Littoral Sedimentary Processes- — Inman, Gayman and Cox 
123 
reef is shallow, and causes waves to break in all 
weather. The seaward slope of the reef rises from 
a depth of about 15 ft, and is made irregular by 
numerous channels and solution and abrasion 
cavities (Figs, 9, 10). Beyond the base of the 
reef, the sea floor has a gentle slope out to the 
60- ft deep terrace. This terrace, which is com- 
mon to the submarine topography of Kauai, oc- 
curs about 1 mile offshore in the vicinity of 
Kapaa. A sea-valley extends from near the inlet 
between North and South Kapaa Reefs, across 
the shelf and into deeper water (Figs. 2, 8). 
The surface of the reef platform is very ir- 
regular and consists of a series of low intermit- 
tent channels and ridges (described by Munk 
and Sargent, 1954) which trend east- west and 
resemble in miniature the channels on the reef 
at Bikini Atoll. The channels are most pro- 
nounced on the northern and central portions 
of the reef and, although discontinuous, traverse 
the reef from the breaker zone to near the beach, 
where they enter the north-south trending de- 
pression which commonly exists at the. toe of 
the beach. 
Littoral Processes on the Reef 
The circulation pattern of water over North 
Kapaa Reef is from north to south; over that 
portion of South Kapaa Reef near the inlet, it 
is from south to north ( inset, Fig. 8 ) . The cur- 
rents flowing from the north and south reefs 
converge on the inlet and result in a seaward 
flow of several knots through the inlet. The 
anomalous depths of 27 and 38 ft, found rela- 
tively near shore in the inlet channel, are prob- 
ably maintained free from sand by scour as- 
sociated with the seaward-flowing current. 
Measurements on North Kapaa Reef by Helf- 
rich and Kohn (1957) show that both current 
velocity and the southerly component of velocity 
increase to the south. They obtained average 
values of current of about 1 ft per second on the 
central portions of the reef and a maximum flow 
of about IV 2 ft per second near the Moikeha 
Jetty. The most intense southerly flow of water 
occurs roughly one-third of the way between the 
beach and the seaward edge of the reef; currents 
at the toe of the beach were somewhat weaker. 
The currents appear to result primarily from 
the mass transport of water associated with 
waves breaking over the reef. Winds may also 
be a factor in driving the currents, but their 
effect is minor, as evidenced by the prevailing 
northerly flowing current over portions of South 
Kapaa Reef. Also, on several occasions, southerly 
flowing currents were observed flowing over the 
north reef in opposition to brisk winds blowing 
from the south. 
a-a ! section across north kapaa reef 
SAMPLE 55 56 59 60 
DISTANCE IN FEET 
* I 
Fig. 9. Section across North Kapaa Reef along line shown on Figure 8. Vertical 
exaggeration is 10 x. Survey by Sam Keala, Jr., and Hiro Murashige of Lihue Planta- 
tion; outer reef and sea floor offshore from the reef based on soundings by authors. 
