Flooding and Inundation
Los Angeles County is subject to a wide range of flood hazards, including those caused by earthquakes, intense storms, and failure of man-made structures. Storm conditions, topography, drainage patterns, and the adequacy of the stormwater system combine under certain conditions to create areas of flooding.
Aside from Ballona Creek, no other large bodies of water are present in the vicinity of the project area. According to the Safety Element of the General Plan, West Adams is not within a tsunami zone or an inundation area. West Adams is located more than five miles inland from the Pacific Ocean and the elevation ranges from approximately 100 to 425 feet above sea level.
The Federal Emergency Management Agency (FEMA) has identified areas affected by both the 100-year storm frequency flood and the 500-year storm frequency flood. A 100-year flood hazard zone is located in the vicinity of Ballona Creek in the northern portion of the West Adams, as well as in the northern central portion of the West Adams, south of the I-10 Freeway. A substantial portion of the eastern and central portions of the West Adams are located within a 500-year flood hazard zone.
Ballona Creek Watershed
Ballona Creek is a nine-mile long flood protection channel. Historically, Ballona Creek was a meandering stream.
Ballona Creek remains underground in the eastern portion of its watershed, and becomes an open channel near Venice Boulevard and Pickford Street (West of La Brea Boulevard) in West Adams.
Ballona Creek is highly modified, having been lined with concrete along most of its length.
Ballona Creek is a major flood control measure for draining storm water from the West Adams and directing it safely to the Pacific Ocean.
The City’s storm drain system is a vast network of underground pipes and open channels that were designed to prevent flooding. Runoff drains from the street into the gutter and from there, flows into underground tunnels that empty into flood control channels such as Ballona Creek.
Storm water runoff within the West Adams is directed toward Ballona Creek via storm drains, curbs and gutters. Outside of the designated flood hazard area, local flooding may also occur at low points where clogged storm drains cause storm waters to back up.
The severity of floods tends to get put in terms of years: a 100-year flood, a 500-year flood.
Instead, the standard set for mapping flood-prone areas was a compromise between the existing Army Corps of Engineers standards, and the standards that most communities had set for flood prevention.
The areas deemed at risk of a bad flood were the areas that had about a 1 percent chance of flooding in any given year: in other words, the areas that would flood approximately one year out of every 100.
A 500-year flood is based on the same principle: Experts estimate that in any given year, there’s a 1-in-500 (or 0.2 %) chance a flood this bad will strike a particular area. In theory, that means that over 500 years, that will happen once: so there will be one flood that bad over a 500-year period.