between the change in the input (cause) and resultant change in the output 

 (effect) for the specific project. 



Kl. K2. and median grain size 



399. Figure 44 shows the results of sensitivity tests examining changes 

 in the calibration parameters Kl and K2 and median grain size D50 . An 

 increase in Kl from 0.42 to 0.52 resulted in a slight increase in sand 

 volume inside the study area, but the shape of the shoreline was almost 

 identical to that in the verification. An increase in K2 from 0.12 to 0.22 

 produced more pronounced salients, as expected, but slightly more sand was 

 lost from the system than for the verification simulation. Both cases show 

 that the simulated change was only moderately sensitive to reasonable changes 

 in the calibration coefficients . 



400. Almost all of the material lost was removed from the beach section 

 adjacent to the western groin. The probable explanation for the localized 

 loss of sand is the bias for the transport to be from west to east because of 

 wave shadowing by Lorain Harbor; in other words, this is simply a downdrift- 

 groin erosion phenomenon. 



401. It is known that fill with a median diameter smaller than that of 

 the native material requires larger initial quantities to create the same 

 stable beach as a fill of larger diameter. However, the present structure 

 configuration is very efficient in preventing the beach from eroding. The 

 calculation using a median sand grain size 0.2 mm, half the diameter used in 

 the actual project, shows very pronounced salients behind two of the break- 

 waters and gives a net increase of sand of about 780 cu yd as compared with 

 the net loss of 340 cu yd by using the actual grain size 0.4 mm. The finer 

 grain size produces a gentler equilibrium profile and places the breaker line 

 farther offshore. However, the structures were not moved offshore to their 

 depth of placement by changing the START file, making this example somewhat 

 unrealistic . 



402. It is important to note again that GENESIS does not take losses to 

 the offshore into account, which are expected to be greater for finer 

 material, and the model is expected to overestimate the performance of the 

 finer fill material. 



170 



