Structure I was built during wave action from the first layer of bags 

 to the last and demonstrated that sandbags could be dropped through waves 

 in a pattern with little dispersion. After the successful construction of 

 structure I, the effect of wave action was considered of little importance 

 and subsequent structures were built through still water. For structures 

 11, 111, and IV, replacement of damaged bags and placement of the first 

 layer were accomplished before the tank was refilled with water. These 

 three breakwaters were not subjected to wave action until the day following 

 completion of construction through still water, allowing at least 16 hours 

 for the bags to leak the trapped air. 



4. Wave Conditions . 



From the tank calibration curves, the four generator settings that 

 produced wave heights closest to 4 and 6 feet (1,22 and 1.83 meters) for 

 wave periods of 6 and 10 seconds were selected to produce the test waves. 

 The test conditions were scheduled in the order of increasing wave energy. 

 In each test the structure was subjected to approximately the following 

 wave conditions (structure IV was subjected to only the first three con- 

 ditions), as measured at station 0-46 during calibration: 



Condition 



Height 



:, H^ 



Period, 



T 





(ft) 

 4.0 



Cm) 

 (1.22) 



(s) 





a 



6 





b 



3.9 



(1.19) 



10 





c 



5.8 



(1.77) 



6 





d 



5.7 



(1.74) 



10 





The calibration wave heights, measured without a breakwater in the 

 tank, were considered to be the incident wave heights, H^, and were 

 compared with transmitted wave heights, Ht, measured at station 0-46 with 

 a structure in the tank. During each test and at various times during each 

 wave condition, the wave heights shoreward and seaward of the structure 

 were measured visually and electronically to the nearest 0.1 foot. The 

 transmitted wave height was calculated as the average of wave heights mea- 

 sured shoreward of the breakwater during a wave condition or, at the begin- 

 ning of test III, before a radical change in the structure configuration. 

 The attenuation factor, A, was defined in dimensionless form as: 



A - "^ - ^^ . 



The procedure for generating waves was determined by the severity of 

 wave reflection from the test structure and of resulting changes in the 

 wave conditions. Structures I and 11 produced little wave reflection, 

 permitting waves to be generated continuously for up to 2 hours. In con- 

 trast, the higher crested structures of tests III and IV produced 



27 



