3
Longshore Current
Recirculation System
Introduction
This chapter describes the development of a large-scale longshore current
(LSC) recirculation system for the LSTF. An LSC recirculation system is
essentially a closed-loop system that continuously recirculates longshore current
from the downdrift to the updrift lateral boundary of the beach while waves are
being generated. The objective of this system is to accurately control and
recirculate the wave-driven longshore current through the lateral boundaries of
the facility, and therefore maximize the length of beach over which longshore
uniformity of waves and wave-driven longshore currents exist in the facility.
The majority of the material discussed in this chapter was published previously
by Hamilton et al. (1996 and 1997).
Conceptual Design
During the past 5 decades, seven types of longshore current recirculation
systems have been used to conduct laboratory investigations of longshore
currents (Figure 10). The earliest systems were fairly simplistic, whereas the
most recent systems are more complex and are, in general, physically larger
which makes them substantially more expensive to design and construct. Each of
these seven types of systems will be discussed briefly in this section. Visser
(1991) and Svendsen (1991) also provide a description of several of these
systems.
Type 1: Putnam, Munk, and Trayler (1949) used a completely enclosed wave
basin and allowed the longshore current to recirculate in the offshore section of
the wave basin.
Type 2: Galvin and Eagleson (1965) and Mizuguchi and Horikawa (1978)
terminated the downstream wave guide at about the location of wave breaking,
allowing the longshore flux to exit the testing region. The longshore current
recirculated outside of the downdrift wave guide and reentered the testing region
beneath the wave generators.
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Chapter 3
Longshore Current Recirculation System
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