Christian Leduc

Dryland hydrology in Mediterranean regions—a review

CHRISTOPHE CUDENNEC, CHRISTIAN LEDUC & DEMETRIS KOUTSOYIANNIS 1 INRA, Agrocampus Rennes, UMR 1069, SAS, F-35000 Rennes, France cudennec@agrocampus-rennes.fr 2 IRD, UMR G-EAU, Case MSE, BP 64501, 34394 Montpellier cedex 5, France leduc@ird.fr 3 Department of Water Resources, Faculty of Civil Engineering, National Technical University of Athens, Heroon Polytechneiou 5, GR 157 80 Zographou, Greece dk@itia.ntua.gr

Water table fluctuation and recharge in semi-arid climate: some results of the HAPEX-Sahel hydrodynamic survey (Niger)

Groundwater level measurements taken over a 4-year period from an extensive network of wells and boreholes within the HAPEX-Sahel (Hydrologic Atmospheric Pilot Experiment in the Sahel) degree square (south Niger), together with existing data, have provided an insight into infiltration and recharge processes taking place in the porous phreatic aquifer of the Continental Terminal formation. Despite high spatial and temporal variability of aquifer response to rainfall (rises of between 0 and 9 m are recorded), a pattern of recharge can be recognised. Aquifer responses vary from site to site, but the type of response at any single point tends to be consistent from year to year. Recharge is dominated by infiltration from temporary drainage networks (pools and streams) and aquifer response depends to a large extent on aquifer hydraulic characteristics and distance from the nearest infiltrating zone. In many wells, for which data extending back to 1987 is available, water levels show a consistent year by year rise. This is interpreted as a process of aquifer recovery following the severe drought of the 1970s and early 1980s, though part may also be attributable to changing patterns of land management (e.g. woodland clearance). Initial estimates of regional recharge are from 50–60 mm year−1, or in other words about 10% of annual rainfall. The figure is supported by other methods of investigation (hydrochemical analyses; water budgets of pools).

Integrated surface water–groundwater modelling in the context of increasing water reserves of a regional Sahelian aquifer

Abstract Despite the Sahelian drought of the 1970s–1990s, the unconfined aquifer in southwest Niger exhibits a multidecadal increase in groundwater reserves. Recent changes in land surface conditions have enhanced runoff and thus indirect groundwater recharge below endorheic ponds. This paper presents a model-based investigation of surface runoff and groundwater recharge at mesoscale (∼5000 km2). A new lumped-conceptual runoff model applicable to the large number of ungauged endorheic catchments is specially developed, derived from an existing fine-scale, physically-based hydrologic model. Runoff simulated for sites identified as groundwater recharge sources are used to derive recharge forcing for a Modflow-based model of the aquifer. The rising water table trend and its spatial distribution over the period 1992–2003 are generally well simulated, albeit smoothed year-to-year dynamics. Comparison with alternative methods of recharge estimation suggests, however, that there may presently exist more recharging sites and/or contributing surfaces than those considered so far. Citation Massuel, S., Cappelaere, B., Favreau, G., Leduc, C., Lebel, T. & Vischel, T. (2011) Integrated surface water–groundwater modelling in the context of increasing water reserves of a regional Sahelian aquifer. Hydrol. Sci. J. 56(7), 1242–1264.

Implementation of a 3-D groundwater flow model in a semi-arid region using MODFLOW and GIS tools: The Zéramdine-Béni Hassen Miocene aquifer system (east-central Tunisia)

In this work, an integrated methodology was developed to investigate hydrological processes in Zeramdine-Beni Hassen Miocene aquifer and to validate the groundwater proprieties deduced from the geological, geophysical, hydrodynamic and hydrochemical studies done in the region, using the coupling of groundwater flow model MODFLOW 2000 code with Geographic Information System tools. A 3-D groundwater flow model was developed for this aquifer using a large amount of available geological and hydrological data. The groundwater flow model was calibrated and validated with datasets during the 1980-2007 period. The results show that the ZBH aquifer exhibits the highest sensibility to changes of water infiltration and hydraulic conductivity. The model simulation shows a good degree of understand to the aquifer hydrogeology. The model can be regarded as a useful tool for analyzing the hydrological processes for complex groundwater that have similar geological and hydrogeological conditions and will help to propose a management rescue plan for the studied aquifer, especially for aquifer characterization in arid and semi arid regions.

Variabilité isotopique des précipitations sahéliennes à différentes échelles de temps à Niamey (Niger) entre 1992 et 1999 : implication climatique

Abstract The isotopic content of rainfall was measured in Niamey (Niger) over a period of eight years (1992–1999). Seasonal distribution of rainy events depends on the monsoon movement over the region. At the beginning and at the end of the rainy season, low rainfall, high temperatures and low relative humidity favour isotopic enrichment. In the middle of the rainy season, heavy rainfall, low temperatures and relative humidity close to saturation lead to isotopically depleted contents because of the mass effect; moreover, in the case of low rainfall, marked vertical convective development favours high altitude condensation. How far the Intertropical Front moves north, determines the quality of the rainy season and influences the isotopic contents. Thus the isotopic contents of rainfall are good climatic indicators. To cite this article: J.-D. Taupin et al., C. R. Geoscience 334 (2002) 43–50

Réponse hydrologique d’un bassin semi-aride aux événements pluviométriques et aménagements de versant (bassin du Merguellil, Tunisie centrale)

RÉSUMÉ L’influence cumulée des aménagements de versants sur les écoulements en zones semi-arides demeure peu étudiée et comprise à l’échelle de grands bassins versants. En Tunisie centrale, nous étudions les variations de la réponse hydrologique du bassin du Merguellil à l’échelle annuelle et pour 114 événements entre 1989 et 2010. Sur cette période, les aménagements de conservation des eaux et des sols ont progressivement drainé de 5% à 30% des surfaces du bassin. L’analyse statistique révèle la forte variabilité des pluies et des débits annuels, mais ne distingue aucune tendance déficitaire. L’approche événementielle démontre que les variations des écoulements annuels sont liées aux apports générés par un nombre très limité (cinq à six par an en moyenne) d’épisodes pluvieux supérieurs à 15 mm. Le nombre très variable de ces évènements ainsi que les écarts importants observés sur leur coefficient de ruissellement (KR) respectif sont déterminants sur les apports annuels. Pour les événements de plus de 60 mm, les différences d’intensités pluviométriques, de couvert végétal et d’humidité du sol réduisent le ruissellement jusqu’à 80%. Toutefois, les KR d’averses de moins de 40 mm, sur des sols au couvert végétal et d’humidité semblables, ont également diminué de 45% après l’extension des aménagements de CES à la fin des années 1990.

Réponse hydrologique d’un bassin semi-aride aux événements pluviométriques et aménagements de versant (bassin du Merguellil, Tunisie centrale) / Hydrological response of a semi-arid catchment to rainfall events and water & soil conservation works (Merguellil catchment, Central Tunisia)

RÉSUMÉ L’influence cumulée des aménagements de versants sur les écoulements en zones semi-arides demeure peu étudiée et comprise à l’échelle de grands bassins versants. En Tunisie centrale, nous étudions les variations de la réponse hydrologique du bassin du Merguellil à l’échelle annuelle et pour 114 événements entre 1989 et 2010. Sur cette période, les aménagements de conservation des eaux et des sols ont progressivement drainé de 5% à 30% des surfaces du bassin. L’analyse statistique révèle la forte variabilité des pluies et des débits annuels, mais ne distingue aucune tendance déficitaire. L’approche événementielle démontre que les variations des écoulements annuels sont liées aux apports générés par un nombre très limité (cinq à six par an en moyenne) d’épisodes pluvieux supérieurs à 15 mm. Le nombre très variable de ces évènements ainsi que les écarts importants observés sur leur coefficient de ruissellement (KR) respectif sont déterminants sur les apports annuels. Pour les événements de plus de 60 mm, les différences d’intensités pluviométriques, de couvert végétal et d’humidité du sol réduisent le ruissellement jusqu’à 80%. Toutefois, les KR d’averses de moins de 40 mm, sur des sols au couvert végétal et d’humidité semblables, ont également diminué de 45% après l’extension des aménagements de CES à la fin des années 1990.

Comprehension and hydrogeological conceptualization of aquifer in arid and semi-arid regions using integrated hydrogeological information system: case of the deep aquifer of Zéramdine-Béni Hassen (east-central Tunisia)

In arid and semi-arid regions, the groundwater overexploitation caused drawdown in piezometric levels and a degradation of chemical water quality. That is why the groundwater monitoring needs a good comprehension of the hydrogeological aquifer properties. This is specially the case of Zéramdine–Béni Hassen deep aquifer (east-central Tunisia). Seismic profiles interpretation highlights the existence of the Zéramdine fault corridor, the Boumerdès anticline, the Moknine and Mahdia grabens that represent lateral boundaries for the study aquifer. The outcrop of the aquifer is located in the Zéramdine, Béni Hassen and Ain Ben Jannet regions, where two lithostratigraphic sections were realized. The piezometric study shows that the principal groundwater flow is from west to east. A secondary flow is from NW to SE. The hydrochemical study of 22 sample shows that the aquifer is characterized by freshwater, dominated by Na–Ca–Cl–SO4 facies. The salinity increase is from the west to the east, which coincides with the principal water flow direction. The integration of all results deduced from the hydrogeophysic, hydrodynamic and hydrochemical studies is developed to investigate hydrological processes of Zéramdine–Béni Hassen aquifer and consequently to propose a conceptual model, which will help to propose a rescue plan for the studied aquifer and to implement a spatial hydrogeological database using the global information system and then to characterize the complex aquifer system.

Improving the visibility of hydrological sciences from developing countries

Abstract The increasing level of competition in scientific publishing arguably has a greater negative impact on hydrologists from developing countries and specifically young scientists. This paper discusses the constraints they face and offers suggestions to authors and the hydrological community about how these may be mitigated. These include a lack of access to resources to assist with creating good publications, the difficulty of publishing research based on relatively scarce data, a common problem in many developing countries, and a lack of familiarity with the process of publishing scientific material together with limited access to mentorship from experienced authors. A key point is to ensure that the research question addressed has a broad interest beyond the local study area. However, the more limited hydrological knowledge and the water resources problems of developing countries represent opportunities for internationally relevant research, particularly within the nexus between hydrology and society, or between science and practice. Both of these are high on the international hydrological research agenda. Editor D. Koutsoyiannis

Modalités de recharge d’un aquifère en zone semi-aride : cas de la nappe du Trarza (Sud-Ouest Mauritanie)

Résumé L’aquifère du Trarza s’étend sur environ 40 000 km2 dans le Sud-Ouest mauritanien, entre le fleuve Sénégal au Sud, l’Océan Atlantique à l’Ouest et la chaîne métamorphique des Mauritanides au Nord et à l’Est. La nappe libre est contenue dans les sédiments du Continental Terminal et du Quaternaire. Les campagnes de terrain menées entre 2010 et 2012 ont significativement complété les quelques mesures anciennes. Le croisement d’approches hydrodynamiques et géochimiques a montré que, dans cette zone semi-aride, la dynamique de la nappe est influencée par les multiples changements, actuels et anciens, de l’environnement (depuis les transgressions quaternaires jusqu’aux différents barrages régulant le cours du fleuve Sénégal). La nappe est principalement alimentée par l’infiltration latérale des eaux de surface du fleuve Sénégal et, dans une moindre proportion, par les précipitations. La minéralisation des eaux souterraines résulte d’interactions eau-roches et minéraux silicatés et alumino-silicatés et est localement influencée par des traces des transgressions quaternaires. L’évaporation marque fortement les eaux de surface avant et durant leur infiltration. Des calculs encore très préliminaires suggèrent une recharge annuelle inférieure ou égale à 5% des précipitations, soit de 5 à 10 mm. Editeur Z.W. Kundzewicz Citation Mohamed, A.-S., Marlin, C., Leduc, C., et Jiddou, M., 2014. Modalités de recharge d’un aquifère en zone semi-aride: cas de la nappe du Trarza (Sud-Ouest Mauritanie). Hydrological Sciences Journal, 59 (5), 1046–1062.