Ch. 15] 



SHORE-CONTROL PROBLEMS 



277 



the patient is ill, in many cases in extremis, and his problem is to plan 

 and construct defenses or works that not only will resist the attack of 

 the sea but also will regain at least a part of the shore already lost. 

 Often the problem is presented as treatment of a limited area, say a 

 few hundred feet of frontage, within a large region of erosion, the re- 



Fig. 1. Atlantic City, New Jersey. The highly vulnerable position of structures 



built without allowance for an adequate margin for erosion is well illustrated. 



September 1944. (Photo by U. S. Navy.) 



mainder of the region being endangered but the property owners being 

 in economic circumstances precluding any corrective action. 



Another typical problem frequently encountered is that arising from 

 the provision of deep navigation channels from the sea or lakes into 

 rivers or inlets. To illustrate this problem we may assume an inlet 

 into a bay. Initially, under natural conditions, the inlet channel might 

 have had a controlling depth of, say, 10 feet, and would have migrated 

 within certain limits. As the channel approached one limit of its 

 migration, a new channel would break out near the opposite limit, 

 with the old channel closing as the new channel improved, the new 

 channel then migrating to repeat the cycle. In the usual case there 

 would be a submerged bar associated with the inlet channel. Now de- 

 mands are made for a channel of greater depth, say 20 feet, and the 



