Change in Waterfall

Waterfall approach is a plan heavy methodology. Requirements and scope are fixed upfront, what in results implies approach to change. 

Basically, project manager’s role is to constrain change as much as possible. This is because any change which needs to be made will strongly impact highly detailed plan prepared in a project. In this methodology, there is a formal process to go for a change. There are specific procedures that need to be followed to approve a change request. 

That is why, waterfall approach works good for projects with more stable requirements, which lead us to definable plan, less risky (so with less change) and can be done in a linear fashion.