FOEEST LANDS FOR THE PROTECTION OF WATERSHEDS. 91 



The scheme has recently been revived in a more attractive form, with data 

 not hitherto available, and at a time when a period of heavy floods and much 

 loss therefrom has turned public attention strongly upon the subject. More- 

 over, it comes supported by a comparatively new element in its favor the vast 

 expansion of water-power development made possible by the electric trans- 

 mission of energy. The new presentation of the project is by M. O. Leighton, 

 Assoc. M. Am. Soc. C. E., Chief Hydrographer, United States Geological Survey, 

 ,and is understood to bear the approval of both the Interior and Agricultural 

 Departments. Mr. Leighton does not claim that his presentation is at all final 

 or complete, but is rather a " statement of possibilities " which he believes are 

 sufficiently promising to justify the Government in giving the scheme thorough 

 investigation before further extensive steps are taken on present lines in the 

 matter of flood control and channel improvement in the main rivers of the basin. 

 Although an estimate of cost is submitted and certain conclusions are based 

 thereon, it is stated that the data are too meager to give much confidence therein. 

 Subject to these qualifications, the system, as set forth in Mr. Leighton's paper, 

 embraces reservoirs on nearly all the tributaries of the Ohio; the total cost is 

 estimated at .$125,000,000; the income from resulting water power at $20 per 

 horsepower, and a certain computed lowering of flood heights on the Ohio and 

 Mississippi rivers, and a corresponding increase in low stages, are given. The 

 full details of the scheme are set forth in quite elaborate form. So far as the 

 present criticism is concerned, the practicability of finding the necessary sites 

 will be accepted, and only the estimate of costs and revenues and the deductions 

 .as to benefits will be called into question. 



In their effect upon floods, admitting that all the reservoirs proposed can be 

 built, the result must fall short of the claims put forth. If built at all, they 

 must be built, as will be shown later, primarily for power development. It will 

 never be possible, until science can forecast the weather more perfectly than it 

 is yet able to do, to regulate reservoirs for the maximum benefit of both pur- 

 poses. This consideration is sometimes made light of, but nevertheless it is one 

 of real importance. For industrial purposes the reservoirs should be full be- 

 fore the rainy season ends; for flood protection they should be so far empty 

 that they may be able to hold back any flood-producing storm that is likely to 

 come. While, doubtless, in a majority of years a middle course could be pur- 

 sued that would not involve much risk on the flood side of the question nor 

 much loss on the power side, yet there would surely come exceptional seasons 

 the seasons of flood-producing rains or the seasons of great drought when the 

 reservoirs would be caught too full on the one hand or too empty on the other. 

 Their full calculated capacity would not then be available for either purpose, 

 and it is difficult to conclude that this would not happen frequently. In partic- 

 ular, if the reservoirs are really operated to prevent floods, it must often happen 

 that dry weather will find them only partially filled, and that their full capac- 

 ity will not be available either for power or navigation. This would not apply, 

 of course, to a reservoir great enough to store all the run-off from its watershed 

 in the greatest known flood, unless considerable storage were left over from 

 previous years as is often done in the upper Mississippi reservoirs. Mr. 

 Leighton's estimates are based upon the mean discharge of the streams, which 

 is, of course, greatly exceeded, possibly doubled, in very wet years. In any case 

 it would seem to be necessary to hold ample capacity in the reservoirs as late 

 as the end of March each year to provide for possible emergencies; but if this 

 is done there will be many years when the reservoirs will not fill. 



An important consideration in the use of the reservoirs for flood control is 

 that of a proper combination of their outflow. To anyone who will try to figure 

 out how this can be accomplished over a watershed of such vast extent, with 

 storms arriving at different times in the various portions, with no way of telling 

 when, where, or with what intensity they will arrive, with the varying dis- 

 tances of the different reservoirs from those points where flood control is par- 

 ticularly important, the problem seems almost impossible that is, impossible to 

 realize the full effect based upon the aggregate capacity of the system. It is 

 understood that Mr. Leighton has endeavored to do this, but it would be inter- 

 esting to see the application to some of the great floods that might be designated. 



The author has seen the description of the proposed system only as pub- 

 lished in Engineering News, May 7, 1908. He has had some correspondence 

 with Mr. Leighton, and is under great obligation to him for a complete set of 

 topographic sheets showing the various reservoir sites. 



