# HydroGeoSphere/Surface Runoff

## Default surface flow transport values

By default, all surface flow zones (and elements) in the domain will be assigned default transport properties which are listed in Table 5.24:

Table 5.24: Default Values for Surface Flow Transport Properties
Parameter Value Unit
Longitudinal dispersivity ${\displaystyle {\alpha }_{lo}}$  1.0 m
Transverse dispersivity ${\displaystyle {\alpha }_{to}}$  1.0 m
Coupling dispersivity 0.0 m

The following instructions can be applied to the surface flow domain, as discussed in Section 5.8.1, to modify the default transport parameters. For each instruction we will indicate its scope (i.e. .grok, .oprops). Recall that if an instruction is used in the prefix.grok file, it will affect the current set of chosen zones, while in a properties (e.g. .oprops) file, it will only affect the named material of which it is a part.

## Longitudinal dispersivity

Scope: .grok .oprops

1. val Longitudinal dispersivity [L], ${\displaystyle {\alpha }_{lo}}$ . Analogous to ${\displaystyle {\alpha }_{l}}$  in Equation 2.97.
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## Transverse dispersivity

Scope: .grok .oprops

1. val Horizontal component of the transverse dispersivity [L], ${\displaystyle {\alpha }_{t}}$ . Analogous to ${\displaystyle {\alpha }_{t}}$  in Equation 2.97.
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## Coupling dispersivity

Scope: .grok .oprops

1. val Dispersivity value [L] to be applied during exchange between the overland flow and subsurface domains.

Default value is 0.0.

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## Dry albedo

Scope: .grok .oprops

1. Value Dry albedo for soil type, ${\displaystyle {\alpha }_{dry}}$  in Equation 2.123. Default value is 0.35.
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## Saturated albedo

Scope: .grok .oprops

1. Value Saturated albedo for soil type, ${\displaystyle {\alpha }_{sat}}$  in Equation 2.123. Default value is 0.18
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## Heat coupling length

Scope: .grok .oprops

1. Value The heat coupling length [L], is the depth of the surface/subsurface exchange zone used to compute ${\displaystyle {\alpha }_{o}}$  in Equation 2.142. Default value is 1.0 × 10−4 m.
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