Abstract
Direct measuring method for soil-water flow rate is developed theoretically and its availability is examined by experiments. In the present paper, temprature response of soil system is analyzed based on a heat equation for mixed material which was developed by the same author. All of soil-water does not move in soil. Some amount of water is trapped on surface of and between soil particles. A ratio of moving-water-content to total-soil-water-content cannot be measured. By the developed method, however, a product of average velocity of soil-water and the ratio can be measured. This product is sectional average flow rate of soil-water.
The method utilizes a phase difference between measured signals at two different sensoring points responding to input sinusoidal temperature signal. Thermal diffusivity of soil should be known in application of the method. In field application, however, the diffusivity changes with such circumstances as velocity of soil-water and soil temperature.
The temperature diffusivity can be eliminated by two phase differences corresponding to two different angular frequencies of input. Square wave input was adopted in the experiments, because the wave includes higher harmonics of primary frequency. Therefore, measured temperature signals are processed by Fourier analysis method to get phase differences corresponding to the primary and the third higher harmonics.
Measured flow rate showed good accordance with actual flow rate in the experiments.
