364 THE WATER SUPPLY FOE THE NICARAGUA CANAL 



Commission, page 65, showing a rate of inflow to Lake Nicaragua 

 corresponding to the recorded rainfall at Rivas. This table was con- 

 structed b}' the chief engineer upon an assumption made b}' me and 

 expressed as follows : 



Wliile we have no conclusive data upon which to estimate the percentage of 

 run-off to rainfall in tiie basin of Lake Nicaragua, it is well established as a 

 general nde that in any given basin the greater the rainfall in a given time the 

 greater the percentage of run-off, so that if the rainfiill were increased 21 per 

 cent the run-oft" should be increased somewhat more, say 25 i)er cent. — Report 

 Nicaragua Canal Co)nmis>iion, page 295. 



It will be seen that this is a mere assunijjtion adopted for the want 

 of any actual data, and, as slunild always l)e done in such cases, it is 

 made on the side of conservatism, for the pur])ose of comparing the 

 rainfall of 1898 — the only year for which we have records of the fluc- 

 tuations of the lake — with other 3'ears. If, however, this assumption 

 should lead us into obvious absurdity, it should be modified or re- 

 jected, but up to the present time this necessit}^ has not api)eared. 



Tlie second assumption is that the Rivas rainfall is reliable and 

 beai^ a reasonabl}' uniform relation to the rainfall and run-off in the 

 basin of Lake Nicaragua. This matter was discussed by me in the 

 Report of the Nicaragua Canal Commission, page 297, where it is 

 shown that the fluctuations are greater in quantit}' than is usual in 

 other parts of the world, so that if this record is in error, it also is 

 j)r(>l)abl3' on the side of conservatism. 



Professor Heilprin's third assum|)tion is that the outflow from Lake 

 Nicaragua in the seventeen 3'ears from 1880 to 1896, inclusive, averaged 

 42 inches per annum. This assumption is entirely gratuitous, appar- 

 ently' with no l)asis whatever, and, together with his table quoted from 

 the chief engineer, leads Professor Heil})rin to the astounding con- 

 clusion that the lake has declined 20 feet and 9 inches in nineteen 

 years, or 249 inches. To reach this conclusion he has assumed a total 

 outflow in that time of 798 inches, or 549 inches more than the alleged 

 decline of the lake. A conservative estimate of the water required for 

 the use of the canal is given on page 66 of the report of the Commis- 

 sion, showing that a liberal allowance for leakage, lockage, and power 

 requires three inches annuall}' from the surface of Lake Nicaragua, 

 or a total of 57 inches for the nineteen 3'ears. AVi)en the canal is con- 

 structed provision will be made for storing the run-off" from Lake 

 Nicaragua so far as necessary, and Professor Heilprin's own figures 

 show that 549 inches will be available where onl3' 57 are required. 



