@article{PAR00008563,
  title = {{T}he contribution of {MRS} and resistivity methods to the interpretation of actual evapo-transpiration measurements : a case study in metamorphic context in north {B}enin},
  author = {{D}escloitres, {M}arc and {S}{\'e}guis, {L}uc and {L}egchenko, {A}natoli and {W}ubda, {M}. and {G}uyot, {A}. and {C}ohard, {J}. {M}.},
  editor = {},
  language = {{ENG}},
  abstract = {{A} quantitative budget estimate of actual evapo-transpiration is a key issue for enhanced hydrological modelling in northern {B}enin. {A}ctual evapo-transpiration is estimated using large aperture scintillometer equipment, devoted to sensible heat flux measurements. {H}owever, a previous study reported that the actual evapo-transpiration cycle is not fully understood. {I}ndeed, the actual evapo-transpiration depends strongly on several factors such as climate, vegetation pattern, soil water storage and human activities. {T}he respective contributions of the aquifer and vadose zone to the actual evapo-transpiration budget are not known. {W}hen 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. {I}n 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. {W}e 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. {T}hirteen {MRS} soundings implemented in key areas reveal a clear classification of the main geological units on the basis of their water content. {T}he {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 {T}-1 is less discriminating (150-250 ms), indicating a small variation in pore size. {T}hen, as a first modelling exercise, we assumed that the {MRS} water content (the effective porosity) maximizes the specific yield. {T}he actual evapo-transpiration budget given by a previous study ({G}uyot et al. 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. {E}ven 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 {B}enin.},
  keywords = {},
  booktitle = {},
  journal = {{N}ear {S}urface {G}eophysics},
  volume = {9},
  numero = {2},
  pages = {187--200},
  ISSN = {1569-4445},
  year = {2011},
  DOI = {10.3997/1873-0604.2011003},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00008563},
}