transforming the digitized data from latitude and longitude coordinates into the 

 engineering (lineal) distances in feet. To obtain depth data at nodal points, 

 interpolation and smoothing schemes were applied to the digitized bathymetry 

 data using three-dimensional surface contour mapping. 



Output 



Wave estimates by numerical model were made over the entire rectangular 

 computational domain. The grid origin was located in the northeast comer of 

 the model area with the x-axis pointing toward the coastline in the east-west 

 direction, and the y-axis nearly paralleling the north-south direction. As stated 

 earlier, numerical model results were output at a transect specified by the 

 physical model study task personnel. This output location is denoted by TR 3 

 and labelled on Figure Al, together with five other transects. TR 3 is oriented 

 approximately -60 deg to the grid setup, clockwise from the x-axis. Assuming 

 that some comparison of the physical model study with numerical model pre- 

 dictions may later be desirable, five other transects (TR 1, TR 2, TR 5, TR 6, 

 and TR 7) were selected for additional output. These transects are located just 

 north of the north jetty where erosion problems have been observed. 



A nodal point in the x-y two-dimensional grid space may be specified as 

 P(I,J), where I and J are the grid node or cell numbers in the x- and 

 y-direcUons, respectively. A line drawn over a grid hereafter called a transect 

 may either pass exactly through these grid points or be near them. The output 

 along a transect may therefore represent values at the nodal points or it may 

 correspond to the nearest neighboring nodes. Transect output may also corre- 

 spond to some average or interpolated value for several grid points assumed to 

 represent a given transect. The list output lor TR 3, approximately where the 

 wave generator is situated, includes all 25 nodal points on or close to the tran- 

 sect line from start to end. Example plots, on the other hand, show model 

 predictions for TR 3 for 10 nodal points on this transect. In summary, when 

 interpreting numerical model output, it is important to recognize that TR 3 is 

 arbitrary, and that points selected at equal intervals or randomly on this tran- 

 sect may not necessarily coincide with the actual grid points. This is not the 

 case for TR 1 and 2, which are along the x-axis (i.e., y=constant or 

 J=constant), and their output will tiierefore be at the nodal points. Likewise, 

 the output for TR 5, 6, and 7, which are along the y-axis (i.e., x=constant or 

 I=constant), is also at the actual nodal points. 



Description of Numerical IVIodel REFDIF 



REFDIF is a combined refraction/diffraction model based on Booji's (1981) 

 weak current parabolic approximation for Berkhoff's (1973) mild slope 

 equafion, where backward refiected waves are neglected, but forward reflected 

 waves are considered. Kirby and Dalrymple (1983a,b, and 1986a,b), Liu and 

 Tsay (1984), Kirby (1984 and 1986), Dalrymple (1988 and 1991), and 



Appendix A Saco Bay Nearshore Wave Estimates 



A13 



