CHAPTER III. 



DIKES AND THEIR EFFECTS. 



THE structures for guiding a stream along a caving bank and protecting the same 

 from undermining, for confining and directing the water at bars and shoals, and for 

 closing secondary arms of a river, are all known under the general name of Dikes.* 



Types. There are three general types of dikes in use in this country and abroad 

 called from their location and construction, spur-dikes, longitudinal dikes, and sub- 

 merged spurs or "Grundschwellen," which have been used to a considerable extent in 

 Europe. 



The two forms of spur and longitudinal dikes are not infrequently combined. 

 When this arrangement is adopted it is known as the mixed system. 



Spur-dikes. This system has had an extended application in Germany, on the 

 Rhine, Elbe, Vistula, Oder, and other navigable streams, and has been employed in 

 several other countries, including the United States. It attempts to perform its 

 mission by means of dikes placed at intervals along the shores, and projecting more 

 or less into the stream (either normal to the channel or slightly inclined down stream), 

 and partially closing its low- water bed, instead of lying parallel with it, as in the 

 longitudinal dikes. The chief object of these works is the improvement of navigation, 

 but the deposit of alluvium between the various spurs where they have been in existence 

 for a long time may become a matter of considerable importance; and is in fact one 

 of their most useful and most valuable features. In the course of time these deposits 

 reach the level of the dikes and solidify them and protect them from ice and floods. 

 A new and continuous bank uniting the heads of the dikes is thus formed. It is stated 

 that 8400 acres of mean river-bed on the Prussian part of the Rhine has thus been 

 transformed into alluvial soil. This class of dike at first decreases the flowing section 

 of the river at the head or outer extremity only, so that it is evident that there must 

 be more than one, in fact a system, in order to effect a longitudinal deepening across 

 a bar. The bank also may be cut away opposite these various spurs, in which case 

 recourse must be had to another system for protection, built upon the opposite shore. 



Mention of the spur dikes used in America will be found in the chapter on " Bank 

 Protection." 



Longitudinal Dikes are built along the bank about parallel to the direction of the 

 current. Their use has been very extensive in Europe and they have met with consider- 



* Some of the plates accompanying this and the next chapter are republished by permission from "The 

 United States' Public Works' Guide and Register," by Captain W. M. Black, Corps of Engineers, U. S. A., 

 and from the papers by H. St. L. Coppe'e on "Bank Revetment," published in Transactions American Society 

 of Civil Engineers, January, 1896. 



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