Jetty as completed in 1913, and it has proven effective. The width of the 

 south jetty crest varies from 45 to 70 ft, with a crest elevation of 

 +26 ft mllw and side slopes of 1:1.5. The jetty is constructed of stones up 

 to 25 tons each, 45 percent having an average weight of 10 tons each. The 

 base width of the outer portion is approximately 350 ft, and the total height 

 ranges up to 76 ft. 



69. The design wave on the south jetty is the depth-limited breaking 

 wave and varies from 19 to 22 ft. 



70. The north jetty was constructed between 1913 and 1917. The crest 

 elevation was +28 to +32 ft mllw, with a crest width of 25 ft and side slopes 

 of 1:1.5. The Jetty started on the west side of Cape Disappointment, extended 

 southwestward for about 2 miles to a point 2 miles north of the south jetty, 

 then turned westward for about 1,700 ft. The Jetty contained nearly 3 mil- 

 lion tons of stone. 



71. The outer portion of the north jetty was flattened by wave action 

 to mean low water by 1930, but the 2-miles-long southwesterly leg was backed 

 up by a natural sand fill on the northerly side and was thus protected. Some 

 damage resulted along the southeasterly side from river undercutting. The 

 Jetty was rehabilitated during 1938 to 1939 and a concrete terminal placed at 

 the end of the southwestward segment. The outer portion extending westerly 

 was not reconstructed and serves as an apron on the sea slope. 



72. In conjunction with the rehabilitation of the north jetty, two spur 

 Jetties were proposed to help maintain the channel. Jetty "A" started at Cape 

 Disappointment and extended in a southerly direction for about 1 mile. The 

 Jetty has experienced frequent problems with scour at the head of the Jetty, 

 and most repair work has been a result of the scour. Jetty "B" was not con- 

 structed and has been classified "inactive". A chronology of events related 

 to the development and repair of the Jetty structures is given in Table 22. 

 Coos Bay, Oregon 



73. Coos Bay is located on the southern Oregon coast about 200 miles 

 south of the mouth of the Columbia River and 445 miles north of San Francisco 

 Bay. The project includes two jetties at the mouth of the bay and a small- 

 boat mooring basin at the Town of Charleston, about 1 mile from the mouth of 

 the bay. 



74. The initial study for navigation improvements, authorized in 1878, 

 recommended that two parallel jetties be constructed seaward from the mouth of 



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