made by determining the wave-energy transmission characteristics of the pro- 

 posed structure in a two-dimensional model using a scale large enough to 

 ensure negligible scale effects. A section then was develop)ed for the small- 

 scale, three-dimensional model that would provide essentially the same relative 

 transmission of wave energy. Therefore, from previous findings for structures 

 and wave conditions similar to those at Saco River and Camp Ellis Beach, it 

 was determined that a close approximation of the correct wave-energy trans- 

 mission characteristics could be obtained by increasing the size of the rock 

 used in the l:l(X)-scale model to approximately two times that required for 

 geometric similarity. Accordingly, in constructing the rubble-mound structures 

 in the Camp Ellis Beach model, rock sizes were computed linearly by scale, 

 then multiplied by two to determine the actual sizes to be used in the model. 



Ideally, a quantitative, three-dimensional, movable-bed model investigation 

 would best determine the erosion and sediment patterns at Camp Ellis Beach. 

 However, this type of model investigation is difficult and expensive to con- 

 duct, and each area in which such an investigation is contemplated must be 

 carefully analyzed. TTie following computations and prototype data are con- 

 sidered essenfial for such investigations (Chatham, Davidson, and Whalin 

 1973): 



a. Computation of the littoral transport, based on the best available wave 

 stafisfics. 



b. Analysis of the sand-size distribufion over the entire project area 

 (offshore to a point well beyond the breaker zone). 



c. Simultaneous measurements of the following items over a period of 

 erosion of the shoreline (this measurement period should be judiciously 

 chosen to obtain the maximum probability of erosion during as short a 

 time span as possible): 



(1) Continuous measurements of incident- wave characteristics. Such 

 measurements would mean placing enough redundant sensors to 

 accurately estimate the directional spectrum over the entire project 

 area, and in addition, would mean conducting a rather sophisti- 

 cated analysis of all these data. 



(2) Bottom profiling of the entire project area using the shortest time 

 intervals possible. 



(3) Nearly continuous measurements of both littoral and onshore- 

 offshore transport of sand. A wave-forecast service would be 

 essential to this effort to prepare for full operation during the 

 erosion period. 



As indicated, large amounts of prototype data are needed to conduct movable- 

 bed model studies. These data were non-existent for the Camp Ellis Beach 

 area. Currently, state-of-the-art in movable-bed modeling tends to be restricted 



Chapter 2 The Model 



