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 PROCEDURESFigure 1-1: Typical Features of an Embankment Dam(see glossary in Appendix A for term definitions)Materials used to construct embankment dams include natural soil or rock obtained fromborrow areas or nearby quarries. If the natural material has a high permeability, then azone of very low permeability or impervious material is normally included in the dam toprovide resistance to flow and dissipate the hydrostatic pressure caused by the reservoirover a short distance. Some embankment dams use a masonry or concrete corewall tocreate the impervious barrier within the embankment. The ability of an embankment damto resist the hydrostatic pressure caused by reservoir water is primarily the result of themass or weight of the structure and the internal strength of the soil materials.Many small dams and older dams consist of a homogeneous earth embankment where thedam is constructed of similar material throughout. Modern embankment dams arenormally constructed with a zoned embankment and are composed of zones of selectedmaterials having different degrees of porosity, permeability and density. Most zonedembankments include a chimney drain and toe drain to collect and filter seepage throughthe embankment and increase the stability and long-term performance of the structure.The chimney and toe drain consist of coarse-grained material which has little resistanceto the flow of water and is not prone to shrinking or cracking. Water entering the drainsflows freely through the drain and exits safely beyond the dam without saturating thematerial in the downstream zone.In general, embankment dams are designed to minimize seepage and the chance for waterto exit on the downstream face.Revision No. 01-2 October 2008

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