Dams are very expensive, so they aren't a very good idea in low economically developed countries (even though they are great help to prevent flooding). Remember also that prices vary depending on when they are built, how large they are, and many other factors.
Some examples of building prices:
$300 million dollars to build hydroelectric dam......
From less than $ 100,000 (for a tiny one) to many billions for a truly big one.
Yes, The Wolf Creek Dam is a Hydroelectric dam.
A hydroelectric river dam like, Three Gorges Dam.
a hydroelectric dam is efficient because it generates power
Yes.
Stevenson Dam Hydroelectric Plant was created in 1917.
what geogaphical features are needed when building a hydroelectric dam
It costs about 0.7 cents per kilowatt hour (kWh) of electricity
The country that has the largest hydroelectric dam in terms of annual energy generation and is on the border of Paraguay and Brazil. It is the Itaipu dam.
Sayano Shushenskaya hydroelectric dam
The Gorges Dam in China is hydroelectric and crosses the Yangtze River. The dam is not only the biggest of it's kind in China but is also the most powerful dam in the world.