Ch. 16] SUMMARY 297 



harbors are found in the Great Lakes ports such as Chicago, Mil- 

 waukee, and Duluth. Both Chicago and Milwaukee rely on man- 

 made structures for protection from lake waves, whereas the main 

 protection at Duluth is afforded by a natural sand barrier. Other 

 examples of shore-line harbors are San Pedro, Santa Barbara, and 

 Port Hueneme, California; Leixoes, Portugal; Algiers, Algeria; and 

 Hong Kong, China. Sedimentation in such shore-line harbors results 

 principally from the littoral drift of beach material due to wave ac- 

 tion and alongshore currents or, at times, from detritus brought into 

 the harbor by the fresh-water streams emptying directly into the har- 

 bor. 



Corrective measures in the improvement of shore-line harbors have 

 been confined generally to: 



(1) Dredging to remove the excess shoal. 



(2) Construction of breakwaters and jetties to protect the harbor 

 from either wave action and shoaling from littoral drift or both (Port 

 Hueneme, California) . 



(3) Construction of detached (island) harbors completely separated 

 from shore to allow normal movement of littoral drift along the shore 

 line with bridges provided between the harbor and the mainland. The 

 harbors of Arnager and Snogeback on the Danish island of Bornholm 

 in the Baltic Sea are examples of island harbors. 



(4) Improvements in tributary watershed that decrease bed load 

 carried by stream and thereby decrease water-borne detritus deposited 

 in harbor by tributary streams (Los Angeles, California). 



(5) Diversion of tributary flow away from harbor area (Mission 

 Bay, California). 



Studies leading to a clearer understanding of the character and mag- 

 nitude of the movement of littoral drift under the influence of wave 

 action and alongshore currents would be of great immediate benefit 

 in the correction of shoaling in shore-line harbors. To a lesser degree, 

 investigations leading to more successful erosion control in the tribu- 

 tary watershed would be of benefit in the correction of shoaling in this 

 class of harbors. 



SUMMARY 



For the purposes of this chapter, harbors have been divided into five 

 types, and the sedimentation problems generally encountered in each 

 type have been described. Means presently employed to overcome or 

 mitigate the shoaling have also been listed together with a statement of 



