The lateral saturated hydraulic conductivity (k) must be obtained for each discrete layer to the effective drainage barrier. These values are input in the Lateral Saturated Hydraulic Conductivity tab of the Drainage Design screen.  Model outputs are very sensitive to hydraulic conductivity values.  On sensitivity analyses, errors in hydraulic conductivity ranked next to potential evapotranspiration (PET) in having the greatest effect on results.

 

Field evaluations of hydraulic conductivity should be done for any detailed site specific design analysis.  Recommended methods to obtain field hydraulic conductivity are either the augerhole method or the well permeameter method.  Depending on the conditions, additional methods, i.e., the packer typedrilling and pumpingout test, using observation wells, may be more feasible.  Explanation and procedures to perform these tests may be found in SCS, National Engineering Handbook, Sections 8 and 16.

 

Hydraulic conductivity values can be specified for up to a maximum of 5 layers.  The first parameter, bottom depth of the layer, is the depth (cm) from the soil surface to the bottom of each discrete soil layer.  The bottom depth of the last layer should be at least as great as the effective depth of the profile, i.e. DDRAIN+HDRAIN.  The hydraulic conductivities for each layer are specified in cm/hr.