436 / 2024-03-17 09:32:35

Numerical Study on Effectiveness of anti-flood pond in Awano-Gawa River basin

aniti-flood pond, flooding, heavy rain, numerical simulation, Awao-Gawa river

Subtheme 1: Water-related Hazard and Risk Reduction > Topic 5: Resilient City Against Water Hazard

Awano-Gawa River is the 2nd class river passing through Shimonoseki City, Yamaguchi, Japan. The watershed area is 185.9 km², the total length is 29.8 km. In the Asano River basin, heavy rainfall in June 1999 caused flooding in 25 houses and isolated 150 houses. Restoration work for the Awano-Gawa River included raising the ground level, securing anti-flood pond, and reinforcing embankments. The ant-flood ponds are the flood water storage system utilizing farming field. The flooding water can be stored temporary in the anti-flood ponds. Therefore, we had conducted the numerical study to examine the effectiveness of the ant-flood ponds in Awano-Gawa River.

For numerical simulations, four rainfall scenarios were used. Initially, runoff analysis was conducted using hydrographs extended from the rainfall conditions during the heavy rainfall in June 1999, scaled to 0.75 times, 1 time, 1.25 times, and 1.5 times. Flood simulations were then performed using the runoff discharge obtained from this analysis as boundary conditions. In all simulation scenarios, flooding was observed throughout the anti-flood ponds. Additionally, the amount of water retained in the anti-flood ponds during the flood period (10 hours) was determined to be 11.6×10⁶ m³, 15.7×10⁶ m³, 17.3×10⁶ m³, and 32.5×10⁶ m³ for the respective scenarios. Furthermore, an investigation of the flooding situation at the raised areas in the Asano District revealed that those areas were not flooded in any of the cases. In other words, it was found that the anti-flood ponds and the ground raising were effective even with rainfall 1.5 times greater than the actual rainfall in July 1999.