The mechanism of unsaturated flow through a volcanic ash layer under humid climatic conditions
✍ Scribed by Jun Shimada
- Book ID
- 102860850
- Publisher
- John Wiley and Sons
- Year
- 1988
- Tongue
- English
- Weight
- 947 KB
- Volume
- 2
- Category
- Article
- ISSN
- 0885-6087
No coin nor oath required. For personal study only.
✦ Synopsis
It 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 1600mm. 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 20m) 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 volcanic ash.