The only dam that poses a threat in the City of Ontario is the San Antonio Dam. Failure of this dam is very unlikely, but under the right set of conditions, could occur with severe consequences. These conditions are:
- Failure while the dam is at or near full capacity.
- Complete and sudden breach of the dam, rather than partial failure which would allow water to be released slowly into containment channels.
Such conditions could only occur as a result of sabotage, earthquake or erosion during periods of extremely heavy rain. There is no guarantee that a warning will be issued before the dam fails.
Estimates by the U.S. Army Corps of Engineers state that six feet of water would reach the northern most areas of Ontario in a little over thirty minutes. This water would reach most of south Ontario with a depth of two feet in four hours.
Your response to such a situation should follow these guidelines:
- Gather up pre-identified important items such as supplies, equipment and documents if time permits.
- Turn off utilities.
- If possible, travel by automobile.
- Never try to outrun fast moving water. Choose the most direct route and avoid moving further into the path of the water.
- Generally, to be safe, you should relocate to an area west of Highway 71 or Garey Ave. in Pomona, or east of Archibald Ave. For a detailed map of the inundation area, contact the Ontario Office of Emergency Management.
- Monitor news reports and do not return to the flooded area until told to do so.
- Plan to spend at least 24 hours away from the area before all water has subsided.