Following an extreme flood in 1964, no maintenance work was needed. Small trees have
become established on the riprapped highway embankment and along the base of the cut
slope.
Landslides, the major potential for instability along the relocated channel, are very common in
some California terrains, but are not evident here along the valley of the Outlet Creek. The
lack of naturally occurring landslides, which is attributed to the resistance of the underlying
bedrock, was an indication that the cut slope would not be particularly susceptible to failure by
mass movement. Except for the bare upper part of the cut slope, the appearance of the
relocated channel is not unnatural for a mountain stream in a narrow valley.
9.5.12 Nojoqui Creek at US-101 At Buellton, California (Example 12)
The lowermost reach of this creek was relocated to enter Santa Ynez River upstream from
the US-101 bridge, for purpose of avoiding a stream crossing at an interchange (Figure 9.13).
The performance period of 16 years (1964-1979), during which major floods occurred in 1969
and 1978, showed no evidence of degradation or lateral erosion in the relocated channel, but
a sinuous low-water channel had developed in the wide bottom of the relocated channel.
Severe bank erosion occurred in the natural channel at the bend upstream from the relocation
during flood of 1978, but this is not attributed to the relocation.
Figure 9.13. Plan sketch of Nojoqui Creek channel relocation (Example 12).
The site is located on US-101 about 1.3 km (0.8 mi) south of Buellton. Nojoqui Creek is
adjacent gaged stream of similar drainage area (Alisal Creek) has an average discharge of
0.15 m3/s (5.3 ft3/s), with no flow 64 percent of the time. This point-bar braided stream is
generally incised into terraces. Tree cover along the channel is less than 50 percent. Bed
material is gravel, cobbles, and small boulders; bank material is moderately cohesive silt, clay
and gravel.
The lowermost 760 m (2,500 ft) of natural channel was relocated into a straight artificial
channel 640 m (2,100 ft) in length, resulting in a length change factor of 0.84. The width of the
natural channel was in the range of 15-20 m (50-65 ft). The relocated channel has a top width
of 42 m (138 ft), a bottom width of 31 m (102 ft), and is bounded by riprapped dikes that rise
about 1.5 m (5 ft) above the flat bottom. Slope of the natural channel was 0.0044; of the
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