REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.13


 The Isthmiari Canal Commission of 1889-1901 ganged the Gatuncillo and Trinidad in January and May, 1900, yielding for the former stream (8 gaugings) 207 second-feet, and for the Trinidad (15 gaugings) 608 second-feet, or jointly 815 second-feet, the corresponding volume measured at Bohio being 1,872 second-feet. These gaugings indicate for the minimum flow at Gatun in thle five months in 1900 a volume of 2,687 cubic feet per second; no contributions from the small tributaries below Bohio are added, as the rain records for this basin during these five months show a slightly less downfall in 1903 than in 1900. Adopting the Bohio ratio between the minimum and average flow in these five months, the latter is shown to be 6,203 cubic feet per second. That this greatly exceeds any possible demand appears from the following considerations:
 It will be shown below that the maximum demand for reserves for a traffic of about 10 million tons annually, with locks equipped with iterior gates, wi.1L be 1,871 cubic feet per second, and for a traffc of about 35 million tons, 2,759 cubic feet per second. Without such gates the figures will be 2,122 and 3,492 cubic feet, respectively. On page 167 of Part II of the documents supplied to the Board will be found a table giving the monthly volume carried past Bohio for fou rteen years. As the -flow at Bohio is about six-tenths of that at Gatun, the volumes at the former to compare with the above figures are 1,125, 1,643, 1,257, and 2,095, respectively It will be found that in no single rainy month did the measured flow fall below that requisite for a traffic of 10 million tons. Even for 35 million tons, using the interior gates, there would have been shortages only in three of the fourteen years, amounting to 28, 32, and 4 cubic feet, respectively, and these are more than covered by the safety coefficient of about 10 per cent used inl computing the gaugings. Without interior gates the shortages would have been larger, but this only proves the necessity of introducing them.
 It is very desirable to form a closely approximate idea as to the entire area of the basin above Gatun, with a view to check the above estimates for the low-water supply of the canal. The bounding crest of the Gatuncillo basin is laid down with precision onl the best map extant, and I have carefully computed the area, finding it to be 158 square miles. Unfortunately the crest of the Trinidad basin is not known, but it would seem probable that the area may be closely inferred from the known low-water discharges of the Gatuncillo and Trinidad and the known area of the basin of the former. To verify the idea I computed the area of the Gatuncillo basin by assuming it to bear the same proportion to that of the Chagres above Bohio as exists between their lowwater discharges. The result indicated an area of 150 square miles, differing only 8 miles from that shown by the map. Applying the same computation to the Gatuncillo and Trinidad rivers, an area of 320 square miles is indicated for the latter. The following table, therefore, indicates the figures -for the entire basin of the Chagres above Gatun:
 Area of the basin above Gatun.
 Square miles.
 Basin above Aihajuela ----------------------------------------------------------- 320
 Basin, Alhajuela-Gamboa -------------------------------------------------------- 130
 Basin, Gamboa-Bohio------------------------------------------------------------- 250
 Basin of Gatuncillo -----------------0-------------------------------------------- 158
 Basin of Trinidad --------------------------------------------------------------- 320
 Other small basins, say ----------------------------------------- 7------------------ 22
 The Chagres above Gatun ---------w---------------------------------------- 1,200

 Assuming that the minimum and average flow past Gatun and past Boio, both in the dry season and annually, are proportional to the areas of the respective basins-that is, to 1,200 and 700, respectively-a direct check is afforded upon the values deduced above based on the known discharges. The table following compares the indications given by the two methods of computation:
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