Field Observation and Numerical Simulation of Bed Evolution in Agricultural Drainage Canal with Eco-Friendly Physical Structures

An excessive sediment deposition in eco-friendly physical structures introduced to agricultural canals sometimes damaged the function of the structures as fish habitat. In this study, field investigations and numerical simulation using the flow and bed evolution models, Nays2DH, have been conducted in a section of agricultural drainage canal with artificial fish nests and pool in Japan, aiming at describing circumstances of the deposition problem in the structures. The bed topography of the canal section was surveyed nine times during 2016 - 2018 at 19 transverse cross-sections of the area. Nays2DH was applied to the study section to investigate sedimentation and erosion in the fish pool and nests at a flood event. The field survey clarified that deposition and erosion of almost similar magnitude in the fish nests occurred periodically in one year. The deposition in the whole section increased. Results of the numerical computation of flow and bed evolution indicated points that require modification of the model.