Profile line 8 also experienced relative stability during the early years 

 and considerable recession during 1974 (see Fig. 9). A possible cause was the 

 concrete "road debris" revetment placed just north of the profile line where 

 the road bends very close to the lake. The recession at profile line 8 con- 

 tinued after December 1974, with an additional loss of 4 meters recorded in 

 May 1976 during a field trip to the area. 



5. Bluff Composition . 



If the average volume changes given in Table 4 are recomputed without pro- 

 file lines 4 and 16, they provide some insight into the effect of bluff compo- 

 sition. The average volume lost by the 15 profile lines was 27.8 cubic meters 

 per meter, which is almost equal to the median amount of 28.1 cubic meters per 

 meter. 



Of the three profile lines with till bluffs (13, 15, and 17), only profile 

 line 13 eroded less than the mean volume, while profile line 15 eroded the 

 most of all 15 profile lines. The three profile lines with mixed sand and 

 till (5, 7, and 10) all eroded an amount nearly equal to or less than the 

 mean. 



Although on the average, till or mixed sand and till bluffs appear to 

 erode less than pure sand ones, the data are inconclusive. Profile line 11, 

 which has a low sand bluff, eroded the least of all profile lines, followed 

 closely by the sand bluff at profile line 2. Any clear difference between the 

 erodibility of sand and till bluffs is probably obscured in other factors; 

 e.g., differences in ground waterflow, vegetation, offshore bathymetry, and 

 wave climate between profile lines. 



VI. BEACH SEDIMENTS 



During the last 15 months of surveys (October 1973 to December 1974), ex- 

 cept when ice prevented it, surface sediment samples were collected from the 

 beach face (foreshore) and from the base of the dune or bluff (backshore) at 

 each profile line. Because the beach sediments are glacial derived, they 

 include a wide range of sediment sizes from fine silt to coarse pebbles. This 

 variation in sediment size is obvious in the photo of the beach at profile 

 line 2 (Fig. 14). 



In order to better understand the nature of the sediments, an attempt was 

 made to collect representative surface samples. This differed from Davis, 

 Fingleton, and Pritchett (1975) and Davis (1976) who collected and reported 

 only on sand-size sediments. A total of 246 foreshore and 273 backshore sam- 

 ples were collected. The laboratory analysis consisted of (a) wet sieving the 

 silt (less than 0.062 millimeter) from samples with significant silt content, 

 (b) dry sieving the remaining sample into sand (between 2.0 and 0.062 milli- 

 meter) and gravel (greater than 2.0 millimeters) fractions, (c) computing the 

 dry weight of each size fraction, and (d) using a visual accumulation tube to 

 obtain the size distribution of the sand. In addition, a visual estimate was 

 made of the percentage of heavy minerals in the sand fraction. The sand-size 

 distribution was plotted to graphically determine the "median sand size." 

 Median sand size is defined as the size (in millimeters) that divides the sand 

 fraction so that half, by weight, is coarser than the median size and half is 

 finer. 



30 



