profile and where wave forces may act on a structure (EM 1110-2-1617). The 

 use of water levels in structural design is described in Chapter 4. 



Water level variations are caused by astronomical tides, storm tides, and 

 for the Great Lakes, long-period hydrologic factors and seiches. Design water 

 levels are usually described statistically in terms of the frequency, or 

 probability that a given water level will be equaled or exceeded, or its return 

 period in years. The design may also include storm surge with a specified 

 return period, and/or may account for increased water levels due to sea level 

 rise. Detailed information on the prediction of tides and storm surges is 

 provided in EM 1110-2-1414, Water Levels and Wave Heights for Coastal 

 Engineering Design, and EM 1 1 10-2-1412, Storm Surge Analysis and Design 

 Water Level Determination. 



As described in EM 1110-2-1617, water level data for coastal areas are 

 available from the National Oceanic and Atmospheric Administration's 

 (NOAA) National Ocean Service (NOS) for areas where NOAA operates tide 

 gauges. Tide tables containing water level information are published annually 

 by NOAA. Data on historical water levels of the Great Lakes are available 

 from NOS and from sources such as the USAED, Detroit (for example, 

 USAED, Detroit (1986)), which provides monthly summaries of actual and 

 predicted lake levels. Other sources of water level data include USACE 

 General Design Memoranda for specific project sites and Federal Emergency 

 Management Agency flood insurance studies. Water level statistics for the 

 east coast are presented in Ebersole (1982), and in Harris (1981) for predicted 

 astronomical tides. 



Waves 



Wave data are required for both the functional and structural design of 

 detached breakwaters. Structural design generally focusses on larger waves in 

 the wave climate, whereas functional design examines a complete data set and 

 includes smaller waves that can cause sediment transport. Data requirements 

 for structural design are discussed in Chapter 4. 



Waves primarily control beach planform development at a breakwater 

 project since they contribute to both cross-shore and longshore sediment 

 transport. For functional design, time series of wave height, period, and 

 direction are needed for determination of longshore transport rates in the 

 vicinity of the project. Incident wave heights, periods, and direction are also 

 used to determine wave conditions in the lee of the breakwater and to estimate 

 the resulting beach planform. The average, extremes, and seasonal variability 

 of the waves define the energy available for sediment transport. However, the 

 equilibrium beach planform is generally determined by the average range of 

 conditions rather than extreme events. The prevailing wave direction will 

 generally determine shoreline orientation as the shoreline aligns itself parallel 

 with the wave crests (see Figure 21). If wave direction changes and persists 



Chapter 2 Functional Design Guidance 



33 



