A12 



High Head Peninsula and Richmond Island, both situated in the northeast side 

 of the modeling area, since diffraction and sheltering effects from land boun- 

 daries and bathymetry were not included in the WIS hindcast. By positioning 

 the offshore edge of the modeling region beyond WIS station 99, combined 

 effects of diffraction, refraction, and shoaling will properly be modelled by 

 REFDIF, especially for waves entering Saco Bay from the northeast or the 

 straight in east directions. 



The bathymetry for Saco Bay was digitized from NO A A chart 13287 

 (1:20,000 scale), dated April 11, 1981. Data from bathymetric surveys were 

 later incorporated to supplement the chart information. This included survey- 

 ing data for the area north of the north jetty. Boundaries of the modeling 

 domain covered a rectangle 21.8 x 19.4 sq km (8.4 x 7.5 square miles) in size, 

 with the following coordinates: southwest comer (70° 24' W, 43° 26.2' N), 

 southeast comer (70° 12.5' W, 43° 26.2' N), northwest comer (70° 24' W, 

 43° 33.7' N), and northeast comer (70° 12.5' W, 43°33.7' N). Between 

 70° 20' W and 70° 18' W, the nearshore bathymetry was digitized using each 

 depth sounding value available from the NOAA chart. Large and small islands 

 present inside this sub-region, including Basket Island, Stage Island, Negro 

 Island, Wood Island, Gooseberry Island, Ram Island, Bluff Island, and Stratton 

 Island were defined as land boundaries in the input bathymetry file. The 

 Prouts Neck to north side extruding into the area of interest was also dis- 

 crefized in the input data. From 70° 18' W to the deepwater offshore edge of 

 the modeling region, bathymetry was digitized using every other depth value 

 from the chart. Length scales for the x- and y-axes of NOAA chart 13287 are 

 1.17 and 1.6 km (0.73 and l.(X) mile) per minute of longitude and latitude, 

 respectively. On-offshore extent of the model domain was 15,545 km 

 (51,000 ft) and alongshore extent of the model domain was 14,020 m 

 (46,000 ft). 



Next, the REFDIF model parameters related to the size of the modeling 

 area were determined. Grid spacing of 152 m (500 ft) (Ax = Ay = 500.0 ft) in 

 the X- and y-directions was used. These grid spacings are adequate for wave 

 modeling transformation in the Saco Bay for the range of wave periods listed 

 in Tables Al and A2. The total number of nodes in the x- and y-directions 

 are 102 and 91, based on these grid sizes. However, to ensure computational 

 accuracy of the numerical model predictions, these 152-m (5(X)-ft) nodal spac- 

 ings were further divided into finer increments in the x- and y-directions by 

 specifying certain model input parameters. Actual computafions in the 

 REFDIF model were made with grids ranging from 3 to 7.6 m (10 to 25 ft), 

 depending on wave periods. This model requires six or more grid points per 

 wavelength, and its predictions improve if this condition is met. In terms of 

 computing and storage needs, this requirement may force mnning the model on 

 large and fast computer platforms for large domains. The CRAY Y-MP com- 

 puter was used in this study. 



With the excepUon of digitizing the NOAA chart with the AUTOCAD 

 program, all numerical modeling tasks of this study were performed on the 

 CRAY Y-MP computer. Interface software was developed and tested for 



Appendix A Saco Bay Nearshore Wave Estimates 



