The website in the problem isn't the greatest. Please feel free to use another source; just make sure you provide a address.
1. McNary Dam
a. How tall is McNary Dam?
b. What is the change in the potential energy (in joules) of a cubic meter of water falling this distance?
c. How much water flows per second through McNary Dam (in cubic meters per second)? You may find the information on the web in thousands of cubic feet per second (kcfs). Use the average value, not the flood stage value (both are on their web site).
d. Assuming a 30% efficiency to convert all of this energy to electricity through a hydropower plant, what would be the power output in watts of McNary Dam?
e. How does this compare to the actual power output of the Dam? What might account for the difference? (Your answer should be close to this value, certainly within a factor of 2).
This posting contains the solution to the given problems.