There are three main types of hydroelectric schemes, these are:
· Run of the River (tidal water storage)
· Diversion
· Pumped Storage
· Water storage in lakes

In the Run of the River type of scheme, the turbine and generator are located either in the dam or found along side it. The dam uses the flow of the river to create the hydrostatic head, this method can also be applied to tidal barrage systems.
A Diversion scheme is where the supply of water is taken from a dammed river or lake to a remote powerhouse containing the turbine and generator. A Canal or low-pressure tunnel transports the water to this end point and then back to the river to continue its course.
Pumped storage is a scheme that incorporates two reservoirs. At times of low demand, generally when electricity is cheap like at night, electricity is bought to pump water from the lower to the upper basin. This extra water can then be released to create power at a time when demand is high and prices high. This means that the companies make money on their investment of electricity for pumping. This enables the scheme to perform with greater efficiency when matching supply and demand. This type of scheme is also similar to pumping for tidal barrages to increase supply and income.
Water Storage in lakes power station

Of artificial lake arrives the water over penstocks and shafts at the power station. There it meets a turbine, which propels a generator. This machine produces current. Depending on the higher or lower downward gradient of the penstocks (few bent) and the shaft (more strongly bent), different turbines are used.



Source 1 : http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/Hydro%20Power.htm
Source 2(Really good): http://library.thinkquest.org/26663/en/4_2_2.html
Other sources which might be useful:
Source 3: http://www.nationmaster.com/encyclopedia/Hydroelectricity
Source 4: http://www.worldofenergy.com.au/factsheet_water/07_fact_water_whatis.html