The Hawaiian star. [volume] (Honolulu [Oahu]) 1893-1912, 1907-04-24
.SCHUYLER'S REPORT
ON NUUANU DAM

ter in various Irregular strata WhlcH
water appears in every deep excavation
which intersects these strata and flows
out in little streams; the highest OF
these strata is about at elev. go or
some II feet above the lowest part of
the original stream bed and percola-
lions from it are coming into the
stream on both sides above the core
wall. In excavating the core trench on
the Eva side a stratum of porous ma
terial was encountered at elev. $50,
from which some As gallons per minute
came into the trench. An attempt was
made under Mr. Kelogg's direction to
give free drainage to this water by put
ting in a crushed rock drain IS in
ches deep makai of the core wall. When
the trench was refilled over the rock
drain it appears to have stopped the
flow while the rehling on the mauka
side is also tight and solid without
appearance of seepage at the Eva side
of the stream. In other words,
the core-wall and reilling of
the trenches have made an effectual
stoppage of the percolation down
stream past the line of the dam. On
the Waikiki side the core trench is
still open, giving an opportunity of
thoroughly inspecting the character of
formation throughout.
In this trench at a point $50 feet wal
kiki of the stream channel, small
spring was encountered at elev. 1853, 30
feet below the surface flowing 20 gal
Ions per minute. An attempt has been
made under my direction to confine this
spring in such way as to produce a
head. but without success as the water
finds it's water through porous strata
around all the original point of exit
The only way in which such a spring
can injure the dam is to develop suffi'
! Gent head to work it's way upward tt
the original surface and find ext
i through the embankment. I am nov
fully convinced that the refilling of tn
trench with earth will restore the orr
Il pinal conditions, and the water vii
henceforth percolate out underneath tn
1t heavy blanket of soil OVERLAPPING with
ont any possible connection with tn
reservoir
If the Nuuanu stream bed had neve
crt down lower than elevation $40 o
975 at the place where the dam is locat
ed I think there would be no seepage
appearing along it's banks, as are nov
IL to he seen, but the water would perco
u late slowly underneath the surfac
al down the valley The velocity of sue
~ rercolation through the fine characte
d of material in these porous sub-strat
is almost inconceivably slow and pow
IL erless TO carry away the finest silt, 9th
III erwise the water would not come GU
III clear as it invariably does The veto
az CITY of such percolating waters as de
en- tarmined by experiment is as slow a
Gu 1000 to 1000 feet in year. Those dee
XII living strata have been intercepted b
We the concrete core wall which rests O
o. he'd rock Is to % feet deeper than tn
~ bed of the stream and extends well int
the bank on either side of it's channe
!" total length of $50 feet, while beyon
u the ends of the concrete the wood cor
e wall rests on impervious material 10
ne the remaining length of the dam-lou
ne Teet. Thus the downstream percola
lions will necessarily either be checke
al at the dam or diverted around the dar
oy at either end. The condition then ma
Ill be compared to the excavation of
IT, well or shaft through various waite
bearing strata. AS long as the well
Vi kept pumped out water will come int
m it from all sides, but when pumping
~ ceases the water will assume a certail
d static level and remain quiet withou
Sc visible motion. If the well were to b
n filled solidly with earth the effect o
the percolating water upon such cart
filling would be nil. The slow dow
stream movement would continu
around the filling without in any wa
Up affecting or moving the earth film
At in the well. SO it must be with tn
et dam: which would constitute the cart
De- filling in the we'll illustration. tn
ne stream channel may be likened to
W broad, shallow well which has been ex
ls cavated through the porous strata
H. When the earth filling of the dam is
'p place it will restore the condition
De that might be imagined to exist had nc
the stream channel been cut dow
through the porous strata carrying fl
Oh trations of water and the core wall wi
IS form an impervious side to the wei
III In order that any water shall escap
from the reservoir by leakage it mus
7u find it's way into the porous strata an
pass entirely around the dam. 1t ma
do so to some small extent but in es
Gaping IT can do no possible injury
This reasoning think is incontroverti
IL BILE.
ne PRESENT APPEARANCE OF WORl
D. To the layman unfamiliar with daT
construction the present appearance q
the work is not encouraging, and 1t
m difhcult to appreciate what has bee
accomplished or where the money ha
ne been spent, The most difficult part O