It's part of an effort by the city to reduce the amount of pollution that enters the nearby ocean, the majority of which is carried by urban runoff that's transported by the sewer system.
"Before the water can reach the curb, much of it percolates into the ground through a permeable concrete layer six inches deep that allows the water to infiltrate into the soil below.
Infiltration basins under the parking lanes store the water during a storm or in the event there is dry weather runoff. The runoff is collected by the basins with filters in the gutters.
The water is stored until it percolates into the surrounding soil, helping to replenish groundwater supplies."
Thanks to Curbed L.A.