ex/GP. Their performances are analysed and compared. The Geheyan and the Baiyunshan reservoirs were chosen for the case study. The application and statistical experiment results show that each model has its merits and that the Po-Ex/GP model performs best. Use of the Po-Ex/GP model is recommended in seasonal flood frequency analysis for the purpose of deriving reservoir operation rules.Key words seasonal flood; frequency analysis; POT sampling; non-identical model Modèles non-identiques pour l'analyse fréquentielle saisonnière des cruesRésumé L'objectif est de construire un modèle d'analyse fréquentielle saisonnière des crues et d'estimer des crues de projet saisonnières. L'importance de l'analyse fréquentielle saisonnière des crues et les avantages de la prise en compte de crues de projet saisonnières pour la planification et les règles de gestion des réservoirs sont discutés, compte tenu de l'utilisation de modèles fréquentiels saisonniers de crues depuis plus de trente ans. Un ensemble de modèles non-identiques avec des paramètres nonconstants est proposé et développé pour décrire les écoulements qui reflètent les variations saisonnières des crues. La méthode d'échantillonnage par renouvellement-dépassement (POT) a été utilisée, étant considérée fournir significativement plus d'information sur la saisonnalité des crues que l'échantillonnage du maximum annuel (MA) et ayant une meilleure performance pour l'estimation de la saisonnalité des crues. Le nombre de dépassements est supposé suivre une distribution de Poisson (Po), tandis que les pics des dépassements sont décrits par des distributions exponentielle (Ex) et Pareto généralisée (PG) et par une combinaison des deux, ce qui conduit à trois modèles: Po-Ex, Po-GP et PoEx/GP. Leurs performances sont analysées et comparées. Les réservoirs de Geheyan et de Baiyunshan ont été choisis comme cas d'étude. La mise en oeuvre et les résultats de l'analyse statistique montrent que chaque modèle a des avantages et que le modèle Po-Ex/GP a les meilleures performances. L'utili...

In this article, a data matrix of 20 indicators (6960 observations) was obtained from 29 water quality monitoring stations of the Middle Route (MR) of the South-to-North Water Diversion Project of China (SNWDPC). Multivariate statistical techniques including analysis of variance (ANOVA), correlation analysis (CA), and principal component analysis (PCA) were applied to understand and identify the interrelationships between the different indicators and the most contributive sources of anthropogenic and natural impacts on water quality. The water quality index (WQI) was used to assess the classification and variation of water quality. The distributions of the indicators revealed that six heavy-metal indicators including arsenic (As), mercury (Hg), cadmium (Cd), chromium (Cr), selenium (Se), and lead (Pb) were within the Class I standard, while the As, Pb, and Cd displayed spatial variation. Moreover, some physicochemical indicators such as dissolved oxygen, 5-day biochemical oxygen demand (as BOD5), and total phosphorus (TP) had spatio-temporal variability. The correlation analysis result demonstrated that As, Hg, Cd, Cr, Se, Pb, copper (Cu), and zinc (Zn) had high correlation coefficients. The PCA result extracted three principal components (PC) accounting for 82.67% of the total variance, while the first PC was indicative of the mixed sources of anthropogenic and natural contributions, the second and the third PCs were mainly controlled by human activities and natural sources, respectively. The calculation results of the WQI showed an excellent water quality of the MR of the SNWDPC where the values of the stations ranged from 10.49 to 17.93, while Hg was the key indicator to determine the WQI > 20 of six stations, which indicated that the Hg can be the main potential threat to water quality and human health in this project. The result suggests that special attention should be paid to the monitoring of Hg, and the investigation and supervision within the areas of high-density human activities in this project should be taken to control the impacts of urban and industrial production and risk sources on water quality.

As a giant newly built man-made canyon-shaped reservoir, the Three Gorges Reservoir (TGR) receives much attention around China and other parts of the world. Bays were deemed to be the most critical zone for water management of TGR; thus, a 3.5-year temporal and spatial investigation was performed to disclose water quality variation in TGR bays and to elucidate the potential affecting factors based on an integrated hydrographical analysis. The results showed that TGR bays had been moderately polluted with averaged nitrogen (N) concentration over 2 mg L(-1) and phosphorus (P) concentration less than 0.1 mg L(-1) in dry season and while high P over 0.2 mg L(-1) and low N of 1.54 mg L(-1) in average in flooding season. The interaction of dam regulation and flooding events influenced the temporal pattern of water quality in the TGR bays, in which particulate nutrients dynamic played an important role. Urban effluents and agricultural catchment area also influenced water quality in the bays, showing local spatial distribution characteristics via diffusion mechanism. Backwater ends might be the most critical areas of water quality degradation. Alleviation measures had been proposed for sustainable development of TGR region.