The herald., 1897-04-04
SAN PEDRO
An Examination of It's Geographical
Position


San Pedro Bay is OF somewhat similar
shape to Santa Monica Bay, but is very
much smaller. Its western boundary il
distinctly marked by Point Firmin, while
its eastern limit is somewhat indetermi
nate; it is, however, practically not more
I than u miles wide and less than five
miles deep The heaviest undulations oi
the ocean, which might otherwise reach
San Pedro from the southwark from al
most unlimited ocean distances are hrs'
impeded in their northward progress tow
ard the coast by the shores of San Glenn
ente Island, approximately 20 miles south
of Santa Catalina Island. This last
named island the nearest point of which
is IS miles from San Pedro, acts as a
more or less efficient barrier to storm
waves generated far out to the southwark.
San Pedro Bay is protected on the west
by Point Firmin and San Pedro hill; il is
protected on the north and northeast by
the general shore line; it has some pro-
lection on the southwest from Santa Cata-
lima Island; it is entirely exposed to the
southeast and between Santa Catalina ISL
and and Point Firmin on the southwest;
The north shore of the bay is low and
tide flats extend in placed more than
channel between jetties 700 feet apart,
the opening facing the southeast
and being little east of Point Firnin::
line drawn from the mouth. of the letties,
past Point Firmin, bears south 81 degrees
west, magnetic, and strikes Santa Cata-
lima Island near its west end. The east
end of Santa Catalina Island bears south
IL degrees east, magnetic, from the mouth
of the ietties. The most southerly point
on the main shore which can be con-
sidered as affording any protection what
ever is San Juan Point, about 30 miles
distant and bearing south rs degrees east,
magnetic, from the mouth of the jetties.
The harbor entrance is therefore fully
exposed for "a degrees, the mean of this
exposure being south 4S degrees east,
magnetic. 1t is partially exposed for AZ
degrees, being the angle between the east
end of Santa Catalina Island and Point
Firmin; as Santa Catalina Island Is IL
miles nearer to San Pedro than to Port
Los Angeles, the protection afforded by
it is proportionately greater, but this en-
trance to the jetties is wholly or partially
exposed for log degrees, the center OF the
exposed area being south % degrees east
magnetic.
A considerable growth of long kelp in
the western part of San Pedro Bay in
dicates the existence of rock on the bot
tom. A rock marked by the bell buoy
on the five fathom line is about half an
acre in extent, the highest point being II
feet below mean low water With this
exception, the rock wherever examined
has been found to be nothing more seri-
Gus than loose bowlders, and this char
acteristic is confirmed by the fact that
there are no abrupt changes in the bottom.
The limited portion of the bay back OF a
line connecting Point Firmin with Dead
mans Island is more rocky than the rest,
indicating that the point may once have
extended eastward and included this
island. The eastern part of San Pedro
Bay appears to be free from all sub
merged or hidden dangers, while the 10
fathom line is generally from two and
half to three miles from the shore.
A BREAKWATER NEEDED.
At neither location can a deepwater
harbor which will meet the requirements
of the law be constructed within the linn
its of the present shore line; il can only
be made by breakwater which will fur
nish the necessary area OF protected
smooth water behind it. At Port Los An
peles this breakwater must afford protec-
ton against southwest seas and swells,
the mean exposure being very nearly in
the direction of the heaviest swell. At
San Pedro the breakwater must afford
protection from southeast to southwest.
As the breakwater at Port Los Angeles
must be some distance outside of the
per and that at San Pedro some distance
outside of the present harbor entrance,
the exposure will be somewhat increased
at the breakwaters, this being especially
the case at San Pedro, where a portion of
the breakwater must necessarily be be-
yond the protection of Point Firmin. So
far as can be judged from the evidence
placed before the board, from personal
observations and from the direction of
exposure, the duties which must be per-
formed by a breakwater at Port Los An
geles would probably be greater and the
seas which it might have to resist may be
heavier than would be the case with a
breakwater at San Pedro. In view OF the
fact, however, that violent storms and
point, it has been thought right to esti-
mate on the same construction at each
place. At either site a breakwater OF
lighter section than would generally be
demanded is admissible.
The general form of breakwater select
ed consists of random stone structure
terminating at mean low water, sur
mounted by superstructure OF more reg
ularly shaped rock, roughly placed and
finishing II feet above mean low water,
this being about seven feet above extreme
spring tides, the superstructure to be pro-
tected at each end by block of con-
crete 40 feet square, finishing 20 feet
above mean low water. A cross Sec
ton of this breakwater accom-
finishes 80 feet wide at mean low water
and 80 feet wide at the assumed approx
mate plane of rest, u feet below mean
low water; it has slope of 1.3 horizontal
to vertical for the whole height on the
harbor side and below the assumed plane
of rest on the ocean side, this being the
slope which random rock dumped in water
NAV be expected to assume. For the IL
feet above the plane of rest on the ocean
side the slope is 8 horizontal TO l vertical,
affording flatter slope for the waves to
break upon; at the ends the substructure
finishes square with slope of 1.3 hori-
zontal to / vertical, corresponding to that
OIL the harbor side. These are close dimen-
sions, to which the actual construction
would conform approximately and when
are used in the preliminary estimates.
The superstructure is 80 feet wide at the
base at mean low water, and 20 feet wide
at the top it is formed of heavy stones OF
approximately rectangular shape, these
stones heing laid with their greatest
dimensions at right angles to the break
water and in the form of rough steps, the
retreat of these steps being 10 feet on the
ocean side and feet on the harbor side.
To protect the work from injury from
waves passing around the ends, II single
block of concrete 40 feet square and y
feet high is substituted for the ordinary
slIperstructure at each end, this block oi
concrete forming monolith of 80, O0C
cubic feet, weighing 2000 long tons.
(Here follows technical study of the
uuarries from which the material could
be had.)
:. Before considering the special features
Of the two harbors it is important to CON
slider the action of the breakwater. Much
4 e. xx~l.t .tx.I.