Rick Hardy, age 12, of Victoria, B. C., for his question:
Why are dams so useful?
A major dam may compete with nature's best plunging cataracts. The network of a major system of man made dams may cover a province or several states. Yet the basic principle of a working dam is very simple. It is merely a way to store and use nature's water supplies.
Damming streams to conserve future water supplies is nothing new and man was not the first to think of it. Dams were invented by the busy beavers and built with great success by their remote ancestors. These bright eyed smarties are rated as aquatic mammals. This means they are equipped for expert swimming and diving and depend on plentiful supplies of water for the security of their daily lives. The streams, of course, depend on rainfall and in most regions rainfall varies with the seasons. The beavers barricade streams with dams to conserve the gushing springtime flow from season to season.
A beaver dam is a barrier of sticks and stones plastered together with mud. It walls off the flowing water and forces it to collect in a pond behind the sturdy dam. In front of the dam, the stream may dry up or dwindle to a trickle. The pond is a reservoir of water stored to last the beaver and his kinfolk through future dry spells. It is his private swimming pool where he can retreat from his hungry foes. Out in the center he builds a high and dry family home with an underwater entrance leading up through the floor.
This simple structure seems a far cry from a huge man made dam. But the working principle is the same. A mighty wall is built across a sizeable river. Behind it a large area of hollow land is cleared to hold a reservoir lake of stored water. However, man has improved on the beaver's basic dam idea. A sturdy system of conduits, valves and power lines are built into the massive concrete wall. Another system of canals and pipelines is connected to the water supplies of surrounding communities. Machinery to control the inner working in the dam is housed in block houses on one or both sides of the great wall. ,
The dam is a barricade in the path of the flowing river. Its water backs up to fill the reservoir to a level higher than the dry stream bed in front of the massive wall. Valves in the concrete wall are opened to allow the required water supplies to spill down from the reservoir. Falling water happens to be a mighty force and this fact adds an extra unexpected usefulness to the dam. Water falling from the spillways can be trained to turn wheels. It is used to turn mighty electric generators and power lines carry the electricity to communities far and near in all directions. Also, a dam can prevent disastrous floods by holding back the waters of a rampaging river.
A system of dams can be used to control the seasonal flow of a river and supply a vast human community with year round water plus year round electric power. The river may be rather small and its dry season may dwindle to a trickle. But a well¬ engineered dam project can tame it to perform far reaching duties. The planning job begins with surveys of the river, its tributaries and the natural drainage slopes of the surrounding land for many miles around. The dam barricades are built at the right spots in this natural geographical structure.