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 PROCEDURESface; these can collect runoff and cause severe erosion. Vehicles, except formaintenance, should be banned from dam slopes and kept out by fences or barricades.Repair any ruts as soon as possible using the methods outlined in Section 5.4.5.Maintenance vehicles should only travel on the soil and grass portions of the dam whenthe surface is dry unless necessitated by an emergency.Any traffic damage that occurs should be handled by Refuge law enforcement authorities.Damage should be assessed and responsibility for repair should be determined. Repair ofthe damage should be performed by the Refuge.5.4.8 RiprapAn erosion problem called benching can develop on the upstream slope of a dam. Wavescaused by high winds can erode the exposed face of an embankment by repeatedlystriking the surface just above the pool elevation, rushing up the slope, then tumblingback into the pool. This action erodes material from the face of the embankment anddisplaces it down the slope, creating a “bench.” Erosion of unprotected soil can be rapidand, during a severe storm, could erode the dam. Figure 5-11 illustrates wave erosion.Figure 5-11: Example of Wave Erosion and BeachingThe upstream face of a dam is commonly protected against wave erosion and resultantbenching by armoring with a layer of riprap on bedding material. Materials such asbituminous or concrete facing, bricks, or concrete blocks have also been used to armorupstream slopes. Protective benches can also be built into the upstream slope of smalldams by placing a berm (8–10 feet wide) along the upstream face a short distance belowthe normal pool level, supplying a surface on which wave energy can dissipate.5-19Revision No. 0October 2008

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