PART II. 



IMPROVEMENT OF OPEN RIVERS. 



CHAPTER I. 



REMOVAL OF BARS AND OTHER OBSTRUCTIONS. 



Desiderata. The conditions to be fulfilled in the betterment of navigation in open 

 rivers are: 



1. A sufficient depth for navigation at all seasons. 



2. A sufficient width of channel for safe passage of all craft traveling in opposite 

 directions or in the same direction. 



3. The works necessary to secure such results must not be of an obstructing char- 

 acter, nor must they cause the formation of obstacles to navigation, nor lower the 

 water-level sufficiently to uncover those in the river-bed. 



4. The cost of construction and maintenance must not be out of proportion to 

 the benefits to be derived. 



Expedients. The fact that it may cost a larger sum of money to render a river 

 satisfactorily navigable by employing the best methods often leads to the acceptance 



of makeshift or temporary forms of improvement. This has brought about the appli- 



, 

 cation and suggestion of numerous plans and contrivances, some with merit, some 



wholly impracticable, and usually all undesirable where it is important to attain per- 

 manent and satisfactory results. The temporary contrivances used for this purpose, 

 or suggested for trial, are of great variety, and consist of trellis-work, basket-work, 

 movable gates, swinging mattresses, etc., for deflecting the current, and scrapers and 

 stirring devices of various designs for loosening the bars and assisting the current in 

 their removal. 



/ C" 



The principal trouble with all these appliances, however, arises from the fact that 



I V ** 



the current cannot be relied upon to carry away the material after it has been loosened, 

 notwithstanding the general belief that when the crust of a bar has been broken it is 

 an easy matter to wash it away. Janicki has called attention to one effect produced 

 by them in these words: "Such machines have a moral effect, if I may be allowed the 

 term. Boat-owners, who have to suffer from low water on the bars, complain less w 

 they see that something is being done to relieve them." 



NOTE. A number of the illustrations are taken from a paper by J. A. Ockerson on " Dredging in the 

 Mississippi," Trans. Am. Soc. C. E., vol. xl.; others are furnished by the Bucyrus Co., South Milwaukee, 

 Wis. 



