The column classification should probably be avoided today because the models have become more complex, MIKE SHE has become more efficient and computers have become faster.
Calculating unsaturated flow in all grid squares for large-scale applications can be time consuming. To reduce the computational burden MIKE SHE enables you to compute the UZ flow in a reduced subset of grid squares. The subset classification is done automatically by the pre-processing program according to soil and, vegetation distribution, climatic zones, and depth to the groundwater table.
Column classification can decrease the computational burden considerably. However, the conditions when it can be used are limited. Column classification is either not recommended or not allowed when
· the water table is very dynamic and spatially variable because the classification is not dynamic,
· if the 2 layer UZ method is used because the method is fast and the benefit would be limited,
· if irrigation is used in the model because irrigation zones are not a classification parameter, and
· if flooding and flood codes are used, since the depth of ponded water is not a classification parameter
If the classification method is used, then there are three options for the classification:
· Automatic classification With automatic option, the UZ columns are divided up based on the internal classification rules. The depth to the water table, Groundwater Depths used for UZ Classification (V1 p. 291), is the lower UZ boundary condition.
· Specified classification With the specified option, you must supply a list of grid codes, Specified classification (V1 p. 293), that defines the computational column and the columns to which the results will be applied.
· Calculated in all Grid points (default) In many models the classification system is not feasible or recommended. In this case, the UZ flow will be calculated in all soil columns.
· Partial Automatic Finally a combination of the Automatic classification and the Specified classification is available, where an. Integer Grid Code file must be provide (see Partial automatic classification (V1 p. 292)) to define the different areas.