Geoff Morris, age 14, of Eugene, Oregon, for his question:
Why are dams so important to irrigation?
Beavers build dams to store the plentiful spring rains for the dry months ahead. This budgeting of seasonal rainfall rates as basic irrigation. But the beavers do not stop at building sturdy walls across a few streams. They extend this use of natural streams by digging networks of connecting canals, thereby irrigating and enriching the local scenery. Man made irrigation systems dam up the seasonal rains to budget the seasonal water supply on a much grander scale.
Our mighty dams are breathtaking feats of architecture and the work they do so simply and successfully is astounding. Basically such a dam is a high wall across the channel of a river. In the rainy seasons and after the snow melts, the untamed stream surges with surplus water ¬perhaps flooding the land on either side and eroding its soil. The dam's wall of steel and concrete stops the surging spring flow from flooding away to waste itself in the sea. The seasonal surplus backs up and fills a large reservoir lake. The dam system also is constructed to dole out this reserved water through a far reaching network of channels. A dam is the most important part of an irrigation system that conserves a natural water surplus and distributes it where and when it is needed.
In this role, the marvelous man made structure helps to irrigate a vast area throughout the year, supplying water to teeming communities and often transforming arid deserts into fertile farmlands. But a dam also brings a wealth of other surprising benefits. It prevents seasonal floods from slopping over and eroding the land. The reservoir behind the wall is a lovely fresh water lake, often many miles long. Its moisture enhances the surrounding scenery with thriving greenery that supports a local ecology of wildlife. In many cases, this man made wonder is stocked with fish and set aside as a serene recreational area.
And just in case all these benefits are not enough, sometimes a dam also is constructed to provide electric power. The calm water in the reservoir is blocked from pouring down in disastrous floods and controlled amounts are released into the main river. The dam may be engineered to jet this water through under pressure. Powerful jets are geared to turn turbines and make giant generators hum with electric power.
This man made marvel is a multi purpose dam. It is the center and star performer. of a network of irrigational channels pipes and conduits to supply populations and in¬dustries, canals and dikes to budget water to fields and farmlands. From it, tall pylons carry wires bearing electric power to cities and industries. Such a dam is truly a structure for all seasons. For when vacation season rolls around, we can go off and enjoy the scenic beauty around its reservoir, practice our swimming or take a boat ride, water ski or catch a few flavorful fish for breakfast.
The most admirable thing about a dam is its variety of surprisingly different bene¬fits. And usually where there is one dam there are others. As a rule, our marvelous irrigation systems are designed to budget nature's seasonal water supplies over a vast area. Several dams along the way may be needed to tame a temperamental river and the complete irrigation system may connect and utilize the flow of many natural streams and waterways.