APPLICATION OF THE BASIN RAINFALL INDEX FOR HYDRODYNAMIC SIMULATION OF ISE BAY, JAPAN

Abstract

 This study has evaluated the applicability of the Basin Rainfall Index (BRI) as a proxy for river discharge in hydrodynamic simulations of Ise Bay using ten Class A rivers that discharge into the bay. By comparing BRI-derived discharge with observational data and incorporating it as a boundary condition in salinity simulations, we assessed both the reliability of the BRI and its sensitivity in modeling estuarine dynamics. The results indicated that the BRI-derived river discharges were generally comparable to or slightly greater than the observed values. Major rivers such as the Kiso, Ibi, and Nagara Rivers, which are key inflows to Ise Bay, exhibited small differences between the BRI values at the observation points and those near the river mouths. This supports the suitability of the BRI for approximating the downstream river discharge. Hydrodynamic simulations showed that BRI-based river inputs successfully reproduced temporal variations in salinity during high-flow periods when salinity decreased sharply. This suggests that the BRI is responsive to hydrological fluctuations and can therefore be effectively used as river discharge input in coastal models. However, limitations of the BRI have also been noted, as it does not account for factors such as artificial flow regulation, snowmelt, or precipitation from accumulated snow. These limitations may have led to deviations in specific seasons or regions. Overall, this study demonstrates the potential of the BRI to support real-time hydrodynamic modeling in semi-enclosed bays, such as Ise Bay. Future research should focus on expanding their applications to other regions and conditions.