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Surface Water


Dam Hazard and Size Classifications

The Department bases the hazard potential classification on an evaluation of the probable present and future incremental adverse consequences that would result from the release of water or stored contents due to failure or improper operation of the dam or appurtenances, regardless of the condition of the dam. The evaluation includes land-use zoning and development projected for the affected area over the 10-year period following the classification of the dam.  We consider all of the following factors in hazard potential classification: probable loss of human life, economic and lifeline losses, and intangible losses identified and evaluated by a public resource management or protection agency.

Hazard Potential Classifications

Class

Loss of Life

Economic or Intangible Losses

Very Low

Not Likely

Limited to Owner or 100-year Floodplain

Low

Not Likely

Low

Significant

Not Likely

Low to High

High

Likely

Low to High

 

One of the major issues facing dam owners and the Dam Safety Section is known as "hazard creep."  This term refers to a dam originally constructed and operated as low or significant hazard that is now reclassified as high hazard due to new downstream development.  Such dams often do not meet design and maintenance requirements for high hazard dams and must be improved or removed at the owner’s expense. If the reclassified dam is considered Unsafe, the owner potentially becomes eligible for grants or loans from the Dam Repair Fund.

Dams are classified by size as small, intermediate, or large.  The size is determined by the following table.  An owner or engineer determines the size by storage capacity or height, whichever results in the larger size.

Arizona Size Classifications

Size

Capacity

(acre-feet)

Dam Height

(feet)

Small

50 – 1,000

25 – 40

Intermediate

1,001 – 50, 000

41 – 100

Large

50, 000+

100+

 




 

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