A Hydrological Study on Streamflow Characteristics of Small Forested Basins in Different Geological Conditions

To clarify the streamflow characteristics, a hydrologic analysis focusing on the input -output relationship between precipitation and streamflow was carried out.Streamflow characteristics and its processes were attempted to be clarified in reference to the inputoutput analysis and basin characteristics on different geological conditions.During mid-winter and early summer, streamflow in the investigated basins was minimum.Heavy increases occurred in the early spring from melting snow and in the late summer following precipitation increases.Streamflow hydrographs showed that streamflow in Kiyokawa increased faster during and after precipitation than streamflow in Horonai.Concerning the sources of streamflow, Kiyokawa was maintained by subsurface and groundwater, whereas Horonai was mostly fed by groundwater.Basin storage in Kiyokawa was poor due to impermeable or shallow soil layers, the steep slopes and high drainage density, while Horonai had an excellent storage properties and permeable soils.Basin waterflow processes in releasing precipitation were faster in Kiyokawa Basin (Tertiary mudstone) than that in Horonai Basin (Quarternary volcanic).Consequently, the seasonal changes of streamflow in Kiyokawa fluctuated greatly, whereas those of Horonai were relatively steady under the changes of seasonal precipitation.