Anchor ice formation in streams: a field study

In northern steep streams anchor ice is commonly observed during winter, and plays a key role when considering in-stream conditions. The understanding, however, of the nature of anchor ice formation is less understood, in particular, under natural conditions. In the following, observations of anchor ice formation in three stream environments with different physical characteristics are presented. Results demonstrate that anchor ice not only form in riffle areas, but also in shallow and slow running stream sections. No linkage between spatial distribution of anchor ice and calculated dimensionless numbers (Froude and Reynolds number) was found. Furthermore, analyses oil growth and density showed that anchor ice may be distinguished by two main types. (1) Type I: Lower density forming oil top of substrata. (2) Type II: Higher density forming between the substrata filling interstitial spaces. Distribution of anchor ice Types I and II suggests a relation between intensity of turbulence expressed by the Reynolds number, growth pattern and density. As anchor ice has both physical and biological implications on in-stream environments, findings from the present study may be of particular interest to cold region freshwater stream management. Copyright (C) 2009 John Wiley & Sons, Ltd.