Engineering Wonders of the World
Volume I

THE PANAMA CANAL. 139 POWER DRILLS AT WORK IN THE BAS OBISPO CUT. {Photo, Topical.) EXCAVATING ON THE SITE OF THE GATUN LOCKS. 500 feet wide has been cut to the first struc- tural wonder of the Canal—the locks at Gatun, by which, in three steps of 29| feet each, the ships will rise to or descend from the so-called summit-level. As regards the vexed question of sea-level versus lock canal, one must look beyond com- parisons of time, labour, and expense—all obviously in favour of the ad- Lock versus voca^eg of ßie accepted design. Sea-level x Canal The contr°Uing factor is the annual rainfall, which averages 140 inches at Colon and in the Lower Chagres Valley, 95 inches in the neighbour- hood of the mountain chain, and about 70 inches on the Pacific side. Note that to these totals the three dry months (January to March) usually contribute only about 2’5 inches. The Chagres and other rivers, which during the dry season are mere trickling brooks, rapidly develop, after a few falls of tropical rain, into raging floods. For every waterway therefore, sea-level or lock, planned to take advantage of the Lower Chagres Valley, protective measures are necessary against the floods, which gather in the bold watershed to the north-east, and periodically descend into the Canal line. At Gamboa the river-bed is 50 feet above sea-level, and the flood dis- charge towards the end of the rainy season sometimes exceeds 65,000 cubic feet per second. It is evident that, the lower the level of the Canal, the greater is the need for protection against floods. To obtain this for a sea-level canal it was proposed to build at Gamboa a great masonry dam as a check to the Chagres, and elsewhere smaller dams to regulate other streams. The best solution of the problem, however, was to adopt a lock canal, impound the flood waters, and press them into the serv- ice of the Canal itself. In the present scheme this solution is made as complete as it well can be by the brilliant expedient of making the impounding reservoir part of the summit- level. This will be effected by a monster dam thrown across a valley between high lands' situated to the south of the uppermost of the Gatun locks. By this means Gatun Lake. a basin will be completed, to be known hereafter as Gatun Lake, of such capacity as to receive all the flood waters of the Chagres and other streams, and satisfy all storage and supply demands. Its area will be 171 square miles, its length about 30 miles, of which 23 will be navigated by ships crossing the Isthmus, and its normal water surface 85 feet above the mean level of the oceans. In length and width, though not in height, in which particular it is surpassed by the New Croton, Roosevelt, and other dams, the Gatun