Keeping Large Channel Trench Drain Clear
If leaves are the only thing getting it it will take years to decades.  Leaves decompose down to aobut 1/50th their volume.  The usually problem with a drain is sand and dirt.

That said:  The grate bolts in.  5 years from now, those bolts may be very hard to remove.  If the grates don't shift unacceptably without the bolts, take them out now, or just leave one in each grade to keep it from sliding sideways.  As an annual measure, remove the bolt, apply a layer of grease, and refasten it.  Garage drains here get a nasty mix of road de-icer and sand.