264 POPULAR SCIENCE MONTHLY. 



at the bottom is 30 ft., but at an elevation of 30 ft. below sea-level its 

 sides begin to batter at such a rate as to make the thickness of the wall 

 8 ft. at its top. On either side of this wall are heavy masses of earth 

 embankment of selected material properly deposited in layers with 

 surface slopes of one on three. As shown by the plans the lower por- 

 tions of the core wall of this dam would be sunk to bed rock by the 

 pneumatic process, the joints between the caissons being closed and 

 sealed by concrete and by cylinders sunk in recesses or wells, also as 

 shown by the plans. 



The profile of this route shows that the summit-level would have 

 an ordinary elevation of 85 ft. above the sea, but it may be drawn down 

 for uses of the canal to a minimum elevation of 82 ft. above the same 

 datum. On the other hand, under circumstances to be discussed later, 

 it may rise during the floods of the Chagres to an elevation of 90 or 

 possibly 91 or 92 ft. above the level of the sea. The top of the dam 

 therefore would be from 8 to 10 ft. above the highest possible water sur- 

 face in the lake, which is sufficient to guard against wash or over- 

 topping of the dam by waves. The total width of the dam at its top 

 would be 20 ft, and the entire inner slope would be paved with heavy 

 rip-rap suitably placed and bedded. 



This dam would create an artificial lake having a superficial area 

 during high water of about 40 sq. miles. The water would be backed 

 up to a point called Alhajuela, about twenty-five miles up the river 

 from Bohio. For a distance of nearly fourteen miles, i. e., from Bohio 

 to Obispo, the route of the canal would lie in this lake. Although the 

 water would be from 80 to 90 ft. deep at the dam, for several miles 

 below Obispo it would be necessary to make some excavation along the 

 general course of the Chagres in order to secure the minimum depth 

 of 35 ft. for the navigable channel. 



The feature of Lake Bohio of the greatest importance to the safe 

 and convenient operation of the canal is that by which the floods of the 

 Biver Chagres are controlled or regulated. That river is but little less 

 than 150 miles ]ong, and its drainage area, as nearly as can be estimated, 

 contains about 875 sq. miles. Above Bohio its current moves some sand 

 and a little silt in times of flood, but usually it is a clear water stream. 

 In low water its discharge may fall to 350 cubic feet per second. 



As is well known, the floods of the Chagres have at times been re- 

 garded as almost if not quite insurmountable obstacles to the construc- 

 tion of a canal on this line. The greatest flood of which there is any 

 semblance of a reliable record is one which occurred in 1879. No direct 

 measurements were made, but it is stated with apparent authority that 

 the flood elevation at Bohio was 39.3 ft. above low water. If the total 

 channel through which the flood flowed at that time had been as large 

 as at present, actual gaugings or measurements of subsequent floods 



