Water balance analysis of hydrological processes in cyclic irrigation: A case study of the Imbanuma irrigation area in Chiba, Japan

Study region: Flat, low-lying paddy fields subjected to cyclic irrigation in Chiba, Japan. Study focus: This study investigated hydrological processes in flat, low-lying paddy fields with cyclic irrigation. From 2021–2022, the climatic conditions, operation of pumping stations, and surface drainage were monitored. The water balance was analyzed to comprehend discharge conditions using Acoustic Doppler Current Profiler (ADCP) monitoring. The dynamic hydrological relationship between surface and lateral flow discharge is discussed. Water and lateral flow use efficiencies were also evaluated to examine the applicability of cyclic irrigation in preserving natural water bodies. New hydrological insights for the region: The relatively wet year (791 mm/period) of 2021 maintained higher lateral flow (1438 mm in the North block, 1363 mm in the South block) from paddy plots, with discharge processes primarily influenced by surface water levels. Conversely, in the relatively dry year (410 mm/period) of 2022, lower drainage water levels due to limited rainfall, facilitated a quick response of the lateral flow (851 mm in the North block, 917 mm in the South block) in the discharge processes. During the drought in 2022, water use efficiency increased by 11–13 %, while the cyclic water use ratio decreased by 9 %, indicating a significant contribution of lateral flow reuse in cyclic irrigation. These findings suggest that hydrological processes in flat, low-lying paddy field areas should be considered in irrigation management, and cyclic irrigation may influence hydrological processes by conserving renewable water resources. • Water balance in flat, low-lying paddy fields was analyzed. • Dynamics of surface and lateral flow in discharge processes were revealed. • ADCPs can collect continuous canal discharge data in backwater conditions. • Supply water in cyclic irrigation included rainfall-fed groundwater in blocks.