Technical Manual: Conduits through Embankment Dams (FEMA 484)

PrefaceTens of thousands of conduits through embankment dams in the United States areaging and deteriorating. These conduits often were poorly constructed and are notfrequently inspected, if at all. Deteriorating conduits pose an increasingly greater riskfor developing defects that can lead to embankment dam failure with each passingyear. In an effort to deal with this problem, this document has been prepared tocollect and disseminate information and experience that is current and has a technicalconsensus.This document provides procedures and guidance for “best practices” concerningdesign, construction, problem identification and evaluation, inspection, maintenance,renovation, and repair associated with conduits through embankment dams. Most ofthe available information on these topics was reviewed in preparing this document.Where detailed documentation existed, it was cited to avoid duplicating availablematerials. The authors have strived not to reproduce information that is readilyaccessible in the public domain. This document attempts to condense andsummarize the vast body of existing information, provide a clear and concisesynopsis of this information, and present a recommended course of action. Thisdocument is intended for use by personnel familiar with embankment dams andconduits, such as designers, inspectors, construction oversight personnel, and damsafety engineers.In preparation of this document, the authors frequently found conflicting proceduresand standards in the many references they reviewed. Where conflicts were apparent,the authors focused on what they judged to be the “best practice” and included thatjudgment in this document. Therefore, this document may be different than someof the various participating agencies’ own policies.Embankment dams, regardless of their size, create a hazard potential from the storedenergy of the water they impound. Examples, such as Kelley Barnes Dam, whichfailed suddenly in 1977, show the destructive power of water when it is releasedsuddenly from behind even a small embankment dam. This embankment dam wasless than about 40 feet high and about 400 feet long, but when it failed, it releasedwater downstream at an estimated flow rate of over 24,000 ft 3 /s, killing 39 people.The hazard potential of an embankment dam is based on the consequences offailure, rather than its structural integrity.Embankment dams can be classified according to their hazard potential for causingdamages downstream should they fail. Various State and federal agencies havedifferent systems for rating the hazard classes of embankment dams. A single,universally accepted hazard classification system does not exist. All of the hazardclassification systems group embankment dams into categories based on the potentialiii