(average of highest one third of the ranup values). Wave runup periods also were 

 obtained from the time series. 



Wave overtopping 



To measure and quantify wave overtopping at the St. Paul Harbor main break- 

 water during storm wave events, a water collection container placed in the lee of the 

 structure and flow meters were used. An open top container, approximately 12.2 m 

 X 3 m X 2.4 m (40 ft x 10 ft x 8 ft), was modified to serve as a collection box for 

 waves overtopping the breakwater. The container was lined with metal to prevent 

 leakage and included 20.3-cm (8-in.) pipes, extending from its base, in which flow 

 meters were installed to determine flow rates. 



During the period 25 through 30 August 1 994, a crew of WES personnel visited 

 St. Paul Island to prepare a concrete slab to be used as a base for the container, to 

 install the container, and to construct an apron from the top of the container up the 

 breakwater slope. Heavy equipment was rented from the City of St. Paul. A 

 20.3-cm (8-in.) reinforced concrete slab was initially constructed in the lee of the 

 breakwater (sta 8+20 - 8+60). The open top container then was placed on the slab 

 and anchored into position with chains. An apron extending from the top of the 

 container up the slope of the breakwater then was constructed to direct overtopping 

 volumes into the container. The apron consisted of 10.2 cm x 10.2 cm (4 in. x 4 in.) 

 wooden frames and bracing with a metal skin attached to the framing. A view of the 

 completed container setup is shown in Figure 19. 



To measure overtopping rates, ultrasonic flow transducers were mounted to the 

 3. 1 -cm (8-in.) pipe at the base of the container and connected to a recorder (Fig- 

 ure 20). By knowing the water level in the container at the beginning and end of a 



Figure 1 9. View of collection box used for measurement of wave overtopping 



Chapter 2 Monitoring Program 



25 



