Rock Riprap

Natural rock of appropriate size, density, and gradation is placed on shaped streambanks and in open-toe trenches. A gravel filter is placed under the rock to prevent erosion of soil material from beneath (fig. 11). Extensively eroded outside curves are generally realigned with enough "bend" left for necessary energy dissipation. Environmental considerations include impacts at sites where rock is obtained; preservation of as much existing streamside vegetation as possible during construction; construction during low-flow or dry stream conditions; preservation or enhancement of fish and wildlife habitat; fencing; and seep trenches. Stabilization of streambed grade may be an integral part of this measure.

Concrete grout may be incorporated where channel alignment problems and/or flow velocities require greater protection from the influence of scouring or high-energy flows. Environmental considerations include the use of vegetation,

Figure 11.
A typical streambank in cross section protected with natural rock over gravel bedding and willow cuttings.
The toe trench is used to trap bank seepage and encourage better growth of cuttings and natural vegetation.

visual impacts, aquatic life, and use of colored grout.