REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.


 It will be noted that, these dams have a small section in proportion to the depth of water behind them when compared with the Gatun dam.
 Earth dams are in such common use, are so generally indorsed by engineers, many of whom prefer them to other forms, that this extended discussion has been given only because the proposed use of earth dams has been unduly criticised in the report of the Board.
 The nearest precedent in general design for the Gatun dam is the north dike of the Wachusett reservoir of the Metropolitan Water Works, of Massachusetts, which is two miles long and at the deepest place will have 65 feet of water against it. The highest portion of this dike was built on exactly the plan proposed for the Gatun dam, namely, the fine material of which the dike is composed was deposited on the fine underlying material without the use of either masonry or sheet piling to prevent the filtration of water. Under portions of this dike the depth to the rock is as great as at the Gatun dam.
 PLAN OF THE DAM.
 Plate XI shows a plan of the dam. Its total length from the locks to the westerly end is 7,700 feet. About midway in the length of the dam there is rising ground in which it is proposed to excavate, as already indicated, a diversion channel through which the Chagres will flow during the construction of the earth dam.
 The regulating works, to be subsequently described, will be built mainly of concrete and will be located in part in the diversion channel and on each side of it. On each side of the rising ground referred to, and extending from it westerly to the high ground and easterly to the locks back of Gatun, there will be great earth embankments of the cross section already described, which will together contain 21,200,000 cubic yards of material. The westerly embankment will cross a French diversion channel. The easterly embankment will cross the French canal and the Chagres.
 It will be feasible to begin at once the construction of one of the earth embankments, permitting the water to flow through the channel or channels at the site of the other embankment. It will also be feasible to begin at once the construction of the diversion channel, utilizing the material excavated in the embankments of the dam.
 In the construction of the dam it is proposed to remove all trees, stumps, and roots from its site and to excavate the surface material to such an extent that the impervious material of the embankment will come in direct contact with the impervious clayey material which is found nearly everywhere in this region; also to do any other work required to cut off the flow through any pervious material which further investigations may disclose. For such work an allowance of $400,000 for all dams has been made in the estimate of cost.
 The diversion channel is to have a minimum width of 150 feet and is to be excavated to sea level, or somewhat below it; although the lower part of the channel will be through indurated clay, it is proposed to place in it concrete where required for the protection of the channel or for the regulating works up to sea level, and to build in the channel to an elevation about four feet above sea level the foundations of certain piers and walls, which will remain for a time at this elevation, so that they will form only a slight obstruction to the discharge of flood waters.
 After the earthwork of the dam reaches a suffiCient height to be beyond all danger of overflow, the piers and walls, which will be above water at low stages of the river, and which will have in them grooves for stop planks, will be built to higher elevations to furnish a ready means of turning the river through half of the diversion channel while the other half is pumped dry to permit the placing of the concrete of the regulating works, and by turning the river alternately from one side to the other the regulating works may be built without special difficulty.
 REGULATING WORKS.
 The general design of the regulating works is shown on Plate XIII. The central 150 feet of their length, which will be built up from the bottom of the diversion channel, is to be a solid mass of concrete, having its crest at elevation 69. The crest is to be made wide with the downstream slope two horizontal to one vertical, making an unusually strong section.


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