Backwater Effect of Clogging of Aquatic Plants at Fine-Particle Screens on Inland Flooding in Okayama

In low-lying Okayama city, Japan, the heavy rainfall frequency and intensity have recently increased, subjecting the city to inland flooding. Another factor increasing the inland flooding risk is fine-particle screen clogging by aquatic plants at drainage pump stations, which obstructs drainage and causes backwater. In this study, water level simulations were conducted in drainage pump station channels to clarify the inland flooding risks with and without aquatic plant clogging-induced backwater at fine-particle screens. In the Urayasu West Drainage Pump Station channels, without backwater, no inland flooding occurred under an initial water level of 70% of the channel depth and a 40 m³/s discharge. However, when backwater deeper than 0.2 m occurred under the same conditions, inland flooding occurred, indicating an increased inland flooding risk associated with backwater. Additionally, we conducted an aquatic plant distribution survey in the main Okayama city channels and proposed six priority control sections based on sections with thriving aquatic plants. Although no previous inland flooding studies have considered aquatic plant clogging-induced backwater at fine-particle screens, aquatic plants cause clogging problems and drainage obstructions at water control facilities worldwide. Therefore, this study reveals the importance of conducting water level simulations and distribution surveys in areas other than Okayama city.