Abstract
The Satsunai river fan and the adjacent Sarubetsu river fan located in the southern part of the Tokachi plain, Hokkaido, together form two drainage basins in a composite fan. Groundwater flow from the Satsunai river to the Sarubetsu river fan was previously believed to be negligible. The present study revealed, however, the existence of a buried valley corresponding to the old Satsunai river lying beneath the Sarubetsu river fan. Environmental tracer techniques such as measuring 0.8m depth ground temperature, making use of the altitude effect of stable isotopes of water and the dissolved ions, groundwater flow net and water balance analyses all showed more than lm3/s leakage from the Satsunai river. This represents an important contribution to the groundwater flow system of the Sarubetsu river fan.
Recently, a large project requires an environmental assessment of the groundwater flow system scale. Therefore, the present study suggests the importance of using environmental tracers not only for scientific purposes, but also for civil engineering applications.
