You need to specify for how long the hydroelectric power station is supposed to run. For which time span is the per capita electricity consumption given? Multiply this time with the power that the dam can supply. Then you will obtain the maximum possible energy output over that time.

Note, however, that hydroelectric power stations are seldom used at full capacity.

Hi Nicoletta.  Ideally you need to know something about the hydrology of the catchment feeding the dam, as Jan-Martin said hydro's don't often run at full capacity...but for the few hours a year it does run at "full noise" it will deliver 100 MWh per hour.

As a rough estimate there is a rule of thumb for hydro design that says the optimum sized machine would run at 50% capacity over the course of a year.  So your machine can be expected to deliver 100*8760*.5 = 438,000 MWh.

If you want to go into more detail then Retscreen (Nat Resources Canada) has been helpful for me in making appropriate assumptions in the past.

Good luck

Andrew