U.S. Fish & Wildlife Service Low Hazard Dams - Association of State ...

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U.S. Fish & Wildlife Service Low Hazard Dams - Association of State ...

STANDING OPERATING PROCEDURESInspection Guidelines – SpillwaysProblemProbable Cause andPossible ConsequencesRecommended ActionsAccumulation of slide materials,dead trees, excessive vegetativegrowth, etc., in spillway channel.Reduced discharge capacity;overflow of spillway, overtopping ofdam. Prolonged overtopping cancause failure of the dam.Clean out debris periodically; controlvegetative growth in spillway channel.Install log boom in front of spillwayentrance to intercept debris.Surface runoff from intenserainstorms or flow from spillwaycarries surface material down theslope, resulting in continuoustroughs. Livestock traffic createsgullies where flow concentratesvaries.Unabated erosion can lead to slides,slumps or slips which can result inreduced spillway capacity.Inadequate spillway capacity canlead to embankment overtoppingand result in dam failure.Discharge velocity too high; bottomand slope material loose ordeteriorated; channel and bankslopes too steep; bare soilunprotected; poor constructionprotective surface failed.Disturbed flow pattern; loss ofmaterial, increased sediment loaddownstream, collapse of banks;failure of spillway; can lead to rapidevacuation of the reservoir throughthe severely eroded spillway.Photograph condition. Repairdamaged areas by replacing erodedmaterial with compacted fill. Protectareas against future erosion byinstalling suitable rock riprap. Revegetatearea if appropriate. Bringcondition to the attention of theengineer during next inspection.Minimize flow velocity by properdesign. Use sound material. Keepchannel and bank slopes mild.Encourage growth of grass on soilsurface. Construct smooth and wellcompactedsurfaces. Protect surfacewith riprap, asphalt or concrete.Repair eroded portion using soundconstruction practices.Revision No. 0B-18 October 2008

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