Once melt-water flows vertically through the pack (Vertical MWT) it reaches the saturated area above the ground and below the snow pack. This melt-water moves laterally along the ground through a saturated Darcian flow. GSSHA currently uses methods developed by Colbeck (1974) to determine the flux volumes between each cell. The equation and figure - from Colbeck (1974) - show how the flux rate is calculated for lateral flow.
| c = lateral flux rate (m2/hr)
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| α = hydraulic properties of water, constant (ρ*g/μ ~54.7x10-6 m-1 s-1)
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| Kw = saturated hydraulic conductivity of snow (~0.00555 m s-1)
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| Φ = effective porosity (unitless)
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