Yes, a hydroelectic generator consists of a turbine that is connected to the electic generator. Water passing through the turbine cause the turbine to spin which in turn spins the generator. See the following web page for more details. http://ga.water.usgs.gov/edu/hyhowworks.html
However you should check to see if just building a model of a hydroelectric system is appropriate for your science fair project.
As indicated on the following Science Buddies page: http://www.sciencebuddies.org/science-f ... ndex.shtml
A science fair expermiment should follow the scientific method:
1) Ask a Question
2) Do Background Research
3) Construct a Hypothesis
4) Test Your Hypothesis by Doing an Experiment
5) Analyze Your Data and Draw a Conclusion
6) Communicate Your Results
So you need to think of a question that you can investigate using your model hydroelectic generator. Possible questions you could investigate include:
1) Does the height that the water falls before it hits the turbine blades affect the power output of the generator?
2) Does the size and pitch of the turbine blade affect the power output of the generator?
3) If you stacked two turbines on top of each other and had the water pass through one and then the other would you generate twice as much power?
Let me know what question you decide to investigate.