They're not depicted on the Approach or SID charts, but both of these charts use the "obstacle free zone" extensively. All procedures are designed to keep you above the planar areas defining the lower limits.
In simple terms, the obstacle free zone is the area above a series of planes, horizontal and at a gradient, the lower limit of which is defined by obstacles.
OLS charts (Obstacle Limit Survey, not available to pilots and jealously guarded by airport surveyors), define these very clearly. If the obstacles are not too critical, these are very useful in designing Engine Failure Special Procedures, which have a significantly lesser obstacle clearance criteria than does PANS-OPS.
OzExpat, where are you?
Regards,
Old Smokey