The article evaluates the hydraulic processes in the collectors which constructed in irrigated fields. Illuminated the washing processes under the influence of the flow velocity in the collector bed. In order to study the washing processes in the collector basin, are covered the results of research conducted in the self-washing collector in natural field conditions. Collector 2-K-4 in Khavas district of Syrdarya region was selected as the object of research. Given cases of changes in the project parameters as a result of washing processes in the core of the collector. Were selected 5 sections in the collector and hydraulic parameters were studied. was evaluated the effect of hydraulic processes on the collector core. The studied sections show cases of change of design parameters under the influence of hydraulic processes. Soil samples were taken from the reservoir and the mechanical composition was determined under laboratory conditions. Based on the laboratory and natural field conditions results, a special graph was developed for the design of collectors on the basis of non-washable speed.