Enough data should be obtained during prototype data acquisition to 

 verify that the hydraulic model accurately reproduces the prototype fea- 

 tures of interest. Thus, it is essential that the prototype data of 

 bottom evolution (erosion, accretion, and littoral transport) are accu- 

 rate and that the corresponding incident wave conditions (height, period, 

 and direction) are known. 



Initial verification efforts should be directed toward reproducing 

 the most severe short-term prototype erosion. Hopefully, this would com- 

 prise a storm period of perhaps 1 to 2 days where the wave direction re- 

 mained relatively constant and only a slow variation in height and period 

 occurred. If adequate prototype data were acquired on the erosion rate 

 and littoral transport rates, then attempts can be made to verify the 

 short-term erosion properties of the hydraulic model. However, numerous 

 problems will arise and the sensitivity of the erosion response of the 

 model must be correlated with changes in incident wave characteristics 

 (height, period, and direction). The model response must not vary sig- 

 nificantly within the accuracy of prototype measurements of wave height 

 and bottom evolution. If significant model variations are recorded with- 

 in the accuracy of the verification data, then either the prototype data 

 quality must be improved or the model is too sensitive, and different 

 scales and model materials are probably required. 



After verification of short-term, large-scale erosion characteristics, 

 verification of shoreline accretion is necessary. This is usually a 

 longer term process and may be interrupted by changes in wave direction 

 and possibly by either small or large storms causing additional erosion. 

 An effort should be made to precisely reproduce the prototype wave and 

 tide characteristics during this period. Successful verification of the 

 accretion phase of the prototype measurement period is a major step. 

 Littoral transports are also measured and correlated with the prototype 

 data taken during these periods. 



The next phase of the model verification is to ascertain if correct 

 littoral transport rates are occurring. There will be some periods during 

 the prototype data acquisition phase where waves are at an extreme angle 

 to the shoreline. If the wave heights are significant, then a rapid long- 

 shore transport of material will take place. 



Finally, verification of the prototype beach behavior for the entire 

 measurement period should be attempted. If this is accomplished, the 

 investigator can then be confident of the hydraulic model results. 



Although this brief discussion of model verification does not include 

 the numerous problems involved, it is considered adequate for the present 

 state-of-the-art . 



b. Operational Constraints of the Model . Any scale-model investiga- 

 tion has its limitations and operational problems; however, a completely 

 movable-bed scale-model study contains more than its share of operational 

 problems. Some of these problems and constraints are: 



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