6. The els of various structures and depths on the Great Lakes are 

 based on low water datum (Iwd) which is referenced to mean water level (mwl) 

 at Father Point, Quebec, according to the International Great Lakes Datum 

 (IGLD) of 1955. Figure 4 shows a profile of the Great Lakes region. Horizon- 

 tal and vertical distances have been distorted somewhat to convey visual 

 impression. 



IGLD-INTERNATIONAL GREAT LAKES DATUM 

 LWD-LOW WATER DATUM 

 MWL-MEAN WATER LEVEL 



-LAKE ST CLAIR 

 LWD 



LAKE ONTARIO 

 LAKE SUPERIOR 



Figure 4. Profile of the Great Lakes region (Iwd referenced to mwl 

 at Father Point, Quebec according to IGLD of 1955) 



7. Case histories for NCD's breakwater and jetty structures are pre- 

 sented in Tables 1-107. Figures depicting structure alignments, cross 

 sections, and aerial photographs for some sites accompany the various tables. 

 Sites are presented in the order of west to east and counterclockwise along 

 the lake shoreline (i.e., the first site being presented on the northwest end 

 of Lake Superior and the last on the east coast of Lake Ontario) . General 

 characteristics of the structures at the various sites are shown in the fol- 

 lowing tabulation: 



10 



