Numerical simulation of evapotranspiration using a root water uptake model

The abstraction of ground water by vegetation and its influence on the behaviour of geotechnical structures such as pavements, foundations and slopes has been researched for many years. In recent years, the use of numerical methods in geotechnical engineering has rapidly increased. A major challenge for numerical modelers involves the specification of the surface flow boundary condition to model root water uptake by vegetation. The abstraction of ground water by roots is a complex process which involves the interaction of the atmosphere, vegetation and the ground. Accurate prediction of the pore water pressure changes induced by vegetation requires the development of algorithms which can mimic the process of transpiration by vegetation in the continuity equation of fluid flow. This paper presents a root water uptake model which has been coded into a finite element program that can perform coupled (mechanical and fluid flow behaviour) analyses. The input data includes rainfall, potential evapotranspiration and maximum root depth. The key features of the model are discussed first, followed by a presentation of results from a series of parametric studies.