(Figure 31), which have an extensive repair and rehabilitation history, are 

 showing considerable damage. This damage appears to result primarily from 

 subsidence. Damage on four areas on the channel side of the south jetty most 

 likely result from undermining of the rubble toe. The jetties at Hampton 

 Harbor, New Hampshire (Figure 32), were originally constructed by the State 

 and were turned over to the Corps in 1964. During 1965 to 1966, considerable 

 work was done on both jetties. Since that time the south jetty has remained 

 in good condition, while the north jetty has required continuous maintenance. 

 Most of the repair and rehabilitation work has been needed on the seaward por- 

 tions of the north jetty. The last rebuilding of the north jetty was com- 

 pleted in 1980, and it is thought that part of this recurring damage can be 

 attributed to scour and undermining of the jetty toe. 



North Central Division 



29. There are 38 project sites within the Detroit District which have 

 breakwater and/or pier (jetty) structures that have exhibited stability prob- 

 lems related to the structure toes. At 14 of these sites problems are associ- 

 ated with rubble-mound structures, while at the remaining 24 sites toe prob- 

 lems occur on other structure types. Table 2 is a listing of these 24 sites 

 and the types of breakwater and/or jetty construction associated with each 

 site. The remainder of this section on the Detroit District deals strictly 

 with those 14 sites which are having and/or have had toe stability problems 

 with rubble-mound structures. At some of these sites, toe stability problems 

 have occurred on areas of the structures that are not rubble mound. 



30. Structures at Black River Harbor, Cheboygan Harbor, Hammond Bay 

 Harbor, Harrisville Harbor, New Buffalo Harbor, and Point Lookout Harbor, 

 Michigan, are purely rubble-mound construction (Figures 33-40) . Charlevoix 

 Harbor, Michigan; Duluth-Superior Harbor, Minnesota and Wisconsin; and Leland 

 Harbor, Muskegon Harbor, Pentwater Harbor, Port Washington Harbor, and 

 Traverse City Harbor, Michigan (Figures 41-55), have structures that are com- 

 posed of a combination of rubble mound, timber cribs, timber piles, steel 

 sheet piles, concrete caissons, steel cells, concrete caps, and concrete 

 superstructures. The head of the east jetty on the north end of the Keweenaw 

 Waterway, Michigan (Figures 56 and 57), is an old timber crib which is encased 

 in rubble. For this reason, its response is very similar to that of a purely 



46 



