Overexploitation and continuous drought effects on groundwater yield and marine intrusion: considerations arising from the modelling of Mamora coastal aquifer,Morocco

This paper studies the effect of drought and pumping discharge on groundwater supplies and marine intrusion. The investigation concerns the Mamora coastal aquifer, northwest of Morocco. A large‐scale groundwater model was established to model (a) the amount of freshwater discharge towards the ocean and the sea water volumes flowing inland as a consequence of the inverse hydraulic gradient, (b) the impact of drought and pumping discharge on the water table level and, as a consequence, on marine water intrusion. In fact, the simulated submarine groundwater discharge (SGWD) would decrease from 864 m³/d/km in 1987 to 425 m³/d/km in 2000. The simulated volumes of sea water intruding the aquifer as a result of inverse hydraulic gradient would increase from 0·25 Mm³/y in 1987 to 0·3 Mm³/y in 2000. As a consequence of a negative rainfall gradient of −5 mm/y, the simulated SGWD would decline to 9 m³/d/km and the sea water intrusion (SWI) would increase to 0·35 Mm³/y since the year 2010. Due to insufficient data on the trend of pumping discharge, a hypothetical increase of this latter from 38·3 Mm³/y to 53·2 Mm³/y is simulated to induce an increase of marine water intrusion from 0·25 Mm³/y to 0·9 Mm³/y. Consequently, to optimally exploit this seemingly fragile coastal aquifer, a plan of future actions to implement is proposed. Copyright © 2005 John Wiley & Sons, Ltd.     

Genèse et déformation des bassins néogènes du Rif central (Maroc) au cours du rapprochement Europe-Afrique

Résumé

Après la mise en place des nappes dans le Rif, des bassins intramontagneux se sont créés et ont subi des déformations depuis le Miocène supérieur jusqu’au Quaternaire. L’analyse microtectonique de la fracluration, et les marqueurs de tectonique synsédimentaire (tailles synsédimentaires, discordances progressives, talus de progradation) montrent que ces bassins ont été soumis à un régime tectonique compressif depuis le Tortonien. La direction de la contramte maximale compressive a changé au cours du temps depuis la direction N040 au Tortono-Messinien jusqu’à la direction N000-140 au Plio-quaternaire. L’évolution sédimentaire et tectonique de ces bassins est à mettre en relation avec l’avancée vers l’WSW du bloc d’Alboran et son blocage entre l’Europe et l’Afrique.     

Hydrochemical analysis and evaluation of groundwater quality of a Mio-Plio-Quaternary aquifer system in an arid regions: case of El Hancha, Djebeniana and El Amra regions, Tunisia

A hydrogeochemical approach has been carried out in the Mio-Plio-Quaternary aquifer system of northern Sfax to investigate the geochemical evolution, the origin of groundwaters and their circulation patterns. The groundwater samples collected from different wells seem to be dominated by sodium chloride type to sulphate chloride type. Detail analysis of chemical data including the thermodynamic calculations was used to assess that the chemical evolution of groundwater is primarily controlled by water–rock interactions. The values of sodium absorption ratio and electrical conductivity of the groundwater were plotted in the US Salinity Laboratory diagram for irrigation water. Most of the water samples in northern Sfax fall in the fields of C4S1, C4S2 and C4S3 indicating very high salinity and medium to high sodium alkalinity hazard. Thus, groundwater quality is ranging between doubtful to unsuitable for irrigation uses under normal condition, and further action for salinity control is required in remediating such problem. Principal component analysis of geochemical data used in conjunction with bivariate diagrams of major elements indicates that groundwater mineralization is mainly controlled by (1) water–rock interaction processes, (2) anthropogenic process in relation with return flow of NO₃-rich irrigation waters and (3) domestic discharges.     

Processus de minéralisation de la nappe du Plio-Quaternaire dans la plaine de Segui-Zograta (Sud-Ouest tunisien)

Résumé

La plaine de Segui-Zograta est une cuvette synclinale à remplissage Mio-Plio-Quaternaire où la nappe du Plio-Quaternaire constitue la principale source d’approvisionnement en eau pour l’abreuvement du chaptel et pour l’agriculture. Cette zone présente une hétérogénéité de répartition de la minéralisation des eaux souterraines. L’investigation des outils géochimiques basée sur l’étude des éléments majeurs, des isotopes stables (¹⁸O, ²H) et radioactifs (³H, ¹⁴C) indique la combinaison de différents processus contrôlant la minéralisation de ces eaux. Dans la partie Ouest, les eaux du Plio-Quaternaire présentent un facies de type sulfato-calco-sodique et des salinités élevées. Elles subissent l’effet de la dissolution des minéraux évaporitiques et résultent du mélange par drainance ascendante des eaux fossi des aquifères les plus profonds, à salinité élevée et à faciès chloruro-sulfato-sodique, à travers la faille d’Om Ali où leur contribution peut atteindre 96%. Dans la partie Est, ces eaux sont de type sulfato-calcique, considérées relativement moins minéralisées que celles de la partie Ouest. Elles sont issues de l’infiltration des eaux de pluie récentes et qui ont subi l’effet de l’évaporation.

Editeur Z.W. Kundzewicz     

An inventory of buildings in the city of Tunis and an assessment of their vulnerability

Tunis is a densely populated city. Its building stock was constructed without any seismic design code and mostly over soft soils. These facts make a seismic risk assessment of the city necessary. To prepare a large-scale vulnerability assessment of the buildings of Tunis, the following methodology was employed: (1) a collection of data based on a rapid visual screening procedure was gathered using an inventory form. These data were composed of files and information placed at the disposal of the authors by the municipality of Tunis. The data also contained information gathered by surveys carried out by engineering departments and information gathered from building owners. (2) A classification of building typologies was carried out considering construction material, structural system, age, height, function and state of maintenance. A measure of seismic vulnerability was assigned to each typology considering the first two parameters. (3) A large-scale vulnerability assessment using two methods was conducted for buildings for which few data were available. Vulnerability methods inspired by the EMS98 concepts and the Italian GNDT concepts were modified and applied to pilot-scale buildings located in the downtown zone (Habib Bourguiba Avenue) and in the old zone (Medina). The data analysis, through the application of the two methods, suggests that the vulnerability of buildings surveyed in Tunis is significant and risk mitigation efforts are necessary.     

Seismic Empirical Relations for the Tellian Atlas, North Africa, and their Usefulness for Seismic Risk Assessment

Seismic events that occurred during the past half century in the Tellian Atlas, North Africa, are used to establish fundamental seismic empirical relations, tying earthquake magnitude to source parameters (seismic moment, fault plane area, maximal displacement along the fault, and fault plane length). Those empirical relations applied to the overall seismicity from 1716 to present are used to transform the magnitude (or intensity) versus time distribution into (1) cumulative seismic moment versus time, and (2) cumulative displacements versus time. Both of those parameters as well as the computed seismic moment rate, the strain rate along the Tellian Atlas strike, and various other geological observations are consistent with the existence, in the Tellian Atlas, of three distinct active tectonic blocks. These blocks are seismically decoupled from each other, thus allowing consideration of the seismicity as occurring in three different distinct seismotectonic blocks. The cumulative displacement versus time from 1900 to present for each of these tectonic blocks presents a remarkable pattern of recurrence time intervals and precursors associated with major earthquakes. Indeed, most major earthquakes that occurred in these three blocks might have been predicted in time. The Tellian Atlas historical seismicity from the year 881 to the present more substantially confirms these observations, in particular for the western block of the Tellian Atlas. Theoretical determination of recurrence time intervals for the Tellian Atlas large earthquakes using Molnar and Kostrov formalisms is also consistent with these observations. Substantial observations support the fact that the western and central Tellian Atlas are currently at very high seismic risk, in particular the central part. Indeed, most of the accumulated seismic energy in the central Tellian Atlas crust has yet to be released, despite the occurrence of the recent destructive May 2003 Boumerdes earthquake (M _w = 6.8). The accumulated seismic energy is equivalent to a magnitude 7.6 earthquake. In situ stress and geodetic measurements, as well as other geophysical field data measurements, are now required to practically check the validity of those observations.     

Features of interaction between lake water and springs,and evaluation of hydrochemical composition of water in Ifni Lake (High Atlas Mountains,Morocco, north of Africa)

The National Park of Toubkal is located in the High Moroccan Atlas Mountains, one of the regions sheltering the highest summits of North Africa (Mount Toubkal with an elevation of 4167 m). The park is characterized by very important water resources, including Ifni Lake, which is the highest natural lake in Morocco (with an elevation of 2320 m). This lake is located on the southern side of Mt. Toubkal. This area has never been the object of an environmental or hydrological study. The objective of the current study was the characterization of Ifni Lake and the spring waters located in this area, as the basis of a framework to protect natural resources in northern Africa. The hydrochemical composition of water determines its origin and relationship with its catchment. Hydrochemical studies were carried out to assess the ions water composition, and processes governing the hydrochemistry of Ifni Lake water and the springs in the study area. A total of 20 water samples were collected in 2013 and analyzed for various parameters such as pH, electrical conductivity, and major ions. The physico-chemical analysis of the Ifni Lake water showed that this is the least mineralized water studied in this region, having a bicarbonate, calcium, and magnesium as dominate ions. Also there is a relationship between the hydrochemical composition of Ifni Lake and spring waters.     

Combination of GIS and mathematical modeling to predict floods in semiarid areas: case of Rheraya watershed (Western High Atlas,Morocco)

The Tinitine sub-watershed of Rheraya is renowned for its semiarid climate, irregular supply of water flow, and its historical floods; for these reasons, it is classified as vulnerable areas during a rainfall event. We conducted this study to propose flood prediction models adapted to this risky zone. For this, a hydrological method of flood forecasting rainfall-runoff used to determine a model conforms to the semiarid basin. This model is based on the articulation of the series production and transfer function. The goal of the production function is to determine the portion of the rainfall runoff, which is performed by two approaches that differ in their structures: (1) the first approach is based on the mathematical model of Horton; (2) the second approach is based on the determination of the part of the rain contributes to runoff and obtained by a spatial map of runoff coefficient (GIS). The transfer function is based on the two models of Clark and Nash, rainy efficient routes to the catchment outlet from a unit hydrograph. The characteristic parameters of these models are obtained through the application of mathematical optimization methods such as genetic algorithms. Thereby, the coupling function producing Horton (identified by the parameters: initial infiltration?=?15.03, final infiltration?=?0.3, and phi?=?0.45) and Clark transfer function (identified by the parameters C_A?=?0.21 and C_B?=?0.79) was given very satisfying results, mainly the low difference between observed and simulated hydrograph and Nash coefficient which is about 85%. This shows the interest of this coupling model in flood forecasting.     

Répartition des minéraux argileux et contrôle tectono-eustatique dans les bassins de la marge tunisienne

We have studied the clay assemblages found in the different palaeogeographic domains located at the several Tunisian margin basins, ranging in age from Palaeozoic to Neogene. This study has allowed us to characterize and highlight the relationship between the clay distribution in time and space and the geodynamic and eustatic events. Marine regressions, with the intensification of erosion, seem to be responsible for illite increases, whereas transgressions, in concordance with a warm and dry climate, coincide with the smectite dominance. The minimum marine level coincides with the abundance of palygorskite. Mineralogic changes in the clay assemblages as well as in the proportion of the different clay minerals will tentatively be related to erosive tectonic events and/or to subsiding and rifting events, marked by the inheritance or the neoformation of the several clays.