3 Field-Data Collection 



To support the sedimentation analysis and physical model study, field data 

 were collected in July and September/October 1997. A hydrographic survey was 

 conducted 18 July 1997. and from 29 September to 1 October 1997 current data, 

 sediments, and video footage were collected. Additional current measurements 

 were made on 8 October 1997. 



Hydrographic Survey 



A Scanning Hydrographic Operational Airborne LIDAR Survey (SHOALS) 

 bathymetric survey of lower Lake Huron was conducted by the Joint Airborne 

 Lidar Bathymetry Technical Center of Expertise. The survey area included Lake 

 Huron bank-to-bank from approximately 1.6 km (1 mile) north of the USCG 

 Station to approximately 305 m (1,000 ft) south of the Station along the St. Clair 

 River. SHOALS surveys are collected ft^om a Bell 212 helicopter using light 

 detection and ranging (LIDAR) technology whereby a laser beam is projected 

 from a pod beneath the helicopter. Part of this laser light is reflected from the 

 water surface, which locates the water-surface elevation. Light that is not 

 absorbed in the water is reflected off the bottom, and the difference between the 

 bottom- reflected light and the surface-reflected light gives the water depth. 

 SHOALS uses kinematic on-the-fly global positioning system technology to cover 

 large areas rapidly and produces over 1 15,000 soundings per square kilometer. 

 Flight data are processed in a trailer-based mobile facility to produce final project 

 maps and charts. SHOALS surveys comply with vertical accuracy standards of 

 ±15 cm (0.5 ft) and horizontal accuracy of ±3 m (9.8 ft) (Lillycrop, Parson, and 

 Irish 1996).' 



This survey was used to characterize the bathymetry of the study site and 

 provide depths for construction of the physical model. Latest SHOALS develop- 

 ment allows topographic survey information for subaerial regions around the 

 project site. Figure 5 is a bathymetric map of lower Lake Huron from the 

 SHOALS survey. The lines shown are reference locations for current transects as 

 described below. Figure 6 is a bathymetric map of the USCG boat basin and the 



' Joint Airborne Lidar Bathymetry Technical Center of Expertise and SHOALS web page 

 at: http://shoals.sam. usace. army. mil/. 



Chapter 3 Field-Data Collection 



