Drainage ditches refer to the ditches that lead the water collected in side ditches, intercepting ditches and low-lying places near the subgrade, crops and residential land to the subgrade, crops and residential land. The drainage ditch design shall determine the depth and spacing of field drainage ditches according to the drainage system engineering layout and engineering standards, and analyze and calculate the flow, water level, section size and quantities of drainage ditches and buildings at all levels. The drainage ditch design shall determine the depth and spacing of field drainage ditches according to the drainage system engineering layout and engineering standards, and analyze and calculate the flow, water level, section size and quantities of drainage ditches and buildings at all levels.

Generally, the depth of drainage ditches is initially determined according to the underground water burial depth H required by crops and construction conditions, and then the corresponding drainage ditch spacing is determined. Due to the complex hydrogeological conditions in drainage areas, the depth and spacing of drainage ditches need to be determined through analysis of test data and successful experience in similar areas. The design flow of drainage ditch is divided into drainage flow and rehearsal flow.