Dry Sorptivity of Upper Soil: This may be estimated by considering the catchment soil types and by using the results of ring infiltrometer tests as a guide. Typical values range between 4.5 for urban grassed areas and 30 for certain sands.
The sorptivity value chosen has a significant effect on storm runoff volumes. Consequently it is important parameter to consider in the calibration process. Talsma (1969) conducted infiltrometer tests on many soil types. These are reproduced in the following table:
|Soil Location andType||Sorptivity |
|Bungendore Fine Sand||13.6|
|Charnwood Loamy Sand||1.9|
|Ginnindera Silty Clay Loam||9.0|
|Barton Sandy Clay Loam||4.5|
|Gundaroo Clay Loam||4.5|
Saturated Hydraulic Conductivity: Infiltration constant, related to hydraulic conductivity. This parameter acts as a continuous loss rate in the infiltration function. A typical value is 1 mm/min.
Lower Soil Drainage Factor: This parameter governs the volume of water draining from the lower soil zone to groundwater storage. The value chosen will effect the volume and timing of groundwater runoff. The usual range of values is 0.01 to 0.1.
Constant Rate Groundwater Recession Factor: This will effect the volume and timing of groundwater runoff. Values usually range between 0.9 and 0.99.
Variable Rate Groundwater Recession Factor: Generally set to 1. Any other value will make groundwater runoff a non-linear function of groundwater storage.