(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

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

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