Vegetation
The natural role of vegetation in controlling slope stability is
evident in many different areas of the world. For example tree roots
can have significant positive effects in terms of adding to the effective
strength of the soils. However what complicates this relationship is
the changed hydrological parameterisation of the soil properties that
vegetation provides [for example, by increasing the soil hydraulic conductivity].

The following paper uses CHASM to explore the precise
nature of such complex interrelationships:
Collison, A.J.C., Anderson, M.G. and Lloyd, D.M. (1995) Impact of vegetation
on slope stability in a humid tropical environment: a modelling approach.
Proc. Inst. Civil Eng. Water Maritime and Energy, 112, 168-175, (paper
awarded the Trevithick Premium Triennial award for a research paper
published by the Institution of Civil Engineers in 1996).
In major projects as well as more routine maintenance considerations
bioengineering is seen as a specific option to enhance slope stability.
This can take the form of standard hydroseeding:

as well as other more intricate species mixes on slopes.
To accommodate bioengineering CHASM includes a vegetation
module which allows changes to be made to the effective soil hydraulic
conductivity, the effective rainfall reaching the surface of the slope
and the soil shear strength via root reinforcement