An estimation of subsurface total drainage quantity in non-steady state drainage flow, and its verification in loamy soils

The subsurface total drainage quantity is a very important hydrological indicator to solve the drainage problems in a field of water management in the landscape, especially in a situation after massive floods. Described in this paper is an estimation of the subsurface total drainage quantity, which was developed by the operation of a subsurface pipe drainage system in saturated, middle permeable soil under unsteady state drainage flow with the application of the Dupuit's assumptions and Darcy's law, by analytical approximation. The correctness and applicability of this estimation of the subsurface total drainage quantity was verified by field measurements on the loamy soils of an experimental watershed area of the Research Institute for Soil and Water Conservation (RISWC) Prague-Zbraslav, Czech Republic. The parameters and the shape of this subsurface total drainage quantity equation were also proved with the help of nonlinear regression analysis, with application of the method of Marquardt. This analytical approximation should serve as an elementary tool of water engineering practice for an immediate estimation of the values of subsurface total drainage quantities from field pipe drainage systems in saturated loamy soils. It requires only a minimum amount of information (fundamental soil hydrology data and drainage system basic design parameters) and its use is often viewed, it is simple, user-friendly and is possible for a wide range of drainage policies.