Page:Popular Science Monthly Volume 74.djvu/445

Rh deposits, so that it can not displace the earth particles with which it comes in contact in its passage under the dam. To make a convincing estimate of the volume of flow in the porous sub-surface strata under the dam is almost out of the question, because the extent, character and continuity of these strata can not be definitely ascertained, and it will be difficult, if not impossible to determine at what point or points the water will sink the lake above the dam into these layers. The engineers can, therefore, do no better than make unfavorable assumptions and determine the maximum water loss that may result under such hypotheses. There is no probability that this will be such as to prove embarrassing to the project. It is to be remembered in this connection that nearly always, when a subsurface flow in a river channel has been developed by the construction of a subsurface curtain dam, the result in water output has been disappointing. In other words, the probability is that the under-flow will be over-estimated. Nevertheless, the public seems to expect further assurance that the canal work is progressing along proper lines, particularly as it now appears probable that the cost of the lock canal will be more than double the amount named by the board of engineers in comparing the cost of the two types of canal.

In the writers opinion, it may confidently be assumed that a safe dam can be constructed at Gatun. The situation at Gatun is, therefore, of minor importance in be further discussion of the question that has again arisen: "Would it not still be well to change the approved project and to complete the excavation to sea-level?" This question, if it be again opened, will have to be considered in the light of the views of the experts whose opinions have been herein referred to, in the light of the work already done and the progress already made: in the light of the experience on the isthmus during nearly five years of effective work, and in the light of such additional facts and conclusions as may be submitted by the engineers now about to start for the isthmus.

January 25, 1909.