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**Groundwater Management of the Iullemeden Aquifer System**

C. Alberich, W. Kinzelbach IHW, ETH Zürich, Switzerland A. Dodo Direction National de Ressources en Eau Niamey, Niger

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**Contents Geometry and boundary conditions of model Recharge estimation**

Discharges Piezometry Water balance Conclusions

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Iullemmeden Basin

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**Geometry and Boundary Conditions**

Cristallin Rock B Primary Argiles d‘Irhazer Ci -Ch Marin Cretaceous Adrar des Iforas Massif de l‘Aïr Ct Tombouctou Gao Detroit Soudanaise Rift Oriental LAKE TCHAD Niamey Sokoto N‘guru Kano Maiduguri A

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**Marine and Lacustrine Upper Cretaceous**

(Greigert,1979) Continental Terminal Paleocene - Ypresian Marine and Lacustrine Upper Cretaceous Iullemmeden aquifer system Continental intercalaire - Continental hamadien Argiles d‘Irhazer - Serie Izegouandane West of Massif de l‘Aïr Primary

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**Upper Cretaceous Marine and Lacustrine Formations / Paleocene - Ypresian**

1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 [Cr6a-5] [Cr6b] [Cr7] 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 19 1? 18 17 16 15 14 13 12 11 1 2 3 4 5 6 7 8 9 Calc. à Neobilites Lower sandstones Calcaires et argiles Calc. à Nigecigeras Term I Term IV and mudstones à Libycoceras ismaeli Série Calc. Blancs Term II Mosasaurus shales Argiles sableuses Rima Group Term V Sables à Cocodriliens Série Marnes et Calcaires Upper sandstones Term III TermVI-VII Paleocene and mudstones (Sokoto Group)

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**Nigeria Niger / Mali Model Gwandu Ct3 Ct3 Ct2 Ct2 Ct1 Gwandu Ct1**

Sokoto Terms VI and VII Terms IV and V Rima Terms I to III Lower sedimentary complex [Cr6-5] to [Cr7] Gundumi - Illo Ci -Ch

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**Boundary Conditions Radier,1959 Greigert,1961**

Cristallin Rock Primary Argiles d‘Irhazer Ci -Ch Marine Cretaceous Adrar des Iforas Massif de l‘Aïr Ct Anefis Agades Tombouctou Gao Detroit Soudanaise Rift Oriental Taouardeï Greigert,1961 Greigert and Pougnet,1967 Greigert,1979 Ogilbee andAnderson, 1965/1973 Oteze, 1976 Radier,1959 Pallas, 1971 Zinder LAKE TCHAD Niamey Sokoto N‘guru Kano Maiduguri

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**Bottom of lower sedimentary complex**

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**Top of lower sedimentary complex**

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Top of CT1 (blue)

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Top of CT2 (orange)

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Top of CT3 (yellow)

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**Recharge Single most important figure for sustainable management.**

Water balance methods and Darcy formula notoriously inaccurate (factor of 10) Environmental tracers can often be better (factor of 2-3) Tracers used: Tritium, Tritium-3He, CFC (Freons), SF6, Chloride Remote sensing info combined with groundwater flow and transport models allow to test hypotheses on recharge mechanisms (areal and concentrated recharge) Use of precipitation and evapotranspiration maps obtained with RS methods can help at delineating zones

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**Sampling for CFC in groundwater (Niger)**

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**ATMOSPHERIC CFC CONCENTRATIONS IN THE**

ATMOSPHERE F12 F11

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**Tritium Concentration in Rainwater**

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**Principle of Age Dating With Tracers**

Result: Pore velocity u = L/t delay t With porosity we obtain specific flux q = nu With area we obtain total flux Q = qA L

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**Evapotranspiration for the 5th March 1992 **

calculated from NOAA-AVHRR using SEBAL mm/d

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**Precipitation map from METEOSAT (Example 1-10 June 1995)**

mm/10d 10° – 20° North 0° – 10° East

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**Tritium corrected to 1985 related to depth to the water table**

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Tritium in wells ( )

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**NDVI from Landsat TM of Feb. 1986**

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NDVI Spot image

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**Survey of Mares (from satellite image)**

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**Survey of Mares (ground truth /satellite)**

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**Population Distribution in the Iullemmeden**

Estimated water consumption 50 l/person/day Inhabitants/km2 or more

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**Vertical Distribution of Abstractions by Wells**

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**Discharge by Evapotranspiration**

Potential ET 2000 mm/a Digital terrain model Extinction depth for evapotranspiration up to 50 m Evaporation by vapour transport (Coudrain-Ribstein) E = 71.7 z (E in mm/a, z in m) in Iullemmeden basin negligible

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**Piezometry of CI (observed)**

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**Piezometry of CT1 (observed)**

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**Piezometry of CT2 (observed)**

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**Piezometry of CI (computed)**

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**Piezometry of CT1 (computed)**

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**Piezometry of CT2 (computed)**

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**Groundwater balance (first rough estimate from model)**

+ 70 m3/s - 50 m3/s - 10 m3/s - 10 m3/s

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**Conclusions 1 Model concept available due to previous work**

Mechanisms of recharge can only be identified in more local studies, generalization to the total area requires related remote sensing data Distributed input data such as discharges rely heavily on proxi data such as population maps, soil maps and remote sensing data Accuracy of model fluxes still has to verified. In this task environmental tracers are useful

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**Conclusions 2 Presently overexploitation has not yet started**

New technology can help to do a better job in resource assessment than has been possible in the past Besides the donor driven activities in Niger which lead to a large number of new wells a strategic consideration of the whole is necessary

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