1887
  1. Home
  2. A-Z Publications
  3. Near Surface Geophysics
  4. Volume 9, Issue 2
  5. Article
Volume 9 Number 2
  • ISSN: 1569-4445
  • E-ISSN: 1873-0604

Abstract

ABSTRACT

A quantitative budget estimate of actual evapo‐transpiration is a key issue for enhanced hydrological modelling in northern Bénin. Actual evapo‐transpiration is estimated using large aperture scintillometer equipment, devoted to sensible heat flux measurements. However, a previous study reported that the actual evapo‐transpiration cycle is not fully understood. Indeed, the actual evapo‐transpiration depends strongly on several factors such as climate, vegetation pattern, soil water storage and human activities. The respective contributions of the aquifer and vadose zone to the actual evapo‐transpiration budget are not known. When using piezometric variations of the water table, the aquifer contribution is not easy to quantify since the specific yield may vary in the investigated area, located in a metamorphic rock environment. In the present study, we investigate whether significant differences in the aquifer’s specific yield could exist within the large aperture scintillometer measurement area, leading to different actual evapo‐transpiration water losses. We use joint frequency electromagnetic resistivity mapping, geological surveys and magnetic resonance sounding (MRS) to delineate the effective porosity of the regolith around the scintillometre measurement area. Thirteen MRS soundings implemented in key areas reveal a clear classification of the main geological units on the basis of their water content. The MRS water content varies between 1.5–3% for amphibolite and micaschists formations to more than 12% for quartzitic fractured formations, whereas the MRS relaxation time is less discriminating (150–250 ms), indicating a small variation in pore size. Then, as a first modelling exercise, we assumed that the MRS water content (the effective porosity) maximizes the specific yield. The actual evapo‐transpiration budget given by a previous study (Guyot 2009) is then re‐interpreted using geophysical data: we found that a) the measured water table depletion can explain the actual evapo‐transpiration value providing enough water for the transpiration process and b) the significant discrepancies in actual evapo‐transpiration signals observed between the eastern and western parts of the watershed can be explained by the respective effective porosity of the geological units. Even if further research is needed to link MRS water content to the specific yield and to evaluate a possible role of the deep vadose zone, the hydrogeophysical mapping presented in this study highlights the role of the MRS method for providing relevant information to understand hydrological processes in this complicated geological context of north Bénin.

© European Association of Geoscientists and Engineers © 2011 European Association of Geoscientists and Engineers
Loading

Article metrics loading...

/content/journals/10.3997/1873-0604.2011003
2011-01-01
2024-04-19

  • From This Site

    /content/journals/10.3997/1873-0604.2011003
    dcterms_title,dcterms_subject,pub_keyword
    -contentType:Journal -contentType:Contributor -contentType:Concept -contentType:Institution
    10
    5
Loading full text...

Full text loading...

References

  1. AffatonP.1973. Etude géologique et structurale du Nord‐Ouest‐Dahomey, du Nord‐Togo et du Sud‐Est de la Haute‐Volta.PhD thesis, University of Provence (in French).
     [Google Scholar]
  2. AffatonP.1987. Le Bassin des Voltas (Afrique de l’Ouest): Une marge passive, d’âge protérozoïque supérieur, tectonisée au panafricain (600 ± 50 Ma).Thèse Géologie, University of d’Aix‐Marseille 3 (ORSTOM Editions, collection Etudes et Thèses, Paris, France, 1990) (in French).
     [Google Scholar]
  3. BeauvaisA., RitzM., ParisotJ.‐C., DukhanM. and BantsimbaC.1999. Analysis of poorly stratified lateritic terrains overlying a granitic bedrock in West Africa, using 2‐D electrical resistivity tomography. Earth and Planetary Science Letters173, 413–424.
     [Google Scholar]
  4. BraunJ‐J., DescloitresM., RiotteJ., FleuryS., BarbieroL., BoeglinJ.‐L., VioletteA., LacarceE., RuizL., SekharM., Mohan KumarM.S., SubramanianS. and DupreB.2009. Regolith mass balance inferred from combined mineralogical, geochemical and geophysical studies: Mule Hole gneissic watershed, South India. Geochimica et Cosmochimica Acta73, 935–961. doi:10.1016/j.gca.2008.11.013
     [Google Scholar]
  5. ChalikakisK., Ryom NielsenM., LegchenkoA. and Feldberg HagensenT.2009. Investigation of sedimentary aquifers in Denmark using the magnetic resonance sounding method (MRS). Comptes Rendus Geosciences341, 918–927.
     [Google Scholar]
  6. DescloitresM., RuizL., SekharM., LegchenkoA., BraunJ.J., Mohan KumarM.S. and SubramanianS.2008. Characterization of seasonal local recharge using electrical resistivity tomography and magnetic resonance sounding. Hydrological Processes22, 384–394.
     [Google Scholar]
  7. DewandelB., LachassagneP., WynsR., MaréchalJ.C. and KrishnamurthyN.S.2006. A generalized 3‐D geological and hydrogeological conceptual model of granite aquifers controlled by single multiphase weathering. Journal of Hydrology330, 260–284.
     [Google Scholar]
  8. DunnK.J., BergmanD.J. and LatorracaG.A.2002. Nuclear Magnetic Resonance: Petrophysical and Logging Applications.Elsevier.
     [Google Scholar]
  9. GuyotA., CohardJ.M., AnquetinS., GalleS. and LloydC.R.2009. Combined analysis of energy and water balances to estimate latent heat flux of a Sudanian small catchment using fluxes measurements and energy budget. Journal of Hydrology375, 227–240.
     [Google Scholar]
  10. HillR.J., OchsG.R. and WilsonJ.J.1992. Measuring surface layer fluxes of heat and momentum using optical scintillation. Boundary‐Layer Meteorology58, 391–408.
     [Google Scholar]
  11. HsiehC.‐I., KatulG. and Tze‐wenC.2000. An approximate analytical model for footprint estimation of scalar fluxes in thermally stratified atmospheric flows. Advances in Water Resources23, 765–772.
     [Google Scholar]
  12. KamagatéB., SéguisL., FavreauG., SeidelJ.L., DescloitresM. and AffatonP.2007. Hydrological processes and water balance of a tropical crystalline bedrock catchment in Benin (Donga, upper Ouémé River). Comptes Rendus Geoscience339, 418–429.
     [Google Scholar]
  13. LebelT. and VischelT.2005. Climat et cycle de l’eau en zone tropicale: Un problème d’échelle. Comptes Rendus Geoscience337, 29–38 (in French).
     [Google Scholar]
  14. LegchenkoA.2004a. Magnetic resonance sounding: Enhanced modeling of a phase shift. Applied Magnetic Resonance25, 621–636.
     [Google Scholar]
  15. LegchenkoA., BaltassatJ.‐M., BobachevA., MartinC., RobainH. and VouillamozJ.M.2004b. Magnetic resonance sounding applied to aquifer characterization. Ground Water42, 363–373.
     [Google Scholar]
  16. LegchenkoA., DescloitresM., BostA., RuizL., ReddyM., GirardJ.‐F., SekharM., Mohan KumarM.S. and BraunJ.J.2006. Resolution of MR soundings applied to the characterization of hard rock aquifers. Groundwater44, 547–554.
     [Google Scholar]
  17. LegchenkoA. and VallaP.2002. A review of the basic principles for proton magnetic resonance sounding measurements. Journal of Applied Geophysics50, 3–19.
     [Google Scholar]
  18. Le LayM. and GalleS.2005. How changing rainfall regimes may affect the water balance. A modelling approach in West Africa. In: Regional Hydrological Impacts of Climatic Changes – Hydroclimatic Variability, pp. 203–210. IAHS Publications.
     [Google Scholar]
  19. Le LayM., SaulnierG.‐M., GalleS., SeguisL., MétadierM. and PeugeotC.2008. Model representation of the Sudanian hydrological processes: Application on the Donga catchment (Benin). Journal of Hydrology363, 32–41.
     [Google Scholar]
  20. LubczynskiM. and RoyJ.2004. Magnetic resonance sounding: New method for ground water assessment. Ground Water42, 291–303.
     [Google Scholar]
  21. LubczynskiM. and RoyJ.2005. MRS contribution to hydrogeological system parameterization. Near Surface Geophysics3, 131–139.
     [Google Scholar]
  22. Mc NeillD.J.1980. Electromagnetic terrain conductivity measurement at low induction number. Technical note TN 6, Geonics Ltd, Canada.
     [Google Scholar]
  23. MeijningerW.M.L., HartogensisO.K., KohsiekW., HoedjesJ.C.B., ZuurbierR.M. and de BruinH.A.R.2002. Determination of area‐averaged sensible heat fluxes with a large aperture scintillometer over a heterogeneous surface – Flevoland field experiment. Boundary‐Layer Meteorology105, 37–62.
     [Google Scholar]
  24. RoyJ. and LubczynskiM.2003. The magnetic resonance sounding technique and its use for groundwater investigations. Hydrogeology Journal11, 455–465.
     [Google Scholar]
  25. SchuttemeyerD., MoeneA.F., HoltslagA.A.M., de BruinH.A.R. and Van De GiesenN.2006. Surface fluxes and characteristics of drying semi‐arid terrain in West Africa. Boundary‐Layer Meteorology118, 583–612. doi:10.1007/s10546‐005‐9028‐2
     [Google Scholar]
  26. SeatonW.J. and BurbeyT.J.2002. Evaluation of two‐dimensional resistivity methods in a fractured crystalline‐rock terrane. Journal of Applied Geophysics51, 21–41.
     [Google Scholar]
  27. VouillamozM., DescloitresM., ToeG. and LegchenkoA.2005. Characterization of crystalline basement aquifers with MRS: Comparison with boreholes and pumping tests data in Burkina Faso. Near Surface Geophysics3, 107–111.
     [Google Scholar]
  28. VouillamozJ.M., FavreauG., MassuelS., BoucherM., NazoumouY. and LegchenkoA.2008. Contribution of magnetic resonance sounding to aquifer characterization and recharge estimate in semiarid Niger. Journal of Applied Geophysics64, 99–108.
     [Google Scholar]
  29. WrightE.P.1992. The hydrogeology of crystalline basement aquifers in Africa. In: Hydrogeology of Crystalline Basement Aquifers in Africa (eds E.P.Wright and W.G.Burgess ), pp. 1–27. Geological Society London.
     [Google Scholar]
  30. WynsR., BaltassatJ.M., LachassagneP., LegchenkoA., VaironJ. and MathieuF.2004. Application of proton magnetic resonance soundings to groundwater reserve mapping in weathered basement rocks (Brittany, France). Bulletin de la Société Géologique de France175, 21–34.
     [Google Scholar]
  31. YaramanciU., LangeG. and HertrichM.2002. Aquifer characterization using surface NMR jointly with other geophysical techniques at the Nauen/Berlin test site. Journal of Applied Geophysics50, 47–65.
     [Google Scholar]
http://instance.metastore.ingenta.com/content/journals/10.3997/1873-0604.2011003
Loading
The contribution of MRS and resistivity methods to the interpretation of actual evapo‐transpiration measurements: a case study in metamorphic context in north Bénin
Near Surface Geophysics 9, 187 (2011); https://doi.org/10.3997/1873-0604.2011003
/content/journals/10.3997/1873-0604.2011003
/content/journals/10.3997/1873-0604.2011003
Loading

Data & Media loading...

  • Article Type: Research Article

Most Cited This Month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error