The waters from the river are collected and store in the High-level reservoir which are connected to the dams. In the day time, the dams are opened resulting to gushing of water from the reservoir. This flow of water is used to generate electricity. As the water flows at such a high speed there is a power station
build at the bottom of the dams. This station have Reversible turbines and Generator assembled in them. As the water flows in day time, the Reversible turbines works as generator operator. The flow of water is so massive that the turbines creates and form electricity which are then using generator are distributed to Power lines and National grid.
This process works exactly the opposite in the night time. The turbines are used to pump the water back to the high-level reservior. This process is usually done to get all the excess water from over flowing Low-level reservoir. This process is very nature friendly and cost efficient when compared to hydro power plant.
So the working of Hydroelectric power station is very systematic, cost efficient, durable and can genrate huge amount of electricity with natural resources without affecting the enivornment. 
The  
waters
 from the river  
are collected
 and store in the High-level reservoir which  
are connected
 to the dams. In the day time, the dams  
are opened
 resulting to gushing of  
water
 from the reservoir. This  
flow
 of  
water
 is  
used
 to generate electricity.  
As
 the  
water
  flows
 at such a high speed there is a  
power
  station
 build
 at the bottom of the dams. This station  
have
 Reversible  
turbines
 and Generator assembled in them. As the  
water
  flows
 in day time, the Reversible  
turbines
 works as generator operator. The  
flow
 of  
water
 is  
so
 massive that the  
turbines
 creates and form electricity which are then using generator  
are distributed
 to  
Power
 lines and National grid.
This process works exactly the opposite in the  
night time
. The  
turbines
 are  
used
 to pump the  
water
 back to the high-level  
reservior
. This process is  
usually
 done to  
get
 all the excess  
water
 from over flowing Low-level reservoir. This process is  
very
 nature friendly and  
cost efficient
 when compared to hydro  
power
 plant. 
So
 the working of Hydroelectric  
power
 station is  
very
 systematic,  
cost efficient
, durable and can  
genrate
 huge amount of electricity with natural resources without affecting the  
enivornment
.