FLOOD07755

• County: Statewide
• Basin: Statewide
• Title: Engineering and Design Runoff from Snowmelt
• Date: 1/5/1960
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

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AGE at:" SNOW SURfACE. DAYS
Figure 6. Variation in snow surface albedQ with time.

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excess of 80% cover), the wind variable may be negleeted, and convection-condensation melt may
be computed as a function of air and dewpoint temperatures alone.
The convection-condensation melt equation is based on measurements of air and dewpoint
temperatures at the 10-foot level, and wind speeds at the 50-foot level. For forested areas,
wind values to be applied are those which are representative of the open portions of the basin.
The reductions of wind speed in the forested portions are accounted for in the selection of the
basin convection-condensation melt coefficient, k. Also, as explained in paragraph 3-08, when
measurements of air temperature and wind are at significantly different levels than those speci-
fied above, it is necessary to adjust them to the standard levels, The form of the genera\
eonvection-condensation melt equation is that of equation 14 (par. 2-10), with the additional
effect of the convection-condensation melt coeffieient, k.

4~08. GENERALIZED BASIN SNOWMELT EQUATIONS. The following equations for rain-
free periods have been developed on the basis of the above-stated assumptions and requirements,
for varying conditions of forest environment, Exeept that they compensate for loss by forest
transpiration (by assuming it to be equal to shortwave radiation melt, which is not computed for
forested areas), the melt coefficients represent the actual melt of the snowpack, expressed as daily
ablation in inches of water equivalent over the snow-covered area, The coefficients also express
melt for a ripe snowpack (isothermal at 320 F, and with 3% free water content),

Heavily forested area:

M =0.074(0.53T;+0.47T;)

Forested area:

M ~k(O.0084v) (0.22T' .+O.78T' ,) +0.029T'.

Partly forested area:

M =k' (1- F) (0,00401,) (I-a) +k(0.0084v) (O,22T; +O,78T;) + F(0.029T;)
OlJen area:

M =k' (0,00508/,) (I-a) + (1- N) (O,0212T;-0.84) + N(O,029T;)
+k(O,0084v) (O.22T;+O,78T~)
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