PORT WORKS DESIGN MANUAL PART 5 Guide to Design of ...
PORT WORKS DESIGN MANUAL PART 5 Guide to Design of ...
PORT WORKS DESIGN MANUAL PART 5 Guide to Design of ...
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following paragraphs.<br />
5.5.1 Coordinate System<br />
Shoreline computations involve the determination <strong>of</strong> longshore transport rates and directions<br />
due <strong>to</strong> different incoming wave conditions in different periods. As longshore transport can<br />
take place in either directions <strong>of</strong> the shore, it is necessary <strong>to</strong> set up a coordinate system <strong>to</strong><br />
avoid confusion <strong>of</strong> directions in longshore transport computations. The coordinate system<br />
defines the sign conventions <strong>of</strong> incident wave angles and longshore transport directions.<br />
The original shoreline is usually chosen for convenience as the x-axis. The y-axis takes<br />
account <strong>of</strong> the variability <strong>of</strong> longshore transport perpendicular <strong>to</strong> the shore. As longshore<br />
transport is related <strong>to</strong> long-term change <strong>of</strong> the shoreline, the mean sea level may be taken as<br />
the zero reference datum for the vertical z-axis. An example <strong>of</strong> the coordinate system is<br />
shown in Figure 10.<br />
5.5.2 Longshore Transport Rates and Directions<br />
A number <strong>of</strong> longshore transport formulae have been developed <strong>to</strong> calculate the longshore<br />
transport rates and directions at a point <strong>of</strong> the shore. An example is the CERC formula,<br />
which can be written as follows (CUR, 1987) :<br />
s = BH 2 c K 2 sinφ cosφ<br />
l o o rb b b<br />
or<br />
s l<br />
= BH 2 b<br />
c b<br />
sin 2φ b<br />
where s l = longshore transport due <strong>to</strong> breaking waves.<br />
B = a constant equal <strong>to</strong> about 0.025.<br />
H o = deepwater significant wave height.<br />
H b = significant wave height at breaker line.<br />
c o = deepwater wave velocity.<br />
c b = wave velocity at the breaker line.<br />
K rb = refraction coefficient at the breaker line.<br />
φ b<br />
= wave angle at breaker line.<br />
Other longshore transport formulae include those developed by Bijker, Van Rijn, Bailard and<br />
so forth. Longshore transport models are normally equipped with these formulae for<br />
designers <strong>to</strong> apply in the computations. More details <strong>of</strong> these formulae can be found in