LA is built on an alluvial plain and the river formerly wandered through the basin. But it's now heavily channeled away from it's natural riverbed to prevent flooding. However I saw at least two places where the river had broken through the concrete walls and water was cascading down the side of the culvert, making a nice little waterfall.
Now, if this had been ancient Rome, the river would have been channeled through aqueducts to provide water for gardens and fountains, Instead, it's become an open sewer (in places) and groups are trying to promote wildlife reserves and get the river cleaned up. I found it picturesque but the water level seemed sadly low for January and a reminder of what LA used to be before it became the concrete walled metropolis that it is now.