Calibration and Verification 



89. Model calibration refers to the procedure of reproducing with a 

 model the changes in shoreline position that were measured over a certain time 

 interval. Verification refers to the procedure of applying the calibrated 

 model to reproduce changes measured over a time interval different from the 

 calibration interval. The terms "calibration" and "verification" are often 

 referred to as "verification" alone, since verification implies that calibra- 

 tion has been done. Successful verification is taken to indicate that model 

 predictions are independent of the calibration interval (i.e., that the 

 empirical coefficients and boundary conditions remain constant for the coast) , 

 but it does not guarantee this independence, and conditions can easily change, 

 which will void the verification process. For example, a boundary condition 

 of unrestricted sand transport (pinned beach) may change to a gated boundary 

 condition after construction of an entrance channel through the beach. The 

 modeler must be aware of significant changes in the physical situation that 

 might invalidate the original verification and require new verification. 

 Also, the available wave data set may better represent the wave climate that 

 existed during some calibration and verification periods than other periods. 



90. In practice, data sets sufficiently complete to perform a rigorous 

 calibration and verification procedure are usually lacking. Typically, wave 

 gage data are not available for time intervals between available measured 

 shoreline positions, and unambiguous and complete data on historical shoreline 

 change are often unavailable. This situation increases the number of unknowns 

 in the modeling process and thereby reduces reliability of the calculation. 



In the absence of hard data, estimates of shoreline change with the model may 

 provide the only source of systematic and quantitative information with which 

 to make planning decisions. In situations where data are lacking, coastal 

 experience and experience with GENESIS must be relied upon to supply reason- 

 able estimates of input parameters and to interpret calculated results. 



91. Model predictions are readily compared by graphical means. Plots 

 are made of calculated and measured shoreline positions, normally at exag- 

 gerated vertical scales (shoreline position coordinate). Shoreline positions 

 can also be manipulated mathematically to determine in a least-squares sense, 



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