3 Experimental Conditions and 

 Procedures 



Selection of Experimental Conditions 



Still-water level 



Still- water levels (swl's) for wave action models are selected so that various 

 wave-induced phenomena that are dependent on water depths are accurately re- 

 produced in the model. These phenomena include refraction of waves in the 

 project area, overtopping of harbor structures by waves, reflection of wave 

 energy from various structures, and transmission of wave energy through porous 

 structures. 



In most cases, it is desirable to select a model swl that closely approximates the 

 higher water stages that normally occur in the prototype for the following reasons: 



a. The maximum amount of wave energy reaching a coastal area normally 

 occurs during the higher water phase of the local tidal cycle. 



b. Most storms moving onshore are characteristically accompanied by a higher 

 water level due to wind, tide, and storm surge. 



c The selection of a high swl helps minimize model scale effects due to 

 viscous bottom friction. 



d. When a high swl is selected, a model investigation tends to yield more 

 conservative results. 



Swl's of +0.5 and +4.0 m (+1.6 and +13.0 ft) were selected by the Alaska 

 District for use during the model experiments. The lower value (+0.5 m (+1 .6 ft)) 

 represents mean higher high water (mhhw) and was used while obtaining wave 

 heights, wave-induced current patterns and magnitudes, and sediment tracer patterns 

 in the vicinity of the harbor and causeway. The higher value (+4.0 m (+13.0 ft)) 

 represented extreme storm surge conditions and also was used for selected direc- 

 tions while securing wave height data, current patterns and magnitudes, and 



-| 2 Chapter 3 Experimental Conditions and Procedures 



