88 FOREST LANDS FOB THE PROTECTION OF WATERSHEDS. 



Except in a few cases, dry sites are deficient in these advantages. Greater 

 areas of land have to be condemned, and larger and costlier dams are required, 

 with vastly greater danger in case of accident. Really good sites are not a& 

 abundant as one might wish, and the problem of developing storage on such 

 sites is beset with difficulties of many kinds that greatly increase the cost. 



In 189T the author made a careful study of this question of flood control by 

 means of reservoirs, in connection with an official investigation of the advisa- 

 bility of building reservoirs in the arid regions. His view of the difficulties in 

 the way of any general application of such a system is quite fully stated in his 

 report, and the following extracts are directly in point : 



" It is the cost, not the physical difficulties, which stands in the way. It 

 may be stated that as a general rule a sufficient amount of storage can he arti- 

 ficially created in the valley of any stream to rob its floods of their destructive 

 character ; but it is equally true that the benefits to be gained will not ordinarily 

 justify the cost. The reason for this is plain. Floods are only occasional calamities 

 at worst. Probably on the majority of streams destructive floods do not occur, 

 on the average, oftener than once in five years. Every reservoir built for the 

 purpose of flood protection alone would mean the dedication of so much land to- 

 a condition of permanent overflow in order that three or four times as much might 

 be redeemed from occasional overflow. One acre permanently inundated to 

 rescue 3 or 4 acres from inundation of a few weeks once in three or four 

 years, and this at a great cost, could not be considered a wise proceeding, no 

 matter how practicable it might be from engineering considerations alone. The 

 cost, coupled with the loss of so much land to industrial uses, would be far 

 greater than that of levees or other methods of flood protection. * * * The 

 construction of reservoirs for flood protection is not, therefore, to be expected, 

 except where the reservoirs are to serve some other purpose as well." 



The above conclusions are still as applicable as they were when written. The 

 subject has been given renewed prominence quite recently in connection with 

 the Ohio River floods, but, before considering this particular application, atten- 

 tion will be given to certain reservoir systems that have been proposed else- 

 where, and particularly to one already built and put in operation by the Gov- 

 ernment and which will be referred to frequently in the following pages. This 

 is the system at the headwaters of the Mississippi the largest artificial reser- 

 voir system in the world. 



The project of converting the more important of the numerous lakes around 

 the sources of the Mississippi and its tributaries into storage reservoirs as an 

 aid to navigation was originally proposed by Gen. G. K. Warren, and was first 

 put into definite shape by Colonel Farquhar, of the Corps of Engineers. The 

 plan then embraced a large number of lakes in Minnesota and Wisconsin, but 

 only five sites have actually been improved. The dams were first built of 

 timber cribs, but have recently been rebuilt in concrete. The combined storage 

 is about 93,000,000,000 cubic feet. It is about twice the mean annual run-off 

 from the watershed, and the system is probably the only one, except the Great 

 Lakes, which equalizes periodic as well as annual fluctuations of flow. That is, 

 it carries over the surplus from wet years to help out in dry years, and its utility 

 Is, therefore, of the most comprehensive character. The cost of the five reser- 

 voirs is remarkably low, although it is not now possible to tell the exact cost of 

 the present structures on account of the mixture of old and new work ; but it 

 probably does not exceed $750,000, including a lock in the Sandy Lake dam. 

 This is only $8 per 1,000,000 cubic feet, or 35 cents per acre-foot on the basis 



by a rise in the surface equal to that in the outlet necessary to give the in- 

 creased flow. But if the artificial reservoir has reached the limit of its allow- 

 able filling, the outflow must be made equal to the inflow. If this limit is 

 reached before or at the time of maximum run-off, then a quantity equal to 

 this run-off must be let out of the reservoir. This contingency can never happen 

 in a natural lake. The turning point where outflow and inflow balance each 

 other is aiways after the crest of the flood has passed in fact at the time when 

 the diminishing inflow and increasing outflow balance each other and the lake 

 ceases to rise. In the case of the Yellowstone Lake (140 square miles), for 

 example, this rise, in average seasons of snow melting, continues from ten days 

 to three weeks after the inflow has reached its maximum, and surrounding 

 streams have subsided materially before the Yellowstone River (at the lake out- 

 let) ceases to rise. 

 House Document No. 141, Fifty-fifth Congress, second session, p. 46. 



