3. Reach B . 



Reach B (Fig, 9) extends 1.62 kilometers from the southern edge of reach A 

 to the Chalet on the Lake housing development. The sand bluff decreases in 

 elevation from about 15 meters at the northern end to less than 3 meters at 

 the southern end. Except for reach D, reach B is the most heavily developed 

 reach with 28 houses, one-half of which are between stations 22 and 42 where 

 a 5 79-meter-long seawall was constructed during the study. The sequence of 

 development of the seawall is important in understanding the changes that 

 occurred along reach B. 



To facilitate analysis, reach B is divided into five areas. Station 13 

 (Fig. 10) is approximately the same location as CERC profile line 16 discussed 

 by Davis, Fingleton, and Pritchett (1975) and Davis (1976). The section be- 

 tween stations 14 and 22, referred to as the "downdrift cut," is located imme- 

 diately downdrift (south) of the long seawall (Fig. 11) which protects the 

 shoreline between stations 23 and 41. North of the seawall, between stations 

 42 and 46, is a high, unprotected and lightly vegetated sand dune (Fig. 12). 

 Two smaller seawalls, one 91 meters long between stations 47 and 50 and one 

 30 meters long at station 54, are in the northern end of the reach. Both of 

 these seawalls were constructed before the beginning of this study. 



Figure 13 shows reach B as it appeared in November 1970. Note the absence 

 of a beach in front of the sand dune area. A beach averaging 11 meters wide 

 fronts the seawall area; a similarly wide beach also fronts the downdrift sta- 

 tions. The shoreline is straight from the 91-meter seawall southward. The 

 existence of two seawalls at the bluff toe in the area where the long seawall 

 will be built is an indication of previous erosion. 



Figure 14 shows the rates of bluff recession and shoreline change along the 

 reach for the same time periods as reach A. Vertical lines separate the areas 

 shown in Figure 12. 



During the first period, November 1970 to April 1971, the average bluff 

 recession rate for the full reach was 4.3 meters per year. However, most of 

 the recession occurred in two areas of the reach--the dune area between stations 

 40 and 47 and the area between stations 21 and 27. By April 1971, construction 

 of a concrete seawall had started in the vicinity of station 32. The width of 

 the beach gradually increased from zero at the northern end of the reach to 

 about 14 meters at the southern end. 



Construction of the full length of the seawall was completed by November 

 1971, though not in the final steel sheet -pile form. Bluff recession was 

 moderate from April to November 1971, averaging only 1.1 meters with the dune 

 section retreating the most. Beaches had narrowed in front of the seawall while 

 a beach up to 30 meters wide appeared in front of the dune. 



Major changes occurred between November 1971 and April 1972. The beach in 

 front of the dune disappeared along with 8 meters of the dune bluff. The bluff 

 behind the seawall retreated less than the dune area and the downdrift cut be- 

 gan to form. The bluff near station 13, south of the cut, was unchanged prob- 

 ably due to the relatively wide beach between stations 1 and 16. The average 

 recession rate for the reach was 6.8 meters per year. 



24 



