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Western Dam Engineering <br /> Technical Note <br /> <br /> August 2016 <br /> <br />24 <br />Filters! <br />There have been no documented case histories of a <br />dam failing through internal erosion when the use of <br />an engineered filter has been incorporated in the <br />design. Filters located downstream of an erodible <br />material are effective at arresting all internal erosion <br />mechanisms. Filters and transition zones of coarse <br />particle size can be effective in controlling erosion <br />even when not designed as an engineered filter. See <br />our previous article on “FILTER DESIGN AND <br />CONSTRUCTION.” <br />Conclusion <br />Internal erosion remains one of the main causes of <br />failures and accidents at embankment dams worldwide <br />and warrants a heightened understanding. Therefore, <br />it is important that the mechanisms and conditions by <br />which internal erosion can occur, and the related <br />warning signs should govern surveillance and <br />monitoring for embankment dams. Visual inspection, <br />measuring seepage, and monitoring pore pressures are <br />essential tools in identifying signs of internal erosion <br />Look for future articles that will cover monitoring and <br />remediation of seepage failure modes, but in the <br />meantime a recent document by the Federal <br />Emergency Management Agency (FEMA) on <br />monitoring for seepage is an excellent reference on <br />the topic (See reference [6]). <br /> <br />References <br />[1] Bureau of Reclamation and U.S. Army Corps of Engineers, “Best <br />Practices in Dam and Levee Safety Risk Analysis”, Chapter IV-4 Internal <br />Erosion Risks for Embankments and Foundation, July 2015. <br />HTTP://WWW.USBR.GOV/SSLE/DAMSAFETY/RISK/METHODOLOGY.HTML <br />[2] International Commission on Large Dams (ICOLD), “Internal Erosion of <br />Existing Dams, Levees and Dikes, and Their Foundations”, Bulletin 164, <br />February 2015. <br />[3] Fell, R., Foster, M. A., Cyganiewicz, J., Sills, G. L., Vroman, N. D., <br />Davidson, R. R.. “Risk Analysis for Dam Safety: A Unified Method for <br />Estimating Probabilities of Failure of Embankment Dams by Internal <br />Erosion and Piping”, URS Australia, New South Wales, Sydney, <br />Australia. 2008. <br />[4] Sherard, J. L. “Influence of Soil Properties and Construction Methods <br />on the Performance of Homogeneous Earth Dams.” Technical <br />Memorandum No. 645, Bureau of Reclamation, Denver, CO. 1953. <br />[5] Association of State Dam Safety Officials (ASDSO), Lessons Learned <br />from Dam Incidents and Failures, HTTP://DAMFAILURES.ORG/CASE-STUDY/ <br />[6] Federal Emergency Management Agency (FEMA), “Evaluation and <br />Monitoring of Seepage and Internal Erosion”, Interagency Committee <br />on Dam Safety (ICODS) FEMA P-1032, May 2015. <br />HTTP://WWW.FEMA.GOV/MEDIA-LIBRARY-DATA/1436889238781- <br />1B63946BFCB27BAB5D85F7F95A66CE35/FEMAP1032.PDF <br />[7] Federal Emergency Management Agency (FEMA), Training Aids for <br />Dam Safety, Module: Evaluation of Seepage Conditions. <br />HTTP://WWW.DAMSAFETY.NSW.GOV.AU/DSC/DOWNLOAD/LIBRARY/WORKBOOK <br />_17.PDF <br />[8] Garner, S. J., and Fannin, R. J.. “Understanding internal erosion: a <br />decade of research following a sinkhole event,” International Journal <br />on Hydropower and Dams, Aqua~Media International, 2010. <br />