mlw), and five 2-min runs at each of the three highest water levels. As in 

 the earlier set of tests, multiple runs of short duration were used at the 

 highest water levels to allow the overtopped water to be returned to the 

 flume to maintain the swl. 



Determination of model profile 



The existing 1:30 concrete slope in the 18-in flume did not match the 

 beach survey taken after the 1978 storm. Therefore, an entirely new pro- 

 file was constructed and installed seaward of the existing concrete slope. 



The beach profile was displayed on a computer screen and an idealized 

 profile was determined by matching a series of straight lines to the actual 

 profile as closely as feasible, including a horizontal line to use as the 

 flume bottom. The actual profile and the idealized profile are shown in 

 Figure 6. 



With the depth at the flume bottom determined, model scale was estab- 

 lished by limitations of the wave generator. The wave generator was un- 

 able to generate the required signals at scales larger than 1 :20; therefore, 

 the model was constructed at a 1:20 scale. 



The idealized profile was constructed of plywood and placed in the 

 wave flume over the concrete slope. When the slope was within 0.75 in. 

 of the flume bottom (thickness of the plywood), 20-gauge sheet metal was 

 used to extend the slope to the bottom of the flume. A vertical seawall 

 was placed at the top of the plywood slope. Water overtopping the sea- 

 wall accumulated behind the seawall and was pumped into a separate can- 

 ister for accurate measurement of the overtopping volume at the end of 

 each test run. 



Results 



Overtopping rates for the first set of conditions tested are listed in 

 Table 1 ; overtopping rates for the repeated storm profile are listed in 

 Table 3. Data in the tables have been converted to prototype scale. 



To determine total overtopping during the storm, it was assumed that 

 the overtopping rate determined for a given point in the storm profile was 

 constant over the time period extending from half-way between the given 

 point and the preceding point to half-way between the given point and the 

 following point. Because data were available at every 1-hr interval of the 

 storm, overtopping rates at the first and last points tested were assumed to 

 exist for 1/2 hr before and after the point tested, respectively. Multiplying 

 the overtopping rate for a tested point in the storm profile by the length of 

 time the storm was assumed constant at those conditions yielded the vol- 

 ume of overtopping for that test per foot of seawall, and multiplying by the 

 length of seawall contributing to the flood zone yielded the total volume 



Chapter 3 Research Tasks A, B, and C 



13 



