the-effectiveness-and-influences-of-the-navigation-ice-booms-on-the-st-marys-river

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February issue includes Appendix entitled Directory of United States Government periodicals and subscription publications; September issue includes List of depository libraries; June and December issues include semiannual index

Ice problems developed in the Sault Ste. Marie, Michigan, portion of the St. Marys River because of winter navigation Passing ships and natural influences moved ice from Soo Harbor into Little Rapids Cut in sufficient quantities to jam, cause high water in the harbor, and prevent further ship passage. After physical model and engineering studies, two ice booms with a total span of 1375 ft (419 m) with a 250-ft (76-m) navigation opening between were installed at the head of Little Rapids Cut in 1975. A modest field study program on the booms was conducted for the ensuring four winters to determine ice and boom interaction and the effects of ship passages on the system. Forces on some anchors were recorded and supplemental data were taken by local personnel. Several reports have been written about the booms' early operations. This paper presents four-year summary of the main effects of the booms on ice and ship interaction and vice versa. Throughout the four winter seasons, the small quantities of ice lost over and between the booms were manageable. Ships usually passed through the boom without influencing the boom force levels, but at time they brought about large changes. One boom needed strengthening, and artificial islands were added for upstream ice stability. Coast Guard icebreakers were also a necessary part of winter navigation in this area.

The performance of a navigable ice boom was studied by monitoring the progression of the leading edge of the unconsolidated ice cover over a reach of the St. Marys River directly downstream of the boom. Ice and hydraulic data were obtained for four winters from 1975-76 through 1978-79 for the St. Marys River at Sault Ste. Marie, Michigan. The ice cover progression rate was highest in early winter. The unconsolidated ice cover in the channel was estimated to have a thickness of at least 0.91 m and a porosity of 30%. During early winter the ice discharge per vessel passage averaged approximately 5500 cu m. for the four years. Model tests for this site had indicated that without an ice control structure of any type, an ice release of 63,000 cu m per ship passage could be expected; with an ice boom the release would be 12,300 cu m per ship passage. If a 100% effective boom releases no ice at all, then the measured rate indicates that the boom is 92% effective. On-site observations and time-lapse movies provided partial verification. Ice flowed down the ship track and through the navigation opening fairly often. Occasionally ice came over the boom in response to ship movements and natural causes. Keywords: Ice booms; Ice control; Winter navigation.

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