Wessington Springs herald. (Wessington Springs, Aurora County, Dakota [S.D.]) 1883-1891, 1884-09-26
dams are opened for tho water to rcsch

! dams are opened for tho water to rcsch
st. Paul, the head of navigation. The
reservoirs will seldom, if ever, have to
be opened in the interest of navigation
earlier than July l.. From April Is to
| July l it is estimated from careful
measurements that not less than ST.
| 751,903,S4O cubic feet of water passes
the Falls Of Pokegama, the point where
the lowest of the five reservoirs on the
Mississippi proper is located. The
reservoirs, if operated in the interest OF
navigation only, would never be
opened after November l. If the en-
tire flow from November l to April 10
be added, the quantity will be aug
mented by about 1874 600, 900 cubic
fcct-which can be retained outside of
the season OF navigation. This addi-
ton brings the whole supply available
during any season between the latest
assignable Date for closing the reser-
voirs in the fall and the earliest for
their opening in the spripg-two dates
which will never both have to be
adopted in practice IN the same season
up to 40, 095, 903, $40 cubic feet for the
five upper reservoirs only. From the
two reservoirs on Gulf Lake River and
Pine River, cmptying into the Missis-
sippi below the point of the preceding
observations. enough more will be sup
piled to make the aggregate available
for use by the 1st OF July. 80, 792, 9o3,-
$40 cubic feet for the seven reservoirs
above st. Paul. This quantity, if all
used in the interest of navigation, can
be released, and it is expected to re-
lease it, during the low-water months
OF July, August, September, and Octo-
Der. This is the result of Il calculation
based on the most conservative n.y.
pothesis, and therefore an actual mini
mum.
Suppose, now, the gates tobe opened
on the LIST of July, and TO remain open
for 100 days-the longest period that
could possibly be neccssary-what vol
ume OF water could be added to the
river? A discharge of 6,400 cubic feet
per second would amount IN 100 days
to a total of 81, 296, OOa, 700 cubic feet.
1t is therefore claimed that, under the
most adverse conditions supposablc,
the Upper Mississippi reservoirs are ca
pable of adding 6,4OO cubic feet per
second to the volume of the stream.
Figures, however, are distractions.
What does this mean to the Mississippi
River, and to those who use it rs an av-
enue of commerce? When the river is
at its lowest stage at st. Paul, the dis
charge is not less than $500 cubic feet
per second. If the addition calculated
can be secured, it will more than
double the volume of the river, allow.
ance having been made for evaporation
and absorption in so far as they can be
computed. AS to the utility Of such a
change, Major Allen in one of his re-
ports very justly says: 1.-The stream
must be ~despicable whose navigation
could not be assisted BY doubling its
lowest water volume" And in arr wing
at a definite conclusion us to the depth
of channel thus secured, he says: eff
we take for a discharge OF II, POO cubic
feet, the mean velocity at three feet,
and width at 1000 feet, we have,
assuming the area OF cross sec
ton to be a rectangle, a depth
OF about four feet. But the
cross section Of a stream flowing
through a sandy bed does not approach
the rectangular; it varies, sometimes
approaching the parabolic and
times the triangular. The height of a
triangle having q base OF 900 feet and
an + of 1000 square feet would be
eight feet. 1t would certainly be with
in safe limits to say that, supposing tho
width of the water surface to be as
much as 900 feet, the ruling depth
for a flow of l., 200 feet per second
would be at the least four feet.'
Here. then, VIZ rrlve at Il clear idea
Of what the reservoir system proposes
to do, and how it proposes to do it. 1t
promises, with what prospect of sue
cess its OWL figures must witness, to
gather up the supply Of water now run
ming to waste and increasing the de-
vastative power OF floods, together with
the excess OF the spring and fall dis
charge; to impound it until the stream
becomes so low that navigation will
shortly be impeded, and then to release
it IN such measured quantities rs will
maintain a minimum depth OF four
feet in the channel at the head Of navi-
CATION the year round. with correspond
ing benefit to the river Us far as the
point where it broadens out into Lake
! cpin. With the opening to settlement
CT millions OF acres in the Northwest.
and the increasing urgency which their
cultivation will lend to the question OF
transportation to the %sea-board, this is
no inconsiderable promise. The total
cost of the seven dams ia
sos, l3o.-J. G. PyIc, IN Hayvcr's Mag
anne.