the river width (where bordered by natural vegetation) is 24 m (79 ft). The stream is
perennial, alluvial, sand bed, in a valley of moderate relief and in a wide floodplain. The natural
channel has a sinuosity of about 2.5 but the channel has been straightened; it is equiwidth,
not incised, cut banks are rare, with silt-sand banks.
The channel was first straightened and enlarged in the 1920s by local drainage districts; but,
probably because the natural floodplain forest was not cleared, the banks remained stable. In
1969, the Corps of Engineers straightened and enlarged a reach about 4.8 km (3 mi) in length
downstream from the bridge, reducing the length about 20 percent. During the 1960s, and
particularly early 1970s, the floodplain was cleared of trees for agricultural purposes.
Figure 9.9b illustrates the Corps of Engineers' channel modifications that reduced the channel
length and increased the channel slope. Figure 9.9b also provides a profile of the channel
before any modifications were made in 1975.
Between 1970 and 1971 the left bank (near bent 7) at the bridge receded an average distance
of 4 m (13 ft). The peak discharge during this period was 215 m3/s (7,592 ft3/s) (1.5 year
recurrence interval). Timber pile retards were built at the left bank near bent 7 and a single
row of pile with wood face planks extending from the downstream end of bent 7 for a distance
of 37.5 m (123 ft) upstream (Figure 9.9c).
Figure 9.9b. Channel modifications to South Fork of Deer River at U.S. Highway 51 near
Halls, Tennessee (Example 8).
9.28
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