FOREST LANDS FOB THE PROTECTION OF WATERSHEDS. 103 



THK EQUALIZING INFLUENCE OF FOKKSTS ON THE FLOW OF STREAMS AND THEIB 

 VALUE AS A MEANS OF IMPROVING NAVIGATION. 



[Being mainly a rejoinder to the paper of Col. H. M. Chittenden, U. S. Army, entitled 

 " Forests and reservoirs in their relation to stream flow, with particular reference to 

 navigable rivers," presented before the American Society of Civil Engineers. Prepared 

 at the request of His Excellency Curtis Guild, jr., governor of the State of Massa- 

 chusetts, by George F. Swain, LL. D., professor of civil engineering in the Massachusetts 

 Institute of Technology.] 



It is the opinion of probably the great majority of engineers conversant with 

 the subject, that forests act as equalizers of the flow of streams by diminishing, 

 in general, the frequency and violence of freshets, and increasing the low-water 

 flow, and by preventing the erosion of the soil and the consequent silting up of 

 water courses. 



Based on these premises, it is believed to be of much importance to the inter- 

 ests of navigation as well as to other interests, that the United States Govern- 

 ment should establish forest reserves in the Southern Appalachian and White 

 Mountains, the object of such reserves being : 



First. To aid in the protection of certain given watersheds. 



Second. To enable the Government to give an object lesson to private owners 

 in the vicinity as to what may be accomplished by proper forest management, 

 and to cooperate directly with such private owners in encouraging them to use 

 the best methods. 



Third. To aid in preventing forest fires and the consequent deterioration of 

 the soil and destruction of timber on both government and private lands. 



Fourth. To aid in and encourage reforesting, and by this means and by proper 

 management to augment and prolong the timber supply. 



In September, 1!)08, a paper, the title of which has been quoted above, was 

 published in the Proceedings of the American Society of Civil Engineers by 

 Col. H. M. Chittenden, of the Corps of Engineers, U. S. Army, in which argu- 

 ments were advanced which in a measure seem to controvert the generally 

 accepted opinions. The present paper is a brief rejoinder to that article, pre- 

 pared with special reference to its bearing upon the Appalachian and White 

 Mountain Forest Reserve bill. 



The paper of Colonel Chittenden is exceedingly well written, and upon first 

 reading might seem to contain strong arguments against the regulative action 

 of forests. Upon analyzing its statements, however, it will be perceived that 

 Colonel Chittenden practically acknowledges most of the claims made for 

 forests, that the paper contains many contradictory assertions and illogical 

 deductions, and that his arguments are largely conjectural and unaccompanied 

 by proof. 



The paper states that the commonly accepted opinion is that forests have a 

 beneficial influence on stream flow (1) "by storing the waters from rain and 

 melting snow in the bed of humus that develops under forest cover * * * 

 preventing their rapid rush to the streams and paying them out gradually 

 afterwards, thus acting as true reservoirs in equalizing the run-off; (2) by 

 retarding the snow melting in the spring and prolonging the run-off from that 

 source; (3) by increasing precipitation; (4) by preventing erosion of the soil 

 on steep slopes and thereby protecting water courses, canals, reservoirs, and 

 similar works from accumulations of silt." 



This will probably be admitted to be a fair statement of what the believers 

 in the benefits of forests consider to be true, except that some do not consider 

 that there is yet sufficient demonstration that they increase the rainfall, and 

 also except that the water is not stored simply in the bed of humus, but also 

 in the ground beneath. 



With reference to the first of these points, the author states that it is " strictly 

 true of average conditions." He says : " It is true, therefore, as popularly under- 

 stood, that, in periods of ordinary rainfall, with sufficient intervals for the forest 

 bed to dry out somewhat, forests do exert a regulative effect upon run-off. 

 They modify freshets and torrents and prolong the mn-off after storms hav<T 

 passed, and therefore realize in more or less perfection the commonly accepted 

 theory." 



He believes, however, that this beneficial effect is not exerted under extreme 

 conditions, i. e., great floods and excessive low waters, and he states that these 

 extreme conditions " determine the character and cost of river control." 



Even if it be admitted that the presence of forests does not affect "ex- 

 treme conditions," this is no argument against the value of forests, for it is 



