532 IRRIGATION AND WATER RESOURCES ENGINEERING
15.5. SLOPE PROTECTION If the upstream slope of an earth dam, retaining a large reservoir, is composed of materials other than cobbles or rocks, it must be protected against damage by wave action. Based on past experience, the methods of upstream slope protection are: (i) dumped rock riprap, (ii) hand-placed stone pitching, (iii ) monolithic RCC slab, and (iv) asphaltic concrete. Of these four methods, the dumped rock riprap overlying a finer filter layer (or layers) provides an excellent wave protection measure as it is least damaged by post-construction embankment settlement and is an effective dissipator of wave energy. A riprap layer should be designed such that: (i) the individual rocks are not moved out of place by the wave forces, and (ii) the filter underlying the riprap will not be washed out through the voids in the riprap layer. The filter itself should be able to prevent erosion of the underlying embankment material. The thickness and size of dumped rock riprap, as recommended by Bertram (15), are given in Table 15.4. Table 15.4 also gives the minimum thickness of underlying filter layer as recommended by the US Army Corps of Engineers.
