surveys selected for modeling. Therefore, a value indicating no beach fills 

 was given on this line. 



Data for the SHORL files 



372. There are several ways of obtaining shoreline positions, for 

 example, from closely spaced beach profile surveys, shoreline surveys, 

 stereoscopic photogrammetry, and controlled aerial photography. Numerous sets 

 of vertical aerial photographs were available to this study for which the 

 water level was known. From these photographs, the shoreline position was 

 digitized with respect to an arbitrary straight baseline drawn along the 

 revetment and parallel to the trend of the coast. The digitization was done 

 by hand because the longshore extent was short. Through a field investi- 

 gation, the average distance between the contour defining the water level and 

 a shoreline datum was determined for representative portions of the modeled 

 beach. These distances were then added to or subtracted from the distances 

 determined in the digitizing operation. 



373. Aerial photographs were available for biannual flights flown 

 between 1 October 1977 and 18 September 1984. Among these, three were chosen 

 for use in this case study: 24 October 1977, 9 October 1978, and 17 November 

 1979. No beach fills were placed between October 1977 and 1980, making this 

 period uncomplicated and most suitable for simulations. The scale on the 

 available photographs was about 1:2,300 as determined from known lengths of 

 structures; these photographs were enlarged to a scale of 1:1,500 for hand 

 digitization, allowing shoreline position to be determined to the nearest 

 foot. An average error of 1 ft in shoreline position corresponds to a 

 volumetric error of 1,100 cu yd [(8+16)1,250/27]. 



374. Pope and Rowen (1983) reported average lake levels for the dates 

 of the selected aerial photographs to be 2.6, 2.4, and 2.5 ft, respectively. 

 The initial slope of the fill was 1:5, gradually approaching 1:12 during the 

 first 6 months after placement. By using an average foreshore slope of 1:12, 

 horizontal distances of 31.2, 28.8, and 30.0 ft, respectively, were added to 

 the digitized positions to estimate the true location of the shoreline. As 

 GENESIS cannot account for this transient profile adjustment, the transition 

 from the steeper to the gentler slope was assumed to have taken place at the 

 start of simulation on 24 October 1977. This transition was schematized and 



158 



