foot of structure and the efficacy of pneumatic and hydraulic breakwaters 

 in preventing the transmission of wave energy into areas where protection 

 was desired from storm wave action. 



Selected examples of such investigations are discussed below. Reports 

 on a few model studies and experimental investigations pertaining to the 

 stability and wave-transmission characteristics of coastal structures are 

 referenced in the examples. 



(1) Rubble-Mound Breakwater Trunk; Nonbreaking Waves . 



(a) Example of a Typical Study . 



1^ Proj ect . Proposed rubble-mound breakwater. Burns 

 Waterway Harbor, Indiana. 



2_ Reference . Jackson (1967). 



3^ Laboratory . WES. 



4 Test Period . April to July 1966. 



5 Problem . Bums Waterway Harbor was proposed for 

 construction on the south shoreline of Lake Michigan, 15 miles east of 

 Indiana Harbor, Indiana, to consist of north and west breakwaters, east 

 and west outer bulkheads, inner bulkheads, and an outer harbor area with 

 east and west inner harbor mooring areas (Fig. 6-17). The harbor would 

 be exposed to storm waves from the northerly directions with heights to 

 about 13 feet and periods to about 11 seconds. The maximum water depth 

 along the toe of the breakwater was about 43 feet referred to low water 

 datum (LWD) for Lake Michigan and the selected high water level for test- 

 ing was +4 feet LWD. 



6^ Purpose of Model Study . The model study was con- 

 ducted to determine the stability of the proposed breakwater designs, to 

 develop alternate designs if necessary, and to investigate the effective- 

 ness of the proposed breakwater in reducing transmitted wave energy. Two 

 basic designs were investigated, one with tribar armor units and the other 

 with generally rectangular limestone blocks from quarries near Bedford and 

 Bloomington, Indiana. Since the majority of the proposed designs involved 

 a protective cover layer of the limestone blocks, determining whether this 

 type of stone (in the sizes and shapes available) could provide the re- 

 quired stability using the random-placing technique was desired. 



7_ The Model . Stability and wave transmission tests 

 were conducted with section models of the proposed structures in a wave 

 flume 119 feet long, 5 feet wide, and 4 feet deep. A plunger- type wave 

 generator was used and wave heights were recorded using two-wire resistor 

 rods, an amplifier and control system, and an oscillograph similar to the 

 one shown in Figure 6-15. The model was designed and operated based on 

 Froude's law. The linear scale of the model was 1:35, model-to-prototype. 



370 



