Table 3 



Knife River Harbor Breakwater 



Knife River, Minnesota 



Date (s) Construction and Rehabilitation History 



1957- Construction of a 245-ft-long breakwater occurred at the site (Fig- 

 1958 ure 9) during this time frame. The shoreward 215 ft of the structure 

 was of rubble-mound construction, and the lakeward 30 ft was a stone- 

 filled timber crib breakwater (Figure 10). The rubble-mound portion 

 of the breakwater had a crest width of 8 ft and an el of +8 ft Iwd. 

 Side slopes of 1V:1.5H were constructed, and armor stone ranging from 

 3 to 5 tons was used. The timber crib structure was 30 ft wide with 

 a crest el of +9 ft Iwd. It was constructed on a stone mattress and 

 had a timber deck. Rock was placed around the toe of the structure 

 comprised of cover stone ranging from 1 to 5 tons. After construc- 

 tion it was noted that a design deficiency existed in that the break- 

 water did not effectively protect the harbor entrance from adverse 

 wave conditions from northeasterly storms. 



1974 A modification to the project authorized the construction of a 



451-ft-long rubble-mound breakwater with four 62.8-ft diam steel 

 sheet-pile cells (250 ft) at its head (Figure 9). Construction of 

 the breakwater has not been initiated. 



1986 Since the original breakwater was completed, it has sustained some 



localized damage which was repaired during routine maintenance. The 

 structure is presently in good condition. 



26 



