@ossobuco,
We tried to design for 100 yr floods, in (yes) california. There are arroyos there too. And there are famous failures, Sepulveda basin being one. And some places where the mud ate the civil engineered efforts and the whole thing came down. A lot of the grading does work and there have been decades of efforts to keep the water perking on the land.
I'm not sure I've ever seen a drain here. Maybe that is the idea, do it all naturally - but from some roads I've noticed, there's not even a trench drain, or a pitch to the sand, where the road flattens out at lower grades. Coors Blvd, for example - Lake Coors. Maybe a slight pitch, way too shallow, and no place to take up the water.
I'm a little biased. Both Dys/Di's and my place have patios/hardscape that grade toward the house. I am guessing building contractors here don't have to pass grading in an exam.