Wave hindcast data and 

 selection of experimental waves 



Measured prototype data covering a sufficiently long duration from which to 

 base a comprehensive statistical analysis of wave conditions were unavailable for 

 the Nome Harbor area. However, a wave hindcast study was developed based on 

 wind data in the area to define the wave climate (Applied Coastal Modeling 1997) 

 at the Nome Harbor site. The objective of the hindcast was to define the general 

 range of wave heights, periods, directions, and frequencies of occurrence at the 

 project site. In general, the study indicated a relatively moderate wave climate at 

 Nome with wave periods 12 sec or less, and heights 2 m (6.6 ft) or less 

 occurring about 95 percent of the time (when waves are present). Waves up to 

 6 m (19.7 ft) in height, however, may occur on a 50-year recurrence interval. In 

 addition, the study indicated that waves approach from a southwesterly sector 

 about 66 percent of the time (when waves are present). Model experiments were 

 actually initiated prior to completion of the hindcast study. The Alaska District 

 initially selected the following wave conditions for use in the model investigation, 

 which cover a large range of wave directions, periods, and heights. However, 

 upon completion of the hindcast, the number of wave conditions was reduced. 



Unidirectional wave spectra were generated based on Joint North Sea Wave 

 Project (JONSWAP) parameters for the selected waves and used throughout the 

 model investigation. Typical wave spectra are shown in Figure 7. The solid line 

 represents the desired spectra, while the dashed line represents the spectra repro- 

 duced in the model. Figure 8 is a typical wave train time series. Selected waves 

 were defined as significant wave height, the average height of the highest one-third 

 of the waves or H 5 . In deep water, H s is very similar to H mo (energy-based wave) 

 where H mo = 4 (E) 1/2 , and E equals total energy in the spectra, which is obtained by 

 integrating the energy density spectra over the frequency range. 



River discharges 



The Snake River runs generally southerly from the mountains and turns easterly 

 near the Norton Sound coast. It flows through the currently authorized turning basin 

 and the existing sheet-pile-lined navigation channel into Norton Sound. The mean 

 annual discharge measured by the U.S. Geological Survey is 5.4 cms (190 cfs) 

 northeast of Nome (USAEDA 1996). The typical maximum monthly mean flow 

 occurs in June following the spring snowmelt. After the summer rains, progres- 

 sively lower discharge peak flows occurs, and discharge continues to decline 

 through the winter. During the period 1965-1991, the Snake River's maximum 

 monthly mean discharge was 47 cms (1,655 cfs). The mean annual discharge of 5.4 

 cms (190 cfs) was selected for use during all model experiments. 



14 Chapter 3 Experimental Conditions and Procedures 



