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10 Figure 5: Dumped rock placement detail. Where construction of a berm is impractical or on an existing slope, keying of the riprap into the slope is recommended to prevent displacement of riprap down the slope. A reference published by the Minnesota NRCS state office titled “Slope Protection for Dams and Lakeshores” (USDA 1989) provides alternatives for keying riprap into existing slopes where the riprap will not extend the full height or length of the dam. The placement of riprap should be done by mechanical means, such as a hydraulic excavator. Dumping riprap from a truck down an embankment should be avoided as it can cause segregation of the rock by size and result in unsuitable gradation. Placement should be performed to produce a well-graded, even mass of rock with uniform cover and minimal voids. Laborers should be provided during placement for rearrangement of loose rock fragments, “chinking” of void spaces, and hand-placement as needed to provide a well-keyed and stable layer of riprap. Figure 6 shows dumped riprap being placed over bedding on the upstream slope of a small dam in South Dakota. Figure 6: Placing riprap bedding and riprap on the upstream slope of a small dam in South Dakota. Conclusion Properly designed and installed riprap can provide erosion protection from wave action that would otherwise cause significant damage of earthen embankment dams. For riprap to be effective the designer must calculate the required riprap weight, size and gradation, and specify acceptable material properties. The designer must carefully consider bedding and/or filter requirements to ensure that they are compatible with the embankment material and the riprap itself. References (with Links where available) To aid the designer through the process, the following is a list of design references that can be used:  USDA (1983), Technical Release No. 69: Riprap for Slope Protection against Wave Action.  USDA (1989), Minnesota Technical Note 2: Slope Protection for Dams and Lakeshores.  Reclamation (1992), “Design Standards No. 13: Embankment Dams”, Chapter 7 – Riprap Slope Protection, U.S. Department of Interior, Bureau of Reclamation, Technical Service Center, Denver, CO. Look for the revised version of this reference at the following link soon: Reclamation Dam Design Standards  Reclamation (1987), “Design of Small Dams”, U.S. Department of Interior, Bureau of Reclamation.  FHWA (1989), “Design of Riprap Revetment”, Federal Highway Administration, McLean, Virginia.