The mechanism of unsaturated flow through a volcanic ash layer under humid climatic conditions
作者:
Jun Shimada,
期刊:
Hydrological Processes
(WILEY Available online 1988)
卷期:
Volume 2,
issue 1
页码: 43-59
ISSN:0885-6087
年代: 1988
DOI:10.1002/hyp.3360020105
出版商: John Wiley&Sons, Ltd
关键词: Environmental tritium;Unsaturated zone;Soil water movement;Volcanic ash layer;Recharge rate
数据来源: WILEY
摘要:
AbstractIt is very interesting and meaningful to investigate the rainfall‐groundwater recharge process under the humid climatic condition of Japan, where mean annual precipitation is about 1600 mm. The present study has investigated soil water movement in the unsaturated zones of a volcanic ash layer, called the ‘Kanto Loam formation’, using environmental tritium as a tracer. The site selected is a flat ground surface on a terraced upland which has a deep unsaturated zone (about 20 m) with a relatively high water content (about 70 per cent) consisting of nearly uniform Kanto Loam formation.The tritium concentrations in groundwater, soil waters having different matric potentials, precipitation, and the seepage water moving through the formation into a man‐made cave were measured to characterize the rainfall‐groundwater recharge process and the effect of large pore spaces in the formation mentioned by previous studies.Because of the humid climate of Japan, there appears to be a unique soil water flow characteristic which may involve percolation through large pore spaces during heavy rainfall. However, in a fine grained and high water content soil like the Kanto Loam formation, the existence of this flow through large pore spaces does not have a significant effect upon the whole recharge process. The recharge model of displacement flow with dispersion is useful in estimating the tritium concentration profile of soil water. The calculated result shows a recharge rate of 2.5 mm/day. The value obtained reflects the hydrological characteristics of the uplands covered with vol
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