These two graphics compare the drop in elevation of the Mississppi River to the Los Angeles River. While the area around the Mississippi River is primarily open land and can therefore allow the infiltration of stormwater, the length that runoff drops from is over 2,000 miles.

By comparison, the runoff elevation drop in Los Angeles travels from 3,000 feet to sea level (that’s twice the height!) in a fraction of the distance at approximately 51 miles. In addition, because much of the land surface in Los Angeles has been paved in concrete and is mostly non-permeable surface, it does not allow rainwater to be absorbed into the ground but instead, drains off the land and into the ocean.