The distribution of evaporation rate on some rock walls of drifts in two mines, i. e., the Stripa Mine, Sweden and the Tono Mine, Japan. Although the relative humidity in the drifts of the Stripa Mine was lower than 85%, the humidity in the drifts of the Tono Mine was higher than 95%. The obtained results were as follows;
(1) The evaporation rate could be well measured even under the high humidity condition.
(2) Considerable amount of water could evaporate from a dried fracture.
(3) Evaporation rate spatially changed along a fracture.
(4) The evaporation rate might be identical to the groundwater discharge comming through a rock mass if the permeability of rock mass was low.
It was clearly found that the technique of the evaporation measurement was quite useful for mapping the groundwater discharge on a tunnel wall of the low permeable rock mass.