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A variety of methods are available for measuring and estimating infiltration rates.  Selecting an appropriate method will depend on the size and scale of the area over which infiltration rates are being determined.  For further information on this topic, click here. (link to wiki page on infiltration measurements)

A variety of methods are available for measuring and estimating infiltration rates.  Selecting an appropriate method will depend on the size and scale of the area over which infiltration rates are being determined.  For further information on this topic, click here. (link to wiki page on infiltration measurements)

===LID design adaptations on low permeability soils ===

==LID design adaptations on low permeability soils ==

The rationale for variations in practice design for sites with fine textured soils is based on the relationship between hydraulic head and infiltration. Figure xx shows this relationship for an infiltration trench in Caledon that was filled to the outflow elevation during an intense rain event, and then allowed to naturally infiltrate over a 23 day dry period (ref tech brief).  As head decreased, infiltration rates from from 2.5 to 3.8 mm/h during the first two days when trench water levels were above 1.5 m , down to rates of only 1 to 1.5 mm hour after six and half days when water level elevations declined below 1 m.  

The rationale for variations in practice design for sites with fine textured soils is based on the relationship between hydraulic head and infiltration. Figure xx shows this relationship for an infiltration trench in Caledon that was filled to the outflow elevation during an intense rain event, and then allowed to naturally infiltrate over a 23 day dry period (ref tech brief).  As head decreased, infiltration rates from from 2.5 to 3.8 mm/h during the first two days when trench water levels were above 1.5 m , down to rates of only 1 to 1.5 mm hour after six and half days when water level elevations declined below 1 m.  

#onfiguring the storage to be more vertically oriented to foster higher hydraulic head.  As such, the facility would be deeper, with higher ratios of side wall to bottom areas, and a portion of the total storage regarded as effectively permanent.     

#onfiguring the storage to be more vertically oriented to foster higher hydraulic head.  As such, the facility would be deeper, with higher ratios of side wall to bottom areas, and a portion of the total storage regarded as effectively permanent.     

Another important element of infiltration practice design in the context of fine textured soils relates to the attraction of soil surfaces to water, which are strong in fine textured clays and silty clays and weaker in coarse textured sands or sandy loams.  This attraction, referred to as the matric potential, allows water to move up from the groundwater table into the soils.  In fine textured soils, this distance can be in excess of one meter.  Therefore if the base of the infiltration practice is only one meter above the seasonally high groundwater table, a direct connection between the practice and groundwater may form, bypassing the treatment properties of the soils.  It is recommended, therefore that the groundwater table be 1.5 m or lower when practices are installed on fine textured soils.          

Another important element of infiltration practice design in the context of fine textured soils relates to the attraction of soil surfaces to water, which are strong in fine textured clays and silty clays and weaker in coarse textured sands or sandy loams.  This attraction, referred to as the matric potential, allows water to move up from the groundwater table into the soils.  In fine textured soils, this distance can be in excess of one meter.  Therefore if the base of the infiltration practice is only one meter above the seasonally high groundwater table, a direct connection between the practice and groundwater may form, bypassing the treatment properties of the soils.  It is recommended, therefore that the groundwater table be 1.5 m or lower when practices are installed on fine textured soils.

==Performance studies on fine textured soils==

==Performance studies on fine textured soils==