Los Angeles daily herald., 1873-12-31


available will be sufficient for this pur-
pose, as well as to complete the other
parts of the work.
Amount available July ,46l Al
Amount appropriated by Act OF 20 ooo M
Amount e. expended during fiscal year
ending June 30, !49,Si4 ~
Amount available July /. lS73,~...... l45,647 VI
No additional appropriation is re-
quired for the next fiscal year.
U. S. ENGINEERS OFFICE,
San Francisco, July %, 1873. !
General:-I have the honor to sub
nit report of operations on the break
water at Wilmington, California, for
the year ending June 30, 1873.
This work is intended to improve
the estuary at Wilmington, in the bay
of San Pedro, by connecting Rattle
snake and Deadman's islands In a
manner to compel the tidal currents
to follow defined channel. :.
The distance between these islands,
which is the length of the work, is
600 feet, along 400 feet of which the
construction is of timber, and on the
remaining 1900 feet it is of stone.
Commencing at Rattlesnake Island,
for a distance of 800 feet the work
consists of line of double-sheeting
piles, substantially braced, driven as
far as practicable in the sand, and ris-
ing about a foot above high water.
For the next 1000 feet the work con-
sists of two parallel rows OF II inch
piles 10 feet apart, the piles in each
row being in juxtaposition. and all
substantially braced. For part OF
this length the work is filled with
brush and stone, but the greater part
has no filling. The last section, next
Deadman's Island, 1000 feet in length,
is training wall Of stone, rising to
half tide, 10 feet wide on top, with an
exterior slope Of and an interior slope
Of / II
These difficulties eliminated in what
appeared to be serious disaster. Du-
ring high course Of spring tides in
July, three portions of the work close
together, and in all $50 feet, with l20
feet Of wings or jetties, were carried
away, and the tidal currents resumed
their original routes across the line of
the work.
1t soon appeared that the disaster
was blessing in disguise. No eft0rt
was made to close the breaks, and no
further difficulty, as far as scour was
concerned, was encountered. The
three tidal rivers as they might be
called, for they excavate channels %
feet in depth, were an outlet or vent
for these troublesome forces. After
all was done, it became evident that
it would have been wiser course to
have provided this escape in the be-
ginning.
The work now advanced free from
similar difficulties. The main trouble
now was in securing the requisite PEN
tration for the piles. In some cases
$50 blows from 2, 400 pOnnd hammer
were required to produce penetration
of II feet.
The pipe-work was finished in OctO-
ber, and by the end of November the
carpentry work was completed. This
for 400 feet.
The gaps, however, remained open,
except that, as opportunity offered,
stone was thrown in. AS soon as the
timber work was completed, the work
of filling the breaks was prosecuted.
They were filled with stone to a level
about feet below low water. The
stone was levelled, and upon it were
placed cribs feet deep, which were
also loaded with stone. On these cribs
q superstructure similar to that OF the
rest of the work was placed. 1t was
January before these breaks were
closed. AS the closure was gradual
and slow, there was abundant OppOr-
| tunity and time for the tidal forces and
channels to be accommodated to the
new conditions, and new direction
was successfully given to these cur
rents, without impairing the work
constructed. Two OF these breaks were
fitted with tide-gates, open on the
flood, but closed on the ebb. The ebb
current is thus materially reinforced,
and its securing power increased.
1t became necessary to embank the
timber work, and for months back this
has been in progress. The first section,
3,700 feet in length, is nearly COM
| pleted. The embankment is protected
by jetties of stone or cribs placed at
| right angles to the work. The materi-
ais used for the embankment are clay,
sand, gravel, and beach shingle. I'll
Of this training-wall, 1000 feet in
length, 600 feet are finished; for anoth-
er distance of 900 feet is two-thirds fin
ished; for the remaining 800 feet it
is half finished. 1t is expected that
the whole will be completed during the
autumn.
AS the work progresses noticeable
changes took place in the channel. No
perceptible deepening of the water in
the shOalest part of the entrance re-
suited until the line of stOne-work was
extended to Deadman's Island. The
channel had been widened, however.
The horizontal curves have since been
advanced inside the bar. The 9.fOOt
curve has been moved forward about
25O feet, and the l5-foOt curve has
changed to about the same extent. In
the last course of spring tides, the water
on the bar has been deepened about
one foot.
1t is proposed to make a channel 200
feet wide and 10 feet deep at low water.
According to the survey made by
Lieutenant Sears, during last summer,
it will be necessary to move about
l04, 900 cubic yards to attain this re-
suit. The ebb-current is now moving
part of this amount. AS soon as this
action ceases, it is proposed to resort
to artificial means to remove the in
durated sand and bowlders. It is i'm
possible to be exact in an estimate of
what it will be necessary to do by az
tificial means until we know what to
expect of the current.
1t has been assumed that the loose
sand would be carried out by the cur
rent. If this expectation be realized;
there will remain to be moved arti-
ficially about 1000 cubic yards of in
durated sand, with spots of bowlders