that the erosion volume (above the surge level) be increased by 5 to 10 

 percent for each hour (over 5) that the storm surge is within 1 m of the peak 

 surge level (with a maximum increase of 50 percent). This suggested increase 

 is based on the results of long duration model tests with constant surge 

 level . 



71. Note that as a result of the simplicity of Equation 3, the post- 

 storm profile shape is dependent only on the prestorm profile, wave height, 

 surge level, and grain size. After a storm passes, only a larger storm, with 

 a higher surge level, will cause additional erosion. The model is based on 

 the assumption that the profile adjusts to equilibrium and that all sediment 

 movement is in the offshore direction (no gradients in longshore transport 

 and no overwash). The model does not account for the formation and movement 

 of bars and, in fact, Vellinga (1983b) noted that the model overpredicted the 

 erosion for model tests with offshore bars. 



72. Despite these limitations, the model has been shown to produce 

 reasonable dune erosion estimates (Vellinga 1983b, 1986, and Sargent and 

 Birkemeier 1985). Based on all available model and field data (Figure 13), 



600 



LEGEND 











> 



> 

 • 



/ y 









/ 



/ 



/ 



•a / 

 o / 



• 







• 

 V 



y •/ 



• 



i 



/ 



• 



V 







/ 



*y 



/ 







* 



$ 



V 



= 0.10 A s 20m 3 /m 











y 











• MODEL TESTS, SCALE SERIES 



O MODEL TESTS, VARIABLE HYDRAULIC 



CONDITIONS 

 O LARGE-SCALE TESTS, VARIABLE HYDRAULIC 



CONDITIONS 

 ■ FIELD MEASUREMENTS 1976 - STORM 



SURGE 



200 300 



MEASURED A. 



Figure 13. Predicted volume changes above-surge level versus measured 

 laboratory and field data (Vellinga 1983b) 



Vellinga (1983b) specifies the standard deviation of the predicted, above- 

 surge level, eroded volume A s as 



36 



