Delaware gazette and state journal. (Wilmington, Del.) 1883-1902, 1897-10-21
TO RESIST WAVES
Interesting Facts Regarding the First River
and Harbor Improvement.

the ftfst IiiVer
and HRrbor Improvement.
At recent meeting OF the Engineers
Club, in Philadelphia, Louis Y. SGher.
merhorn, president Ut the American
Dredging Co., read an interesting
paper on "Breakwnter Construction on
the American Coast. ~ The company
which Mr.. Schermerhorn represents has
the contract for completing the Della
ware Breakwater, work on which is
now rapidly progressing, and the
speaker gave many interesting facts in
connection with the Broakwater, which
is the very first work ever undertaken
by the United States Government in
the way of river and haTbor improve
ments.
1t had lite inception in 1929, under
an appropriation for improving harhor
facilities, and work on ii was continued
under subsequent appropriations until
lSl0. Nothing further was done for a
quarter OF a century, until, in 1866, the
work was resumed and the hreakwuter
was completed in 1860, at q total cost
of 80, 1872, 600 The work now in progress
is to connect tho breakwater with thu
ice breaker, which will make quiet
bHrhor in which it had bean aaid
thousand vessels could ride at anchor.
ialthough the speaker thought the esti-
mate too high.
In the designing of such work the
ability of the structure to withstand
| the impact Of the waves is an import
ant consideration. Waves arc OF vary
ing heights. On the Atlantic the waves
are frequently 80 feet high. and the
highest are 40 feet. OF Cape Horn
waves have been observed 30 feet high.
The energy Of great waves has been cal
oulated. from measurements with a
| dynamometer, to be az much as 6, 600
pounds per square foot applied along
| the entire depth of the wave, which
gives some idea of the forcs which
hreakwater must sustain. The waters
recoding from the breakwairr carry
with them any loose stones. The
activity of the waves is felt to q CERTAIN
depth, below which the water is quiet.
| This necessitates a construction
which IS divided into three parts; first.
| the foundation. or tho part lying below
the depth of wave action; second, that
portion including the depth from the
commencement of wave action to the
! high tide level; third, the superatruc-
turs, or portion above high tide level.
| The portion lying below wave action is
made Of small stones lying on the hot
ION with Just the slope on the sides in
which they naturally lie when dumped
on the line OF the breakwater. This ~
| all idle material and performs no Office
except as u support. In American
waters the surface of this portion would
be from IL to 10 feet below the surface,
varying with the amplitude of the tide.
which is from three to eight feet.
The slone of the material on the
| second portion will be modified by the
wave action. A receding wave will roll
the stones down the side to points
1 where they will bu no further affected
by the waves or by gravity. These
slopes are represented by proportion
for the lowest purtion OF | on ll3; this
is, slime l high and ll5 horizontal.
The portion affected by wave action be-
low high tide mas slope of on 3.
The puperstruuture is very much
sleeper, viz, 7.lu on |. The super.
structure has width on the top of 20
feot.
The Delaware Breakwater, heing the
oldest structure of the kind in this coun-
try, has furnished data TO the govern.
inept engineers for many similar struc.
lures, several of which are now being
huilt. 1t was originally modelled after
| lluTUpthu DTbdhhh WulCu ~
resam bieH, but tbs experience gained has
modified the plans of recent structures.
1t is not now thought necessary to have
tha foundation portion so wide in pro-
portion to the superstructures as in the
earlier plans.
The cost of such works has been
much reduced since the introduction OF
dredging machinery and vessels for
handling the materials. Stone ia now
foated over the line of thu work ard
dropped out of tho bottom of tho scows
where in eGrly days it required much
labor to load il upon sailing vessels,
and to unload it and put it in place.
Much larger stones can now be used in
the superstruGture, as they can he
handled readily by steam machinery.
In many places whore very large
blocks arc required they are made OF
cement in the position they are to ro-
main. In Franco cement blocks weigh
ing more than 100 tons have beun put
into such structures. 1t is especially
necessary where the wave action is very
marked that the stones in the super
structure ahall be large. In some
places whore great waves strike per-
pendicular wall the water has been oh.
served TO shoot up 200 feet, falling upon
tue top OF tne 6tpneS anu tontlnE To
wash them oil. In some cases large
stones have apparently been pulled out
of the wall into the aea. Several OK
plantations have been offered for this,
the speaker inclining to the belief that
the impact of the wave forces the air
through the interstices between the
stones to an air space at the back, and
that the expansive power of the air
pushes the st9ne seaward.
Mr.. Schermerhorn expressed the
opinion that work of this character
would be done cheaper and more eXpe-
ditiously by awarding the whole Oh one
contract instead of in separate con
tracts. 1t would enable the contractor
TO arrange to do the work on such q
scale as would greatly cheaper the cost
to him. The work now being done
costs 81. 1888 ton against So 30 for the
average cost per ton OF the breakwater
up to this time.
Bistorieai society of Delaware.
In the absence of Chief Justice
| Gbarlap r T,nra Inuio n Nnnnaurif N