REPORT OF BOARD OF CONSUl



 Date of flood.


LTING ENGINEERS, PANAMA CANAL. 48

Cubic feet per second. Period when disHeight charge
 above low was above
 Maximum water at 20,000 cuMaximum. average in Gamboa. bic feet
 48 hours. per second.


 November- Feet. Hours.
 1879.............................. 78,614(?) 65, 000(?) 36.65(?) ............
 1885.............................. 64,488 43,404 31.50 46
 December1885.............................. 44,923 32,421 24.11 43
 1888.............................. 58,132 48,278 31.37 58
 1890............................ 65,371 34,752 31.82 35
 1893.............................. 43,086 27,971 25.33 32

 The data relating to the floods between 1885 and 1893 have been deduced from accurate observations; but such is not the case with that of 1879, the greatest of all. No hydrographic observations along the river were made at that time, but certain high-water marks were approximately determined subsequent to the flood, largely from such information as could be obtained from the memory of ordinary observers. These have been compared with high-water marks of floods since 1879, whence maximum discharges at Bohio have been estimated and corresponding maximum discharges at Gamboa inferred from them. The approximate results given in the above table for the 1879 flood are those which have been found in this manner by the careful work of Gen. Henry L. Abbot, member of the Board.
 Certain general results of value in connection with the problem of the Chagres River at Gamboa follow from an inspection of the preceding tabulation. It is seen at once that the maximum discharge of any flood of record during the past fifty years has not exceeded about 65,000 cubic feet per second, but that the approximate maximum discharge of the 1879 flood reached nearly 79,000 cubic feet per second. Inasmuch as there have been but six severe floods in half a century, it is obvious that they areof infrequent occurrence.
 The next important conclusion established by this long record is the fact that these floods are of short duration. A discharge in excess of 20,000 cubic feet per second has never been observed to last more than 58 hours, although that limit may have been exceeded in 1879. It is convenient, in view of this fact, to deduce the maximum average discharge for a period of 48 hours in each case, as the resulting aggregate volume will represent what may practically be considered the total flood flow of the river. The third column of the table shows that the maximum average 48-hour discharge in the six severe floods has ranged from about 28,000 cubic feet per second to an estimated maximum average of 65,000 cubic feet per second for the flood of 1879. Finally, the greatest high-water elevation above low water during these floods is seen in the fourth column of the table to vary from about 25 feet to the estimated elevation of 36.65 feet for, 1879. The preceding data are sufficient for the determination of complete reservoir control of the Chagres floods by a dam at Gamboa.
 A reservoir created by the proposed damn may have two important functions-that of control only, in the case of a sea-level canal, and those of control and water supply in the case of a lock canal. It will be seen that if the reservoir is of sufficient capacity to control satisfactorily the floods of the Chagres, there will be abundant storage capacity for supplying the summit level of any lock plan.
 In providing reservoir capacity for the control of the Chagres floods, it is to be borne il mind that two floods may follow each other with only a short intervening period, and that such a succession of floods may be both preceded and followed by comparatively high water in the river, although not sufficiently high to be considered a flood flow. It is obviously impracticable to estimate the severest combined effects of such conditions for the future, but the observed records of flow during the past twenty years are sufficient to make an entirely safe provision for any' exigency of combined high water and flood flow, especially in view of the fact that two