Table 2-10. Maximum Seasonal Depth of Frost for an Air-freezing 

 Index of 1800 degree-days°F 



Soil type 



Frost penetration (in.) 



Bare ground 



Turf 



Turf + 12 in. 



snow 



Clay and damp top soil 



Silt and sandy silt 



Silty sand 



Sand and silty sandy gravel 



Gravel and sand 



Glacial till 



Well-drained, sandy gravel 



38 



50 

 58 

 65 

 73 

 78 

 99 



27 

 38 

 44 

 48 

 56 

 60 

 71 



20 



29 

 34 

 38 

 43 

 48 

 53 



communication; September, 1979), which span a 19-year period (1959 to 1978) in 

 the Eastport area. Mr. Rhine's observations, in combination with the Coast 

 Guard records, provide the only available record of ice occurrence along the 

 Maine coast. 



Coast Guard records for the six winters prior to and including 1978 indicate 

 that sufficient ice forms on the Penobscot River to require breaking by the 

 first week of December. The latest breaking in the season occurred on 20 

 December 1973, whereas the earliest occurred on 3 December 1972. River and 

 harbor ice usually is a navigation problem through early March, varying from 

 12 February in 1976 to 17 March in 1974 and 1975. The last ice-breaking 

 operation of the year is usually in the Kennebec River, where flood control 

 requires the use of ice breakers in removing floating-ice buildup during the 

 main thaw. The average breaking period is 91 days. 



Midwinter maximum ice thickness of the Penobscot River has varied from 6 

 inches (15 cm), broken and moving, to 12 inches (30 cm). Ice thickness at 

 pressure ridges and areas of rafting can vary from 24 to 36 inches (61 to 91 

 cm) . Protected waters of the river have average maximum thicknesses in excess 

 of 20 inches (51 cm). The ice jams in spring on the Kennebec reached a 

 maximum thickness of 15 feet (4.6 m) in 1978. Average ice thickness during 

 mild years is 1 to 4 inches ( 3 to 10 cm) on the Penobscot. In more severe 

 years the average has been 2 to 6 inches (5 to 15 cm). The upper Penobscot is 

 always more prone to freezing over than is the lower Penobscot. 



2-33 



10-80 



