Reservoirs (Tanks)

Elephant foot buckling is typical damage on tanks or reservoirs that have jumped on their foundations during an earthquake.

Reservoirs (in the context of SAP evaluations) are tanks typically constructed of steel or concrete, rather than impounded waters with dams. Many jurisdictions use tanks to store domestic water supplies, and the tanks are highly susceptible to damage from earthquakes. Although tanks may need to be evaluated after other types of events, earthquakes are more likely to damage tanks than high winds or fires.

Maintaining or restoring water supply is critical to a jurisdiction’s emergency response efforts. The water is needed for firefighting operations and drinking water.

The type of damage seen in storage reservoirs depends mainly on the type of event, including the type of earthquake movement.

• Unanchored steel tanks will uplift, breaking connecting piping.


• When uplift is extreme, a tank may fail structurally when it slams back down. The result is elephant’s foot buckling, as shown in the photo above.


• In severe cases, the wall-floor seam can burst.


• Sloshing water can damage the roof (rarely resulting in loss of service).


• Wire- or cable-wrapped concrete tanks may experience failure of the wrapping as a result of corrosion or inadequate design. 


• Theoretically, older tanks can slide off their floor slab foundations (undocumented to date).

When the assessment is complete, the team decides on a recommended posting for the reservoir. Do not physically post a reservoir with a placard, but consider whether immediate action is needed.

• If damage is so severe that it warrants an UNSAFE posting, immediately inform the jurisdiction representative. The representative will contact Public Works to take the appropriate steps, which may include evacuation of neighboring areas.


• When recommendations are not time sensitive, pass them along when you return to the staging area. 

Reservoir Evaluation Form

Completing the Reservoir Evaluation Form