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) below 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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