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imity of the ocean. Before 1910, the floating 
relationship with underlying salt water was pos- 
tulated (Stearns, 1935, Hawaii Div. Hydrog. 
Bui. 1: 256), but it was not until the late 1920’s 
that the applicability of the Ghyben-Herzberg 
principle and its consequences were fully ac- ' 
cepted (McCombs, 1927, U. S. Geol. Survey, 
Water-Supply Paper 596A; Palmer, 1927, Hono- 
lulu Board Water Supply, Sup. 1st Bien. Rpt.). 
According to this principle, the head of fresh 
water above sea level should be balanced by a 
depth of fresh water below sea level about 40 
times as great, the exact ratio being dependent 
on the densities of the fresh and salt water. 
This relationship is correct only in static con- 
ditions, as has been demonstrated theoretically 
by Hubbert (1940, Jour. Geol. 28: 924-926), 
and requires modification in the near-shore area 
under dynamic conditions. Furthermore, it as- 
sumes steady-state conditions that do not per- 
tain. As shown by Wentworth (1942, Amer. 
Geophys. Union, Trans. 23: 683-693), changes 
in the depth of the salt-fresh contact zone must 
lag greatly behind the changes in the water-table 
elevation that initiate them. As yet there is no 
theory expressing the lag in terms of the per- 
meability and geometry of the aquifer and the 
nature of the fluctuation in head. The uncer- 
tainty is critical in attempts to estimate storage 
volumes and their changes. 
Good records of many years or even decades 
of head variation exist for many aquifers, but 
the only indications of salt-fresh contact fluc- 
tuations lie in the voluminous records of salinity 
at wells, generally analyzed at random times 
without regard to the variation in pumping 
conditions. Though attempts have been made 
for several years now to collect salinity records 
under standardized conditions, there is still a 
further difficulty, pointed out by Wentworth 
( 1947 , Pacific Sci. 1(3): 172-184), that the avail- 
able sampling points are ail in the upper part of 
the zone of mixture, which is capable of varying 
in thickness as well as position. 
At this point it would seem best to approach 
the whole problem from three directions si- 
multaneously: ( 1 ) development of an adequate 
mathematical theory of Ghyben-Herzberg func- 
tioning under nonsteady dynamic conditions 
for simple cases; (2) checking and extension of 
the theory by models, very likely electrical ana- 
logues; and ( 3 ) further experimental checking 
from test holes penetrating the zone of mixture 
in the simplest Ghyben-Herzberg bodies avail- 
able, for example, that on the isthmus of Maui, 
where there is practically no cap of sediments 
on the coast. The analysis of the experimental 
results in terms of the theory will depend on the 
measurement of permeability not only at the 
surface but also very deep in the aquifer. For- 
tunately, a method seems now to be available 
from the analysis of the progression of tide 
waves, induced by ocean tides, across the ground- 
water body (Cox and Munk, 1953, Amer. Geo- 
phys. Union, Trans. 34: 345). 
The development of an adequate dynamic 
Ghyben-Herzberg theory will be of very great 
importance to an evaluation of basal ground- 
water resources in Hawaii. It will also be of 
importance in many other coastal areas where 
Ghyben-Herzberg conditions pertain and in 
some of which the problems of salt intrusion 
are critical, but where the development of theory 
is rendered difficult by the complexity of struc- 
ture. — Doak C. Cox, Experiment Station, Hawaiian 
Sugar Planters' Association, Honolulu, Haivaii. 
