Depending on the direction of a storm it can make all kinds of changes to the sand on the beach. From the sand left on these steps, which is next to the creek, we can see that it lost a lot of sand. Since the storm came from the north and Laguna Beach, generally, faces southwest we didn't lose the amount of sand we could have if the storm was from the south.
Also notice that they have block off the boardwalk above the creek.
I saw a video that showed where the creek goes underground at Beach St. The water level was about a foot below the roof of the storm drain. Yes, it's just a plain old storm drainage system.
Remember in 2010 the water in the creek flowed over the storm drain and flooded downtown. And the amount of water in the creek that year was reduced by a shipping container that was in the creek. That blockage forced run-off onto Laguna Canyon Rd. So this year wasn't nearly as bad as 2010.