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7 Design of Riprap for Slope Protection against Wave Action Introduction This article is intended to provide practical guidance to engineers for the design and construction of riprap for embankment dams, particularly small embankment dams. This article is not intended to be an all-inclusive guide. A list of commonly used references on the topic is provided at the end of this article. As discussed in the previous article of this issue, earthen embankment dams can be subject to erosion by wave action within the reservoir. In 1983 the USDA developed a technical release (TR-69) that describes procedures for the design of rock riprap protection for earthen embankments to protect against wave action. TR-69 was used as the basis for this article. Detail not found herein can be found in TR-69 and the associated references. As mentioned in the previous article the design procedures described in TR-69 are generally limited to reservoirs having an effective fetch length of less than 10 miles and significant wave height of less than 5 feet. Additional relevant publications for guidance on the design of riprap slope protection include Chapter 7 of “Embankment Dams” (Reclamation 1992), “Design of Small Dams” (Reclamation 1987), “Design of Coastal Revetments, Sea Walls, and Bulkheads” (USACE 1995) and “Design of Riprap Revetment” (FHWA 1989). Why Riprap? Slope armoring acts as primary protection against embankment erosion caused by wind and wave action within the reservoir. Excessive erosion of a dam embankment can lead to embankment failure. Inadequately designed or installed riprap can pose a dam safety risk. For successful performance, a riprap layer must be designed to:  Protect the individual rock particles from displacement by the wave force, and  Keep the protected earth, filter, and bedding underlying the riprap from being washed out through the voids in the riprap. Figures 1 and 2 are examples of the embankment erosion that can occur without adequate protection against wave action. Figure 1: Erosion of a small embankment dam in Montana caused by wave action. Figure 2: Erosion of a small embankment dam in Montana caused by wave action. Riprap is one material commonly used as armoring for upstream slope protection. There are other commercially available armoring materials, each with their own design considerations and methodologies.