ENVIRONMENTAL SIGNIFICANCE OF ICE TO STREAMFLOW IN COLD REGIONS

1. The five major hydrologic regimes of cold regions are typically cla ssified as proglacial, wetland, spring-fed, arctic nival and subarctic nival. Each has a distinctive hydrograph determined by the source and timing of runoff. 2. The hydrologic response of streams in cold regio ns is influenced significantly by the source and pathways of moisture from the landscape to the stream channel. Snow and ice masses, such as snow cover, permafrost and icings, play principal and unique roles as major moisture sources, and in affecting runoff pathways. 3. Once flo w has been routed from the landscape into a channel system, the effect s of floating ice begin to control the flow system. Notably, many of t he most significant hydrologic events in cold regions, such as floods and low flows, are more the result of in-channel ice effects than of l andscape runoff processes. This has not been adequately recognized in general assessments of cold-regions water resources. 4. Only recently have the broader environmental effects of river ice been addressed in any concerted fashion. This paper reviews the various stages of ice fo rmation, growth and break-up, and summarizes the major hydrologic and ecological effects associated with each. Priority research topics are also identified.