What does the delta look like.
In the "Wet" season how gallons/min do you have and how about in the "dry" season.
How much head do you have?
Which type of turbine are you thinking about using Waterwheel, Impulse or Reaction turbine.
Any particular sub-type.
As to your original question because you are generating over 15KW you are going to have to go with a synchronous alternator (due to capacitor size). Most likely a 4-pole 1800rpm one. With a synchronous alternator you are also going to need a ELC (Electronic Load Controller)
Check out this article for some cool info
http://www.oregon.gov/energy/renew/hydro/docs/microhydroguide.pdf
Iterations are fine, we don't have to be perfect
My 2nd Location:Florida HardinessZone:10 AHS:10 GDD:8500 Rainfall:2in/mth winter, 8in/mth summer, Soil:Sand pH8 Flat