Dams

Dams have huge social, economic and environmental benefits.

The vast majority of dams in Victoria have been built to store rainfall, when it is plentiful, for use in times when it is most needed. We depend on dams to supply water to our homes, businesses, industries, and farms.

Some dams have multiple purposes. Some common uses of dams are:

• On farm: these dams store water for domestic use, for stock or for irrigating crops and pasture;
• Urban and irrigation water supply: these large dams – or storages – store and supply water for use in towns, cities, industry or large farming areas. These dams are managed by water corporations on behalf of the Government. The areas around some of these dams may be closed off from public use to protect the quality of the water;
• Generating power: these large dams hold water for cooling coal or gas-fired power stations or to generate hydro-electric power;
• Recreation: some of the lakes created by dams are used for recreational activities such as boating and fishing. These dams can be popular tourist destinations and the tourism generated by these dams can be important to the social and economic well being of regional communities;
• Minimising flood damage: these dams protect residential areas from flooding. Often quite small, they are built in urban areas and are commonly known as retarding basins. These basins are empty during dry periods and fill up with storm water when it rains. This water is then slowly released into the drainage system minimising flooding impacts from the storm. But if more rain falls than the basin can hold, the additional water will spill and may cause flooding; and
• Protecting the environment: these dams hold the liquid waste material from industrial and mining processes, allowing sediment to settle over time for later disposal. These dams are called tailings dams or mine tailings facilities and have an important job of protecting the environment.

There are many types of dams.

• Embankment dams: are made of earth or a combination of earth and rock. Embankment dams are heavy enough to hold back the force of the water that builds up behind the wall and different types of earth are selected carefully to form a barrier that stops water flowing through the dam;
• Concrete gravity dams: use large amounts of concrete to hold back the force of the water. Some of these dams are able to withstand a flood going right over the top of the whole structure, and may be tied to their foundation by large steel cables within them; and
• Arch or buttress dams: are special kinds of concrete dams that use their shape to transfer the force of the water to strong rocks around or under the dam. Arch dams use part of a circle or an ellipse to transfer the load of water to the sides (abutments), while buttress dams use their shape to transfer the load to the base (foundation) of the dam.

Dams are built with a way to get water from the dam and a way to let excess water out of the dam.

Outlet pipes are typically put through the bottom of the dam wall while it is being built. They are used to supply water from the dam and to empty the dam when needed.

Spillways are channels that are cut lower than the top of the dam. They are designed to allow water to flow out of a full dam in order to stop water from flowing over the top of the dam and causing damage. Small dams may have a simple depression on the ground or an overflow pipe to provide the function of a spillway. Spillways in larger dams are channels made of concrete.

Some spillways have gates inside of them, although in Victoria many of these gates were included for the purpose of increasing the amount of water stored in the dam, not for controlling floods.

Although dams with spillway gates can make some difference to downstream flooding, dam owners operate their dam primarily to protect the safety of the dam and to conserve water for future use. They do this by closely watching weather forecasts, actual rainfall and river flows and adjusting their dam management strategies when required.