The model QSOIL is able to describe
various infiltration and runoff processes, that can occur when rainfall hits natural
soils on a hillslope. The different modules of QSOIL and required
parameters are shown in the figure. Overland and pipe flow are computed
according to the one-dimensional kinematic wave or diffusion wave
schemes. Matrix and macropore flow are modelled using a the double porosity
approach to describe flow in structured soils by linking these two domains. The
first domain consists of the soil matrix, in which flow is described by means of
the Richards equation, the second domain (macropores) uses average flow properties (macro-porosity and flow
velocity in macropores) to model the system by a one-dimensional vertical diffusion wave. The exchange of
water between the two domains is established by an interaction module which depends on the hydraulic potential
difference between the matrix and macropore domains.
The model is very flexible to use because of its modular structure. It is possible to simulate one-dimensional
infiltration processes as well as complex two-dimensional runoff and infiltration processes on hillslopes.
Additionally modelling scenarios in terms of different boundary conditions is also possible. The stringent hydraulic
principles used to describe the different paths of soil water movement make the effects of a chosen set of
parameters clearly visible.