The daily dispatch. [volume] (Richmond [Va.]) 1850-1884, 1872-07-29

Except the facts Were forced upon our at
tcnion. we should be little likely to apprc-
ciatc the changes which are frequently ci-
ffcIcd by large rivers flowing from noun
famous regions into the sea. Bit little re-
Election will convince lis that these changes
must DC very great II is not difficult by
careful observations to determine the amount
of water running in any stream; not tiiai
great accuracy in such measurement Is 10 De
expected, but approximation only more or
less exact. Moreover, frequent observations
for il lon. period would also establish rule
in regard to the character of the water, elll-
bling lis to determine the amount of earthly
matter which we should expect to find. The
Missouri, for example, is remarkable as Il
turbid stream, and the Mississippi also par
takes Of the same character. Careful OBJ
scrvatiuns At New Orleans lmNc established
the fact that the average amount 81 Walcr
running in the river nt that point is not far
from III 300 cubic feet prr second; and also
the amount of scdnrnt;rry uatCr which
thi. water contains is about one l'iicc-thnl!-
sundth part OF its volume, or one twelve hun
drcd and forty.fth part Of it. weight. WITH
these figures rs data. Il simple aI1lhnic-
teal calculation will show that 10 less
| than !. 0Si JOS, 900 cubic feet OF sediment Is
carried down past New Orleans every year;
| more ttlau enough to cover one hundred ana
| fnrty-tour square miles one foot deep. DAILY
| observations Of the river Pc, below the ell
trance of its last tributary, fora period OF
| fourteen wears, from 1871 to 1870 inclusive,
| made the average amount of water running
| there 60 T45 cubic feet per sCcond-tllr small
| Isl amount being 6,,JGJ cubic feet, End the
| largest lS2 ,09l per second. The amount Of
| solid matter which it annually carries down
| has been computed at 1,lS5 100000 cubic
| feet, or enough TO cover ninety square miles
seven inches thick each year. With such
facts lis these before us, we can hardly won
der at any changes which arc alleged to have
taken place from these causes in long periods
of time.
But what are scno of the changes to lie
expected? III the first place, in sluggish
stream, and where the water Is set back ny
any barrier, either natural or artificial Il
| large part OF this sediment will be deposited
| upon the plains which are overlooked. Thus
! the annual overflow Of the Nile has elevated
ull tine adjacent lands in lis valley. III
upper Egypt this change has been paltcul.
larIy rapid, because there the waters of the
river have been most fully charged with
earthly matter. The soil in the it5ion Of
| ThcbcS has thus been raised about seven feet
within the last seventeen hundred years, and
around the mouth of the river the elevation
| has been more than half as great. 1t has been
computed that within the period during which
| existing monuments have stood. the Nile has
spread 4 deposit averaging ten feet deep over
nearly eight thousand square mile. Of terri
| tory; or, in other words. that ii lGt> brought
down and scattered upon its valley about fit
teen cubic miles OF fertile earth.
But in cases where the stream IT, more
rapid larger portion of the earth. matter
is carried TO the mouth of the river, and
sometimes, if circumstances favor, far out To
sea. Heavier sand, however, is deposited
all along the bed Of the stream, and some Of
the lighter matter along its margin, SO that
both bed and banks are sometimes thus
raised above the level of surrounding lands.
Thus not uutrequently it happens that the
low and nHrShy regions are at some distance
back from the stream, While the immediate
banks are dry. illustrations of this will Of
cur to almost every one.
Artificial embellishments are often raised to
restrain the overflow of rivers. But these
do not prevent accumulations in the bed OF
the stream, which, gradually filling up. the
enbankmcnt has to be raised in cor
responding degree. Thus it sometimes hap
pens in the process of time that the river
flows OH Il much higher plane than the grade
of the city which is built upon its banks.
The breaking of Il levee in such case Is a
catastrophe especially to he dreaded.
But the entertainments by restraining the
water must increase the rapidity OF the cur
rent, and anything which does this will in
crease also the proportionatc amount OF sedi-
mcnt which it carries to the sea. The lower
half of the 20 is hemmed in with dikcs,
many OF which are very old, aud this, 10
doubt, together with the rapditv of contl.u-
Gus streams, has conduced to the rapid filling
up of the eastern coast Of Italy. The present
rate Of deposit at the mouth Of the 20, it Is
said, has continued since the year 1000, the
record Of the previous four hundred years
Qrom 1900 to 160O) having made it only one
third rs rapid. But the entire result is nota
little remarkable. Since about the com.
lnencement of the Christian era that whole
coast hlS been carried from two to twenty
miles into the gulf by the sediment of few
comparatively small rivers, Rayema, forty
miles south of the principal mouth of the
20, ut the commencement of this era was a
seaport; now it is four miles inland. Adria,
standing between the Pc and the Adige,
some four or five miles from each, by the
combined action Of the two is removed four
teen miles inland. Formerly it was q port
famous enough to give its name to tho aea.
Similar changes are everywhere going on,