Difference between revisions of "Vertical MWT"
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'''Default Method of Vertical MWT'''<br> | '''Default Method of Vertical MWT'''<br> | ||
| − | Currently, the default method of vertical MWT uses the SNAP model to calculate the depth, density, hydraulic permeability, and effective porosity of the snow pack within each cell. Methods by Bengtsson (1982) are then used to calculate the vertical liquid flux of water created by each melt occurrence. Because the fluxes typically originate at the top of the snow pack and move vertically downward, multiple fluxes can exist traveling through the snow pack at the same time | + | Currently, the default method of vertical MWT uses the SNAP model to calculate the depth, density, hydraulic permeability, and effective porosity of the snow pack within each cell. Methods by Bengtsson (1982) are then used to calculate the vertical liquid flux of water created by each melt occurrence. Because the fluxes typically originate at the top of the snow pack and move vertically downward, multiple fluxes can exist traveling through the snow pack at the same time. To account for this, GSSHA creates multiple melt-waves (up to 6 simultaneous waves) that distribute the melt to the overland. |
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Latest revision as of 00:10, 29 December 2013
As explained in Colbeck (1979) and Gray & Male (1981), the vertical flow of water through a snow pack is dominated by gravitational forces. Since capillary forces are typically ignored in vertical flow through a snow pack (Colbeck 1979; Gray and Male 1981; Colbeck and Anderson 1982), a gravity flow theory, such as used in the SNAP model (Albert & Krajeski, 1998) can be utilized. The hydraulic conductivity used within the SNAP model changes with saturation as seen in Equation 1. Vertical flow velocities ranging from 2 – 60 cm/min have been observed through a snow pack (Gray and Male 1981). For more information on the vertical flow equations used within the SNAP model the interested reader is encouraged to review Albert & Krajeski (1998).
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Kw = K * Sn | (1) |
| Kw = hydraulic conductivity of snow at saturation, S | K = unsaturated hydraulic conductivity of snow |
| S = snow saturation (0-1) | n = constant, typically 3 (Colbeck 1973) |
Default Method of Vertical MWT
Currently, the default method of vertical MWT uses the SNAP model to calculate the depth, density, hydraulic permeability, and effective porosity of the snow pack within each cell. Methods by Bengtsson (1982) are then used to calculate the vertical liquid flux of water created by each melt occurrence. Because the fluxes typically originate at the top of the snow pack and move vertically downward, multiple fluxes can exist traveling through the snow pack at the same time. To account for this, GSSHA creates multiple melt-waves (up to 6 simultaneous waves) that distribute the melt to the overland.
SNAP Method of Vertical MWT
Although not currently recommended, a method is included in the GSSHA model that uses the SNAP model to distribute melt-water vertically through the snow pack and to the overland. Numerous issues have arisen with this method, and therefore is not recommended.
