The report is the summary of the result of the investigation on the run-off from two small basins near Shionoe, northern foot of the Sanuki Mountains, Kagawa perfecture. The investigation was made in the summer of 1963 The two basins studied are located about 2km apart. The geological condition of basin No. 1 forms a striking contrast with that of basin No. 2. Basin No. 1 (0.947 km²) consists of Shale belonging to Izumi group (Cretaceous). Basin No. 2 (0.677 km²) consists of Granite. There is little difference in other condition except geological one between two basins. They have equal mean-elevation (about 380m), equal mean-slope (about 27°), and have same vegetation, including conifer and broad leaved deciduous trees.
The author separated the hydrographs, which were constructed by the measurement of streamflow at the outlets of the basins, into two components, direct-runoff and ground-water flow. By the analysis of these hydrographs together with the self-recording graphs of rains, the following results were obtained.
(1) As for the direct-runoff from both basins, there are considerable variations in the shape of hydrographs and the rate of runoff. These variations are mainly due to the characteristics of rainfall, as rain intensity, duration and total depth of rainfall, and the initial soil moisture within the basins. The effect of geological condition upon the runoff is indirect.
(2) However, these meteorological factors being same, the shape of hydrograph of basin No. 1 is flat-ter than that of basin No. 2. The basin lag (the time difference between the center of rain and resulting peak runoff) is also longer in basin No. 1.
(3) As for the ground-water discharge, there is a tendency to maintain a slightly higher flow rate in basin No. 1.
(4) The features of runoff from two basins as mentioned above are not completely explained by the influence of the area and the shape of basin, or the vegetations. It is considered that the depth and texture of weathered soil on the slope and the deposits in the river-beds have an clear effect on the feature of runoff. Basin No. 1 (Shale) has coarser, deeper and more permeable soil and rougher river-bed, whose resistance to the stream flow is greater, so it produces less surface runoff, slower stream flow, lower peak-flow, gradual recession of flow, and longer duration of direct runoff. On the other hand, basin No. 2 (Granite) has shallower, less permeable soil, and smoother river-bed, so it produces sharp hydrographs.