高潮発生時の越波・越流による浸水対策工の検討
二重パラペット護岸設計手法の提案
近年，地球温暖化に伴う気候変動等の影響により，国内外で甚大な高潮災害が発生しており，高潮に伴う越波・越流に対する適応策を検討する必要がある。越波や越流による浸水リスクが見込まれる護岸において護岸改良が困難な場合には，陸側にパラペットを新設することで海水の流入量を軽減する二重パラペット護岸による防護が有効である。二重パラペット護岸は，検討するパラメタが数多くあり，これらのパラメタと越波流量の定量的関係は明らかとなっていない。そこで本研究では，二重パラペット護岸の越波流量を計測する水理実験を実施し，二重パラペット護岸の各諸元と越波流量の関係を把握した。また，各諸元と既存の越波越流量算定式をもとに，二重パラペット護岸における越波流量の算定式を提案した。推定式は，実験値をよく再現しており，高潮浸水対策としての二重パラペット護岸の設計に活用可能であることを示した。
キーワード：高潮，浸水対策，越波，二重パラペット，水理実験，CFD
＊１ 技術センター 社会基盤技術研究部 水理研究室
Study on Countermeasures against Storm Surge Inundation by Wave Overtopping and Overflow
Proposal of Design Method for Double Parapet Seawall
In recent years, enormous storm surge disasters have occurred due to climate change and other factors associated with global warming, and countermeasures for wave overtopping and overflow due to storm surges are required. In cases where it is difficult to improve an existing seawall parapet that is at risk of storm surge flooding, installing a new parapet on the land side, i.e., a double parapet, is effective to reduce the seawater inflow. There are many parameters to be examined for a double parapet seawall, and the quantitative relationship between these parameters and the overtopping discharge has not been clarified. Therefore, in this study, hydraulic and numerical experiments were performed to measure the overtopping discharge over a double parapet seawall, and the relationships between each parameter of the double parapet seawall and the overtopping discharge were determined. In addition, a formula for estimating the overtopping discharge was proposed based on parameters and the existing overtopping discharge estimation formula. It was shown that the proposed estimation formula reproduced the experimental results accurately, and can be utilized for the design of a double parapet seawall as a storm surge inundation countermeasure.
Keywords: storm surge, prevention of inundation, wave overtopping, double parapet, hydraulic experiment, CFD
*1 Hydraulic Research Section, Infrastructure Technology Research Department, Taisei Advanced Center of Technology