

. .<- 















: 













i\ 















, 



•m 

 1 



1 





h mi 





>l- 



41* 1 



1 





1 



m^ i^m 



B^K . is 



41 



^^^J 





1 



^H 



^^^^^^ 



«. 















Figure 10. The U.S. Army Engineer District, Buffalo, 

 tugboat Washington. 



d. Data Collection . Before the fieldwork began, seismic survey tracklines 

 were plotted on navigation charts of the survey area. Position, spacing, and 

 length of the tracklines were determined by several factors. The primary 

 concern was spacing the lines to achieve maximum coverage of the study area 

 within the limits of time and budget. After the survey tracklines were selected, 

 the locations of the shore stations for the navigation system were determined. 

 Of high priority were stations at elevated positions (for adequate line-of- 

 sight), which also offered good triangular position in relation to the survey 

 vessel and adjacent shore stations. (Acceptable results are achieved when the 

 angle of range intercept of the vessel is greater than 30° and less than 150°; 

 optimum range angle intercept is 90°.) A total of 32 shore navigation stations 

 were used along 207 kilometers of coast from Conneaut to Marblehead. Positions 

 and spacing of the tracklines were altered at times to gather additional infor- 

 mation on geologic features such as buried stream channels, sediment contacts, 

 and probable lake bottom exposures of sand. 



Interpretations of the seismic profile records were made to select coring 

 sites with the greatest potential for sand and subsurface information. These 

 records were visually examined and marked to establish the primary geologic 

 features (e.g., regional sedimentary reflectors, sediment contacts, buried 

 stream channels) . Selected acoustic reflectors were then mapped to provide 

 areal continuity of horizons considered significant because of their areal 

 extent and relationship to the general structure and geology of the study area. 

 The use of seismic data- to interpret geologic conditions before selecting the 

 core sites maximizes the usefulness of both sources of data and provides the 

 most efficient use of funds. 



19 



