March 1973 storm). Most of this change is attributed to the single storm, a 

 fact supported by Johnson and Hiipakka (1976) who noted the severity of the 

 1972-73 storm season and its effect on bluff erosion near the powerplant. 

 Davis (1976) reported that between August 1970 and July 1973 the largest total 

 monthly change occurred between 11 March and 14 April 1973. 



4. Littoral Material and Transport . 



Littoral material is supplied by the eroding bluffs and dunes. Depending 

 on bluff type, only 20 to 49 percent of the eroded bluff material is suitable 

 beach material (Beach Erosion Board, 1956). Beaches are composed of fine 

 quartz sand (diameter between 0.20 and 0.30 millimeter) with occasional deposits 

 of heavy minerals and gravel. 



The estimated net littoral transport rate for St. Joseph Harbor (north of 

 the study area) equaled 76,460 cubic meters (100,000 cubic yards) per year 

 (Beach Erosion Board, 1956) . This estimate was based on profile changes (from 

 the bluff to the 6-meter depth contour) and on the volume trapped by the harbor 

 jetties between 1907 and 1954. A subsequent study by the U.S. Army Engineer 

 District, Detroit (1973) updated the data but quoted the same transport rate 

 which was also the amount of material required by the Detroit District to 

 nourish the beach to the south of the powerplant. 



Although the net direction of longshore transport is to the south, rever- 

 sals are common. Visual observations of wave climate since 1974 indicate that 

 about 32 percent of the gross transport moves to the north. This is not ion- 

 expected since Seibel (1972), using wind data from Muskegon, Michigan, showed 

 that the direction of onshore winds shifts during the year. In siommer the 

 winds are generally from the southwest quadrant; in winter the winds are from 

 the northwest where the fetch is longest. 



5. Ice . 



Lakeshore ice controls the amount of bluff recession by protecting the shore 

 during January, February, and part of March. This is evident in an aerial photo 

 taken 16 February 1972 of reach B (Fig. 4), which shows a maximum of 120 meters 

 of solid ice bordering the shoreline. A thorough analysis of the development, 

 buildup, and eventual disappearance of shore ice over the winter of 1973-74 was 

 done by Seibel, Carlson, and Maresca (1975) in conjunction with the construction 

 of the Donald C. Cook Nuclear Plant. ■ 



To compute bluff recession rates based on the assumption that no recession 

 occurs during the period of ice cover (Davis, 1976), it was necessary to esti- 

 mate when protective ice developed and disappeared using aerial photos and ice 

 maps published by the Lake Survey Center, NOAA (Assel, 1972a, 1972b, 1974a, 

 1974b). The results given below (and used in Section IV, 3) are considered 

 the best estimates of ice-cover periods from November 1970 to November 1974. 



30 December 1970 to 14 March 1971 



5 January 1972 to 20 March 1972 



29 December 1972 to 9 March 1973 



5 January 1974 to 6 March 1974 



