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Western Dam Engineering <br /> Technical Note <br /> <br /> <br /> May 2017 <br /> <br /> <br />11 <br /> <br />The intervention: <br /> Outlet gates immediately fully opened <br /> Use of inverted filter approach <br /> Backfilled test pit with sand and gravel already <br />stockpiled on site due to historic seepage issues <br /> Mounded filter sand over sand and gravel to 6 feet <br />above original grade to mitigate seepage <br />reappearing at top of filter <br /> Full-time surveillance overnight until seepage <br />stabilizes at about 1 gpm by late morning <br /> Permanent solution included constructing a gravel <br />chimney drain downstream of chimney filter to <br />prevent surcharging of the chimney filter <br /> <br />Lessons Learned and <br />Recommendations <br />Key points to keep in mind in preparation for and <br />when faced with a concentrated seepage event <br />include: <br /> Consider developing an Emergency Intervention <br />Plan to identify preparedness actions in advance. <br /> Stay calm; panic does no one any good. <br /> Assess conditions quickly, but accurately, and <br />update as appropriate. <br /> Choose intervention actions carefully, with as <br />much awareness as possible of the potential <br />downsides of those actions. <br /> Reduce seepage exit velocity first with a diffuser, <br />and then address controlling piping (internal <br />erosion) with a filter. <br /> Availability of materials and equipment in an <br />emergency can make the difference between a <br />close call and a dam failure. <br />A functional outlet works with good discharge capacity <br />is very valuable; consider immediately lowering the <br />reservoir pool. <br />References <br />[1] Association of State Dam Safety Officials; http//www.damsafety.org <br />[2] U. S. Dept. of the Interior, Bureau of Reclamation, Dams Without <br />Filters, by Michael Gobla; <br />HTTP://WWW.DAMSAFETY.ORG/MEDIA/DOCUMENTS/FEMA/TS19_FILTERSDRAI <br />NSGEOTEX_EMI2012FEB/GOBLA_DAMSWITHOUTFILTERS(1).PDF <br />[3] https://www.usbr.gov/uc/feature/avwatkins/ <br />[4] Lindon, et al., Rapid Response to Emergencies; <br />http://damfailures.org/wp-content/uploads/2015/07/082_Rapid- <br />Response-to-Emergencies.pdf, September 2010. <br />[5] Eddy, Greg; AV Watkins Dam Near-Failure Incident: Response and <br />Rehabilitation; <br />http://www.damsafety.org/media/Documents/FEMA/TS24_InterimRi <br />skReduction/14_AVWatkins2017NDSP-Eddy.pdf <br />[6] http://mde.maryland.gov/programs/ResearchCenter/eMDE/Pages/vol <br />3no4/needwood.aspx <br />[7] Frank, Andrew; Emergency Response at Lake Needwood Dam, An <br />Owner’s Perspective Following a Severe Event; ASDSO Journal of Dam <br />Safety, Volume 6, Issue 1 – 2008. <br />[8] France, John W.; Washakie Dam Safety Modifications, Wyoming – A <br />Case Study in Seepage Collection and Control in Glacial Foundations; <br />http://ascelibrary.org/doi/abs/10.1061/40758(151)3 <br />[9] France, John W.; Washakie Dam Safety Modifications, Wyoming – A <br />Case Study in Seepage Collection and Control in Glacial Foundations; <br />H2Geo Seminar, Denver, Colorado; October 22, 2004. <br />[10] Gannett Fleming, Dam Owner Emergency Intervention Toolbox, July <br />2016; http://dnrc.mt.gov/divisions/water/operations/dam- <br />safety/cool-tools-for-dam- <br />safety/MDNRCDamOwnerEmergencyInterventionToolbox_Final.pdf <br /> <br />Emergency <br />Seepage Berm