Moumtaz Razack | Université de Poitiers (original) (raw)

Papers by Moumtaz Razack

Water, Nov 8, 2019

The Republic of Djibouti has an area of 23,000 km 2 , a coastline 370 km long and a population of... more The Republic of Djibouti has an area of 23,000 km 2 , a coastline 370 km long and a population of 820,000 inhabitants. It experiences an arid climate characterized by high daytime temperatures and low and irregular rainfall (average of 140 mm/year), resulting in continuous periods of drought. These difficult climatic conditions and the absence of perennial surface water have progressively led to an intensive exploitation of groundwater to meet increasing water demands in all sectors (drinking water, agriculture and industries). In coastal areas, seawater intrusion constitutes a significant additional risk of groundwater degradation. This study is focused on the coastal aquifer of Tadjourah which supplies water to the city of Tadjourah, currently comprising 21,000 inhabitants. The main objective of this work is to assess the current resources of this aquifer; its capacity to satisfy, or not, the projected water demands during coming years; and to analyze its vulnerability to seawater intrusion within the frame of climate change. Three RCPs (Representative Concentration Pathway) were used to simulate different climate scenarios up to 2100. The simulated rainfall series allowed to deduce the aquifer recharge up to 2100. The code Seawat was used to model seawater intrusion into the aquifer, using the recharge data deduced from the climate scenarios. The results indicate that the risk of contamination of the Tadjourah coastal aquifer by seawater intrusion is high. The long-term and sustainable exploitation of this aquifer must take into consideration the impact of climate change.

Water, Jul 15, 2020

The hydrogeological system of the Goda Mountains Range (GMR) in the Republic of Djibouti (Horn of... more The hydrogeological system of the Goda Mountains Range (GMR) in the Republic of Djibouti (Horn of Africa), hosted by volcanic and sedimentary formations, is the only water resource in the Tadjourah region for more than 85,000 inhabitants. Water needs are expected to drastically increase in the coming years, due to fast socioeconomic development of the region. Accordingly, this system is under high pressure and should sustainably be exploited. However, little is known about the hydrogeology of this system. This study aims to improve the understanding of the hydrochemistry and the recharge processes of this system. The study is based on the combined interpretation of major ions, stable isotopes (18 O, 2 H), and radiogenic isotopes (3 H, 14 C). The interpretation of major ions contents using classical hydrochemical methods and principal component analysis highlighted that alteration of volcanic rocks minerals, coastal rainfall infiltration, and evaporation are the main processes from which groundwater acquires mineralization. Stable isotopes revealed that groundwater is of meteoric origin and has undergone high evaporation during infiltration. Radiogenic isotopes showed that groundwater in the basalts is mostly submodern to old, in relation with low hydraulic conductivity of the rocks and/or longer pathways through fissures from outcrop to subsurface. Groundwater in the rhyolites is much younger compared to the basalts due to faster infiltration. The sedimentary part, in connection with the rhyolites, has younger waters compared to the basalts, but older compared to the rhyolites. The overall results show that GMR is a fairly complex hydrogeological system, containing a resource made up of a mixture of waters of different ages. This study has made significant progress in understanding this system and is an initial step towards the sustainable exploitation of resources.

Environmental Earth Sciences, May 30, 2021

Land subsidence analysis using satellite imagery is a consequential subject. Earth scientists hav... more Land subsidence analysis using satellite imagery is a consequential subject. Earth scientists have begun utilizing satellite imagery as an alternative to in-situ measurements and conceptual models. Synthetic aperture radar (SAR) images, moreover, utilize the reformer approach more than traditional satellite imagery with the use of high-resolution radar images. As a natural hazard, land subsidence is mostly attributed to excessive groundwater extraction, which is also the main reason for choosing the Konya Plain in Turkey as the study area for the present work. Since the Konya region is an agricultural and industrial land, groundwater extraction has been a challenging circumstance for the last few years. Change in groundwater level is also correlated with land subsidence rates through hydrogeological conceptualization. In this study, SAR images of the Sentinel 1 satellite are utilized for land subsidence rate calculation with the European Space Agency’s SNAP software. Differential SAR interferometry (DInSAR) technique was used, which makes possible to detect deformation on the ground surface of the same portion of the Earth’s surface using SAR images. The different acquisitions with DInSAR method allow to create differential interferograms that provide information ground motion with accuracy in cm. Three periods were utilized as 2016–2017, 2017–2018 and 2018–2019 the mean land subsidence rates were calculated for each period as 2.2, 1.4 and 1.7 cm/year, respectively. In the sum of the 3-year period, the maximum subsidence value went up to 16 cm.

Journal of African Earth Sciences, Apr 1, 2012

Abstract Integrated approach has been used to investigate the hydrogeological framework of a comp... more Abstract Integrated approach has been used to investigate the hydrogeological framework of a complex fractured volcanic aquifer system in the Upper Awash River basin located at the western shoulder of the Ethiopian Rift. The groundwater flow system and mechanism of recharge of different aquifers have been studied using conventional hydrogeological field investigations, hydrochemistry, and isotope hydrology. Litho-hydrostratigraphic relationships were constructed from lithologic logs obtained from exploratory drilling of deep boreholes. The result indicates quite complex flow pattern and hydraulic characteristics of the different volcanic aquifers. The litho-hydrostratigraphic correlation indicates that the permeable and porous scoraceous lower basaltic aquifer is extended laterally all the way from the Blue Nile Plateau to the study area. New evidences have also emerged on the inter-basin groundwater transfer. Two distinct regional basaltic aquifers (upper and lower) are identified showing distinct hydrochemical and isotopic signatures. In the southern part of the study area the upper and lower aquifers form one unconfined regional aquifer system. In the northern and central part of the basin, it appears that the two systems are separated by regional aquiclude forming confined aquifers, in places with artesian wells. The groundwater from the deep exploratory wells (>250 m) tapping the lower basaltic aquifer and wells located in the south were found to be moderately mineralized (TDS: 400–600 mg/l), with relatively depleted stable isotope composition and with almost zero tritium. In contrast, the upper shallow aquifer has lesser ionic concentration, more isotopically enriched. Evidences from the different methods clearly indicate inter-basin groundwater transfer from the Blue Nile basin to the Upper Awash basin. The evidences also converge to testify common origin of recharge, presence of hydraulic connectivity for systems tapping the lower basaltic aquifer. This has enormous practical implication in finding large groundwater reserve at a greater depth that can solve the current water supply problems of the community including the capital Addis Ababa. It will also have important role in finding more regional aquifers along the plateau-rift margins in many areas having similar hydrogeological setup as the study area.

International Journal of Innovation and Applied Studies, Nov 2, 2016

The Chari-Baguirmi aquifer, located East of Lake Chad, is the main source of water in this region... more The Chari-Baguirmi aquifer, located East of Lake Chad, is the main source of water in this region. The groundwater piezometry is marked by a large depression. The work presented here aims to understand the development of this depression. The approach is based on a sedimentological study coupled to a hydrogeochemical study of the groundwater. The sedimentological analysis revealed the grain size heterogeneity of the different layers. Clay mineralogy showed that the deposition of sediments takes place from the periphery to the center of the depression. This sedimentation mode suggests the existence of a morphological cuvette to which sediments are driven by the transport agent. We deduced the existence of a "structural" depression unlike the common assumption of an origin due to accentuated evaporation of the groundwater over the depression area. The combined study of chloride and oxygen-18 has shown that the area between Lake Chad and the piezometric depression is a special evaporation zone. This means that the process of evaporation of groundwater does not occur mainly in the center of the depression. The first results of this work provide new insights into the functioning of this important aquifer system and the establishment of the large Chari Baguirmi piezometric depression.

Tectonophysics, Mar 1, 1985

Grillot. J.C. and Razack, M., 1985. Fracturing of a tabular limestone platform: comparison betwee... more Grillot. J.C. and Razack, M., 1985. Fracturing of a tabular limestone platform: comparison between microtectonic and photogeological data. Tectonophysics.

Journal of Hydrology, Nov 1, 1985

Grillot, J.C. et Razack, M., 1985. l~volution spatio-temporelle d'un aquif~re alluvial sous l'eff... more Grillot, J.C. et Razack, M., 1985. l~volution spatio-temporelle d'un aquif~re alluvial sous l'effet d'une sdcheresse pluriannuelle exceptionnelle (littoral m~diterran~en, H~rault, France) [Evolution in space and time of an alluvial aquifer under the effect of an exceptional multi-year drought (Mediterranean shore, Hdrault, France)]. J. Hydrol., 82: 155-173. The potentiometric-surface fluctuations and hydrochemical evolution of an alluvial aquifer located along the Mediterranean shore have been observed during a period including a multi-year drought. The ions selected for this study are chloride and sulfate for the following reasons: (1) nearness of the seashore ; and (2) a social and economical local context based upon an intensive polyculture which requires application of sulfur over more than 90% of the area. Two major conclusions are drawn from this study. (1) The water-level fluctuations indicate different hydrodynamical behaviour of the aquifer, probably depending on vertical zoning of permeability. The alluvial aquifer behaves as multilayered with different permeabilities, which produces potentiometric distortions. (2) From a hydrochemical viewpoint, lagged dilution was observed for choride and sulfate. The question of retention of the chloride by clays has not yet been clearly answered. We interpret the phenomena of lagged dilution as resulting from spatial variations of permeability of the reservoir rather than only from the geochemical nature of its heterogeneities. Rl~SUMI~ L'dvolution spatio-temporelle pi~zom~trique et hydrochimique d'une nappe alluviale situde en bordure de mer a ~td observde durant une pdriode incluant un dpisode pluriannuel de s~cheresse. En ce qui concerne l'hydrochimie, le choix s'est portd sur les ions C1-et SO~-pour les raisons suivantes: proximitd du littoral marin; contexte socio-dconomique local dans lequel une polyculture intensive et ndcessitant des traitements par sulfatage occupe plus de 9(7o de la surface. Ce suivi spatio-temporel aboutit h deux types de conclusions. (1) Sur le plan pidzom~trique, diff4rents modes de fonctionnement de l'aquif~re

Environmental Earth Sciences, Nov 20, 2012

The Chari Baguirmi groundwater in the Republic of Chad is undergoing a steady deterioration both ... more The Chari Baguirmi groundwater in the Republic of Chad is undergoing a steady deterioration both qualitative and quantitative due to climatic (severe droughts) and anthropogenic (overexploitation) constraints. However, this major water resource has not been to date the object of any comprehensive scientific investigation. To fill this gap and consider a sustainable exploitation, a hydrodynamic and hydrochemical study was undertaken. This aquifer is located south of Lake Chad and displays a significant natural piezometric depression. Piezometric campaign on an area of 70,000 km2, bounded by Lake Chad, the Chari River, the mountains of Guera and the dunes of Harr, was conducted to understand the hydrodynamics of the groundwater. Water samples were collected on 124 points scattered over the study area. Hydrochemical and isotopic analyses (18O and 2H) were achieved on all samples. The interpretation of hydrochemical data was done using the Piper diagram, the multivariate analysis (hierarchical ascending classification), the index of base exchanges and ratios of Na/Cl, Na/SO4, Cl/SO4, Br/Cl, Sr/Ca. The hydrochemical results coupled with groundwater isotopes data allowed to understand the processes that govern the mineralization and the origin of groundwater salinity. These investigations allowed on the one hand to differentiate between two poles of water mixing and second, to demonstrate that the mineralization process and origin of salinity in the center of depression are both related to the lithology of the geological formations crossed by groundwater flow and climatic events causing evaporation of water from the aquifer.

Hydrogeology Journal, Sep 23, 2006

The ability of artificial neural networks (ANN) to model the rainfall-discharge relationships of ... more The ability of artificial neural networks (ANN) to model the rainfall-discharge relationships of karstic aquifers has been studied in the La Rochefoucauld karst system, south-west France, which supplies water to the city of Angoulême. A neural networks model was developed based on MLP (multi-layer perceptron) networks and the Levenberg-Marquardt optimization algorithm. Raw rainfall data were used without transformation into effective

Journal of Hydrology, Nov 1, 1999

A simple GIS-linked model for groundwater nitrate transport has been developed in the IDRISI GIS ... more A simple GIS-linked model for groundwater nitrate transport has been developed in the IDRISI GIS environment. The transport model, based on advection transport only, is directly incorporated into a GIS subroutine using the Pascal computing language. This model requires less data than classical approaches and provides a user-friendly model environment. The GISmodel was tested on a 20 km 2 hydrogeologic catchment, particularly vulnerable to agricultural nitrate pollution. The model was coupled with an unsaturated zone transport model (AgriFlux), which simulates water and nitrate fluxes leaving the root zone. The results indicated that the simulated nitrate concentrations were in good agreement with measured values. In order to compare the GIS-linked model with a more complete model, simulations were also performed with MT3D-MODFLOW. The similarities between the results of the two models confirm the validity of the GIS-linked model.

Frontiers in Environmental Science, Jul 8, 2022

Plastics are widely used in every part of life. Microplastics (MPs) are classified as emerging co... more Plastics are widely used in every part of life. Microplastics (MPs) are classified as emerging contaminants in nature. Yet, microplastic transportation parameters in groundwater are not characterized well. In this study, microplastic transport in saturated homogeneous media was investigated. For this purpose, one-dimensional column tests were performed using the fluorescent and microplastic tracers to figure out the hydrodynamic conditions for the microplastic transport. Large silica, small silica, sand, and coarse gravel were the tested media. The hydrodynamic transport parameters were calculated by inverse solution methodology using the experimental and the analytical solution results. Only the coarse gravel medium with a minimum 1 mm and maximum 20 mm (5 mm of median) pore sizes and kinematic porosity 40.2% were found to be suitable for the transport of the used polyethylene (PE) whose particle size was between 200 and 500 µm. It is not possible to transport PE particles of selected size from fine-grained media. Transportation occurred in coarse-grained media such as coarse gravel. The calculated dispersivity values for the coarse gravel were 2.58 and 3.02 cm by using fluorescent and PE tracers, respectively. The experiments showed that the used PE particles cannot be transported if the mean flow velocity is lower than 2.02 cm/min in the coarse gravel medium. The microplastic accumulation might be an issue for an actual aquifer rather than the transportation of it considering the actual groundwater flow velocity is generally much lower.

Environmental Earth Sciences, Sep 29, 2012

Transmissivity (T) is a basic hydraulic parameter of an aquifer that is utilized in most groundwa... more Transmissivity (T) is a basic hydraulic parameter of an aquifer that is utilized in most groundwater flow equations to understand the flow dynamics and is generally estimated from pumping tests. However, the cost of performing a large number of aquifer tests is expensive and time consuming. The fact that specific capacity (S c) is correlated with hydraulic flow properties of aquifers simplifies parameter estimation mainly because specific capacity values are more abundant in groundwater databases than values of transmissivity and they offer another approach to estimate hydraulic parameters of aquifers. In this study, an empirical relation is derived using 214 pairs of transmissivity and specific capacity values that are obtained from pumping tests conducted on water wells penetrating the complex volcanic aquifers of Upper Awash Basin, central Ethiopia. Linear and logarithmic regression functions have been performed and it is found that the logarithmic relationship predicting transmissivity from specific capacity data has a better correlation (R = 0.97) than the linear relationship (R = 0.79). The two parameters are log-normally distributed, in which the logarithmic relation is also better statistically justified than the linear relation. Geostatistical estimations of the transmissivity were made using different inputs and methods. Measured and supplemented transmissivity data obtained from estimates using the derived empirical relation were krigged and cokrigged, spherical and exponential models were fitted to the experimental variograms. The cross-validation results showed that the best estimation is provided using the kriging procedure, the transmissivity field represented by the measured transmissivity data and the experimental variogram fitted with the exponential model. Based on the geostatistical approach, the transmissivity map of the aquifer is produced, which will be used for groundwater flow modeling of the study area that will follow this analysis.

Journal of Water Science, Apr 12, 2005

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Ground Water, Nov 1, 2000

Ground Water, Nov 1, 1993

Water, Dec 25, 2019

Karst aquifers have been an important research topic for hydrologists for years. Due to their hig... more Karst aquifers have been an important research topic for hydrologists for years. Due to their high storage capacity, karst aquifers are an important source of water for the environment. On the other hand, it is safety-critical because of its role in floods. Mugla Karst Aquifer (SW, Turkey) is the only major water-bearing formation in the close environs of Mugla city. Flooding in the wet season occurs every year in the recharge plains. The aquifer discharges by the seaside springs in the Akyaka district which is the main touristic point of interest in the area. Non-porous irregular internal structures make the karsts more difficult to study. Therefore, many different methodologies have been developed over the years. In this study, unit hydrograph analysis, correlation and spectral analyses were applied on the rainfall and spring water-level time series data. Although advanced karst formations can be seen on the surface like the sinkholes, it has been revealed that the interior structure is not highly karstified. 100-130 days of regulation time was found. This shows that the Mugla Karst has quite inertial behavior. Yet, the storage of the aquifer system is quite high, and the late infiltration effect caused by alluvium plains was detected. This characterization of the hydrodynamic properties of the Mugla karst system represents an important step to consider the rational exploitation of its water resources in the near future.

Ground Water, Nov 1, 1999

Flow simulation is difficult to implement in heterogeneous media such as karst aquifers, primaril... more Flow simulation is difficult to implement in heterogeneous media such as karst aquifers, primarily because the structure of the rock is extremely complex and usually unknown. The aim of this study was to verify the possibility of using inverse modeling and an equivalent porous media to identify transmissivities in a slightly karstified aquifer, the La Rochefoucauld karst (Charente, France). Different simulation scenarios were tested: using two spatial discretizations with different finite-element cell sizes and using measured or interpolated heads. The inverse modeling was performed with the downscaling parameterization procedure, using a finite-element representation of bidimensional ground water flow. The inverse modeling converged satisfactorily with all scenarios: head residuals were small and spring flow rates and the river/aquifer exchanges were adequately simulated. The scenario using small cells and measured heads generated a highly heterogeneous transmissivity field, indicating an overparameterization of the problem. The calibrated transmissivities and simulated heads of this scenario proved less reliable overall than those of the other scenarios. The use of interpolated heads generated more uniform transmissivities as a result of the head smoothing. A rotation of the initial parameter mesh showed that the scenarios using interpolated heads generate the most stable and reliable results. The scenarios with interpolated heads could therefore be used when head measurements are limited or are unevenly distributed over the aquifer. Overall, the calibrated transmissivities reproduced the entire range of transmissivities measured in the field using different methods. The results indicate that inverse modeling and an equivalent porous media can be used to determine transmissivities in a moderately karstified aquifer.

Carpathian Journal of Earth and Environmental Sciences, 2018