USCG Academy (1974) 



The problem statement says currents in the vicinity of the basin are 1.03 to 

 1.54 m/sec (3.4 to 5.1 ft/sec) and up to 3.09 m/sec (10.1 ft/sec) under the Blue 

 Water Bridge. The boat basin was constructed in 1 93 1 in its present location with 

 wood pilings spaced 1 .2 to 1 .8 m (4 to 6 ft), hi 1940. steel sheetpiling was added 

 north and east of the pilings to provide protection for boat launches from waves. 

 No record of dredging the basin was found prior to installation of the sheet piles. 

 Since its enclosure, the boat basin has required almost annual dredging. Often 

 boat prop wash has been used to help remove deposited sediment. 



Three mechanisms are assumed as a means for sediment to enter the boat 

 basin: 



a. Littoral transport of suspended and bed load moving along the shoreline 

 just lakeward of the breakwater provides the material composing a bar 

 across the mouth of the basin. 



b. Wave overtopping carries a range of particles over the breakwall (up to 

 "fist-sized" cobbles. 



c. Suspended sediment travels into the boat basin and ultimately settles out 

 in the quiescence of the boat basin. 



Proposed solutions include relocating the station, moor vessels in more pro- 

 tected areas along the St. Clair River, use dry boat launches, or use air-cushioned 

 vessels. USCG Academy (1974) states: 



"There appears no easy solution from a scientific/engineering 

 standpoint. The situation that exists does not appear solvable by 

 any known method of boat basin configuration. Any alteration of 

 the southern end of the north-south breakwater could cause the 

 creation of eddies and vortex shedding that does not now exist." 



The recommended solution was to revert to an open mooring whereby the 

 breakwaters would be removed allowing littoral transport to move through the 

 boat basin area. During summer months when protected waters were needed for 

 vessel operation, a semiportable breakwater could be installed on outer pilings. 

 After the boating season concluded, this breakwater system could be removed to 

 allow unimpeded littoral transport. 



A test of this concept was conducted whereby part of the breakwater system 

 (northern section) was removed allowing southward-moving riverine currents to 

 flow through the basin. Because this test was not of the fully open mooring plan 

 that was recommended (i.e.. the eastern breakwall remained, preventing wave 

 action to help move sediments alongshore), increased sedimentation occurred — 

 currents alone were not enough to keep the mooring area flushed clean. 



Chapter 2 Background 



