162 
sion, biological activities, wind, etc., may ac- 
tively contribute sand; whereas paralic sedi- 
mentation (e.g., lagoonal, shallow neritic, trans- 
portation of sand into deep water via submarine 
canyons), the transformation of beach sand 
into beach rock, and wind are factors that are 
responsible for the loss of beach sand. 
In any one locality certain of these processes 
many predominate. For example, in the Ha- 
waiian Islands beach sand is primarily acquired 
through the biological activities of reef orga- 
nisms, and is primarily lost by paralic sedi- 
mentation. Notwithstanding the particular pro- 
cesses involved, if the coast is in equilibrium 
there must exist a qualitative balance between 
the rate of sand production or input and the 
rate of sand loss. Quantitative considerations 
of these rates and their effects upon the beach 
and nearshore sand reservoirs give rise to the 
concept of a littoral sand budget, i.e., a quan- 
titative balance under equilibrium conditions of 
the rates of change and volumes of beach and 
nearshore sand. Basically, the littoral sand 
budget can be divided into three separate parts : 
sand input, alongshore transport, and loss. 
However, a fourth consideration — time — must 
frequently be introduced due to the fact that, 
although short term rates of input, alongshore 
transport, and loss may not balance, the coast 
may yet be in perfect equilibrium over longer 
periods of time. For an example, high rates of 
sand input due to heavy flooding of coastal 
streams may not balance with the loss of near- 
shore sand over the same period of time, yet 
the fluctuations of this sand input may be such 
that over long periods of time the rates of sand 
input, alongshore transport, and loss are in 
equilibrium. 
Considering beaches and coasts from the 
viewpoint of such a littoral sand budget, it 
can be shown that there exist certain stretches 
or units of coast along which the rates of sand 
input, alongshore transport, and loss are in 
equilibrium and between which there is little 
or no exchange of nearshore sediment. Typ- 
ically, in the Hawaiian Islands these littoral 
units or littoral cells are separated by rocky 
promontories or long stretches of high, nearly 
vertical sea cliffs around which little or no sand 
is transported (Fig. 1). 
PACIFIC SCIENCE, Vol. XXII, April 1968 
DISCUSSION 
Littoral Sand Reservoirs 
Sand-size material, contributed to the littoral 
sand budget by a variety of agents as discussed 
above, is transported into the nearshore zone, 
moves onto and along the beach, and after a 
rather long and complicated journey within the 
nearshore zone is finally transported out of that 
zone into deeper water, blown inland by the 
wind, or otherwise lost. Various reservoirs of 
sand therefore exist, corresponding to the vari- 
ous zones or environments through which the 
sand passes as it progresses toward its final de- 
positional environment. Two types of sand 
reservoirs are common within the Hawaiian lit- 
toral cells: (1) the beach reservoir and (2) the 
nearshore reservoir, in turn composed of reef 
channel, reef flat, or river mouth. 
beach reservoirs (comparisons) : Large 
volumes of sand are found between mean sea 
level and the upper limit of wave action on two 
of the seven major islands of the Hawaiian 
group, while on the other five the total volume 
is extremely small. Moreover, the average vol- 
ume of the beach sand reservoir per mile of 
sandy coastline varies greatly from island to 
island. The subsurface base of the beach was 
determined by water- jet probing; essentially it 
is the contact between the beach and indurated 
rock or cobbles. The landward limit of the 
beach was taken as the upper limit of wave ac- 
tion as determined by the beach contact with 
growing vegetation, sea cliffs, windblown 
dunes, etc. The seaward edge of the beach is 
mean water level. As can be seen from Table 
1, more than one-third of all beach sand in 
the Hawaiian Islands is found on the beaches 
of Kauai, and more than one-fourth, on the 
beaches of Oahu. Together these two islands 
hold 61.4% of the total beach sand found in 
the State of Hawaii. 
In order to compare the intensity and/or 
nature of the littoral processes of the various 
Hawaiian islands, it is necessary to weigh the 
total beach sand reservoir of each island by 
some parameter, such as length of coastline, 
which in turn can be related to the zone or area 
over which the littoral processes are active. 
Table 1 gives the average beach reservoir vol- 
