MODELING WATER-FLOW FROM SUBIRRIGATION WITH DRAINAGE

The stream function for a flow domain, if properly chosen, can be used analytically to generate the boundary conditions of the domain and obtain flow velocities at all points in it. To illustrate the procedure, we developed and mathematically analyzed a physical model that describes saturated water flow from a subirrigation system with drainage. The theory takes the radius of drain and irrigation tubes into account and thus refines earlier work, which hypothesized slit irrigation tubes and slit drain tubes of thin rectangular cross section rather than circular ones. The theory additionally shows how the subirrigation water table changes when the drain tubes are switched to an irrigation mode. A series of three flow nets are included representing subirrigation alone, subirrigation with simultaneous drainage, and dual-pipe subirrigation. The three cases show how the problem parameters influence heads and flows and thus give insight into strengths and weaknesses of the three water management systems.