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

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

STANDING OPERATING PROCEDURESIf the opening is located, it may be possible to block the seepage flow at its entry point,since blocking the entry point may take much less time than constructing a sandbag ringdam. If the entry point is blocked, both the blockage and the location of boil need to beclosely monitored for any changes (see Section 6.3.3 - Whirlpools in the Reservoir).A geotextile covered by coarse aggregate may also be used as a filter to prevent the lossof material. If relief wells or standpipe piezometers are nearby, they can be pumped toreduce uplift pressure.6.3.5 SinkholesIf sinkholes are observed on the embankment or downstream from the dam with noindication of seepage flow, the area should be closely monitored until detailedinvestigation and analyses can be performed and the cause is determined.If the sinkholes exhibit seepage flow, or increase in size or number, consider filling theholes with graded material similar to the treatment recommended in Section 6.3.3 -Whirlpools in the Reservoir. The reservoir should be lowered if the condition worsens.Sinkholes that appear in the reservoir floor or rim upstream of the dam represent seepageentrance locations. Unless the reservoir is drawn down periodically, these may not bedetected. They should be filled with an impervious material to seal the entry, and thearea carefully monitored thereafter. Investigation and analysis should be undertaken todetermine the need for a more permanent solution.Figure 6-17: Sinkhole in Upstream Slope of a Dam at Waterline (left); TemporaryRepaired Sinkhole w/Gravel, Geotextile and Sandbags (right)6.3.6 Embankment DeformationAn embankment slope failure or slides may be caused by seepage pressures, a saturatedslope, a slope which is too steep, or an unusual loading condition such as a flood orearthquake. Earthquakes can cause structural damage to the embankment orappurtenances, which might lead to liquefaction of the soils and significant slumping ordeformation of the embankment. If a large slide in the upstream or downstream slope has6-17Revision No. 0October 2008

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