REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.


 Mr. GUIfRARD. How much dredging has been done in the maritime channel at La Boca to keep it clear for 21'or 22 feet?
 Mr. WALLACE. 1 think there has been almost continuously at work there a dredge with a capacity of about 2,500 cubic yards a day. It has not been working continuously to that capacity, but there has been one in commission. Sometimes it would be out of commission or it would be idle for a few days or a week or two at a time, repairing machinery or something of that sort, but one dredge has been sufficient to keep that channel open as it was constructed
 Mr. WELCKER. More dredging is necessary on the sea side.
 Mr. WALLACE. The drift of the current seems to bring the sand along the coast and silt up the channel, although some sediment is occasionally brought down by the Rio Grande.
 Mr. NOBLE. What proportion do you think that would be compared with the amount brought in by the shore currents?
 Mr. WALLACE. I think there is more brought in by the shore currents. I did not make any examination to determine that definitely. That was placed under Mr. Harper, an engineer, some months before I left there, and he was supposed to investigate all those things, but up to the time I left he had not made a report.
 Mr. STEARNS. Is it not true that the channel has been widened as well as maintained?
 Mr. WALLACE. It has to some extent; yes. The situation there, I should judge, has been and will always be this: That between the tidal locks and the deep water in the sea one dredge will always have to be maintained, but I think one dredge will be sufficient to always keep the channel open to a proper depth and width.
 Mr. HUNTER. Are you assuming in that answer, Mr. Wallace, that there will -be a tidal lock at Miraflores ?-Mr. WALLACE. Yes.
 Mr. HUNTER. Suppose the tidal lock were in the Ancon-Sosa saddle?
 Mr. WALLACE. You would have to have a dredge available there all the time. You might not have to have it in continuous operation. By working it a comparatively short time it might keep the outer channel clear; but I am judging simply from what I saw when I was down there and from my general observations as to the Rio Grande River and the work being done there, that with a tidal lock at Miraflores a dredge would be necessary. Now, a dredge would be necessary in any case, although it might not have to work over thirty days in the year.
 Mr. WELCKER. Is it known to you, Mr. Wallace, that there is great difficulty now in retaining the depth of 22 feet in the channel of La Boca after it is dredged to that depth, and that in half a year that depth may diminish to 15 feet if dredging is not constantly continued?
 Mr. WALLACE. I have not heard of any such great filling as that. If you have even a 40foot channel, a certain amount of material would come in each day in each month, but that should not be any more for a deep channel than a smaller one. Your source of supply would not be increased by the depth of the channel. The ability to catch the material would of course be increased slightly, but if you have a depression at all and you create the conditions that are going to cause sediment to catch there, I do not think the increased depth would materially increase the accumulation of the sediment. It might do so to some extent.
 Mr. WELCKER. Do you think if it were all mud there the difficulties would be increased?
 Mr. WALLACE. Yes; it would because it would make it necessary to widen your section and give a flat slope; but that mud, as I understand it, does not occur out where the maximum dredging has been necessary. Around La Boca pier there is a great deal of that mud, and of course the deeper you dredge the channel the flatter the slope will necessarily be; but after you once get your channel it does not mean that any more mud will come into the deep channel than into the shallow one, practically. I am speaking on the theory now that you do not increase the supply of mud that comes down there in suspension.
 The CHAIRMAN. I suppose if we have finished with Mr. Wallace we ought to make a state, ment to that effect.
 Mr. RANDOLPH. I move that we give Mr. Wallace a vote of thanks for- the papers he has submitted and for the able way in which lie has informed us of his views on the subject.


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