@article{fdi:010062410,
  title = {{E}stimating storage properties of aquifer with magnetic resonance sounding : a field verification in northern {C}ambodia of the gravitational water apparent cutoff time concept},
  author = {{V}ouillamoz, {J}ean-{M}ichel and {S}ophoeun, {P}. and {B}ruyere, {O}. and {A}rnout, {L}.},
  editor = {},
  language = {{ENG}},
  abstract = {{M}agnetic {R}esonance {S}ounding ({MRS}) has already showed its capability for estimating some aquifer properties, but very little work has been carried out concerning the storage properties used for calculating groundwater reserve and recharge. {F}or unconfined aquifer, this storage property (i.e., the specific yield) is often estimated from the {MRS} water content. {H}owever, a recent study carried out in a poor sandstone aquifer of {N}orthern {C}ambodia found that the {MRS} pore-size related parameter is probably more appropriate because the {MRS} water content can be dominated by water which does not contribute to the specific yield. {A} main output of this study is that a threshold value (so-called apparent cutoff time {ACT}) of the {MRS} decay time {T}-2* can be defined for discriminating gravitational water ({T}-2* > 130 ms) from capillary and bound waters. {S}ince measuring such short {MRS} signal is quite common, a validation of this result is compulsory to avoid the misuse of the {MRS} water content. {T}his paper presents an experiment that we set up to check the validity of the {ACT} approach. {W}e compared two {MRS} carried out at the same location in a clayey-sand layer 15 metres thick. {T}he first {MRS} was carried out with a static water level located at 1.7 metres below the ground level. {I}t revealed a layer with a water content of 3.8% and {T}-2* = 120 ms. {A}ccording to the {ACT} approach, this short value of {T}-2* indicates water that is not part of the specific yield and that can not be released by pumping. {T}hus, we carried out a second {MRS} after pumping and lowering the water level to an average of 15 metres. {A}s predicted by the {ACT} approach, we observed that the second {MRS} signal was the same as the one obtained before pumping. {T}o cross-check our observation, we carried out a pumping test at the same location. {W}e found a very low value of specific yield, confirming that the main part of the {MRS} signal is generated by water which was not drained by the pumping. {W}e calculated that the volume of water removed from the aquifer by the pumping was far too low to generate a measurable magnetic resonance signal. {F}rom our experiment, we conclude that the {ACT} approach can be successfully used to estimate the specific yield of poor aquifers, and to avoid a misuse of the {MRS} water content which can lead to strong overestimates of aquifer reserve and recharge.},
  keywords = {{CAMBODGE}},
  booktitle = {},
  journal = {{N}ear {S}urface {G}eophysics},
  volume = {12},
  numero = {2},
  pages = {211--216},
  ISSN = {1569-4445},
  year = {2014},
  DOI = {10.3997/1873-0604.2013038},
  URL = {https://www.documentation.ird.fr/hor/fdi:010062410},
}