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El-Fahem, Tobias (2008): Hydrogeological investigations in the upper Ouémé catchment in Benin, West Africa [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.816619, Supplement to: El-Fahem, T (2008): Hydrogeological conceptualisation of a tropical river catchment in a crystalline basement area and transfer into a numerical groundwater flow model - Case study for the Upper Ouémé catchment in Benin. PhD Thesis, Rheinische Friedrich-Wilhelms Universität Bonn, 178 pp, urn:nbn:de:hbz:5N-15094

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Abstract:
The scope of this PhD thesis was the hydrogeological conceptualisation of the Upper Ouémé river catchment in Benin. The study area exceeds 14,500 km**2 and is underlain by a crystalline basement. At this setting the typical sequence of aquifers - a regolith aquifer at the top and a fractured bedrock aquifer at the bottom – is encountered, which is found in basement areas all over Africa and elsewhere in the world. The chosen regional approach revealed important information about the hydrochemistry and hydrogeology of this catchment.
Based on the regional conceptual model a numerical groundwater flow model was designed. The numerical model was used to estimate the impact of climate change on the regional groundwater resources.
This study was realised within the framework of the German interdisciplinary research project IMPETUS (English translation: "Integrated approach to the efficient management of scarce water resources in West Africa"), which is jointly managed by the German universities of Bonn and Cologne. Since the year 2000 the Upper Ouémé catchment was the principal target for investigations into the relevant processes of the regional water cycle. A first study from 2000 to 2003 (Fass, 2004, http://nbn-resolving.de/urn:nbn:de:hbz:5n-03849) focused on the hydrogeology of a small local catchment (~30 km**2).
In the course of this thesis five field campaigns were underdone from the year 2004 to 2006. In the beginning of 2004 a groundwater monitoring net was installed based on 12 automatic data loggers. Manual piezometric measurements and the sampling of groundwater and surface water were realised for each campaign throughout the whole study area. Water samples were analysed for major ions, for a choice of heavy metals and for their composition by deuterium, oxygen-18 and tritium. The numerical model was performed with FEFLOW.
The hydraulic and hydrochemical characteristics were described for the regolith aquifer and the bedrock aquifer. The regolith aquifer plays the role of the groundwater stock with low conductivity while the fractures of the bedrock may conduct water relatively fast towards extraction points. Flow in fractures of the bedrock depends on the connectivity of the fracture network which might be of local to subregional importance.
Stable isotopes in combination with hydrochemistry proved that recharge occurs on catchment scale and exclusively by precipitation. Influx of groundwater from distant areas along dominant structures like the Kandi fault or from the Atacora mountain chain is excluded. The analysis of tritium in groundwater from different depths revealed the interesting fact of the strongly rising groundwater ages. Bedrock groundwater may possibly be much older than 50 years.
Equilibrium phases of the silicate weathering products kaolinite and montmorillonite showed that the deeper part of the regolith aquifer and the bedrock aquifer feature either stagnant or less mobile groundwater while the shallow aquifer level is influenced by seasonal groundwater table fluctuations. The hydrochemical data characterised this zone by the progressive change of the hydrochemical facies of recently infiltrated rainwater on its flow path into deeper parts of the aquifers. Surprisingly it was found out that seasonal influences on groundwater hydrochemistry are minor, mainly because they affect only the groundwater levels close to the surface.
The transfer of the hydrogeological features of the Upper Ouémé catchment into a regional numerical model demanded a strong simplification. Groundwater tables are a reprint of the general surface morphology. Pumping or other types of groundwater extraction would have only very local impact on the available groundwater resources.
It was possible to integrate IMPETUS scenario data into the groundwater model. As a result it was shown that the impact of climate change on the groundwater resources until the year 2025 under the given conditions will be negligible due to the little share of precipitation needed for recharge and the low water needs for domestic use.
Reason for concern is the groundwater quality on water points in the vicinity of settlements because of contamination by human activities as shown for the village of Dogué. Nitrate concentrations achieved in many places already alerting levels. Health risks from fluoride or heavy metals were excluded for the Upper Ouémé area.
Coverage:
Median Latitude: 9.520841 * Median Longitude: 2.079069 * South-bound Latitude: 7.500710 * West-bound Longitude: 1.386010 * North-bound Latitude: 10.215240 * East-bound Longitude: 3.212770
Date/Time Start: 2004-03-20T00:00:00 * Date/Time End: 2007-02-22T17:00:00
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
36 datasets

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Datasets listed in this publication series

  1. El-Fahem, T (2008): (A-1.1) Hydrochemistry measured on water samples from Benin, West Africa, at the end of dry season in 2004. https://doi.org/10.1594/PANGAEA.816556
  2. El-Fahem, T (2008): (A-1.2) Hydrochemistry measured on water samples from Benin, West Africa, at the end of rainy season in 2004. https://doi.org/10.1594/PANGAEA.816557
  3. El-Fahem, T (2008): (A-1.3) Hydrochemistry measured on water samples from Benin, West Africa, at the end of dry season in 2005. https://doi.org/10.1594/PANGAEA.816558
  4. El-Fahem, T (2008): (A-1.4) Hydrochemistry measured on water samples from Benin, West Africa, at the end of rainy season in 2005. https://doi.org/10.1594/PANGAEA.816559
  5. El-Fahem, T (2008): (A-1.5) Hydrochemistry measured on water samples from Benin, West Africa, at the end of dry season in 2006. https://doi.org/10.1594/PANGAEA.816560
  6. El-Fahem, T (2008): (A-1.6) Heavy metal concentration measured on water samples from Benin, West Africa, at the end of rainy season in 2004. https://doi.org/10.1594/PANGAEA.816565
  7. El-Fahem, T (2008): (A-1.7) Heavy metal concentration measured on water samples from Benin, West Africa, at the end of dry season in 2005. https://doi.org/10.1594/PANGAEA.816566
  8. El-Fahem, T (2008): (A-1.8) Hydrochemistry measured on rainwater samples from Benin, West Africa. https://doi.org/10.1594/PANGAEA.816574
  9. El-Fahem, T (2008): (A-1.8) Hydrochemistry measured on surface water samples from Benin, West Africa. https://doi.org/10.1594/PANGAEA.816573
  10. El-Fahem, T (2008): (A-2.1) Stable isotopes measured on water samples from Benin, West Africa. https://doi.org/10.1594/PANGAEA.816586
  11. El-Fahem, T (2008): (A-2.2) Tritium measured on water samples from Benin, West Africa. https://doi.org/10.1594/PANGAEA.816588
  12. El-Fahem, T (2008): (A-3.2) Pegel measurements and air temperature at station BM-1. https://doi.org/10.1594/PANGAEA.816603
  13. El-Fahem, T (2008): (A-3.2) Pegel measurements and air temperature at station BM-2. https://doi.org/10.1594/PANGAEA.816604
  14. El-Fahem, T (2008): (A-3.2) Pegel measurements and air temperature at station BM-3. https://doi.org/10.1594/PANGAEA.816605
  15. El-Fahem, T (2008): (A-3.1) Water temperature in borehole HVO-1 at 5h. https://doi.org/10.1594/PANGAEA.816589
  16. El-Fahem, T (2008): (A-3.3) Water temperature measured in borehole HVO-1, 3h resolution. https://doi.org/10.1594/PANGAEA.816608
  17. El-Fahem, T (2008): (A-3.1) Water temperature in borehole HVO-2 at 5h. https://doi.org/10.1594/PANGAEA.816593
  18. El-Fahem, T (2008): (A-3.3) Water temperature measured in borehole HVO-2, 3h resolution. https://doi.org/10.1594/PANGAEA.816609
  19. El-Fahem, T (2008): (A-3.1) Water temperature in borehole HVO-3 at 5h. https://doi.org/10.1594/PANGAEA.816594
  20. El-Fahem, T (2008): (A-3.3) Water temperature measured in borehole HVO-3, 3h resolution. https://doi.org/10.1594/PANGAEA.816610
  21. El-Fahem, T (2008): (A-3.1) Water temperature in borehole HVO-4 at 5h. https://doi.org/10.1594/PANGAEA.816595
  22. El-Fahem, T (2008): (A-3.3) Water temperature measured in borehole HVO-4, 3h resolution. https://doi.org/10.1594/PANGAEA.816611
  23. El-Fahem, T (2008): (A-3.1) Water temperature in borehole HVO-6 at 5h. https://doi.org/10.1594/PANGAEA.816596
  24. El-Fahem, T (2008): (A-3.3) Water temperature measured in borehole HVO-6, 3h resolution. https://doi.org/10.1594/PANGAEA.816612
  25. El-Fahem, T (2008): (A-3.1) Water temperature in borehole HVO-7 at 5h. https://doi.org/10.1594/PANGAEA.816597
  26. El-Fahem, T (2008): (A-3.3) Water temperature measured in borehole HVO-7, 3h resolution. https://doi.org/10.1594/PANGAEA.816613
  27. El-Fahem, T (2008): (A-3.1) Water temperature in borehole HVO-8 at 5h. https://doi.org/10.1594/PANGAEA.816598
  28. El-Fahem, T (2008): (A-3.3) Water temperature measured in borehole HVO-8, 3h resolution. https://doi.org/10.1594/PANGAEA.816614
  29. El-Fahem, T (2008): (A-3.1) Water temperature in borehole HVO-9 at 5h. https://doi.org/10.1594/PANGAEA.816599
  30. El-Fahem, T (2008): (A-3.3) Water temperature measured in borehole HVO-9, 3h resolution. https://doi.org/10.1594/PANGAEA.816615
  31. El-Fahem, T (2008): (A-3.1) Water temperature in borehole HVO-10 at 5h. https://doi.org/10.1594/PANGAEA.816590
  32. El-Fahem, T (2008): (A-3.3) Water temperature measured in borehole HVO-10, 3h resolution. https://doi.org/10.1594/PANGAEA.816616
  33. El-Fahem, T (2008): (A-3.1) Water temperature in borehole HVO-11 at 5h. https://doi.org/10.1594/PANGAEA.816591
  34. El-Fahem, T (2008): (A-3.3) Water temperature measured in borehole HVO-11, 3h resolution. https://doi.org/10.1594/PANGAEA.816617
  35. El-Fahem, T (2008): (A-3.1) Water temperature in borehole HVO-12 at 5h. https://doi.org/10.1594/PANGAEA.816592
  36. El-Fahem, T (2008): (A-3.3) Water temperature measured in borehole HVO-12, 3h resolution. https://doi.org/10.1594/PANGAEA.816618