sheet-aluminum screeds were used alongshore. Harbor structures in the 

 model are constructed of various materials depending on the type of pro- 

 totype structure. Rubble-mound breakwaters, jetties, and wave absorbers 

 are constructed of quarrystone or concrete blocks, and the sizes of the 

 material are adjusted as necessary to obtain approximate similarity of 

 wave reflection and transmission coefficients. Impervious, vertical -wall 

 breakwaters and jetties are reproduced in concrete, and piers supported 

 by piles are reproduced using a sheet metal or wood top with heavy-gage 

 wire or solder rod used as piling. The perimeter walls of the model are 

 usually constructed of brick. A freshwater supply is preferable because 

 of the necessity to keep the model as clean as possible. Leakage of water 

 from the model is minimized by an elastic sealer which is applied to the 

 upper part of the templets and in all joints and cracks in the model. 



b. Operation . 



(1) Short-Period Wave Models . Before actual model operation is 

 begun, prototype wave data for deepwater conditions are transferred to 

 the outer contour limits of the model by wave-refraction techniques; the 

 wave directions and heights for the range of wave periods that occur in 

 nature and are important to the problems under consideration, are then 

 selected for use in the investigation. The dimensions and directions 

 selected for the test waves must ensure a realistic test of the improve- 

 ment plans proposed or devised during the model study to permit accurate 

 determination of the optimum plan. In most harbor model studies the 

 reproduction of tidal variations in the water surface is unnecessary. 

 Therefore, it is customary to use selected Stillwater levels for the 

 different tests. The Stillwater levels should be selected so that the 

 various wave-induced phenomena that are dependent on water depths are 

 accurately reproduced in the model. These phenomena are the refraction 

 of waves within the harbor area, the overtopping of harbor structures by 

 wave action, the reflection of wave energy from harbor structures, and 

 the transmission of wave energy through porous structures. A few of the 

 most important factors contributing to selection of the optimum model 

 Stillwater level are: (a) The maximum amount of wave energy that can 

 reach a given area will ordinarily do so during the period of a severe 

 storm that coincides in time with the highest water level normally ex- 

 perienced in the area; (b) severe storms moving onshore are character- 

 istically accompanied by an additional increase in the normal water level 

 due to wind setup and mass transport, whereas storms moving offshore tend 

 to lower the water level; and (c) a relatively high Stillwater level in 

 the model is beneficial in minimizing the effects of bottom friction, 

 which can be excessive in shallow areas of small-scale models. There- 

 fore, in consideration of the various factors contributing to and 

 affected by the Stillwater level in the prototype, and in view of the 

 tendency toward more conservative results from the model investigation, 

 a model Stillwater level should be selected that closely approximates 

 the higher water stages that normally prevail during severe storms in 

 the prototype. This entails the study of water level records in the 

 prototype locality, with proper attention given to the higher levels 

 experienced in the area in the past. The test data obtained during the 



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