Integrated hydrology is the simultaneous consideration of surface and subsurface flow. Here, subsurface flow often is thought of as the fast component of subsurface flow, that is to say we often only consider the contribution of shallow subsurface flow rather than the deep groundwater flow.

The surface flow in hydrology is often described by a simplified
model such as the zero-inertia equation, or worse, the kinematic
wave equation. Subsurface flow is usually simulated through the
Richards equation, which is valid for flow through unsaturated
porous media. The Richards equation can be formulated in terms of
pressure head, water saturation, or in terms of both (mixed type).
The equation requires a closure in the form of a soil constitutive
model, which links the water content to the soil conductivity. The
*de facto* soil constitutive model is the Mualem-van Genuchten
model.

Last modified: 2021-04-20 Tue 09:41