July 20, 1906.] 



SCIENCE. 



75 



plan by a dam across the Chagres River at 

 Gamboa, about thirty-one miles from Colon, 

 n6ar the point where the Chagres River in 

 its downward course first cuts the canal 

 line. At that point bed rock is about fifty- 

 five feet below the surface of the water in 

 the river, affording a comparatively easy 

 masonry construction resting directly upon 

 bed rock, and thus securing an undoubted 

 foundation for a dam. The maximum ele- 

 vation of water surface in this lake would 

 be about 120 feet above the present surface 

 of the water in the river at Gamboa, or 

 about 170 feet above mean tide. The dam 

 would be fitted with suitable controlling 

 gates of sufficient capacity to meet the re- 

 quirements of the highest floods. The 

 available storage volume created by this 

 lake would be sufficient to take in quick 

 succession two of the greatest floods which 

 have ever occurred in the Chagres River, 

 so far as is known either by exact records 

 or by reliable report. 



It would be the purpose in this system 

 of control to allow flood waters of the 

 Chagres River to escape through the con- 

 trolling gates into the canal prism at a 

 maximum rate not exceeding 15,000 cubic 

 feet per second, producing a current in the 

 canal, if all flow should be in one direction 

 only, of about one and one quarter miles 

 per hour, a negligible quantity as far as 

 its effects on navigation are concerned. It 

 would require but two or three days after 

 high floods in the Chagres to depress the 

 surface of water in the lake so as to be in 

 readiness for another flood whenever it 

 might occur. 



The only other stream of magnitude, dis- 

 charging into the Chagres River within 

 limits affecting the canal, is the Gatun 

 River, Avhich joins the Chagres near the 

 little native town of Gatun, seven miles 

 from Colon. The discharge of this river, 

 however, would be carried into Manzanillo 

 Bay entirely outside of the canal in an 



independent artificial channel on which 

 much work was done by the old Panama 

 Canal Company. The other and much 

 smaller streams intersecting the canal line 

 throughout its entire course would be either 

 kept out of the canal altogether by dams 

 high enough to reverse their flow into other 

 drainage basins than their own, or received 

 into settling basins outside of the canal and 

 quietly discharge their small flows into the 

 canal prism over wiers in the usual manner. 

 All streams of this latter class, however, are 

 extremely small. By these means all sen- 

 sible amounts of silt or other heavy ma- 

 terial carried in floods would practically 

 be kept out of the canal, thus reducing the 

 cost of maintenance in this respect to a 

 small annual amount. 



A minority of five of the consulting 

 board reported their judgment in favor of 

 a lock canal with two terminal lakes and 

 with a summit level eighty-five feet above 

 the mean level of the ocean. In this plan 

 it is proposed to construct a great earth 

 dam 135 feet high across the Chagres River 

 at Gatun. This dam would retain a large 

 lake backing the water in the river up to 

 Alhajuela, a point over thirty miles from 

 the site of the dam. The surface of the 

 water in this lake constitutes the summit 

 level of the lock plan. Three locks in 

 series or flight, each with a clear length of 

 900 feet and a clear width of 95 feet, 

 would be built at the site of the dam, each 

 with a lift between 28 and 29 feet to pass 

 vessels up from the approach channel lead- 

 ing to the locks from the harbor of Colon 

 to the summit level. The southern ex- 

 tremity of the summit level of this plan 

 would be at Pedro Miguel on the southerly 

 side of the continental divide where the 

 channel issues from the Culebra cut. At 

 this point, between thirty-nine and forty 

 miles from Colon, there would be located 

 a lock with a lift of about thirty feet, con- 

 necting with the terminal lake at the 



