EM 1110-2-1100 (Part III)
30 Apr 02
EXAMPLE PROBLEM III-2-12
FIND:
The level of protection (i.e., width of beach) afforded to a historical lighthouse as a consequence of
the nourishment project at the end of 3, 6, 8, 9, and 12 months after initial fill placement. The lighthouse
is situated at the shoreline 1 mile (. 1,609 m) south of the south end of the proposed beach at the
initiation of the project fill.
GIVEN:
A long beach fill is placed along a north-south directed stretch of shoreline along the east coast of
the United States (i.e., the azimuth of the offshore direction is 90 deg). The project is to be constructed
and maintained continuously to design project width throughout the project fill area. The project will
be constructed in two stages; Stage 1 will provide a fill width of 50 m, and Stage 2 (to be placed
3 months after initial placement) will add another 50 m of beach width, making the total finished project
width = 100 m. Assume that: Hb = 1 m; T = 10 sec; αb = 5 deg (from the north) K is assumed = 0.77,
and κ = 1.0. Sediment density to water density ratio (i.e., specific gravity) = ρs/ρ = 2.65; porosity n =
0.4; dB + dc = 6 m. Note that except for breaking wave height Hb, these are the same wave and sediment
parameters as given in Example III-2-8.
SOLUTION:
For Hb = 1 m, with other parameters the same as the previous problem;
0.77 (1)2 9.81 @ 1
1
1
1
ε'
8
2.65 & 1
1 & 0.4
6
m2
0.0508
sec
At the end of the first 3 months, the solution of Equation 2-37 (graphical solution provided by Figure III-
2-34) can be utilized with t = 3 months . 7.78 106 sec, and x = 1 mile . 1,609 m:
1,609
y (1 mile, 3 months)' 50 @ erfc
meters
2 0.0508 @ 7.78 106
. 50 @ erfc (1.28)
. 50 (0.07) 3.5 m
(Continued)
III-2-76
Longshore Sediment Transport
Previous Page
