GATUN LAKE AND THE CHAGRES RIVER That section of the Canal, which for the convenience of engineering records and directions is known as the Central Division, comprises within its boundaries two of the great spectacular features of the Isthmus--Gatun Lake and the Culebra Cut. I have already described the scenic characteristics of this lake, but some discussion of the part it plays in the economy of the Canal will not be out of place. In the first place the creation of the lake depended on the type of canal to be selected. A sea-level canal could not exist with the lake; a lock canal could not have been built without it. The meanderings of the Chagres, crossing and recrossing the only practicable line for the Canal, and its passionate outbursts in the rainy season made it an impossible obstacle to a sea-level canal, and all the plans for a canal of that type contemplated damming the stream at some point above Gatun--at Bohio, Gamboa or Alhajuela--and diverting its outflow into the Pacific. On the other hand the lock canal could not be built without some great reservoir of water to repeatedly fill its locks, and to supply the waterpower whereby to operate them. Hence Gatun Lake was essential to the type of canal we adopted. The lay reader will probably be surprised when he hears how carefully the area of the Chagres watershed and the average rainfall were studied, and the height of the dam and the spillway adjusted to make certain a sufficient supply of water for the locks. The only locks with which these could be compared are those at the “Soo”, or outlet of Lake Superior. That canal, the busiest one in the world for eight months in the year, averaged 39 lockages a day during that period on the American side and a smaller number through the Canadian locks. The water in Gatun Lake will be sufficient for 41 passages, if the full length of the locks is used or 58 if only the partial length is used, which will be the case with steamships of less than 15,000 tons--and in ships of this class the bulk of the world’s trade is conducted. If the limit of 41 lockages seems low, it must be remembered that time is quite as much a factor in the case as is the water supply. It will take an hour and a half to put a ship through the locks. That time therefore technically constitutes a “passage”. In the 24 hours there would be 36 passages possible, and under the circumstances that would draw most heavily on the lake there will be water enough for 41. [Illustration: THE CHAGRES, SHOWING OBSERVER’S CAR From the swinging car the observer measures the crest of the flood and rapidity of the current] For the creation of this lake our engineers found the Chagres River available. It had dug the valley in which would be stored the vast volume of water needed, and the unfailing flow from its broad watershed could be relied upon at all seasons--though indeed in the rainy season its contribution is sometimes embarrassingly lavish.