Table 10.4. Bank Migration for Alternative 4.

Design for Alternatives 4 and 5

Table 10.7. Size and Filter Design for Riprap at Spur Noses and Spur Shanks

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Table 10.4. Bank Migration for Alternative 4.

Strip Distance* (ft)

*The eroded bank should be restored to its present alignment after each flood to maintain an

adequate buffer zone.

Alternative 5. The fifth alternative is to construct a series of rock riprap spurs to guide the flow

away from the existing north bank (Figure 10.9). The design of the spurs includes: the form of

spurs, the angle of spurs to the bank, the length of spurs, the spacing between spurs, the

height or elevation of spurs, the construction materials, the crest width and slopes, and the

local scour. The design of the spurs is summarized in Tables 10.5, 10.6, and 10.7. Table 10.5

gives a summary of spur designs for different design floods including buffer strip distance,

number of spurs, spacing of spurs, height of spur above the existing thalweg level, riprap size

at the spur nose, and riprap size in the spur shank. Table 10.6 provides the suggested design

dimension of spurs including spur form, spur length, angle of spur to bank, the portion requiring

riprap the same size as used on the nose, and length requiring shank protection. Table 10.7

summarizes the sizes of riprap and filter design at the nose of the spurs and for the spur

shanks. HEC-23 (Lagasse et al. 2001) also provides design guidelines for a typical round nose

spur recommended by FHWA.

Table 10.5. Summary of Spur Design.

T is the flood return period in years, Q is the design discharge, Bm is the minimum buffer strip distance between the

railroad and the spur nose, Ns is the number of spurs, Sd is the spur spacing, ha is the design height of spur above the

existing thalweg level, hb is the design depth of spur at the spur nose below the existing thalweg level, K 50 is the

median size of riprap at the spur nose, and K 50 is the size of riprap for the spur shank.

Table 10.6. Dimension of Spurs.

Protection (ft)

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