Dams Going Safely over the Top

by R. Lee Wooten, (M.ASCE), Project Mgr.; GEI Consultants, Inc., Raleigh, NC,
George R. Powledge, (M.ASCE), Western Regional Representative; GEI Consultants, Inc., Denver, CO,
Stephen L. Whiteside, (M.ASCE), Vice Pres./Mgr.; GEI Consultants, Inc., Raleigh, NC,

Serial Information: Civil Engineering—ASCE, 1992, Vol. 62, Issue 1, Pg. 52-54

Document Type: Feature article


Many older dams can't pass updated design floods without overtopping the embankment crest. Conventional upgrade methods, enlarging spillways or raising crests, are expensive. Modifying dams, by covering the downstream slope of the embankment with cellular concrete mats (CCMs) to prevent erosion during overtopping floods is a cost effective answer to the problem. Researchers at the Bureau of Reclamation had found that all three earth embankment dams will overtop during their inflow design floods. Last year, GEI Consultants, Inc., Raleigh, N.C. successfully tried this method, the first North American application, on three dams located in the National Park Service's Blue Ridge Parkway, near Blowing Rock, N.C. Originally designed to prevent wave erosion along coastlines, CCMs are prefabricated mats of precast cellular concrete blocks tied together by cables and anchored in place. Other components of a CCM overtopping system are an underlying geotextile filter fabric and mechanical anchors. At all three dams the CCMs were extended from the dam crest to the downstream toe. The downstream ends of the CCM aprons are either buried 5 ft deep and anchored with helical anchors or attached to a 10 ft deep concrete toe wall.

Subject Headings: Embankment dams | Cables | Wave overtopping | Floods | Precast concrete | Materials engineering | Lightweight concrete

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