U.S. Fish & Wildlife Service Low Hazard Dams - Association of State ...

damsafety.org

U.S. Fish & Wildlife Service Low Hazard Dams - Association of State ...

STANDING OPERATING PROCEDURESoccurred which significantly lowers the dam crest and threatens to release impoundedwater, the reservoir should be lowered or drained and sandbags or other methodsapproved by the RDSO used to temporarily raise the dam crest to prevent overtopping.Figure 6-18: Example of a Deformed Embankment Caused by an Earthquake6.3.7 Piping and Other Uncontrolled Embankment SeepageFailures from piping in the foundation and from the embankment to the foundation aremostly from backward erosion, or backward erosion following blowout or heave. Itshould not necessarily be expected that seepage increases as the erosion is graduallyworking back from the downstream exit point. However, when the erosion hasprogressed to within a short distance of the reservoir/foundation interface, it can breakthrough very rapidly.Approximately two-thirds of failures from piping occur on the first filling or in the firstfive years of operation. In the vast majority of the remaining one third of piping failurecases, the reservoir was at or near historic high level when progression of the erosionfrom piping occurred. This is an important factor in dam safety management as it showsthat more aggressive surveillance and monitoring should be carried out on embankmentdams during flood events.The success of intervention measures are dependent on the detailed circumstances for adam. Factors which will influence this include the rate of progression of internal erosion,6-18Revision No. 0October 2008

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