This research had the objective of presenting a general equation for the hydraulic design of subsurface drains, since the equations available in the literature were obtained using specified drain roughness coefficient and water temperature. To develop the equation, it was considered that the drain is closed at the beginning and that the flow rate increases linearly along the entire drain length. The developed equation may be used to design subsurface drains having any specified hydraulic characteristics and using any uniform steady state equation for open channel design, which can be adapted to different drain roughness coefficients and fluid characteristics. Therefore, the calculations done using this equation bring more realistic results.
subsurface drain; general equation; flow rate
