Extreme hydrologic events are commonly described by several dependent characteristics, such as duration, volume and peak flow for floods. Traditionally in Algeria and North Africa, flood frequency analysis (FFA) is conducted as a univariate approach focusing separately on each single of flood characteristics. On the other hand, elsewhere, multivariate FFA studies have been conducted focusing on some FFA steps (especially modelling). The current study aims to consider complete multivariate FFA at-site case studies in northern Algeria using 11 hydrometric stations. It is also among the first studies dealing with multivariate FFA in a complete way by considering all the required steps of the analysis (multivariate outliers detection, multivariate assumptions testing and copula fitting) and on datasets from Algeria. Multivariate stationarity, homogeneity and independence assumptions have been well verified before modelling. The Weibull distribution is mostly selected as margin distribution for the duration, volume and peak flow series. Frank, Clayton and Gumbel copulas are commonly selected to describe the dependence structure on the three flood pairs of variables. These findings should be interesting in water management and flood risk assessment in these regions. Combining these flood characteristics enables the design of more efficient hydraulic structures.

Water plays a major role in the Algerian Sahara; it is the main cause of sustaining life of all living in an arid environment. Farmers in Beni Abbes exploiting groundwater for irrigation and to supply the urban center of the oasis, now the size of the palm grove of Beni Abbes shrink by over 50%, that is to say from 40 hectares to 20 hectares only, the oasis suffers from several causes of degradation, which are many: the overexploitation of groundwater aquifers by the anarchical use of pumps and boreholes,salinity of water and soil after the lowering of the groundwater level, the narrowness of the land due to inheritance, the negligence of the earth by the youth due to lack of their production efficiency. The fellahs of the oasis used several traditional techniques to bring water from the groundwater aquifers to its land and dwellings, as foggaras, the pendulum wells (shadoof wells), the accumulations basins and open channels (seguias). Our objective of this work is to study the current state of the oasis and the impact of the use of modern irrigation systems on water and soil of the oasis.

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This work focuses to the study of the coastal aquifer of Tipaza in the north of Algeria, for highlights mechanisms of potential seawater intrusion into groundwater. Tipaza aquifer has been overexploited for irrigation and water supply, which caused a negatively impacts on its water quality. To investigate these impacts, many tools have been carried out as: monitoring of piezometric level and physico-chemical analysis of 24 wells from 2008 to 2012 and pumping tests. The piezometric map shows the existence of zero meter level inside the plain; which making this area vulnerable to seawater intrusion, where isovalue curves of some chemical parameters are in increasing towards the sea. Results show also a high concentration gradient of some parameters in the first two kilometers, at 1 mS.cm-1.km-1 for EC and 600 to 900 mg.L-1.km-1 for sodium and chlorides respectively. The hydrochemical study confirmed the hypothesis of seawater intrusion in the coastal aquifer of Nador.