I went out to take a look at what the current state of the LA River is. The LA river was concretized in the 1930s due to extreme flooding and damage. The river was prone to flooding which resulted in the great flood of 1862, 1938 and many others. Now, the river is completely concrete except for a trickle of water through the middle. The river is severely polluted due to the amount of industrialization and development around it. Projects are in place to revitalize the river in ways that minimize the flood risk, while also providing green space for all of Los Angeles to explore. I am extremely excited to see where these projects go in the future.
Here is the plan for anybody interested.
http://lariver.org/blog/la-river-ecosystem-restoration
These photos are from the Glendale area where there is some vegetation still in the river. Largely, the river is completely concrete.