The Pacific commercial advertiser. [volume] (Honolulu, Hawaiian Islands) 1885-1921, 1896-07-02


into the sea through underground
drainage. excepting what is returned
/ to the air by the cane, trees, etc On
| the other hand. there are land surfaces
SO impact and close that. where the
slope is great and the rain comes i'm
gluts, the greater portion OF the water
goes directly to streams or the sea by
| surface drainage.
In the light of these general con-
siderations we may now look at the
Island of Oahu. First, there are the
low lands which reach from the sea
gradually up to the forest bearing al
| titudes. Their baroness. relative to the
| forest attitudes, is a result OF a much
smaller rainfall. Only trees, like the al
geroba, which subsist with very little
water, thrive on these lower levels.
Continued rain measurements tell us
that the actual rainfall il comparatively
small The surface drainage from these
lands, even under heavy rains, Is but
small compared with the whole IL we ex-
cept the surfaces OF the city and roads.
On the other hand, the return OF moist
ure to the air by direct evaporation
from these low lands is vast. 1t is true
there are few trees to aid the evapora-
tion, but there are high temperature
and almost constant and uninterrupted
solar light and heat acting upon the
moisture of the soil. Moreover, expert
| ments that have been conducted In the
Hawaiian Experiment Station labora-
tory, bearing upon the moisture alb
.sdrptive properties Of different soils,
furnish cause for belief that little OF the
rainfall can pass through TO the under
strata, most of 1t being absorbed by
the G11rfaQn Gnil a M ad n, ha afr
These experiments have shown that the
lands, baked by the sun, give up almost
all their moisture.
Again, the same experiments have
shown that the sun-dried soil will alb
sorb so per cent of it's own weight of
water This means that an sacre OF soil.
to depth of feet, will absorb 1000
tons of rain water, which 1t will gradu-
ally return to the air by direct evapora-
ton. II a crop of cane is growing upon
the land, as at Eva, then the moisture
is pumped out of the soil quickly and
even at the end of two or three weeks
the water left in the ground is not
enough to keep the cane in growth.
Eva has to pump up the underwater
brought from the mountains by strata
drainage to keep the crop going. At
the same time 1T is observed that the
underground of the lower lands is
abundantly porous to take down all
water that is not absorbed by the sur
face soil. Many examples of this are
seen on the windward side of the Is
land, and notably at Waimanalo, where
in many places the streams coming
down the rock sides, as soon as they
touch the land, disappear without any
surface flow. Where great number of
I<.e -
stream is formed
All these considerations however
tell us that we must go to the mount
aims, not only to estimate the rainfall
but also to form any approximate ideas
of what becomes of it. The average of
a number of rain gauges gives the rain
fall near the sea level at about 80
inches. Readings that have been made
for Is years at level of 900 feet, and
~ miles up show an annual rainfall
of 116 inches. The rainfall for the same
level differs, however with the locali-
ty. Nuuanu Valley has greater rainfall
at 1000 feet than is found in other
places. These facts have to be borne
in mind in the effort to approximate ay-
erages. Nevertheless, as rule, the
rainfall rises with the altitude, and at
highest levels it, of necessity (ex-
planned by several considerations),
reaches more than double the average
for the Island Then there is to be con-
sidered the extent in length, as well as
in breadth, of the windward attitudes
of the Island, not to mention the Wal
anae elevations; from Makapuu Point
to the drop of the mountain range at
Kahuku the length is about twice that
of the plain from Pearl City to Waialua.
That the great body of the rain falls
upon the mountains, is question that
consider what becomes of the water?
Here are to be chiefly kept in view the
conditions which control evaporation,
and Transportation of water by plants;
because the great body of moisture not
given back to the air must chiefly find
it's way by strata drainage to lower
levels, the surface discharge being only
small part of that total, which is
shown by the fact that it is only after
occasional great rains that the most
of the streams fiow whilst rain falls
upon the mountains majority of days
in the year.
Evaporation and Transportation of wa
ter by trees and plants, are chiefly con-
trolled by light, temperature, and the
humidity of the air. Deherain has
shown that Transportation is ten times
greater in full sunlight than in dark
ness, and during dull, cloudy days
without rain and with the same air tenn
perature, the Transportation is one-half