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L__1 Beth MitcheU._And_4Don Donaldson March 24;'3995 Page 3 As agreed, the numerical model was supposed.to incorporate the laboratory results obtained by the University of Florida during the physical model study. This has not been accomplished, which prevents the model from incorporating or predicting the ponding and associated currents. To proceed with the project based on modelling which has not been validated by existing available data is not good engineering or scientific practice. it is not clear why wave refraction around the ends of the segments was not incorporated into the model. Refraction, along with the reflection phenomena is a potentially important factor which could affect patterns of erosion and deposition along the shoreline. The model fails to incorporate the pumping mechanism due to the use of a negative water level set-up inside the surf zone. This is caused by the assumed wave reduction of the reef. There apparently is no consideration for the constriction of flow caused by the presence of the reef units. Because of these assumptions, the numerical model is fundamentally flawed. Therefore, the Department cannot use the numerical model to make decisions as to the probable performance of the proposed project, especially in the lee of the proposed structure. No data or analysis has been presented that would indicate that the proposed project would not accelerate erosion an has occurred with the Midtown PEP reef. There are concerns regarding the boundary conditions used in the modelling. On page to a -"periodic" boundary condition is described. Was it used? What was the effect of the periodic boundary condition? On page 15, closed boundary conditions are described which are not realistic. Why couldn't open boundary conditions be used? What effects do these closed boundary conditions have on the model results? on page 23, it is stated that bathymetric changes predicted by the model are not "updated" based on "accumulated" elevation changes and therefore results are only "qualitative". How can these results, then, be considered sufficient for drawing conclusions about the reef? 7. This item requested a written response discussing how the proposed project addresses'the six recommendations contained in the physical model report by the University of Florida. Based on the reasons cited below, the Department disagrees that the County has considered and adequately responded to the recommendations contained in'the physical model report. This item remains 25 MARCH 28, 1995 BOOK 94 PA 70 7 07