Example Problem III-2-5 (Concluded)

(d) A weighting procedure using wave period bands similar to that used for the wave height bands

can be used to calculate an average peak spectral wave period *T*p = 8.4 sec; that is,

Tp = [(4)(1146) + (6)(2955) + (8)(7951) + (10)(4898) + (12)(1812) + (14)(330) + (16)(14)] / 19106

= 8.4

(e) Compute the wave celerity *C*1 and group celerity *C*g1 for the offshore wave data in water depth

Raphson iteration (or a similar technique) to solve Equation 2-16 for the breaking wave height *H*b

using the offshore wave height value *H*1 = 0.93 m and angle *α*1 = -33o, and find

Hb 1.2 m (3.9 ft)

The breaking wave angle is then computed from Equation 2-14:

αb = -8.8 deg

(f) Compute the potential longshore sediment transport rate for *K*sig = 0.39 using Equation 2-7b:

Q = (0.39) [ (1025)(9.81)0.5 / (16)(2650-1025)(1-0.4) ] (1.2)5/2 sin(2(-8.8)) = -0.038 m3/s

Convert the result to annual equivalent transport and multiply by the percent annual occurrence of this

event, 32.7%:

Q = (-0.038 m3/sec) (3600 sec/hr) (24 hr/day) (365.25 day/yr) (0.327)

= -393,000 m3/yr (-514,000 cy/yr) (directed to the left).

Note that a similar approach can be utilized to find an answer using the CEDRS database (see

Part II, Chapter 8) which provides "percent" occurrences (rather than number of observations) in

22.5E energy bands.

III-2-24

Longshore Sediment Transport

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