The Topography and The Hydrogeology of The Lower Coarse Plain of The Tokachi River

Abstract

Considering that hydrogeology essentially comes under Quaternary research, the author emphasizes that aquifers should be arranged in time scale series by means of compiling geomorphic history of the concerned area, taking a serious view of the relations between geomorphic surfaces and geologies (aquifers).
Based on this principle, the author compiled the hydrogeology of the lower course plain of the Tokachi River.
1. Along the lower course plain of the Tokachi River, the author found 9 terracegroups as well as a buried terrace (connected with one of the terrace-groups) and a buried valley (connected with one of the terrace-groups) by means of the electric restivity method, test borings, topographic and geological surveys.
2. The author found 2 aquifers of Miocene,2 aquifers of Pliocene,3 aquifers of Pleistocene and 1 aquifer of Alluvium. Among them, the“ Sunagawa” formation of Pliocene is the most excellent aquifer in this area.
3. The sedimentary basin of the Pliocene series has been separated into 2 parts at Moiwa town, effected by the NNE-SSW directional anticline structure of the pre-Pliocene series; and the distribution of the above-mentioned“ Sunagawa” formations restricted only under the upper side alluvial plain from Moiwa town.
4. Aquifers of Pleistocene are diluvial terrace gravels, diluvial buried terrace gravels and diluvial buried valley gravels. The first contains groundwater of superior quality but small in quantity; however, the second and the third contain groundwater of inferior quality and abundant quantity.
5. It may be possible to obtain superior groundwater resembling the surface water of the Tokachi River at the natural-levee along the river.