V


188 REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.

 VOLUME OF FRESHETS AND GREAT FLOODS.

 A comparison of the difference in flow between Gamboa and Bohio for twenty-four hours, during 12 freshets occurring between August, 1899, and January, 1904, at dates when the rain records established that the downfall was well distributed throughout the valley, indicated as to be dealt with an average volume of about 5,000 second-feet, ranging as high as 12,000 second-feet. Four freshets in the same period, when the rainfall was chiefly in the upper basin, indicated an average volume of about 4,000 second-feet, ranging up to 6,000 second-feet; and three freshets with rainfall chiefly in lower basin indicated about 9,000 second-feet, ranging up to above 14,000 second-feet. These figures demonstrate that even to control what would remain, after the diversion of the upper Chagres, during ordinary freshets would call for artificial channels of no small dimensions.
 The following table presents a brief r6sum6 of what goes before, including a list of the more important affluents of the Chagres below Gamboa, arranged in the order in which they would naturally enter the canal, together with their probable individual contributions and heights of cascades, based so far as possible upon the data given above. For the upper Obispo and the Camacho the figures represent the average measured volumes during the two years 1892 and 1893; for the five streams measured by the old company the figures reported by Monsieur Berges are adopted, and for the rest estimates are formed from the comparative size of their drainage areas and their locus as to rainfall, which rapidly increases as the Gulf is approached:
 Contributions of affluents below Gamboa, in second-feet.

 Affluent. Dry Rainy Freshets. Cascades. Affluent. Dry Rainy Freshets. Cascades.
 season. season. season. season.

Upper Obispo (km. 49)....... 2 16 466 165 Quebrada Agua Bendita.... 8 80 300 35
Rio Camacho (km. 49)....... 2 80 982 165 Rio Cano.................... 75 773 3,850 33
Rio Mandinga (km.. 45) ...... 5 300 1,500 45 Rio Gigante................. 18 185 920 30
Quebrada Cuatra Calles...... 10 50 500 45 Rio Frijoles Grande ........ 31 321 1,593 26
Rio Carabali................. 15 150 760 40 Rio Frijolito................. 20 200 1,000 20
Rio Juan Grande............. 15 300 1,200 38 Rio Agua Salud............ 19 198 982 25
Rio Pisco..................... 15 300 1,200 34 Quebrada Aojeta............ 20 200 1,000 15
Quebrada Culo Seco....... 5 80 300 40 Total.283 3,466 17 613 Rio Baila Monos-..............15 153 760 45 - 
Quebrada Caimito Mulato ... 8 80 300 35 Measured total, 14 years .... 213 2, 039 (?) ..........

 The measured total" here represents the difference between the discharges carefully measured month by month for fourteen years at Gamboa and Bohio; and when it is remembered that these years cover an epoch of exceptionally low rainfall, giving a discharge much less than that in the time of the old company, the correspondence is as close as could be expected in such estimates.
 Passing now to a consideration of the great floods, which really furnish the only proper standard for estimating the volumes to be dealt with, the available figures will be found in the following table:
 Discharges in the great floods, in cubic feet per second.

 Gamboa. Bohio. Excess at Bohio.
 Flood. Maximum. 48 hours. Maximum. 48 hours. Maximum. 48 hours.

 1893......................................................43,000 28,000 51,000 44,000 8,000 16,000
 1890........-- -............................................. 65,000 35,000 72,000 51,000 7,000 16,000
 1888.................... ... ..................................... 58,000 48,000 79,000 (?) 21,000 (?)
 November, 1885------------.......................................... 64,000 43,000 75,000 (?) 11,000 (?)
 December, 1885........................................................ 45,000 32,000 47,000 (?) 2,000 (?)
 1879.......... ............... ............................. 79,000 (?) 113,000 (?) 34,000 (?)

 It is greatly to be regretted that no hourly records of water level in these floods were kept at Bohio by the engineers of the old company, but the two kept there at later dates demonstrate