Drainage equations for random and irregular tile drainage systems

Subsurface drainage theory has been reviewed and applied to single tile systems in order to predict the hydrology of tile-drained watersheds where irregular or random drainage systems predominate. Simple analytical solutions for subsurface flow towards a single tile are proposed and evaluated. In these solutions, the spacing parameter, which characterizes drainage solutions for parallel systems, is replaced by a variable region of influence for transient scenarios. Evaluation of the proposed solution was carried out by comparisons with results obtained using a robust unsaturated-flow finite element model. The results predicted by the derived solution were found to be in close agreement with those obtained from the numerical simulations. Therefore, it is concluded that the proposed model holds well for situations of practical import and can be used in future work with large-scale hydrologic models.