Flood Mitigation Effect of Paddy Field Dam on Controlling Increase of Flood Risk Under Future Climate Change Condition

Abstract

　We examined the usefulness of a paddy field dam for flood mitigation during extreme storm events, probably induced by effects of future climate change, at a small paddy field catchment. First, after validating the developed rainfall runoff model with a drainage control function by paddy field dam, we confirmed the runoff control effects of a paddy field dam for Typhoon Hagibis in 2019. Then, paddy field dam effects on runoff control were evaluated under climate change conditions by application of current and future projected rainfall data. The paddy field dam installation was estimated to lower the maximum drainage channel water depth by 0.10 m to 0.16 m and to delay the emergence of runoff peak by 60 min during Typhoon Hagibis. Simulation results showed that the paddy field dam did not necessarily perform in terms of the current paddy levee height. In fact, for current and future climatic rainfall data estimated at the four sites in the Abukuma River Basin, results show that overflow from the paddy levee occurred because of the rapid increase in water depth in paddy fields resulting from runoff control. By contrast, a paddy field dam might reduce the rapid rise in the drainage channel water depth and reduce the risk of flooding, even under future climatic rainfall conditions, by raising the paddy levee height to a maximum of 0.42 m to prevent overflow. In conclusion, paddy field dams can be effective for climate change adaptation in conjunction with raising of the paddy levee height.