Littoral Sand Budget, Hawaii — Chamberlain 
181 
cell. The measured high rates of littoral trans- 
port normal to the beach (2 X 10 4 cu yd of sand 
per mile of sandy coast per month) represent 
within-cell transport of an intermittent nature. 
8. There is a definite decrease in the general 
intensity and magnitude of the littoral processes 
throughout the Hawaiian Islands from the 
northwest to the southeast. Both the absolute 
values of the littoral sand reservoirs and the 
rates of change of those reservoirs decrease con- 
tinuously from Kauai to Hawaii. These phe- 
nomena can be partially explained by the in- 
creasing youth of the islands to the southeast 
and consequently the better development of reef 
platforms and fringing reefs on the older islands 
to the northwest. A larger reef structure would 
allow a greater biological production of sand 
and could account for the greater volumes of 
the sand reservoirs on the older islands and for 
the progradation of the shorelines to the north- 
west. Real differences may also exist in the total 
amount of wave energy reaching the individual 
Hawaiian islands. 
APPENDIX 
HAWAIIAN WAVE TYPES 
Almost all of the energy that is available 
along the coasts of the Hawaiian Islands for 
deforming beaches and transporting sediment 
arrives in the form of ocean waves. These waves 
are generated in all parts of the Pacific Basin, 
some even in the South Indian Ocean, and, after 
a complex history, they arrive in the Hawaiian 
Islands exhibiting a wide variety of heights, 
lengths, periods, and velocities. At any one time 
several generating areas may be supplying waves 
simultaneously, and this consideration along 
with the seasonal activity of certain generating 
areas, the interaction of various wave trains, 
the attenuation of waves over long distances, 
and the effect of local winds and waves on 
distantly generated waves, all result in a very 
complex wave pattern along the coasts of the 
Hawaiian Islands. 
It is suggested from a study of available wind 
and wave data that the entire yearly wave 
spectrum in the Hawaiian Islands can be repre- 
sented by a few generalized wave types, typified 
I by a specific range of wave heights, periods, and 
i directions of approach (Fig. A-l). 
1. Northeast Trade Wave. These waves may 
be present throughout most of the year, but are 
largest between April and November when 
they usually dominate the local wave spectrum. 
They result from the strong trade winds blow- 
ing out of the northeast quadrant over long 
fetches of open ocean. These waves typically 
have periods of from 5 to 8 seconds, and heights 
of between 4 and 12 ft. The direction of ap- 
proach may vary from north through southeast, 
but the most frequent direction of approach is 
either from the northeast or from the east. 
Generally, northeast trade waves are present 
from 90 to 95% of the time during the summer 
and from 55 to 65% of the time in the winter 
months (Marine Advisers, 1963 and 1964; 
Moberly and Chamberlain, 1964). 
2. Southern Swell. During the winter season 
in the southern hemisphere (the summer season 
in the Hawaiian Islands) strong winds blowing 
over long fetches produce very large waves in 
the region adjacent to Australia, Antarctica, and 
in the southern Indian Ocean. These waves, 
after traveling distances measured in thousands 
of miles, arrive in the Hawaiian Islands as low, 
long-period waves from the southern quadrant. 
Typically, Southern Swell can be identified 
along the Hawaiian coasts because of its low 
height (generally, 1-4 ft) and long period 
(generally, 14-22 seconds). The direction of 
approach is from the southern quadrant (Snod- 
grass et al., 1966). In a typical year, Southern 
Swell arrives in the Hawaiian Islands during 
53% of the time, usually during the months 
April through October. 
3. Kona storm wave. Kona storm waves are 
generated by the interim winds associated with 
local fronts or Hawaiian lows of extra-tropical 
origin, as discussed above under meteorological 
considerations. These waves are neither frequent 
nor consistent, as they are associated with 
erratic westerly winds. However, since these 
waves may develop to a large size and may 
approach the Hawaiian Islands in a direction 
opposite to that of the normal wind and wave 
regime, they are extremely important in relation 
to beach accretion and erosion and to nearshore 
water circulation. Kona storm waves may ap- 
proach the Hawaiian Islands from any direction 
between the southeast and the west, but the 
larger waves are usually from the southwest. 
