Power from water
For thousands of years, people have used flowing water to do work. Ancient Greeks and Romans used water wheels to grind grain. Today, hydropower is the world’s largest source of renewable electricity, producing about 15% of all electricity worldwide.
How a hydroelectric dam works
A hydroelectric dam turns the energy of falling water into electricity.
| Step | What happens | Energy change |
|---|---|---|
| 1 | A dam blocks a river, creating a reservoir | Water stores gravitational potential energy |
| 2 | Water flows down a large pipe called a penstock | Potential energy → kinetic energy |
| 3 | Rushing water spins a turbine | Kinetic energy → mechanical energy |
| 4 | The turbine turns a generator | Mechanical energy → electrical energy |
| 5 | Transformers raise the voltage for power lines | Electricity travels to homes |
| 6 | Water flows out into the river below |
The amount of power depends on:
- Head: how far the water falls (higher = more power)
- Flow: how much water passes through (more = more power)
Types of hydropower
| Type | How it works | Example |
|---|---|---|
| Dam and reservoir | Stores water behind a dam; can control output | Robert-Bourassa (Quebec), W.A.C. Bennett Dam (BC) |
| Run-of-river | Diverts part of a river’s flow through turbines; little or no reservoir | Many small BC projects |
| Pumped storage | Pumps water uphill when electricity is cheap or plentiful; releases it when needed | Sir Adam Beck Pump Generating Station near Niagara Falls |
| Small hydro | Powers a single community or building | Remote communities |
Hydropower in Canada
Canada is one of the world’s top producers of hydroelectricity. About 60% of Canada’s electricity comes from water.
| Province or territory | Share of electricity from hydro (approx.) |
|---|---|
| Quebec | About 94% |
| Manitoba | About 97% |
| British Columbia | About 87% |
| Newfoundland and Labrador | About 95% |
| Yukon | Most of its grid electricity |
Major projects include:
- James Bay (La Grande) project, Quebec: a huge system of dams and reservoirs built from the 1970s onward.
- Churchill Falls, Labrador: one of the largest underground power stations in the world.
- Niagara Falls: the Sir Adam Beck stations divert water from the Niagara River. Niagara was an early centre of hydroelectric development in the 1890s.
Canada also exports hydroelectricity to the United States.
Advantages
| Advantage | Why |
|---|---|
| Renewable | Rain and snow refill rivers |
| Low emissions | No fuel is burned |
| Reliable and flexible | Output can be increased or decreased quickly to match demand |
| Long-lasting | Dams can operate for 100 years |
| Energy storage | Reservoirs and pumped storage store energy for later |
| Other uses | Flood control, water supply, recreation |
Disadvantages
| Disadvantage | Details |
|---|---|
| Flooding land | Reservoirs flood forests, farmland and communities |
| Impacts on Indigenous peoples | Large projects have flooded traditional lands and disrupted hunting, fishing and travel; the James Bay project led to the 1975 James Bay and Northern Quebec Agreement with the Cree and Inuit |
| Fish | Dams block migrating fish like salmon; fish ladders help some get past |
| Mercury | Flooded soils release mercury, which can build up in fish |
| Changing rivers | Dams change water flow, temperature and sediment downstream |
| Drought | Low water levels reduce power output |
| High building cost | Large dams are very expensive to build |
The future
Engineers are working on ways to reduce hydro’s impacts, such as better fish passages, smaller run-of-river projects, and upgrading old dams instead of building new ones. Pumped storage is becoming more important as a way to store energy from solar and wind.
Common mistakes
- Thinking dams "use up" water. The water continues downstream.
- Thinking hydro has no environmental impact.
- Thinking hydro only works with huge dams.
Try it yourself
- Make a simple water wheel from a plastic plate and spoons. Pour water from different heights. Which spins it faster?
- Find the nearest hydroelectric station to where you live.
- Debate: should a new large dam be built? List the pros and cons, including the views of people who live nearby.
Quick recap
- Hydropower turns the energy of falling water into electricity.
- Dams store water in reservoirs; turbines spin generators.
- Canada gets about 60% of its electricity from hydropower.
- Hydro is renewable, low-emission and flexible.
- Dams can flood land, affect fish and impact Indigenous communities.