The Snow Accretion-Depletion Module uses the Snowmelt Numerical Analysis Package

(SNAP) developed by Albert and Krajeski (1998). It is a physically based approach to

modeling snowmelt, where the physics of flow through snow are considered and the melt

is driven by an energy budget at the snow surface. Snow accretion occurs when a

input air temperature is below freezing. In the latter case, the precipitation amount is

converted to a snowfall amount. Sections 7.1 and 7.2 are from Albert and Krajeski

(1998).

For modeling the movement of water through the snow, the effects of capilarity are taken

as negligibly small compared to the effects of gravity (Colbeck 1972), yielding the

simplified form of Darcy's equation:

ρkg

(7.1)

ηw

where *U *is the volume flux of water, ρw is the density of water, *k*w is the relative

Under some circumstances this will be applicable to the entire snowpack, while

modifications will be necessary under some conditions of layering. The effective

permeability of the water phase is taken to be proportional to a power (*n*c) of the effective

water saturation (Morel-Saytoux 1969, Colbeck 1972):

(7.2)

where the effective water saturation, *S*e, is defined by

(7.3)

1 - *S*wi

where *S*wa is the absolute water saturation and *S*wi is the irreducible water saturation. The

general applicability of the relationship *k*w ∝ *S*enc is discussed in Maulem (1978). Here, *n*c

is taken as a constant with a default value of 3.3.

The flux in terms of absolute water saturation is defined as

ρk g

(7.4)

ηw

The water volume conservation equation (Colbeck 1972) used states that the change in

water volume flux with depth, *U* (where the *z *axis is positive downwards), is equal to the

change in water saturation with time:

58