I dont know about San Bernadino, but in Vegas they close the drainage off around contruction sites that way they dont fill up with dirt, crap, etc.. Few years back there was a street that had almost solid home building for 3-4 miles. When we got a lil bit of rain the street filled up with 5 feet of water. My brother ran one of the job sites for a home builder and the phone call I got was "holy crap it was just a wall of water"