46 PHYSICAL GEOGRAPHY OF 



enable us to control such a flood as that of 1841, so as to render it harmless at 

 Wheeling. 



This volume is just equal to the quantity which the river would discharge in 

 50 days, when there is a depth of 5 feet in the channel. 



If, then, we construct reservoirs upon the Alleghany and Monongahela, or 

 their tributaries, of sufficient capacity to supply the actual discharge for fifty 

 days, at a height of 5 feet, these reservoirs will contain all the water that it is 

 necessary to hold back to protect the upper portions of the valley from the 

 injurious effects of ordinary floods. A reservoir adequate to this object would 

 be four miles square, and very nearly 100 feet deep. 



A single dam, no higher than some of those constructed for the canals of 

 this country, may be built on the Alleghany, which will foi'm a lake nearly thirty 

 miles long, with numerous branches, also many miles in extent, and capable of 

 supplying nearly the whole volume of water required for the navigation from that 

 direction, while greatly restraining the floods which proceed from that arm of the 

 Ohio. Equally available sites can be found on the great tributaries of the Mo- 

 nongahela, where reservoirs can be formed without injury to valuable property, 

 competent to supply the deficiency in periods of drought, and capable of control- 

 ling the floods in that direction also, when the supply of water is there in excess. 



To exercise complete control over all injurious floods will involve a greater 

 outlay than will be required for the efl^ectual improvement of the navigation ; but 

 even this can be accomplished by works which will also secure to the naviga- 

 tion a permanent depth of six feet^ for about the cost of maintaining a ship of 

 the line on a three years' cruise. 



The surface velocity of the central current of the Ohio river, at Wheeling, 

 when the average depth in the channel is 35 feet, is very nearly five miles an 

 hour, and the mean velocity of the whole mass of water, four miles an hour. 

 The total movement of the stream, after the river is filled, is therefore very 

 nearly 100 miles a day; and the velocity of a float in the centre of the channel, 

 about 120 miles a day. 



These are the results of actual measurements. Yet, though such is the rate 

 of motion of the stream, it can be shown that the movement of the top of the 

 flood-wave is a great deal less than this. 



The greatest flood of which we have either recorded or traditionary account 

 on the Ohio, is the famous rise of February, 1833, when the river attained a 

 height of 31 feet at Pittsburg, 44| feet at Wheeling, and 63 feet at Cmcinnati, 

 above its summer surface. 



This flood reached its highest mark, from place to place along the river, at 

 the following dates : 



Pittsburg ■ ■ 

 Wheeling - - 

 Marietta - - 



• - February 



10. 



11 - . 



13 - ^ 



■ - (evening) - - 



■ - (noon) - - ■ 



. - 88 miles. 

 - - 176 " 



Maysville - - 

 Cincinnati - - 

 liOuisville - • 





16 - ■ 



17 - ■ 

 31 - ■ 



-. - (night) - - . 

 ■ - (midnight) - 

 • - (morning) - ■ 



- - 405 " 



- - 460 " 

 ■ - 613 <' 



