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THE NATIONAL GEOGRAPHIC MAGAZINE 



sociated at that time, for a study of the 

 defenses of the canal. When the location 

 of the locks at the Pacific end was fixed 

 I was directed to call the Secretary of 

 War's attention to the military necessity 

 of withdrawing the locks to the interior. 

 This I did, with the result that in for- 

 warding the report of the Board of Con- 

 sulting Engineers to the President he 

 calls attention to the fact as follows: 



"The great objection to the locks at Sosa 

 Hill is the possibility of their destruction by 

 the fire from an enemy's ship. If, as has been 

 suggested to me by officers of this department 

 entitled to speak with authority on military 

 subjects, these locks may be located against 

 and behind Sosa Hill in such a way as to use 

 the hill as a protection against such fire, then 

 economy would lead to the retention of this 

 lake. ... If, however, Sosa Hill will not 

 afford a site with such protection, then it seems 

 to me wiser to place the locks at Miraflores." 



In forwarding the report to Congress, 

 the President calls attention to the 

 change recommended by the Secretary of 

 War in the location of the locks on the 

 Pacific side. The so-called afterthought 

 appears, therefore, as a conclusion 

 reached long before I had any connec- 

 tion with the work. 



WHY THE GATUN DAM WAS REDUCED IN 

 HFJGHT 



Discredit is also thrown on the Gatun 

 dam because there has been a desire to 

 reduce the height from 135 to 105 feet. 

 The original height was arbitrarily fixed 

 to secure an excess of weight, so as to 

 fully compress the underlying material, 

 supposed to be largely silt deposited by 

 the river. Subsequent investigations 

 show that the supposed compressibility 

 does not exist ; that a marine, not a river 

 deposit is encountered. The greater the 

 height of the dam the greater the diffi- 

 culty of constructing the upper portion, 

 and the greater the cost, both in time and 

 money. From present available data, if 

 the lake should take the total discharge of 

 the Chagres River, the water surface 

 would not exceed 90 feet ; the top of the 

 locks, 92 feet above sea-level, would per- 

 mit escape of the water long before it 

 could reach the crest of the dam. Why 



then go to the expense of the extra height 

 of the dam, and what is to be gained 

 thereby ? Assuming the crest of the dam 

 as 100 feet wide, uniform slopes from 

 the rock piles would give a height of 105 

 feet, and this height was suggested. Be- 

 cause as an additional reason it was men- 

 tioned that the pressure over the base 

 would be more uniformly distributed by 

 a dam with the cross-section proposed, 

 the opponents of the present project, 

 without ascertaining the facts, point to 

 the change as a desire to secure a uniform 

 base pressure, and use it as an argument 

 against the stability of the foundation. 



Much also has been made of the fact 

 that in the testimony before one of the 

 congressional committees mention was 

 made of securing the stability of the 

 superstructure by balancing the dam on 

 the underlying material. Naturally the 

 testimony is read and discussed in such 

 a way as to leave the impression that the 

 entire dam is to be so constructed. The 

 ground to be covered by the dam is 

 crossed by three water-courses, the 

 Chagres River, the French Canal, and the 

 West Diversion, and between these 

 streams the ground is undulating, Spill- 

 way Hill reaching a height of no feet 

 above sea-level. It is not remarkable or 

 unprecedented that there should be de- 

 pressions which undrained become soft 

 with the excessive rainfall. Except for 

 these, the ground is firm. It is in the 

 crossing of these soft spots that slips have 

 occurred and are liable to occur, and to 

 which the balancing method referred. 

 They are relatively small in extent and 

 when drained or filled cause no trouble, 

 as experience at the La Boca embank- 

 ment clearly proves. 



As previously stated, the Gatun dam 

 satisfactorily solves the problem of the 

 control of the Chagres, and there should 

 be no doubt in the mind of any one who 

 impartially examines the data that the 

 solution is not only feasible, but abso- 

 lutely safe. As there has never been any 

 question raised as to the safety and sta- 

 bility of the dams at Pedro Miguel and 

 Miraflores, with the Gatun dam accepted, 

 other things being equal, the relative 



