Year: 1877




water will be apparent. If the spring floods
OF 1877 act as did those OF 1876 IL widening
and deepening the channel on Richmond
bar. -t


Although much had been gained in the
removal OF artificial Instructions and rocks.
and in dredging channels through bars, by
which channel fourteen feet in depth was
obtained, yet in order to ascertain the
widths to which the river should be con-
fined so as to maintain the desired depth, it
was necessary to have thorough survey.
No such survey had been made since 1852,
and made then with no particular reference
to improvements. @ h>


The report next gives detailed account
of the survey referred to, made under the
direction of Colonel Craighill.'


SHALL WE HAVE A NARROW, DEEP CHANNEL?


From this survey it is ascertained that
the river requires certain area deepening
upon its slope, and whether this area shall
be deep and narrow or wide and shallow is
within the control Of man. II the charts
OF the river at Hampton Roads are inspect
ed we will find deep channel where the
river is contracted and the reverse where it
is wide. In this, nature seems to indicate
the needed means of Improvement. And
where the river has been lett to the opera
tions OF nature there has been no change
for the worse, so far rs the Engineer is in
formed, since 1852. On the other hand, the
channel over Harrison's bar is said to have
improved by the sitting up one Of the two
old channels, thus confining the current
more to the one now in general use.


The effect OF the obstructions placed on
Warwick bar during the civil war for quite
another purpose than improvement has
been to lower the crest OF the bar, accord
ing to the survey of 1874. And our works
of Improvement, limited in their extent it is
true, give support to this theory-that is, to
the theory that the discharge OF the river
requires u certain area, and il that area is
enlarged, the river will deposit sediment to
compensate for it, and if the proper area is
diminished, the river will restore it by the
removal OF sediment.


The river may have q channel 1,1S0 feet
wide and 8 feet deep at low tide, as for
merly, on Richmond bar, or, as proposed, a
width OF from $50 to 600 feet and Is feet
deep at low tide, with the same area. Either
will discharge the water. II the channel is
contracted the velocity will be increased,
and matter will move which would remain
in slower current. If, on the other hand, the
channel is increased in area, the velocity will
Ire diminished, and matter will be deposited,
due to the decrease, until the proper bal
ancc is struck. The Engineer next gives 4
history Of Richmond bar since the i'm
proyement was begun.


An analysis OF the survey further showed
that the low-water surface on Richmond
bar should have width OF from $50 to 600
feet to maintain IS feet OF water at high
tide; and Wing-damS are now being con-
Structed intended to limit the width to 600
feet.


WISG-DAMS AND sAND-BARS.


The Engineer next refers at length to the
good results obtained from the construction
Of wing-dams. They have been placed as
near each other as the means at our disposal
will warrant. Experience may show that
they are spread too wide apart, or that their
outer ends should be connected by dixie
parallel to the current; but the experiment
will not fail to give valuable information in
the future treatment Of the river.


He is OF opinion that nearly all the
sand-bars in the river may be removed by
similar treatment, more or less time being
required, according TO circumstances. But
nearly all the river bed above Richmond bar,
at eighteen feet depth at high tide, is in ma
teriaI whiciris not easily secured. The bot
tom, with the exception of superficial de-
post OF sand OF varying thickness, seems
to be an ancient deposit, and is certainly
not composed of materials now brought
down by the river. 1t is partly composed
OF granite, sometimes in reef, as at Rock
etts, and in narrow spurs above, but more
frequently in boulders OF varying sizes,
sometimes, as at Goodies Rock, forming a
shoal of considerable extent. These bould-
ers, as they are termed, are water-Worn,
!, do I,o 6aI yyh nE
the boulder proper usually has. They rest on
and in bed of hard material resembling
granite in color, but having consistency
OF hard clay or mari.


WILL 1T PAY TO KEEP THE CHANNEL DEEP?


An election made to the continuation 81
expenditure upon the river is that the river
is constantly carrying down material which
will bill up the eXcavated channels, and their
maintenance will be an endless labor.
Granting this, yet so long as tits expedienL
to maintain railroads, canals, and other
highways by a similar expense, it seems to
be eXpedient to keep this highway open,
which in Importance to the city exceeds
them all. The depth Of channels remained
essentially unchanged from 1852 to 1874,
and why may not the improved channel be
equally permanent if the work is done pro-





ings OF tue river itself? Perfection in such
matters is scarcely to be expected, but we
do expect that the cost OF maintenance will
be tritling compared with the benefits con-
ferred.


In the freshet Of April, 1876, a gallon Of
river water was obtained from near the sur
face to ascertain the proportion Of sediment
carried. The solid matter was separated
and measured, and weighed g. grains and
measured 4-10 OF cubic inch. Its volume,
when finally compressed in dry, powdered
condition, as compared with a gallon, was
as to 564. Supposing that gallon to be
fair average OF the river, then every 5G4
cubic feet OF water carried cubic foot OF
solid matter. In freshet Of ten feet rise
it has been estimated that no less than 277,-
900 cubic yards of solid matter pass Rock
etts in twenty-four hours. At low tide
there are about 25,OO0,000 cubic yards OF
water between Richmond and Dutch Gap;
SO that IL the estimate is correct, one hum
dred such days would completely fill the
river to the level of low tide down to Dutch
Gap, if all the material stopped there; and
supposing tive such days in year, twenty
years would suffice; and to what distance
lower down the two hundred and sixty or
seventy years which have passed since the
white man appeared would suffice to fill, the
Engineer leaves others to calculate.


CONCLUSION.


The present volume OF the James is suffi-
cient to maintain the depth Of channel which
the committee, as we'll rs the United States
engineer, have thought proper to recon-
mend-that is, eighteen feet depth at mean
high-tide. That such a river would be q
cheaper and better mode Of access to the sea
than any railroad could offer, the Engineer