Samples of Typical Dam Failures
Contrary to popular belief:
Most dam failure fatalities are not the result of large dams failing. They are the result of small dam failures. Dam Failures resulting in fatalities:
- 86% of the fatalities resulted from dams between 20 and 49 feet in height
- 47% of the fatalities resulted from dams with a drainage area less than 2 square miles
- 75% of the fatalities resulted from dams with a drainage area less than 10 square miles
- 7 dams had less than 300 acre-feet of reservoir storage area
This description fits many of California dams.
Several factors influence loss of life from dam failures, and an Emergency Action Plan takes into account and attempts to address each of these:
- Number of people at risk
- Flood depths and velocities
- Time of day or time of year
- Ease of Evacuation
- Timeliness of warnings
Dams present formidable consequences if not properly designed, built, and maintained. California has some of the most complex geology in the world, which affects and complicates the design and performance of dams. All dam owners in California must be prepared for the inevitability of earthquakes and flooding. Many of the state's dams are located on or near geologic faults that can cause major earthquakes. A map showing how state-regulated dams overlay fault lines can be downloaded HERE.
Most California dams are more than 50 years old, the typical design life of dams. Even without large-scale natural disasters, there are numerous causes of failure that can occur under less extreme conditions. A complete dam failure is a nightmare for people, property and the environment. Regular dam inspections and maintenance, and creating an EAP, can help avert and mitigate such nightmare situations
Dam problems that can lead to failure
These photos illustrate many of the types of dam "incidents" that can rapidly become dam emergencies and trigger an Incident and Emergency Action Plan if not addressed by the dam owner soon enough. Dam owners, neighbors, or passers-by who see these types of problems at a dam should contact the state dam safety officials immediately.