The author made experiments on ground water flow with two type electric analog models: One is a continuous model and another is adiscrete model.
It is the purpose of this paper to point out several technical problems of these analog models. Two dimensional horizontal flow is dealt with in continuous analog model. In this model, the analogy between fluid flow through porous media and flow of electricity through conductive materials is considered taking two factors into account. They are the form of boundary and the distribution of potentials.
An analog apparatus is comprised of a power supply, an analog analyser, a probe and a pantograph. Potential distribution is measured on analog model. An analogyanalyser which uses the principle of wheatstone's bridge, and a potential dividers which give several potentials separately to analog model were made dy the author A sheet of cardon paper is used as a conductive material. The electrode is made by bending wire plated by tin and is attached to model by conductive silver paint. Areal differences in permeability are expressed by carbon paint. The conductive paper having the same shape as the actual field with a scale of 1/50,000 is constructed and silver paint or carbon paint are painted so as to represent field condition such as flood plain, old river channel, etc. Lastly, error or reliability of the continuous analog model are examined. Following problems are listed up.
1) When a electrode is small, the contact resistance between electrode and conductive paper became important and measured values become unstable.
2) The model can not express areal differences in permeability quantitatitvely.
3) In high voltage area of an analog model, sensibility of galbanometer is too high to measure a potential distribution.
4) The continuous electric analog with conductive paper is suitable of simple systems, for example, a seepage flow an earth dam and a channel.