For MODFLOW and PHAST models, HighestActiveLayer returns then number of the uppermost layer for which ActiveOnLayer returns True. If no layer is active, HighestActiveLayer returns 0. HighestActiveLayer can only be used when it is being evaluated at cells (MODFLOW) or elements (PHAST). It can not be used when it is being evaluated at nodes in PHAST. HighestActiveLayers should not be used with SUTRA models. HighestActiveLayer should not be used to set the Z formula of a specified-head boundary.
