花こう岩地域における地下水流動解析 吉備高原地域をモデルとして

Abstract

Though flow nets offer a valuable means of visualizing groundwater flow fields, accurate drawing of flow nets are generally difficult in complicated hydrogeological structure. A numerical method was developed for automatically generating a flow net, using the finite element method to calculate the stream function and piezometric head. In this paper, a availability of the method is demonstrated in three hypothetical test models and verticalplane models through the granite region of the Kibi Plateau, Okayama Prefecture. Results of the numerical simulation show that a high-permeable zone can converge flow lines, though low-permeable zone can not effectively dam up stream lines. Groundwater flow in the granite region of the Kibi Plateau is approximated by a porous media flow. Flow nets of six cross sections in the region are constructed using the numerical method. Several areas converging flow lines in the basement are detected, but available quantity of water is small. The greater part of groundwater flows in the high-permeable weathering crust (‘Masa’ zone). Flow net analyses can be useful to identify groundwater exploration zones in the granite region.