10:45 AM - 11:00 AM
[AAS05-05] Evaluation of Surface Wind Reduction and Storm Surge Mitigation through Numerical Experiments with Local-Scale Artificial Roughness at the Bay Mouth: BayBlock Experiment
Keywords:Typhoon, Storm Surge Mitigation , BayBlock Experiment, Typhoon Faxai
Major urban areas in Japan feature large bays, which have historically suffered significant damage due to storm surges during typhoons. Traditional measures have primarily involved structures like embankments. Our hypothesis posits that strategically placed blocks in narrow bay mouths could effectively reduce the height of storm surges. Under the Moonshot Goal 8, we conducted a numerical experiment, BayBlock Experiment (BB), targeting Typhoon Faxai in 2019 (T1915) event to evaluate this hypothesis. Faxai caused extensive damage along the coasts of Tokyo Bay due to severe storm surges and wave heights. The observed peak wave heights were estimated at 3.4 meters in Yokohama and 2.6 meters in Tokyo and Chiba, combined with rapidly developing high waves within the bay and pproximately 1.0 m of storm surge.
This study employs an atmospheric model WRF-ARW ver4.2.1 (Skamarock et al. 2019) and the tsunami model JAGURS (Baba et al. 2015), extended for storm surges. The highest resolution within WRF's inner computational domain is 2km. Sea surface pressure and ground-level winds obtained from WRF are used as boundary conditions to calculate storm surge deviations with JAGURS, with a highest resolution of 90m within its inner domain. Astronomical tides are not considered. While normal strong wind conditions have a sea surface momentum exchange coefficient (Cd) of about 0.003, the BB experiment manipulated the friction coefficient Cd to 0.005, 0.010, 0.015, 0.020, and 0.025 at approximately east-west range Y=2, 4, 10, and 20 km over the Uraga Channel in the atmospheric model, compared to the control experiment (CTL).
The track of T1915 in CTL during its approach to Tokyo Bay was slightly west of the Japan Meteorological Agency's best track (BT), landing near Tokyo Port instead of Chiba City. The tracks in all BB experiments deviated only by a few kilometers from CTL. The difference in maximum 2-m wind speeds during the experiment between CTL and BB experiments at Y=10 km with Cd=0.010 and 0.020 showed reductions up to 10 m/s and 21 m/s downwind of the Uraga Channel, extending to the innermost parts of Tokyo Bay. The temporal changes in storm surges at Yokohama Port obtained in D4 showed that the maximum storm surge was 0.98m in CTL, but 1.00m and 0.82m at Y=10 km with Cd=0.010 and 0.020, respectively. No significant reductions were observed in Tokyo, Chiba, and Yokosuka with Cd=0.010, but a reduction of about 20% occurred with Cd=0.020.
These findings underscore the importance of innovative coastal management strategies in mitigating the effects of natural disasters. The feasibility study provides a foundation for future research on the effectiveness of human interventions in similar coastal environments, offering insights into sustainable and practical solutions for storm surge mitigation.
This study employs an atmospheric model WRF-ARW ver4.2.1 (Skamarock et al. 2019) and the tsunami model JAGURS (Baba et al. 2015), extended for storm surges. The highest resolution within WRF's inner computational domain is 2km. Sea surface pressure and ground-level winds obtained from WRF are used as boundary conditions to calculate storm surge deviations with JAGURS, with a highest resolution of 90m within its inner domain. Astronomical tides are not considered. While normal strong wind conditions have a sea surface momentum exchange coefficient (Cd) of about 0.003, the BB experiment manipulated the friction coefficient Cd to 0.005, 0.010, 0.015, 0.020, and 0.025 at approximately east-west range Y=2, 4, 10, and 20 km over the Uraga Channel in the atmospheric model, compared to the control experiment (CTL).
The track of T1915 in CTL during its approach to Tokyo Bay was slightly west of the Japan Meteorological Agency's best track (BT), landing near Tokyo Port instead of Chiba City. The tracks in all BB experiments deviated only by a few kilometers from CTL. The difference in maximum 2-m wind speeds during the experiment between CTL and BB experiments at Y=10 km with Cd=0.010 and 0.020 showed reductions up to 10 m/s and 21 m/s downwind of the Uraga Channel, extending to the innermost parts of Tokyo Bay. The temporal changes in storm surges at Yokohama Port obtained in D4 showed that the maximum storm surge was 0.98m in CTL, but 1.00m and 0.82m at Y=10 km with Cd=0.010 and 0.020, respectively. No significant reductions were observed in Tokyo, Chiba, and Yokosuka with Cd=0.010, but a reduction of about 20% occurred with Cd=0.020.
These findings underscore the importance of innovative coastal management strategies in mitigating the effects of natural disasters. The feasibility study provides a foundation for future research on the effectiveness of human interventions in similar coastal environments, offering insights into sustainable and practical solutions for storm surge mitigation.