Research on the solute runoff mechanism from basin and the marine ecosystem at the flood event using the hydrology and seawater flow model

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The influence that geological features and the difference of the land use gave to the solute runoff mechanism from the basin to the sea area was examined. To achieve the purpose, the field observation and the mathematical model simulation were executed. The water quality and hydrological observation were done in the Umayado river basin(covered in sandstone-mudstone, and forest)and the Kabe river basin(covered in granite, and coexistence ground in forest, urban area, and farmland)at the rain event of Typhoon No. 4 in 2007. The total precipitation was 200mm in both of the two basins.The finding is described as follows.1) In the point of the runoff rate and the solute runoff rate, the Umayado river basin (geological features: sandstone-mudstone)is higher than the Kabe river basin (geological features: granite).2) In the relation between the geological features and the amount of the solute supply from the basin, the Kabe river basin is bigger than the Umavado river basin, for instance the amount of the supply of the silica increases by a factor of 1.63) When the land use upgraded, the runoff loading of silica becomes small The runoff loading of Kabe river basin was 46% fewer than that of the Umayado river basin.Because a large-scale flood event that influenced the seawater quality did not occur, the observation and analyze of the sea areas that were adjacent to the basins were not able to be done. However, it is thought that it was a very important result to be able concretely to examine the difference of the solute runoff mechanism of two basins which have the different geological features and land use, using the mathematical model in the condition like the same rainfall wave form and precipitation.