28 FOREST LANDS FOE THE PROTECTION OF WATERSHEDS. 



as under these circumstances ; but the point I hold, and it seems to- 

 me Mr. Leighton in his report clearly shows, is that the same number 

 of flood-producing rains under conditions of the removal of the 

 forests produce more floods than what would occur were the forests- 

 kept there, and the rapidly increasing percentage, 18 per cent in 

 the last twelve years, as compared with the previous twelve years,, 

 due to the difference in denudation. 



The CHAIRMAN. Are you familiar with a paper written by Col. 

 H. M. Chittenden and read before the American Society of Civil 

 Engineers ? 



Doctor VAN HISE. No; I am not. I have heard of it, but I have 

 never seen it. 



The CHAIRMAN. Colonel Chittenden has been studying this ques- 

 tion for twenty or thirty years. 



Governor GUILD. If you will pardon me at this moment, Mr. 

 Swain is very familiar with that, and if perhaps Doctor Van Hise 

 is not familiar with it, we had better let the expert who is familiar 

 with it answer your questions in regard to it. 



Mr. WEEKS. The floods are not all produced by excessive rains. 

 In the snow regions the floods are produced by excessive melting of 

 the snow ? 



Doctor VAN HISE. Yes; causing an excessive flow of water. In 

 snow areas, where there are heavy snowfalls, that is a factor. I 

 have not said very much about that, because it is not a very important 

 factor in reference to these southern mountains. 



Mr. WEEKS. It would be a factor in the White Mountains? 



Doctor VAN HISE. Yes; it is a very important factor in the White- 

 Mountains. 



The CHAIRMAN. Would you believe it to be true that a heavily 

 forested watershed in a northern latitude, like New Hampshire, might 

 give a result of more disastrous floods that an open watershed? 



Doctor VAN HISE. Do you mean the one that is not timbered? 



The CHAIRMAN. The one that is not heavily timbered. 



Doctor VAN HISE. I would say, as far as the facts are analyzed 

 it bears the other way; that even where there are snow areas the 

 number of floods is less. Although no one stream is accurately ana- 

 lyzed in the same way that the Tennessee is analyzed, yet these tables 

 show that the same thing has occurred, taking the evidence as a 

 whole. 



The CHAIRMAN. As a matter of pure reasoning, we know that in a 

 heavily timbered watershed the wind is broken and the snow falls 

 practically on a level all the way through, and by the shade of the- 

 trees it is held there a long time, until the air becomes warm. Then 

 the warm rains come along and wash it all away at once. 



Doctor VAN HISE. That is comparatively rare. 



The CHAIRMAN. Does it not happen every winter and every spring? 



Doctor VAN HISE. The rain has to be a very long-continued and 

 abundant rain. One of the greatest floods described by John Muir 

 occurred under those conditions. That is a possibility; it is not only 

 a possibility, but it actually occurs. But on the whole the precipita- 

 tion in the form of snow serves to equalize* the flow. In the region 

 of the Rocky Mountains, and also in the great valleys of California,, 

 it is a maxim: " There is a good snowfall; we will have a good year 

 for irrigation." 



