At the close of the fiscal year 1908–’09 three 20-inch suction dredges were depositing material over the area between the rock piles, and the fill had reached an average elevation of 16 feet above sea-level. A total of 2,501,372 cubic yards was placed in the dam during the year.
Excavation through the Spillway Hill was practically completed and 30,464 cubic yards of concrete laid. During the year 359,821 cubic yards of material were removed from Spillway hill by steam shovels and placed on the dam.
The original canal plans provided for a flight of two locks at La Boca, near the Pacific, and one at Pedro Miguel. Steps were taken to construct the former and trestles were built along the toes from which to dump material from Culebra Cut. The trestles failed after dumping began and material overlying the rock moved laterally, the movement continuing for two weeks in some places. After this result these dams were abandoned so that instead of locks at La Boca they will be built at Miraflores. Another reason for the change besides poor foundations is the military advantages of the latter over the former position.
Both the dams at Pedro Miguel and Miraflores will be constructed of two rock piles, the portion between being filled by hydraulic methods. Very little work has been done upon them.
[Illustration: FIG. 3.--PROFILE ON THE AXIS OF THE GATUN DAM SITE SHOWING UNDERLYING MATERIAL AS DETERMINED BY BORING.
(From Report of C. M. Saville, Assistant Engineer, August 29, 1908.)]
[Illustration: FIG. 4.--Revised cross-section of Gatun Dam as recommended by Board of Consulting Engineers, February, 1909.]
[Illustration: FIG. 5.--GENERAL PLAN OF GATUN DAM.]
At Panama the seasons are divided into two well defined periods: the dry, or winter, and the wet, or summer seasons. By this occurrence of maximum moisture and maximum heat, the health conditions are made the worst possible.
The dry season includes the months of January, February, March and April, the rainy season the remainder of the year. During the dry season the average temperature at Colon for 6 years was 70.5° F, with a monthly maximum of 90.9° F, which came in January, and a monthly minimum of 68.4° in the same month. During the rainy season the maximum average temperature for any month occurred in October and was 91.9° F. The minimum was 66.9° F., for August. A record of 15 years at Colon shows a maximum rainfall of 154.9 inches and a mean of 130.2 inches. Four years’ records at Panama show a maximum of 84.73 inches and an average of 66.8 inches. At Culebra the records for 3 years showed a maximum of 98.97 inches and a minimum of 64.25 inches.
