I’m still not sure how this new landscaping is supposed to work. My best guess is that the lower area is supposed to collect runoff and seepage from the surrounding lawn and other plants (and the street gutter behind me, interestingly enough) in order to reduce water usage and actually do something with water that would otherwise be sent into storm drains — a good idea in drought-stricken California.
There does seem to be a drain so that it won’t totally fill up in the rain, like it did a few months ago before they had all the plants in:
Though I can’t help thinking they should have skipped the lawn entirely.
Update: On Google Plus, Jeffrey Price responded that it’s a stormwater retention pond, designed to collect rain and allow the ground to absorb it over several days.
Update 2: And now I’ve seen it in action during a (light) rainstorm.