Philadelphia District 



25. The most common problem occurring on the Philadelphia District's 

 coastal structures is subsidence of structures below design elevation. It is 

 thought that toe scour contributes to this, but the primary cause is poor 

 foundation conditions in the areas where most of the structures have been 

 built. This is especially true for those structures located in the Delaware 

 Bay area. 



26. The jetties located at Reedy Point, where the Chesapeake and Dela- 

 ware Bay Canal intersects the Delaware River, were originally constructed 

 prior to 1938 (Figure 28). Both structures were of rubble-mound construction. 

 In the 1960 's the existing south jetty was removed, and a new south jetty was 

 constructed farther south. This was done to increase the entrance size to 

 accommodate larger vessels and improve navigation safety. The present jetties 

 are both 2,095 ft long, and it was reported that the north jetty has problems 

 with toe scour, loss of armor stone, and overall subsidence. 



27. The rubble-mound and sheet-pile composite jetties at Indian River 

 Inlet, Delaware, were completed in 1939 (Figure 29). The jetties required 

 storm damage repairs in 1956 and 1957. At that time, the north jetty was 

 extended inshore a distance of 320 ft. At present both jetties are 1,566 ft 

 long. Both jetty heads have deteriorated significantly from a combination of 

 toe scour, armor stone slippage and displacement, and overall subsidence. 

 Because of the success of the Manasquan River Jetty repairs, dolosse are being 

 considered for inclusion in the repair and rehabilitation designs for the 

 structure slopes. No details on the proposed toe repair design are available. 



New England Division 



28. Based on review of historical repair data, it appears that three 

 project sites within the New England Division that contain rubble-mound jetty 

 structures have exhibited stability problems which could be related to in- 

 stability of the structure toes. Both jetties at the mouth of the Kennebunk 

 River, Maine (Figure 30), have a history of extension and repair. The latest 

 jetty rehabilitation work was completed in 1982. Recent inspections show that 

 both jetty heads are damaged and that 250 ft of the channel side of the east 

 jetty have been undermined. The most recent inspection reports (1973-74), 

 indicate that the north and south jetties at Newburyport Harbor, Massachusetts 



42 



