Deformation processes on card-checks of Danube rice irrigation systems

A study was conducted on check plots with drainage under long-term operation conditions in the Kiliya rice irrigation system in the Danube delta of Ukraine. The research examined deformation processes associated with sediment deposition and water erosion of the surface of rice check plots and their main element – the drainage-discharge channel. An analysis of the sediment balance in the check plots of the experimental sites over five years of observations was carried out. It was found that during the study period, up to 58.71% of the expenditure part of the sediment balance was deposited in the drainage-discharge channels per season. This leads to a decrease in the channel’s flow capacity and its overgrowth with wetland vegetation. The most intense manifestations of these processes occur within a distance of up to 100 m from the channel’s beginning. On the surface of the check plots, an average of up to 65.8% of the expenditure part of the sediment balance was deposited annually. The thickest sediment layer (up to 0.3 cm) accumulates along the drainage-discharge channel, in close proximity to the water outlet to the plot. However, this is insignificant and does not affect the quality of the plot’s leveling. Some rounding of the slope crest, where water was discharged from the plot, was observed in the areas where it connects to the check plot, indicating a minor impact of water erosion on the degradation of the drainage-discharge channel. The study determined an optimal slope ratio (m = 2.0), which reduces the slumping of the channel slopes and does not negatively affect the channel’s flow capacity or lead to other adverse consequences.