Log Dam for Soft or Sandy Bottoms

In a country where timber is abundant, a log dam is the most economical, affording, if properly built, an ample degree of strength and durability at comparatively small cost aside from the labor involved. This is of course a considerable item, but as the work can be performed by ordinary laborers chiefly, it is of a less costly nature in proportion to its amount than the construction of a frame dam or the building of a solid stone wall, requiring the services of a carpenter and a stone-mason.

The dam here represented may be literally described as a "brush and timber dam," though it comes under the general head of log-dams, the main portion of its structure being of that character, while saplings of any size may be used in making it compact, and brush, clay and boulder stone for filling on the up-stream side. The process of constructing this dam is essentially as follows :

Cut trees of eight or ten inches in diameter, lopping off the limbs on what will be the top and bottom sides, when the logs are placed in position.

Start the first layer (forming the foundation and front of the apron of the dam, and projecting down stream as shown at the extreme left of the cut) placing the logs side by side with the tops up stream, the lower or butt-ends being about fifty feet below the point where the dam is to be raised. Having completed this, fall back about twenty-five feet and place a second layer of logs side by side as before, the limbs being carefully lopped off on the under and top sides. Having now two layers or courses of logs reaching from side to side of the stream, start a
third layer twenty feet back of the second, and carry it across the stream in the same manner as the others.

The fourth course, five feet back of the third, completes the series of successive and overlapping tiers of logs constituting the foundation of the dam and forming the apron. With this last course, you begin raising the dam, using for the purpose trees and saplings of any convenient size, and all the while filling in compactly, especially toward the upstream extremity of the dam, with brush and clay. If boulder stones are readily accessible they should be thrown in along with the clay.

Apron and Trestle Work

The successive courses of logs should now be laid on in such a way that the face of the dam will present a steep
slope, the crest being about two feet farther up-stream than the point at which the dam rests upon the apron. At nearly every course it is well to lay binders lengthwise across the stream, pinning them to the largest logs beneath them. The ends of these binders, which may be three or four inches in diameter, are shown in the cut. They should be placed from two to four feet back of the face of the dam.

Having reached the crest of the dam, a top binder is pinned on as solidly as possible, a pin being driven wherever there is a chance for it to hold. If convenient, two or even three binders may be employed, in which case they should be firmly secured to each other and to the upper tier of logs. The dam should be filled in on the surface, from the crest back to the extreme up-stream tips of the trees, with fine brush and clay.

For this purpose, trestle work may be built out over the stream and planks laid on to serve as a track on which to wheel the dirt out upon the dam. Throughout the whole work, care should be taken to lop the branches from the top and bottom sides of the trees, and the butts of the trees should invariably be laid down stream. The dam should be made in the form of a semi-circle or half-moon, arching up-stream.

To secure the ends of the dam, a log-pen should be built at each bank, (one of which is shown in the cut,) extending back into the bank as far as it can conveniently be carried. Each pen should be chinked from the inside and filled with clay ; or if stone is plenty it may be used instead of clay for filling the pens, which will not then require to be chinked. If clay is used it should be packed in as tightly as possible to prevent it from working out.

Settling

It has been found that a dam of this kind will settle about eighteen inches the first year, for which due calculation and
allowance should be made. After that time, it will remain nearly stationary. It is cheaper, in a favorable locality, than a frame dam, and has an important advantage in the fact that it will hardly ever wash out. It is almost impossible to build on a quicksand bottom a frame dam that will stay in, as the experience of many mill-owners has shown. The use of piling cannot be recommended, as the water forms small whirlpools around the piles, and will in time wash out the earth clear to their bottoms.

It should be remarked that in building a dam of this kind, unless the stream is nearly dry, it will be well to leave a passage through which the water may escape while the building is going on. This need not usually be done until the apron is completed, and perhaps one or two courses of the upright part of the dam laid on ; but after that it will be expedient to leave a space or channel near the middle of the clam for the water to pass through until the rest of the dam is finished, when the gap may be closed up.