EM 1110-2-1100 (Part III)
30 Apr 02
(2) Wave conditions.
(a) As discussed in Part II-2, WIS hindcast wave estimates are compiled in intermediate to deepwater
depths. The examples presented herein use Revised Atlantic Level 2 (RAL2) WIS data, which are presented
in 45-deg wave angle bands. Angles reported for RAL2 WIS Phase III stations αWIS are measured in degrees
"from" in a compass sense, for which due north equals zero and other angles are measured clockwise from
north. For calculation of longshore sand transport, a right-handed coordinate system is more convenient, in
which waves approaching normal to the shoreline are given an angle of 0 deg. Looking seaward, waves
approaching from the right are associated with negative angles, and waves approaching from the left are
associated with positive angles such that transport directed to the right is given a positive value and transport
directed to the left is given a negative value in accord with sign convention discussed earlier. WIS angles
may be converted to angles associated with transport calculations α by means of the following relationship:
α ' θn & WIS angle
(III-2-17)
where θn is the azimuth angle of the outward normal to the shoreline. Angles of α over 900 would be
excluded from calculations. The WIS angle is the azimuth angle the waves are coming from.
(b) RAL2 WIS wave data for one particular wave-angle band are summarized in Table III-2-2. The
number of occurrences are listed for specific wave height and period bands, with the total number of
occurrences listed in the right column (for each wave band) and bottom row (for each period band). The
header gives the time period for the data record (1956 - 1975), location of the station in latitude and longitude,
water depth, and angle band represented by the tabulated data.
(c) Data given in WIS statistical tables may be used in several ways to calculate the potential longshore
sand transport rate. Two examples using the data in Table III-2-2 are given below. In Example III-2-5, the
potential longshore sand transport rate is estimated with the average significant wave height for the given
Table III-2-2
Occurrence of Wave Height and Period for Direction Band 112.5E - 157.49E RAL2 Station 72
WIS ATLANTIC REVISION 1956 - 1975
LAT: 40.25 N LONG: 73.75 W, DEPTH = 27 M
OCCURRENCES OF WAVE HEIGHT AND PEAK PERIOD
FOR 45-DEG DIRECTION BAND
STATION 72
(112.500 to 157.490) mean = 135.00
Tp, seconds
Hmo(m)
3.0-4.9
5.0-6.9
7.0-8.9
9.0-10.9
11.0-12.9
13.0-14.9
15.0-16.9
17.0-18.9
Total
0.00-0.99
1,022
1,509
6,018
3,261
918
120
10
.
12,858
1.00-1.99
124
1,380
1,437
1,095
610
127
4
.
4,777
2.00-2.99
.
66
440
384
183
60
.
.
1,133
3.00-3.99
.
.
56
140
76
16
.
.
288
4.00-4.99
.
.
.
17
22
6
.
.
45
5.00-5.99
.
.
.
1
2
.
.
.
3
6.00-6.99
.
.
.
.
1
1
.
.
2
7.00-7.99
.
.
.
.
.
.
.
.
0
8.00-8.99
.
.
.
.
.
.
.
.
0
9.00-Greater
.
.
.
.
.
.
.
.
0
Total
1,146
2,955
7,951
4,898
1,812
330
14
0
19,106
III-2-22
Longshore Sediment Transport
Previous Page
