No abstract

Les résultats d'analyse graphique des valeurs instantanées des débits solides en suspension dans le cours d'eau de l'Oued Mouilah et leurs relations avec les débits liquides, durant les compagnes de prélèvements de 1977 à 1993, ont permis de montrer l'existence de deux périodes d'érosion actives. Le flux des matières solides en suspension dans le cours d'eau est très variable d'une année à une autre et la dégradation spécifique moyenne annuelle sur les 16 années d'étude est estimée à 126 tonnes par km2. Cette valeur est relativement faible par rapport à celles trouvées pour d'autres régions à régime hydrologique similaire.

The daily rainfall dataset of 35 weather stations covering the north of Algeria was studied for a period up to 43 years, recorded after 1970s. The variability and trends in annual maximum daily rainfall (AMDR) time series and their contributions in annual rainfall (AR) were investigated. The analysis of the series was based on statistical characteristics, Burn’s seasonality procedure, Mann-Kendall test, and linear regression technique. The contribution of the AMDR to AR analysis was subjected to both the Buishand test and the double mass curve technique. The AMDR characteristics reveal a strong temporal irregularity and have a wide frequency of occurrence in the months of November and December while the maximum intensity occurred in October. The observed phenomenon was so irregular that there was no dominant season and the occurrence of extreme event can arrive at any time of the year. The AMDR trends showed that only six of 35 stations have significant trend. For other stations, no clear trend was highlighted. This result was confirmed by the linear regression procedure. On the contrary, the contribution of AMDR in annual totals exhibited a significant increasing trend for 57% of the sites studied with a growth rate of up to 50%.

Dans ce travail on s'intéresse aux sédiments transportés en suspension par le cours d'eau Oued Tafna à Beni-Bahdel. Une analyse de la variabilité de la charge en suspension de l'eau quant aux fluctuations des régimes hydro-climatiques, pour la période allant de septembre 1988 à août 1993, montre que la production des sédiments est très forte en automne mais de faible ampleur au printemps. En été, des crues éphémères fortement chargées sont parfois observées. En automne, le flux des matières solides en suspension représente 44% du flux annuel estimé à 286000 tonnes, alors que les apports en eaux ne représentent que 17% de l'apport annuel moyen évalué à 30,9 millions de m3. Au printemps, malgré l'augmentation des débits (60% de l'apport total annuel), la charge en suspension diminue de façon significative.Cependant, les sédiments ramenés par le cours d'eau sont produits soit par ruissellement superficiel sur les versants soit arrachés du lit et des berges du cours d'eau. On montre alors que la contribution de ces deux mécanismes d'érosion reste remarquablement constante d'une année à une autre. La production du ruissellement superficiel en matières solides représente alors 62% du flux annuel alors que l'érosion du cours d'eau contribue par 38%.Knowledge of suspended sediment loads carried by rivers provides insight into the underlying erosion mechanisms. In Maghreb rivers there are few data available on suspended sediment transport (PROBST and SUCHET, 1992). In this context knowledge of suspended sediment loads in the Oued Sebdou River (Mediterranean Algeria), which is a main stream in the Upper-Tafna basin, is of interest. The purpose of this study was to determine periods of active erosion and estimate the contributions of slope erosion and channel erosion in this basin.Situated in northwest Algeria, the Upper-Tafna basin covers an area of 256 km2 (Fig.1). Rising in Ouled Ouriach, the upper reaches of the river flow through Jurassic soils at altitudes up to 1400 m. These tributary streams join on the Sebdou plain (900 m), which is composed of Plio-quaternary alluviums. The soil is composed of calcareous-marnes, calcareous and Jurassic dolomites (BENEST, 1972; BENEST et al., 1999) until the Beni-Bahdel dam.The study zone is characterized by a semi-arid climate. Analysis of the rainfall data at the Beni-Bahdel station (X=34°42'33"; Y=01°29'48"; Z=660 m) from 1939-1940 to 1997-1998 (Fig. 2) demonstrates that the rain supply has decreased greatly since 1975, with more than an 18% decrease in rainfall amounts.Hydrological data and methodology The study used instantaneous water discharge and suspended sediment load values (1257 values) measured and supplied by the National Agency of Hydrologic Resources [ANRH]. Five annual water years have been investigated during the period from September 1988 to August 1993. The discharge values (QL, in m3/s) were determined from the rating curve for the measured heights of the water at the gauging station. The suspended load (g/l) was determined on water samples taken from the strea...

In this study, the spatial variation of daily and monthly concentration precipitation index and its aggressiveness were used in 23 rainfall stations in the extreme north-east of Algeria over the period 1970–2010. The trend was analysed by the Mann–Kendall (MK) test. The results show that daily precipitation concentration index (CI) values are noticeably higher in places where the amount of total precipitation is low, the results of MK test show that areas of high precipitation concentration tend to increase. The seasonality and aggressiveness of precipitation are high in the eastern and western parts of the study region (eastern and central coastal of Constantine catchments), whereas a moderately seasonal distribution with low aggressiveness is found in the middle of the study area (plains and central Seybouse catchment). As a result, the modified Fournier index (MFI) has a significant correlation with annual precipitation, whereas the CI and monthly precipitation concentration index (PCI) show an opposite correlation in relation to annual precipitation.