How does rainfall influence the stability of natural slopes?

How does vegitation influence stability?
What determines how much water infiltrates the slopes and how much runs off?
How does the slopes react when it is not stable?
Chapter 1 Introduction
Chapter 2 Theory Of Slope Stability
Chapter 3 Water pressure in ground
Chapter 4 Suction
Chapter 5 the effect of rain
Chapter 6 The effect of vegetation
Chapter 7 Discussion
Chapter 8 Conclusion
Yes please include lots of reference