A groundwater model is created when a variety of factors influence the groundwater situation and complex boundary conditions are in place and an analytical solution of the problem is no longer possible.
Possible questions for a groundwater model include:
How is the groundwater flow affected by a change in the withdrawal amounts?
Which depths of groundwater level does it have?
What is the impact of subsidences caused by mining on the present depths of groundwater level?
What are the consequences of a flood wave and how change the flood plains?
What impact do interventions in the water course have: stream relocation, changes to the stream bed?
What happens when constructing new production wells and what is their effect on the existing situation?
etc. etc. etc.
These and many other questions can be answered by a groundwater model.