long measured on its crest, 2 m. wide at the base, 400 ft. wide at the water surface, I oo ft. wide at the top; and its crest is at an elevation of 105 ft. above sea-level. It is really two dams in one, for in its centre there is a natural hill or rock 110 ft. high. In this the spillway of the dam is constructed, and against its two sides rest the two sections of the great dam. The dam itself contains 23,000,000 cu.yd. of material.
The spillway is a concrete-lined channel, 1,200 ft. long and 285 ft. wide, the bottom being 10 ft. above sea-level, sloping to sea level at the lower end.
Across the lake-opening of the channel is a concrete dam in the form of an arc of a circle, making its length 8o8 ft., although it closes a channel with a width of only 285 feet. The crest of this dam is 69 ft. above sea-level, or 16 ft. below the normal level of the lake. On the crest are 13 concrete piers with their tops 115.5 ft. above sea-level, and between these are 14 regulating gates of the Stoney type which move up and down on roller trains in niches in the piers. The gates permit a discharge of water greater than the maximum known discharge of the Chagres river during a flood.
Near the north wall of the spillway is a hydro-electric station capable of generating, through turbines which are supplied with water from the lake through a forebay, sufficient electricity to meet all demands, including the lighting of the canal and all canal zone towns and buildings ; the machinery of the locks, the machine shops, dry-dock and coal-handling plant ; and the telephone and telegraph systems. There is an emergency Diesel electric plant at Miraflores.
A concrete dam across the Chagres river at Alhajuela was com pleted in 1935, creating Madden lake. The entire dam is about 974 ft. long, 223 ft. high, 191 ft. wide at the base, 25 ft. wide at the top, and contains about 497,000 cu.yd. of material. Madden lake covers approximately 22 sq.m. at maximum level, 26o ft.
above sea level, providing reserve storage of 22,000,000,000 cu.ft. of water for use in maintaining the level of Gatun lake during dry seasons. A hydro-electric power plant of 20,000 kva. capacity is located beside the spillway, providing additional and reserve power to that of the Gatun hydro-electric station.
quently covered with earth. On the west side a rock and earthen dam was built with a puddled and rolled impervious core, 1,400 ft. in length. The Pedro Miguel lock raises or lowers ships 31 ft. —the difference between the summit level of 85 ft. and the normal surface of Miraflores lake-54 ft. above sea-level. The Miraflores lake is a mile in length, and its waters are retained by the Miraflores locks and flanking dams. The east dam at Mira fibres is of concrete, and the greater part of it is the spillway of Miraflores lake. This spillway is 432 ft. in length, with the crest of its dam 38.67 ft. above sea-level, and the supporting piers for the gates rising to 85.17 ft. above sea-level. Eight gates, similar to those in the Gatun Spillway, each 47 ft. Ioi- in. long by 19 ft. in height, and weighing 44 tons each are used; but the dam at Miraflores is straight, instead of being in the form of an arc, as at Gatun.
The west dam at Miraflores is of earth and rock and extends almost parallel with the axis of the locks to a hill to the south. Its length is 2,30o ft., top 7o ft. above sea-level, width of top 4o ft., and slope of sides approximately 12 to I.
The Locks.—All locks are in duplicate, constructed in the same manner, and their chambers, with walls and floors of concrete, have the same usable dimensions—I,000 ft. long and II° ft. wide. There are six pairs, making 12 in all. The side walls are from 45 to 5o ft. wide at the surface of the floor, are vertical on the chamber side, and narrowed on the outside from a point 244 ft. from the floor, by means of a series of steps each 6 ft. long, to a width of 8 ft. at the top. A culvert 254 sq.f t. in cross-section, extends the entire length of each middle and side wall, and from each of these large culverts, smaller culverts, 33 to 44 sq.ft. extend to holes in the floors. Fifteen feet above the top of the culvert in the middle wall there is a U-shaped space 19 ft. wide at the bottom and 44 ft. at the top. This space is divided into three storeys; the lowest for drainage; the middle for wires that carry the elec tric current to operate the gates and valve machinery installed in the centre wall; and the upper a passage-way for the operators. All lock walls are 81 ft. high, except in the lower pair of locks at Miraflores, where they are 82 ft. because of the extreme tidal oscillations of about 21 ft. in the Bay of Panama. In the walls at Gatun there are 2,068,00o cu.yd. of concrete, and in those on the Pacific side 2,440,000 cu. yards. All lock walls rest on rock foundations. The approach wall at the north entrance at Gatun, 1,031 ft. long, rests upon piles driven from 35 to 7o ft. into the earth; that at the south or lake entrance 1,009 ft. long, rests on piles reaching to rock, in some places over I oo ft. below sea-level.