FLOOD00950

• County: Statewide
• Title: Rock Riprap Design for Protection of Stream Channels near Highway Structures volume 2
• Date: 1/1/1986
• Prepared By: USGS
• Floodplain - Doc Type: Educational/Technical/Reference Information

ROCK RIPRAP DESIGN FOR PROTECTION OF

STREAM CHANNELS NEAR HIGHWAY STRUCTURES

VOLUME 2--EVALUATION OF RIPRAP DESIGN PROCEDURES

By J.C. Blodgett and C.E, McConaughy

ABSTRACT

Volume 1, "Hydraulic Characteristics of Open Channels," discusses the
hydraulic and channel properties of streams, based on data from several hundred
sites. Streamflow and geomorphic data were collected and developed to indicate
the range in hydraulic factors typical of open channels, to assist design, main-
tenance, and construction engineers in preparing rock rip rap bank protection.
Typical channels were found to have a maximum-to-mean depth ratio of 1.55 and a
ratio of hydraulic radius to mean depth of 0,98, which is independent of width.
Most stable channel characteristics for a given discharge are the slope, maximum
depth, and hydraulic radius.

In volume 2, seven procedures now being used for design of rock riprap
installations were evaluated using data from 26 field sites. Four basic types
of rip rap failures were identified: Particle erosion, translational slide,
modified slump, and slump, Factors associated with riprap failure include stone
size, bank side slope, size gradation, thickness, insufficient toe or endwall,
failure of the bank material, overtopping during floods, and geomorphic changes
in the channel. A review of field data and the design procedures suggests that
estimates of hydraulic forces acting on the boundary based on flow velocity
rather than shear stress are more reliable. Several adjustments for local con-
ditions, such as channel curvature, superelevation, or boundary roughness, may
be unwarranted in view of the difficulty in estimating critical hydraulic forces
for which the riprap is to be designed. Success of rip rap is related not only
to the appropriate procedure for selecting stone size, but also to reliability
of estimated hydraulic and channel factors applicable to the site.

Further identification of channel properties and the development of a new
procedure for estimating stone size are presented in volume 3, "Assessment of
Hydraulic Characteristics of Streams at Bank Protection Sites."

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