Sidewalk runoff goes to Easement Garden

I have been trying to get the rain water from our sidewalk to go into the planting bed between the sidewalk and the street - the boulevard.  It is an erstwhile rain garden, but captures a *lot* of water when it rains.

The water flows down the sidewalk, and between my son and the driveway apron, into the bed.  In this pic, it is POURING.  But you can't necessarily tell.

It took a while to get the water to flow into the planting bed.  I finally had to dig a trench to get it to flow there.  There is a bit of grass there now, but the trench is a good 3" below sidewalk level.