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and riprap shall be mixed as needed to provide a homogeneous, <br />mass and in a separate operation, transported and placed on the <br />slope to be revegetated. Mixing shall be accomplished using <br />mechanical equipment such as dozers, loaders or backhoes, or by <br />batch mixing using equipment designed specifically for such an <br />operation. <br />Placement of the mass shall be accomplished in a manner to <br />assure that no segregation of the various constituents occurs. <br />No bedding will be allowed under riprap with vegetation. Sub- <br />sequent to the placement of the mass, a 6-inch to 12-inch layer <br />of topsoil will be placed above the rock. atypical detail of <br />this installation is shown in Figure 2.3. <br />2.3.3 Jetties (Groins) <br />Jetties may be used to protect river banks when the river is in <br />its existing, unstable alignment. The jetties must be install- <br />ed in such a manner that they not only control river flows dur- <br />ing normal and minor flood events, but also protect against em- <br />bankment erosion during larger events. <br />The geometric characteristics will conform to those shown on <br />Figure 2.4. The jetties will project from the toe of the chan- <br />nel bank a minimum of 15 feet and a maximum of 25 feet. This <br />distance will be measured from the tce of the bank normal slope <br />(after regrading to 4H:1V) where it intersects the channel in- <br />vert. The spacing of jetties shall be such that the ratio of <br />centerline spacing to projection is less than or equal to 3. <br />alI jetties will extend into the bank a minim~un of 15 feet as <br />measured from the toe of the bank slope. Jetties will be con- <br />structed perpendicular to the centerline of the channel or with <br />an orientation in the downstream direction of up to 45 degrees. <br />UD6FCTJ Gc~AVEL GUIDELINES 12/17/87 <br />2-10 <br />