THE PANAMA ROUTE FOR A SHIP CANAL. 549 



rate as to make the thiekness of the wall S feet at its top. On either 

 side of this wall are heavy masses of earth embankment of selected 

 material properly deposited in Ia3'ers with surface slopes of 1 on 3. 

 As shown by the plans, the lower portions 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 cylinders sunk in 

 recesses or wells, also as shown by the plans. 



The profile of this route shows that the sunuiiit level would have an 

 ordinary elevation of 85 feet al)Ove the sea, but it may be drawn down 

 for uses of the canal to a minimum elevation of 82 feet above the 

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

 later, it may rise durino- the floods of the Chagres to an elevation of 

 90 or possibly 91 or 92 feet above the level of the sea. The top of the 

 dam, therefore, would be from 8 to 10 feet above the highest possible 

 water surface in the lake, which is sufficient to guard against wash or 

 overtopping of the dam by waves. The total width of the dam at its 

 top would be 20 feet, and the entire inner slope would be paved with 

 heavy riprap suitably placed and bedded. 



This dam would create an artificial lake having a superficial area 

 during high water of al)out 40 square miles. The water would l)e 

 backed up to a point called Alhajuela, about 25 miles up the river 

 from Bohio. For a distance of nearly 14 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 feet 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 feet 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 river Chagres are controlled or regulated. That i-iver is but little 

 less than 150 miles long, and its drainage area, as nearly as can be 

 estimated, contains about 875 square miles. A])()ve 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 lia\c at times l)een 

 regarded as almost, if not quite, insurmountal)le obstacles to the con- 

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

 any semblance of a relialfle 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 feet above low 

 water. If the total channel through which the flood flowed at that 

 time had been as large as at pres(>nt, actual gaugings or measurements 

 of subsequent floods show that th(> maxinumi dischargt; in 1879 might 

 have been at the rate of 13(!,0(l0 cubic feet per second. As a matter 



