This paper deals with the estimation f o r the percentage of impervious area by land-use categories classified from the satellite remote sensing imagery. The test area is KOMATU watershed,4.64km², located in MIYAZAKI city. The area is divided into 14 zones for the estimation. The percentages are also manually interpreted from aerial photographs observed in 1962,1966,1973,1983, and 1987. Then, these results are compared each other to check the ac curacy of estimation. From this investigation, the followings are clarified; 1) The overall percentages of impervious area in the whole test area change rapidly from 42%to 77 % in the observed terms of aerial photographs. 2) The manually interpreted percentages from the aerial photograph contain about 10% error caused by the misjudgment. 3) High multiple-correlation coefficients are obtained between the percentages derived from the aerial photograph and one from the satellite imagery; 0.74 for LANDSAT-MSS,0.81 for MOSMESSR and 0.91 for SPOT-HRV. 4) The discrepancies between them are 16% for LANDSAT-MSS,19% for MOS-MESSR,13%for SPOT-HRV in the worst sub-area and less then 10% except for the zones where contain the error caused by the misjudgment of aerial photograph and the geometric error of imagery. From these results, it is confirmed that the satellite imagery is useful for the evaluation of groundwater recharge.
This paper presents the numerical analysis results of a field tracer test. The objective of this test was to measure the dispersivity and the effective porosity of a permeable sedimentary layer. The tracer test was performed using two vertical bore holes 90 meters in depth and located 7 meters apart. The sedimentary layer, composed of sandstone, conglomerate, and weathered granite, was 10 meters thick and started 80 meters below the surface. One bore hole was used to inject groundwater with tracer and the other to recover to recirculate groundwater. We used a tracer solution containing Br. Before the tracer was injected, groundwater was circulated through the sedimentary layer between the two bore holes to establish a steady state of groundwater flow. The circulation flow rate and Br concentration initially injected were determined by using Gelhar's analytical solution so that the detectable tracer concentration (several ppm) could be recovered within one month. When the groundwater level at the recovery hole became stable, the tracer was injected into the injection hole and the concentration of Br was analyzed at the recovery hole. The circulation flow rate was 7800cm³/ min. The initially injected Br- tracer concentration was 8300 ppm. Thirty eight hours later, the concentration of Br at the recovery hole reached a maximum level of 10 ppm. The convection-dispersion equation was used for the tracer test's numerical analysis. This differential equation was transformed by F. E. M. Half of the horizontal section of the analytical region was used for numerical analysis and meshes like a semi-circle were used for the circulation-line above the surface between the two bore holes. A dispersion coefficient depends upon flow velocity, dispersivity, and diffusion. Initially, the flow velocity distribution and the permeability of layer were analyzed using F. E. M. as a seepage problem. The analyzed permeability of the layer was 2.2×10-5cm/sec. According to the F. E. M. analysis result, using the breakthrough curve of Br at the recovery hole and the matching technique, the effective porosity was determined to be 7% and the dispersivity 3.5 meters. The effective porosity was determined to be 4.5% and the dispersivity 3.5 meters by Gelhar's analytical solution. The 7% or 4.5% effective porosity value was smaller than the 30% porosity value with the boring core samples. This suggests that the measurement of effective porosity using a field tracer test is important in evaluating groundwater flow velocity and mass transport. The relationship between the dispersivity 3.5 meters and the distance 7 meters agreed well with those of Leonhart (1985).