Experimental Researches on the Relation between Evaporation from Bare Ground and Soil Moisture Content

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  • 裸地における土壌水分と蒸発量の関係についての検討
  • ラチ ニ オケル ドジョウ スイブン ト ジョウハツリョウ ノ カンケイ ニ

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Abstract

The relation between the amount of evaporation from bare ground and its soil moisture content has been investigated experimentally. The materials used were the Toyoura standard and (Soil-A) and the weathered granitic soil (Soil-B). The soil colums had 21cm in diamenter, 27cm in height and the materials were packed 25cm in depth uniformly. The colums were settled in air conditionning room having a constant temperature and relative humidity. The evaporation rate under nonstressed condition in this room was about 2mm/day all the time. The evaporation rate from colums and the mean soil moisture content were measured by weighing and the soil moisture suction was measured by tensiometer attached to the colum. The decrease of the evaporation began on the 26th day using Soil-A and on the 38th day using Soil-B and the mean volumetric moisture contents at the beginning time of evaporation decreasing were 12.1% and 17.3%, respectively. The water movement in the soil colums has been simulated by the one dimensional model of the saturated-unsaturated flow solved by a finite difference method under the condition that the evaporation from surface has been expressed as a function of the volumetric moisture content in the surface layer. The calculated trends of the soil moisture suction and the evaporation rate using the soil water characteristics of both materials have agreed with the measured results adequately. In this simuration, the soil moisture content in the surface layer at the beginning time of evaporation constriction has been estimated 5.4% (PF2.23) for Soil-A and 17.0% (PF2.47) for Soil-B.

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