Minnesota climatology data supports a common rule of thumb that most of the snowpack disappears in the spring over a period of about 10 days. The question can be raised as to why this volume should be important if BMP facilities are generally designed for treating a runoff event lasting only 24 hours. That is, why would on average 1/10 of a snowmelt runoff volume going into a facility designed to treat a much larger volume be a problem? This is a very valid comment. Clearly, if the systems are built to store a large volume of rainfall runoff, there will be no problem. The difficulty arises when complicating factors in cold weather prevent the full storage volume for a pond, or infiltration capacity of an infiltration device, or conveyance for a diversion to be available during the period of time when they are designed to operate. Suddenly snowmelt could receive less than adequate treatment or by-pass any treatment whatsoever.
Snowmelt runoff floods are the most common type of flooding in Canada. These floods generally occur in the spring but will also occur during sudden winter thaws. Heavy runoff results from the rapid melting of the snow under the combined effect of sunlight, winds, and warmer temperatures. When the ground is frozen, the water produced by the melting snow is unable to penetrate and runs off over the ground surface into streams and lakes. The amount of surface runoff is usually within the capacity of the channel to drain off without flooding. However, if there is an above-average snow depth, a sudden thaw, or both, then the potential for high volumes of runoff and subsequent flooding increases. The situation can become of even greater concern if the rising snowmelt runoff is compounded by runoff from heavy rainfall. The later the thaw, the more likely this situation will prevail. Since the climatic factors influencing the rate of snowmelt are often widespread, snowmelt runoff flooding conditions can exist over vast areas.
Snow and Ice Melting Systems: Factors Influencing Design (Part II)
The mass balance of the polar ice sheets is affected by numerous factors, including changes in precipitation patterns over the ice sheets, changes in the snowline, summer melting of snow, changes in ice sheet albedo, changes in the extent of supraglacial lakes, submarine melting of the floating ice shelves at the tongue of marine outlet glaciers, and icebergs breaking off of glaciers. The changing balance between ice accumulation, on the one hand, and melting and sublimation of ice and snow, submarine melting and calving, on the other hand, determines the future development of the ice sheets [i]. 2ff7e9595c
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