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Forest snow accumulation factors in the Colorado Front Range




Froehlich, Henry A., author
Meiman, James R. (James Richard), advisor
Dils, Robert E., committee member
Mogren, Edwin W., committee member
Marlatt, William E., committee member

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Maximum snowpack water equivalent is measured at 123 points in the Spring of 1966-1968. These points are distributed over three transects within a four square mile area in the 9, 580-10, 800 foot elevation zone of the Little Beaver watershed in the Colorado Front Range. Harsh climatic conditions persist through the snow accumulation season with winds of 9.4 m/s estimated for the mean winds during days with precipitation. Average temperatures for these periods were estimated to be -5.2°C. Snowpack water equivalent at maximum ranged from 6.6 to 9.7 inches over the three years of measurement averaged over all points. Individual points vary widely in their relative accumulation from year to year; the R2 for 1966 vs. 1968 water equivalent is only 25%. Consistency of snowpack density is noted with snow water equivalent vs. snow depth giving r values of 0.86, 0.90 and 0.7 3 for the three years respectively. The single most important variable of those tested in this study is a parameter expressing expanse of and distance from a source area of blowing snow. This source ratio is associated with 40% of the total variance when three years data are pooled and 108 sample points are included. Water equivalent increases an average of 5.0 inches per 1000 feet elevation although only 28% of the total variance in water equivalent is associated with elevation. On the 40 points of mid transect the three topographic variables (source, elevation, and steepness of slope) are associated with 85% of the total variance. However, considering all transects, the topographic variables are effectively supplemented by the use of a canopy variable. Canopy percentage was estimated with a Lemmon spherical densiometer read to indued a 114° arc, a 21° arc and crown cover to the windward. Basal area per acre was derived through the use of a cruising pr ism. These four variables are closely correlated and often interchangeable. The most useful of the four is the 114° arc. About 67% of the total variance is associated with the two major topographic variables (source and elevation) and crown cover in a regression involving 108 points and with the three years data pooled. Crown volume and number of stems or sum of stem diameters do not significantly improve any of the regressions. Roughness variables were derived from profiles of the canopy drawn with the aid of a Kelsh photogrammetric plotter. The most useful of the roughness variables tested is a coefficient indexing the projection of the first tree upwind from the sample point. This variable was selected as the second most important one on the lower transect. With basal area and Coef. 1, the R2 was 38%, and with the addition of elevation and the height of trees to the lee of the sample point the R2 was raised to 58%.


Covers not scanned.
Print version deaccessioned 2021.

Rights Access


Snow surveys


Associated Publications

Meiman, James R. Little South Poudre Watershed and Pingree Park Campus. Colorado State University, College of Forestry and Natural Resources (1971).