The Clifton clarion., 1886-12-15
RESERVOIRS.
BY J. H. aARrISEAu, c. E.

dant or other circumstances arc favorable, it may be best to build them of that material. But it will rarely be expedlsnt if the proposed
 dam is to be of considerable height
 The great pressure exerted by wa
 ter of much depth would require
 timber work of very great strength
 to resist it; and to this must be
 added the perishable nature of
 wood when alternately exposed to
 air or to submerslon in water. Of
 course 1t is different where timber
 is always submerged; in such case
 it will remain sound for genera
 tion.
 In regard to the plan of frame
 work needed, it is difficult of ex-
 planaton to the general reader
 without the aid of diagrams; and
 we can therefore give a few gen.
 eral hints only. Almost every dam
 would require different style of
 construction, owing to difference in location and other circum-
 stances. For instance, a dam five
 to elght feet high, but of consider
 able length, might create pond,
 which, though shallow, would
 cover a large sufface-say forty or fifty acres; and again, dam many feet in height but quite short might convert a deep rav1ne into reservolr holding as much water as the other. But the two dams would require entirely different forms of construction. A long low dam, not exceeding six feet in height may be very easily and cheaply built; and we will offer q few suggestions relative to one of that kind. .
 The foundation timbers should be laid several feet below the nat ural bed of the stream, to give proper stability and to prevent undermining.
 The upstream surface of the dam should form an angle with the horizontal of not more than forty degrees, in order that the weight of the reservoir water may press it downward. If the angle exceed forty-five degrees, the pres sure of the water will be horizon tai instead of perpendicular, and will teud to push the dam down stream.
 The under side or floor of the dam should be plank closely laid; otherwise of concrete, or stone so well laid as to prevent any under or erosion by water. In | all cases such a floor or apron | should be made for the water to fall upon as it flows over the dam. If rock be handy, an apron formed of rock carefully laid and of sui ficient size to prevent their dis placement by the falling water will be all that is needed. If rock be not available a very good apron may be made of long willows laid closely together and suitably con- fined in place.
 If the foundation be deeply laid there will be no danger of under but great care will be re- quisite at the ends. It should ex- tend some distance into the natural bank, and when completed, the ex- cavation so made should be care fully refilled, the earth being rammed as solidly as possible. If the dam be built as described the only danger it can encounter, aside from heavy drift wood or ice pass ing over it will be because of the liability of the water to cut around the ends; but thls may be prevent ed by proper care.
 The dam should be so built that its crest will be higher at each end than in the middle; then if the volume of water be suddenly in creased so as to flow over it's top he main current will be in the center and away from the ends. In fact the two ends should be so nigh that no water shall ever flow ,ver them.
 In a dam built of timber or ma sorry waste gate may be easily md safely made, by which means he reservoir may at any time be trained.
 Circumstances may compel the of q dam where a great lepth os sand in the bed of the stream renders any kind of dam Tery unstable because of the liabil- . ty of water to work through the sand under it. The writer recalls instances where dams Tn such To- cations, costing many thousand lollars have either sunk out of tight or have been undermined