Question about how to fix a french drain

[Steve S.]

One of my rentals has an angled driveway with what I believe is a french drain (image below).  Whenever it rains, sediment gets clogged up in the box (circled in blue) and if I go in and scoop it out, the water drains off well.

If I don't scoop it out, it means the tenant may have to walk through 4-6 inches of water to get to their car parked in the driveway or the street.  

Any recommendations on how to fix this?  I didn't have it installed and can't drive over there every time it rains to scoop out the sediment (and the current tenant is not much of a do it themselfer type person).

I suppose i could also give them a little bridge to walk over but I'd rather give them something more permanent for a fix.

Here's the image