### 2.7.2.3. Infiltration[¶](#infiltration "Permalink to this headline")

The surface moisture flux remaining after surface runoff has been removed,

(2.7.33)[¶](#equation-7-71 "Permalink to this equation")\\\[q\_{in,surface} = (1-f\_{sat}) \\ q\_{liq,\\, 0}\\\]

is divided into inputs to surface water (\\(q\_{in,\\, h2osfc}\\) ) and the soil \\(q\_{in,soil}\\). If \\(q\_{in,soil}\\) exceeds the maximum soil infiltration capacity (kg m\-2 s\-1),

(2.7.34)[¶](#equation-7-72 "Permalink to this equation")\\\[q\_{infl,\\, \\max } =(1-f\_{sat}) \\ \\Theta\_{ice} k\_{sat}\\\]

where \\(\\Theta\_{ice}\\) is an ice impedance factor (section [2.7.3.1](#hydraulic-properties)), infiltration excess (Hortonian) runoff is generated

(2.7.35)[¶](#equation-7-73 "Permalink to this equation")\\\[q\_{infl,\\, excess} =\\max \\left(q\_{in,soil} -\\left(1-f\_{h2osfc} \\right)q\_{\\inf l,\\max } ,0\\right)\\\]

and transferred from \\(q\_{in,soil}\\) to \\(q\_{in,h2osfc}\\). After evaporative losses have been removed, these moisture fluxes are

(2.7.36)[¶](#equation-7-74 "Permalink to this equation")\\\[q\_{in,\\, h2osfc} = f\_{h2osfc} q\_{in,surface} + q\_{infl,excess} - q\_{evap,h2osfc}\\\]

and

(2.7.37)[¶](#equation-7-75 "Permalink to this equation")\\\[q\_{in,soil} = (1-f\_{h2osfc} ) \\ q\_{in,surface} - q\_{\\inf l,excess} - (1 - f\_{sno} - f\_{h2osfc} ) \\ q\_{evap,soil}.\\\]

The balance of surface water is then calculated as

(2.7.38)[¶](#equation-7-76 "Permalink to this equation")\\\[\\Delta W\_{sfc} =\\left(q\_{in,h2osfc} - q\_{out,h2osfc} - q\_{drain,h2osfc} \\right) \\ \\Delta t.\\\]

Bottom drainage from the surface water store

(2.7.39)[¶](#equation-7-77 "Permalink to this equation")\\\[q\_{drain,h2osfc} = \\min \\left(f\_{h2osfc} q\_{\\inf l,\\max } ,\\frac{W\_{sfc} }{\\Delta t} \\right)\\\]

is then added to \\(q\_{in,soil}\\) giving the total infiltration into the surface soil layer

(2.7.40)[¶](#equation-7-78 "Permalink to this equation")\\\[q\_{infl} = q\_{in,soil} + q\_{drain,h2osfc}\\\]

Infiltration \\(q\_{infl}\\) and explicit surface runoff \\(q\_{over}\\) are not allowed for glaciers.

