channels (particularly in larger rivers) are needed and can only be developed on the basis of
studies with a far broader scope than the normal project-oriented work funded by developers.
6.9.3 Channel Restoration and Rehabilitation
Over the last several years, numerous agencies and practitioners have published guidelines for
stream corridor restoration and channel rehabilitation design. For example, in 1998, fifteen
Federal agencies and partners published a manual, Stream Corridor Restoration - Principles,
Processes and Practices (Federal Interagency Stream Restoration Working Group 1998). This
document represents a cooperative effort by the participating agencies to produce a common
technical reference on stream corridor restoration. Recognizing that no two stream corridors
and no two restoration initiatives are identical, this technical document broadly addresses the
elements of restoration that apply in the majority of situations encountered. Reference is also
suggested to Rosgen (1996) and U.S. Army Corps of Engineers publications such as Watson
et al. 1999. HEC-20 (Lagasse et al. 2001) provides an introduction to stream restoration
concepts and HEC-23 (Lagasse et al. 2001) presents guidelines and references for
bioengineering bank protection treatments.
6.10 SOLVED PROBLEMS FOR STABILITY OF RIPRAP (SI)
6.10.1 PROBLEM 1 Stability of Particles Under Downslope Flow
^
Downslope flow over a plane bed inclined at an angle θ shown in Figure 6.32 is equivalent to
^
an oblique flow on a side slope with θ = θ and λ = 90. Then, according to Equation 6.4, β = 0,
and from Equation 6.6,
1 + sin 90 + 0
η′ = η
=η
2
It follows from Equation 6.3 that the stability factor is
^
cos θ tan φ
S.F. =
^
η tan φ + sin θ
Alternatively, solving for η yields
^
θ
^ 1 - tan
η = cos θ
φ
S.F. tan
Using this information we wish to calculate (if the angle of repose, φ = 40), what is the
^
maximum bed angle θ at which η will be 5 percent different from that of a horizontal bed.
^
^
Solving for θ with η = 0.95, S.F. = 1 and φ = 40 yields θ = 2.35 or 4.1 percent.
6.55
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