Importance du choix des échelles de temps pertinentes pour l'étude du fonctionnement d'écosystèmes marins littoraux

Semi-continuous (1/30 min) records of physicochemical parameters (T,S, DO and pH) have been measured at 1.50 m in Mediterranean coastal waters (Marseilles) from 1998 to 2000, together with meteorological parameters. Physicochemical data were studied in order to synthesise the information at different time scales (inter-annual, season, day, hour), particularly the semi-conservative DO and pH response to hydroclimatic variables. At a daily time scale, important circadian dynamic has been measured under all circumstances with a strong reactivity to irradiance change under the influence of biological activity. This work may contribute to the definition of new tools for coastal waters observation. To cite this article: N. Bensoussan et al., C. R. Geoscience 336 (2004).     

Comparing the stream re-aeration coefficient estimated from ANN and empirical models / Comparaison d'estimations par un RNA et par des modèles empiriques du coefficient de réaération en cours d'eau

Abstract

Dissolved oxygen (DO) is one of the most useful indices of river's health and the stream re-aeration coefficient is an important input to computations related to DO. Normally, this coefficient is expressed as a function of several variables, such as mean stream velocity, shear stress velocity, bed slope, flow depth, and Froude number. However, in free surface flows, some of these variables are interrelated, and it is possible to obtain simplified stream re-aeration equations. In recent years, different functional forms have been advanced to represent the re-aeration coefficient for different data sets. In the present study, the artificial neural network (ANN) technique has been applied to estimate the re-aeration coefficient (K ₂) using data sets measured at different reaches of the Kali River in India and values obtained from the literature. Observed stream/channel velocity, bed slope, flow depth, cross-sectional area and re-aeration coefficient data were used for the analysis. Different combinations of variables were tested to obtain the re-aeration coefficient using an ANN. The performance of the ANN was compared with other estimation methods. It was found that the re-aeration coefficient estimated by using an ANN was much closer to the observed values as compared with the other techniques.     

Physically-based hydrological modelling for non-point dissolved phosphorus transport in small and medium-sized river basins / Modélisation hydrologique à bases physiques et du transport de phosphore dissous diffus en bassins versants de petite et moyenne tailles

Abstract

Abstract Current research suggests that strategies to control sediment and phosphorus loss from non-point sources should focus on different runoff components and their spatial and temporal variations within the river basin. This is a prerequisite for determining effective management measures for reducing diffuse source pollution. Therefore, non-point source models, especially in humid climatic regions, should consider variable hydrologically active source areas. These models should be able to consider runoff generation by saturated overland flow, as well as Hortonian overland flow. A combination of the hydrological model WaSiM-ETH and the erosion and P-transport model AGNPS was chosen for this study. The models were run in the WaSiM runoff generation mode (Green & Ampt/TOPMODEL or Richards equation approach) and the SCS curve number mode to assess the effect of these different runoff calculation procedures on the dissolved phosphorus yield. A small and a medium-sized river basin, of the area of 1.44 and 128.9 km², respectively, in central Germany were selected for the investigation. The results show that the WaSiM–AGNPS coupling produces more accurate results than the SCS curve number method. For the spatial distribution, the more physically-based model approach computed a much more realistic distribution of water and phosphorus yield-producing areas.     

Etude du phénomène d'eutrophisation dans le Barrage de Hammam Boughrara (Wilaya de Tlemcen,Algérie)

Résumé

Ce travail décrit l'étude du phénomène d'eutrophisation des eaux du Barrage de Hammam Boughrara, situé au Nord-Ouest de l'Algérie, dans la Wilaya de Tlemcen. L'exploitation d'une base de données, de neuf ans, relative à 19 variables physico-chimiques, chimiques et biotiques, a permis de déterminer: l'évolution dans le temps de chaque variable, les corrélations entre variables, le degré d'eutrophisation des eaux, les espèces phytoplanctoniques dominantes (e.g. chlorophycées, diatomophycées) ainsi que leur nutriment principal, le phosphore. L'étude statistique multidimensionnelle, par analyse en composantes principales (ACP), confirme les résultats ainsi obtenus, notamment l'importante pollution et l'hyper-eutrophie des eaux. La lutte contre le phénomène d'eutrophisation des eaux nécessite des moyens adéquats de gestion des éléments polluants. Ainsi, l'élaboration d'un modèle adapté à notre site, permettant de prédire les concentrations en phosphore à partir de sa charge et de gérer ainsi la prolifération d'algues en limitant les teneurs en nutriments, peut constituer une contribution notable à cette lutte.

Editeur Z.W. Kundzewicz

Citation Bouzid-Lagha, S. et Djelita, B., 2012. Etude du phénomène d'eutrophisation dans le Barrage de Hammam Boughrara (Wilaya de Tlemcen, Algérie). Hydrological Sciences Journal, 57 (1), 186–201.