Outdoor Garden Fountains

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STREAMS AND DAMS - 3

The depth of water to be impounded and the total height of wall determine the wall thickness. Modern small dams are usually made of masonry materials, either poured concrete or stone set in mortar. Poured concrete dams are usually reinforced with steel and therefore can be made somewhat thinner than stone masonry dams. They are not necessarily less expensive even though they contain less material because the cost of the reinforcing steel and, also, the cost of the forms must be added to the total cost. A well-designed and constructed reinforced concrete dam is, however, subject to fewer deteriorating influences than a masonry dam containing many joints. The relative cost of these three types of dam construction when applied to small dams depends upon several factors which are local in nature. If earth-moving machinery, such as a bulldozer or power shovel, is available at reasonable rates, an earth dam can be built very reasonably, especially if the soil for the dam can be obtained from the excavation for the pool. If hard sedimentary stone is avail- able in the bed of the stream itself, a stone masonry dam may prove to be the cheapest. On many sites, especially where good stone is not available, a poured concrete dam is the least expensive type when all elements that contribute to the cost are taken into account. Except under very unfavorable conditions, the cost of the typical small dam is not excessive. Fairly substantial ones can be built for $500 or less.

Design of dams
In spite of the number of dams which have been built by boys and other amateurs, a dam should not be designed or constructed by persons without some knowledge of en- gineering principles. It is not unusual for a dam only 4 or 5 ft. high to be holding back several thousand tons of water, and such a quan- tity of water is a destructive agency of great force if it should be let loose suddenly by the failure of a weak dam. One method of dam design is to treat the dam as a retaining wall, but even this method is not applicable to a majority of situations. The type of dam which is arched on the upstream side is de- signed on quite different principles. An important part of the engineering is designing the base of the dam so that there is practically no possibility of it being undermined by water at the forward edge, because a dam so undermined is readily turned over by the force of the water bearing against it.