Conclusions and 

 Recommendations 



Conclusions 



Failure to obtain incident wave data outside the harbor had a negative impact on 

 analysis of some of the other data collected during the monitoring effort. Incident 

 wave data were required for correlation with wave data obtained inside the harbor, 

 wave runup, and wave overtopping data to validate design methods and procedures. 



Wave height data obtained inside the harbor (from the Unisea vessel) appeared 

 to validate the three-dimensional model study. Maximum significant wave heights 

 measured in the immediate lee of the main breakwater during storm wave events 

 were in agreement with those predicted during the physical model study. 



The videotape analysis used to obtain wave runup data along the face of the 

 St. Paul Harbor main breakwater was successful, except during periods of low 

 visibility. The technique is relatively low cost, logistically simple, and provides 

 relatively accurate measurements. 



Trends in wave hindcast data obtained outside the harbor (to define incident 

 wave conditions) correlated reasonably well with runup data in a qualitative sense 

 (i.e. larger wave heights correlated with higher runup and smaller wave heights with 

 low runup). The absolute values of the hindcast significant wave heights, however, 

 appeared to be substantially lower than the waves experienced in the prototype 

 based on runup values measured, overtopping observed, and local forecasts. 



Since construction of breakwater improvements, a scour hole has formed at the 

 head of the main breakwater extension, sediment has accumulated north of and 

 adjacent to the detached breakwater (forming an underwater spit that is migrating 

 toward the entrance channel), and sediment has moved into the harbor between the 

 detached breakwater and the shoreline. To this point, the scour hole has not 

 impacted the structure's stability, nor has the imderwater spit interfered with 

 navigation. Accretion inside the harbor has not occurred in the federal channel or 

 mooring areas. Sediment patterns in the harbor, as predicted by the three- 

 dimensional model, were validated by the prototype data. 



Chapter 3 Conclusions and Recommendations 57 



