Dam incidents are events of engineering and safety interest that provide insight into the structural and functional integrity of dam systems and their operation. Included in this definition are events associated with dam system that are anticipated or unanticipated and satisfactory as well as unsatisfactory.
Collecting information on success stories is as important as events involving failures or other episodes of unsatisfactory performance. Examples of dam incidents that are “successes” include:
- A group of dams located near a fault, experience and survive without ground motion associated with a magnitude 8.2 earthquake.
- A dam successfully passes a flood equivalent to 90 percent of the estimated PMF.
- An emergency action plan is successfully implemented with the population-at-risk evacuated in a timely manner.
- Dam operators are able to successfully open dam gates and low-level outlets to lower the reservoir after a dam has been damaged as a result of an earthquake.
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The term dam system is used to refer to all structural and non-structural, man-made and natural entities, operators, operating procedures, and management that collectively make up the system that maintains control of a reservoir and any releases from it.
The Term ‘Dam Incident’
Use of the term 'incident' is traditional (recall for example, the USCOLD publications, “Lessons from Dam Incidents”), but is somewhat unfortunate because the word "incident" generally has a negative connotation. The implication is that something “bad or unsatisfactory” has occurred. In fact, we are really looking to identify the occurrence of events that allow us to better understand the performance and operation of dam systems.
Guidelines for Determining if a Dam Incident Has Occurred
In the majority of cases, an engineer can determine whether a reportable incident has occurred or not (e.g., events involving dam breach, severe damage, etc.). The following table can be used as a guide to determine if a dam incident has occurred.
|Inspection Findings||The findings of a dam safety inspection that identifies an unsatisfactory or unsafe conditions at a dam (exclusive of ordinary maintenance and repair and findings of inadequacies relative to current design criteria).|
|Damage, Signs of Distress, Instability||Observations of damage, signs of distress or instability of the dam appurtenant structures.|
|Dam Breach||Any event resulting in the breach of a dam (partial or complete).|
|Controlled Breach||Planned (non-emergency, non-incident initiated) breach of the dam. Possibly carried out to remove the dam from service or to make major repairs.|
|Downstream Release -- Controlled or Uncontrolled||Uncontrolled release of the reservoir (e.g., appurtenant structure mis-operation), or controlled releases that result in downstream damage.|
|Earthquakes||The performance of a dam (satisfactory or unsatisfactory, anticipated or unanticipated) generated by an earthquake.|
|Misoperation, Operator Error||Misoperation of appurtenant structures such as failing to comply with the project rule curve.|
|Equipment Failure||Failure of mechanical or electrical equipment to perform the dam safety functions for which they were intended.|
|Deterioration||Deterioration of concrete, steel, or timber structures that jeopardized the structural/functional integrity of the dam or appurtenant structures.|
|Dam Safety Modification||Modifications to improve the safety of the dam or appurtenant structures such as might be required due to changes in the design criteria. Note: Repairs following an incident are reported as part of a follow-up report.|
|Inflow Flood||Inflow events that:
|Landslide or Rockfall||Landslides or rockfalls that impact the reservoir operation of a dam or that causes damage to elements of the dam system.
Landslide or rockfall that produces wave action that impacts the operation of a dam or causes damage to the elements of the dam system.
|Wind Waves||Wave action that impacts the operation of the dam system of that causes damage to elements of the dam system.|
|High Winds||Winds that impacts the operation of the dam system of that causes damage to elements of the dam system.|
|Ice Loading or Icing||Icing that impacts the operation of the dam system of that causes damage to elements of the dam system.|
|Emergency Action Plans||Implementation of the Emergency Action Plan (or emergency actions) in part or whole.|
|Regulatory Action||The regulator has determined an unsafe condition exists, or the dam does not meet applicable design criteria (e.g., inadequate spillway capacity), and requires action to be taken by the owner (e.g., reservoir restriction, safety modification).|