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Watershed Information
Surface Water Quantity — Snowpack
 
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Overview

Snowpack is the accumulated snow cover on the ground. A significant portion of the total precipitation that falls on the Rideau Watershed is in the form of snow.

Snow melt is a major factor contributing to flooding. The quantity of snow is usually expressed in terms of its water equivalent in millimetres (mm). The snow measurements are used in flood forecasting and flood risk studies and for reservoir management.

 



 
   
   
 

Understanding

The device used by Conservation Authorities in Ontario and by many other agencies in North America is the Federal or Mount Rose snow sampler developed by the United States Department of Agriculture. The sampler is a tube made of aluminum or plastic with a cutting ring at the bottom and a measuring scale on the side. The tube is inserted down into the snowpack rotating to cut hardpacked snow and ice layers.

The depth is recorded using the scale on the side and the tube is carefully taken out of the snow retaining as much snow as possible in the tube. The snow-filled tube is then weighed. The weight of the empty tube is then subtracted from the total weight to determine the weight of the snow column that was extracted. The weight of the snow is converted to an equivalent depth of water on the ground, by taking into account the specific gravity of the snow (ice crystals) and the cross-sectional area of the sampling tube.

The snowpack water equivalent is divided by the snowpack depth to get its "density" — which is an important indicator of the snowpack's ability to absorb and retain water added to it from rainfall or its own melting at above-zero temperatures. A density of 0.4 or 40% indicates a snowpack that is "ripe" and ready to contribute runoff to nearby watercourses with any additional rainfall or melting temperatures. The snow water equivalent is used along with weather forecasts of temperature and rain to make a flood forecast streamflows that can be expected in the river.

Snow measurements are done on or about the 1st and 15th of each month from the beginning of December to when the snow is gone in March or April. Five locations are monitored by the RVCA in the lower watershed east of Smiths Falls and another six in the upper watershed are monitored by staff of the Rideau Canal Office of Parks Canada.