Proposed Flood Mitigation using Backwater in Highly Developed Watersheds with Consideration of Crop Calendars and Spatial Resolution: Toward Consensus Formation

Abstract

In this study, we examine the possibility of proactive floodwater diversion to fields via backwater in numerical experiments using multiple elevation data products with different spatial resolutions and explore the optimal timing of water diversion from the perspective of crop calendars. First, a comparison of the elevation data products revealed that photogrammetric data can capture microtopography, such as the footpaths between rice paddies and drainage channels around a field. Numerical experiments using two elevation data products, 5mDEM and LP-derived approximately 5mDEM, revealed that floodwater diversion can reduce the peak to about 19.2 m3/s when using the 5mDEM and can reduce the peak to 16.0 m3/s when using the LP-derived approximately 5mDEM. Interviews with land improvement districts and a review of previous studies revealed that the ear-burst period is particularly vulnerable to flooding. Although the effect of flood peak reduction is reduced due to flooding of the field, it is possible that floodwater can be channeled during the ripening period in August and in late September and October when the ears have been harvested.