Total Storage Comparison Using a Tank Model and Soil Water Index Based on Geology and Watershed Size

Abstract

　The Soil Water Index is used to assess risks of sediment-related disasters. This study compared the total storage of a three-stage tank mode with different geologies and examined the rainfall history of total storage. Furthermore, effects of the granite watershed size on the total storage were examined. Total storage was calculated using hourly precipitation data accumulated for 50 years at the Kyoto Local Meteorological Observatory as an input value. From multiple comparisons, the average value of the total storage during rainfall events based on the geology of the large watershed revealed considerable differences between granite and Paleozoic rock, granite and Tertiary rock, volcanic rock and Paleozoic rock, and volcanic rock and Tertiary rock. Total storage tends to increase with the total rainfall or maximum rainfall intensity during a rainfall event, and the rate of increase of the total storage varied in the order of Tertiary < Paleozoic < granite < volcanic rock. The historical ranking of the total storage was similar by geology, as stated in earlier reports. The total storage in the small watershed with granite geology differed considerably from the total storage in the large watershed with granite geology. The total storage in the small watershed tended to increase concomitantly with increasing total rainfall or rainfall intensity, but the historical ranking of the total storage differed depending on the watershed size. More examples of parameter values for the three-stage tank model in series in small watersheds must be accumulated to quantify the total storage of the tank model based on watershed characteristics.