52 , PHYSICAL GEOGRAPHY OP 



acros^ some of the tributary streams, and hold back a small portion of the sur- 

 plus water in the lakes that are there already formed, and then provide common 

 sluice gates to emit that water into the channel when it is needed. 



This is all that is necessary for the spirit of this and future ages to accom- 

 plish, to obtain a perennial and unbroken navigation of nearly 1,000 miles along 

 the Ohio, and many hundred miles along its tributary valleys. 



The observations which have been recorded in the foregoing pages will serve 

 to teach us how to proceed in thus improving the navigation, cheaply and per- 

 manently, to any practicable extent. 



These observations show that, to supply all the water necessary to produce 

 a depth of 2| feet on the bar at Wheeling — supposing that the natural supply 

 had failed for a brief period entirely — would require a reservoir capable of fur- 

 nishing 310,000,000 cubic feet per diem. But looking over the records of the 

 last eleven years, we meet with but one season — that of 1838 — when a depth 

 of less than 2| feet continued for a longer period than 65 days. That was truly 

 a remarkable year — well remembered by every engineer then occupied with 

 works in any manner depending on the supply of rivers. (See Record, Note D.) 



Taking that season as a guide, we find that to have made up the deficiency of 

 the natural flow of the Ohio, and furnish the excess needed to maintain the 

 depth at 2^ feet, would have required an average augmentation of the natural 

 daily discharge of the stream of 100,000,000 cubic feet, or a total supply for the 

 65 days of 6,500,000,000 cubic feet. 



Now, if we construct a dam across the Alleghany river, near Franklin, no 

 higher than one of those on the Lehigh — 58 feet — and provided with a lock for 

 the accommodation of the upper trade, as is usual at the dams across all navi- 

 gable rivers, we shall observe by the fall of the Alleghany, exhibited in the pro- 

 file, Fig. 2, that this dam will create a reservoir about 25 miles in length, having 

 a depth of 58 feet at one extreme, and reduced to the ordinary depth of the 

 river at the other. But it would do more. It would set back the water many 

 miles up numerous tributary streams which empty into the Alleghany along 

 these 25 miles, and up all the ravines and lateral branches of these tributary 

 streams. There are many artificial pools on the navigable rivers of this coun- 

 try, from 15 to 20 miles in length. The dam near the Grand rapids on the 

 Wabash has formed a pond 17 miles long. The dam at the Horse-shoe bend, 

 on Kentucky river, has created one 27 miles long, and that at Cedar ripple, on 

 the same stream, has produced a pool of 23 miles. Dams of greater height 

 have been built, and lakes of greater length have been created, on many of the 

 rivers of this country, than will be required by the improvement here proposed • 

 though no doubt it will be found to be good economy to construct higher dams 

 and locks of greater lift, and form reservoirs of greater capacity, in carrying 

 out this system to its full extent, than have yet been demanded by existing 

 works. This course may, and probably will, be dictated by true economy ; but 

 it is not at all necessary to success, nor intended to be recommended in the 

 first steps. 



