Technical Manual: Conduits through Embankment Dams (FEMA 484)

Prefacecondition. The hazard classification says nothing about the safety or condition ofthe structure.The guidance in this document is considered valid technically without regard to thehazard potential classification of a particular embankment dam. However, somedesign measures that are commonly used for design of high and significant hazardembankment dams may be considered overly robust for use in low hazard dams. Asan example, chimney filters that extend across the entire width of the embankmentfill section are recommended for most high hazard embankment dams. Manysmaller, low hazard embankment dams are constructed without this feature. Thisdocument recommends that even low hazard embankment dams should containother currently accepted design measures that address seepage and internal erosionalong the conduit. Specifically, a filter diaphragm or filter collar around the conduitis recommended for all embankment dams penetrated by a conduit.Often, low hazard embankment dams are small structures (height or reservoirvolume). The term “small embankment dam” does not have a single widely accepteddefinition. Some designers may consider a 25-foot high embankment dam to be thelargest dam in the small dams category, and others may consider this to be thesmallest dam in the large dam category. The International Commission on LargeDams defines large embankment dams as being more than about 50 feet high. Forthis reason, this document will consider only the hazard potential of theembankment dam. The focus of this document is on significant and high hazardembankment dams due to the concern for loss of life and property damage.However, where appropriate, deviation from the guidance is noted for low hazardembankment dams. This deviation is not all inclusive, and the designer may findadditional guidance on the design and construction of conduits within low hazardembankment dams in Natural Resources Conservation Service (NRCS) NationalHandbook of Conservation Practice Standard Code 378 Pond (2002). The designer shouldbe aware that future downstream development could require revising the hazardpotential classification from low to significant or high. Pressurized conduits are notrecommended at low hazard embankment dams, since these structures often lackregular inspections and may not contain the appropriate safety features as discussedin this document.FEMA’s National Dam Safety Program sponsored development of this document inconjunction with the Association of State Dam Safety Officials, Bureau ofReclamation, Federal Energy Regulatory Commission, Natural ResourcesConservation Service, and U.S. Army Corps of Engineers.The primary authors of this document are Chuck Cooper, P.E. (Bureau ofReclamation), John Cyganiewicz, P.E. (Bureau of Reclamation), James Evans, P.E.(Federal Energy Regulatory Commission), Mark Haynes, P.E. (Colorado Division ofWater Resources), Danny McCook, P.E. (Natural Resources Conservation Service),v