General principles on the definition of blankets can be found in the "Boundary/Individual blankets" menu item.
After going to this menu item several FEM elements can be simultaneously assigned a blanket boundary condition in a defined section, or an existing boundary condition can be deleted. To do this, left-click four points counter-clockwise; a right mouse click resets the selected points. The definition refers to all nodes with their centroids within the quadrilateral. The following dialog box appears:
The "Delete" button deletes any existing water levels. The entered water level is assigned to the selected elements using the "Define" button. The "Water level = blanket top + c" button assigns the selected elements either a water level corresponding to the top of the blanket or the top of the blanket plus a constant c.