Curve Fitting or Modelling: How to choose?(newbie)

[GuyNorth]

Curve Fitting or Modelling: How to choose?(newbie)

I am trying to predict if a large underground water well (artesiam bore) will dry out?
and if it does when?
(The bore is about 50000 liters a day).

I have used Excel but it is too far out.
I think Matlab will be better to do this type of prediction. But I am too new at Matlab to see how to handle this problem.

I have a set of 300 weekly measurements.
Each measurement correspond to the height of the water in the underground water well.(artesiam bore).

What is my real problem with Matlab? #-)
Am I trying to Curve fit a data and then project it in the future?
or
Am I trying to model this data and try to predict what may happen?

At the moment I am not getting anywhere because I am trying to fit a curve(polynomial) then use that polynomial to predict what will happen next week, next month, next year when I should do some modelling (modeling).

I believe my idea of modelling is not detailed enough.
May be I should use Fast Fourier Transform?

Any help would be appreciated?
When do you use curve fitting, FFT or modelling? s-)

Guy