7ay system having a minimum depth of 9 feet. Remarkable imrovements in the design, power, and efficiency of towboats and in the esign and capacity of barges were made. Private capital invested in arge line equipment both for common, contract, and private carrier ervice. The railroads were required to quote joint rail-barge line ates. As a result there are now operating on this system a large numer of well equipped barge lines giving service between ports on the Julf coast and the industrial areas in the Ohio Valley, at the foot of ake Michigan, and at St. Louis and Minneapolis-St. Paul. Sixty arge lines are using all their equipment with great efficiency largely n the movement of gasoline, oil, sulfur, and other materials required n the prosecution of the war. Perhaps the greatest service performed y the river in this emergency has been the movement to the sea of bout 1,000 new Government-owned vessels from the Great Lakes and priver yards where they were built and from which they could not each the ocean by any other route or method of transportation. leet submarines, destroyer escorts, tank landing ships, freighters, ankers, and ocean-going tugs are the outstanding classes of vessels n this movement.

Although the problems concerning navigation and flood control are nextricably related, it was believed for over a hundred years that the Federal Government had no constitutional authority to expend funds n river work except for the improvement of navigation. Consequently no levee could be built with the use of Federal funds except n the theory that it would assist in improving the channel of the river or navigation. Beginning in 1917 a broader view of the responsibility and authority of the United States was adopted and in that year the xpenditure of Federal funds directly for flood-control purposes was uthorized. In 1928 it was finally recognized that flood control in the lluvial valley and navigation on the river south of Cairo constituted single great problem of such magnitude that it could be dealt with ffectively only by the Federal Government. Since then all floodcontrol works have been designed and built by the Government and hannel improvements have been directed toward securing better linement, greater flood discharge capacity, and safer and easier avigation.

II. EXISTING PROJECT

The existing project is authorized by the act for the control of floods on the Mississippi River and its Tributaries, approved May 15, 1928, is amended by the acts approved June 15, 1936, August 28, 1937, June 28, 1938, and August 18, 1941.

The project as now fixed by law provides for works for the control of floods of the Mississippi River between Cape Girardeau, Mo., and he Head of Passes, La., and for the maintenance of a channel for avigation 300 feet wide with a minimum depth of 9 feet between Cairo, Ill., and Baton Rouge, La.; for the control of head water floods on the St. Francis and Yazoo Rivers; for the protection of lands near the mouths of the White, Yazoo, and Black Rivers from Mississippi River backwaters; for certain works upon the Mississippi between Rock Island, Ill., and Cape Girardeau, Mo., and upon tributaries and utlets; and for improvement of the flood carrying capacities of Bayous Rapides, Boeuf, and Cocodrie in Louisiana.

The Intracoastal Canal is now being given a depth of 12 feet.

A detailed statement of the existing project and its state of low-wate pletion is contained in appendix I. This discussion will be limi, dredging therefore, to the features of the project pertaining directly to ns-and the n gation and to those flood control features which either are clos channel related to navigation or have common problems with navigation. 5 crossing

The project contemplated that the main river below Cairo, Ill. Thirty-ni improved in its flood-carrying capacity and for navigation by securg 10 to 11 better alinement and by the construction of stabilization works. 1 The C the last 10 years the alinement of the river from mile 677 above Hd between of Passes to mile 338 above Head of Passes has been radically chard The M by cutting off long bends and by other dredging operations. Tsburg, and work has shortened the length of the low-water navigation chand tween Ca between Memphis and Baton Rouge about 170 miles. Quite a nur buoys sup of troublesome crossings have been eliminated and the reduced miles for the in has more than compensated for the swifter currents encounteredt channel bu high stages by upstream navigation. rule rather

Beginni

At the same time, the realinement of the river has reduced heights of major floods by about 12 feet at Arkansas City and aboudredging h feet at Vicksburg, with lesser reductions above Arkansas City supplement below Vicksburg. The straightening of the river has increased fld regular low slopes and high-water current velocities.

secure a sin

Although the alinement of the river has been fixed at a number the channe bends by bank revetment and in some places by dikes, dredging is hydraulic c main reliance for the maintenance of the project channel in the shift projections river during low-water. The channel is maintained by five pipe-le location, the dredges in the Memphis district, two in the Vicksburg district, a sand dikes two in the New Orleans district.

of chutes an

During the high-water seasons, the crossing bars in and immediat taking is a n below unstable reaches generally shoal up as much as 5 to 15 ft tion of sever above the heights which obtained during the prior low-water seast successful; In addition to the shoaling in crossings, there are a number of locaties because the where the deposition of materials from caving banks obliteratesaving of bar

or later will

low-water channel of the previous year.

While the shoaled crossings scour generally to their former levels that if the ri

the river falls from high stages, they nevertheless act as broaderes ment dredgi weirs over which the currents pass without sufficient concentrationment both fo

can be obtain

flow to scour an adequate channel. To maintain the project chan

through such shoaled locations dredging is necessary at the beginn Existing ri The extent of dredging at a given locations ail or truck,

of the low-water season.

largely dependent upon the stability of the reach upstream. If acte serve the com bank or bar recession continues during the low-water season hifting of cha mediately above a crossing, recurrent dredging is usually requiminals problem

ment of river f

after each minor rise and fall in stage.

Of the 737 miles of river channel between Cairo, Ill., and Badvantage of 1 Rouge, La., regular reconnaissance surveys are required duringiderable num

a

gainst being

river.

low-water season over a distance of 702 miles, or as far down as Bar Bandy be um Sara, La. Below Bayou Sara the channel is relatively changes but little from year to year. In the 702 miles between Ca and Bayou Sara there are about 210 crossings which are regula

examined. Of this number from 30 to 75 may require dredging ever to carry

onnage which vailability of t

or more times during each low-water season. The number of cros ings requiring dredging and the amount of dredging at the varios locations are largely dependent upon the number of minor stage fluctuations during the period of low water and the duration of the

Since there a

ow-water season. The greater portion of the crossings requiring dredging lie within the limits of the Memphis district between Cairo and the mouth of the Arkansas River. In that district a recent typical channel report at a very low stage during the dredging season showed 5 crossings out of a total of 74 on which there was only 9 feet depth. Thirty-nine had a depth of 12 feet or over and 30 had depths of from 10 to 111⁄2 feet.

Sa The Coast Guard maintains adequate shore lights for navigation between Cairo and the Gulf.

The Mississippi River Commission, through the Memphis, Vicksourg, and New Orleans districts, marks the navigation channel between Cairo and Baton Rouge during the low-water season with buoys supplied by the Coast Guard and issues weekly channel reports for the information and guidance of navigators. The shore lights, channel buoyage, and channel reports have made night navigation the rule rather than the exception for all tows operated by posted pilots.

Beginning in 1933, an extensive program of channel improvement dredging has been carried out. This dredging was additional and supplemental to the excavation of cut-offs and also additional to the regular low-water maintenance dredging. Its purpose has been to secure a single and efficient channel of good alinement in reaches where the channel had poor alinement, indefinite location, or inefficient nydraulic characteristics. The work has consisted of cutting back projections in bank lines, making deep cuts on the desired channel location, the deposition of dredged spoil in the form of sand bars or sand dikes to guide flow into the excavated channel and the closure of chutes and back channels with dredged spoil. Each such undertaking is a major operation which involves the excavation and deposition of several million cubic yards of sand. Some have been highly successful; other have not. None can be considered permanent because the constant shifting of the river's alinement through the caving of banks upstream from a job of improvement dredging sooner or later will obliterate it. It can be stated with certainty, however, that if the river's alinement is stabilized upstream from an improvement dredging operation, substantial permanent channel improvement both for navigation and for increased flood-carrying capacity can be obtained.

Existing river terminals for transfer of freight between barge and rail or truck, and between barge and oil tank storage, are adequate to serve the commerce now carried by the river. However, the constant shifting of channels and caving of banks make the future of such terninals problematical. The same uncertainties discourage the developnent of river front properties by industries which otherwise could take advantage of low cost water transportation. The location of any considerable number of industries on the river above Baton Rouge may hardly be expected until good industrial sites are made secure both against being caved into the river and against abandonment by the river.

Since there are no locks and dams south of Cairo the capacity of the river to carry commerce is practically unlimited. The amount of tonnage which is moving at the present time is controlled by the availability of towboats and barges.

The most recent tonnage figures available are as follows:

From mouth of Ohio River to but not including Baton Rouge, La.

Total tons
5, 595, 991

Year-Continued.
1939.

5, 786, 129

1940.

1941.

6, 574, 573
6, 915, 034

1942.

Year:

1935.

1936.

1937.

1938_

is slo

bank

and

Total x

7,009, curre

7,055,

and

9,605,

9,474,3

alinen

Th

creati

would

which involve

Wher

The main Mississippi River levees have a definite effect on navig
tion. Under natural conditions the river spilled out over the alluvi
valley as soon as it rose above bank level in floods. As a result
river channel itself never carried much more water than enough secured
raise the stage to overbank height. As larger and larger floods w
grades
confined between the main line levees flood discharges within t
channel were increased and corresponding higher stages resulte
line, on
The effect of the construction of the main-line levee system has be
to produce a river having greater flood discharges and greater va
ations between low and high stages than originally existed.

back fr

by reve

may di

operatio
A lev

t

down sti

The problem of maintaining the integrity of the main-line len system against attack by the meandering river is inseparable fr the problem of obtaining the best possible river channel both navigation and flood control.

off

Usually

The alluvial valley is divided into a number of great basins drain
by tributary streams which, flowing in general more or less parallel
the general course of main river, enter it at the lower ends of the basi
where the Mississippi approaches a wall of the valley or at its co
fluence with a major tributary. Since the highest land is along
river front, each basin is protected by a single line of levee located
short distance from the river. Thus a single levee line extends fruits rat
Farrenburg, Mo., on St. John's Bayou, to the mouth of the St. Franc
a distance along the levee of 228 miles. A single line of levee
miles long protects the Yazoo Basin. The line from Pine Bluff, Ar
to Point Breeze, La., is 380 miles long. A break in the levee at
upper end of a basin during overbank stages of the river means in
dation of the entire basin. A break lower down means flooding of
the basin below the break and as much of the basin above the bret
as lies below the water level at the break.

21

are many location n

sacrifices t

ti

The project or design flood for fixing the net grade of main ri levees has an assumed peak discharge as follows:

ng leve

back bet of useful

and usua

cannot b

lack

it destrovs

set-back

and can n

s a local

1880 the di

by set-back

Between Cairo and the mouth of the Arkansas, 2,450,000 cubic feet per seco But none (

At the p

At Arkansas City, 3,065,000 cubic feet per second.
At the latitude of Angola, or Old River, 3,000,000 cubic feet per second.

$4.700,000.

Levee grades have been fixed, with the freeboards prescribed

the project, to correspond to the estimated crest flow lines oferees and s
project flood under existing channel and floodway conditions includ below Pine

all cut-offs, channel improvements, and the elimination of the Eudo
floodway in Arkansas and Louisiana.

t Francis (

The levees are massive embankments 25 feet high or more and 20

feet or more through at the base. Frequently they have wide seep proximity o

recently bee situation als

berms extending landward from the landside toe. In some locations
which are inaccessible in times of high water they have gravel roads
on the crown.

Over a te example, t

evee line r

where the r

measures fo

evee are

In its meandering the river is always caving its banks and work Other point:

At some locations the movement

Isl 97001-4

toward the levees at many points.

Falleg slow and regular. At others it is rapid and erratic. The rate of ank caving depends upon the materials in the bank and direction Andy Be nd force of the attack against it.

Par-fina

T

The straightening of the river has increased its flood slopes and urrent velocities. Increased velocities cause increased bank caving and meander. Unless the river is held approximately in its present linement it will regain a considerable portion of its former length by reating new bends and extending existing ones. This, of course, vould sacrifice a proportional part of the reduction in flood heights which has been obtained through shortening the stream and would nvolve a loss of the cost of doing much of the channel work which ecured those reductions. It would also require an increase in levee grades to compensate for loss in the stream's flood-carrying capacity.

h

When it becomes evident that the river is going to breach the levee ine, one of three possible actions must be taken. A levee loop farther -pack from the river must be built; the bank caving must be halted dischargy revetment work; or, in some cases, extensive dredging operations Onay divert the current from the caving bank. Each is a major of operation.

A levee loop or set-back must extend far enough upstream and e down stream to insure that neither of its connections with the existng levee will lie within the danger zone and it must be far enough dback behind the existing levee to give promise of a number of years alcats of useful life. Generally a set-back will have a length of 2 to 4 miles, band usually such a loop contains so large a yardage of earth that it the cannot be built in one working season. If, for any reason, such as

tack of funds, the work cannot be started in time, or the river speeds up its rate of bank caving, a serious situation develops.

moddiy

Usually a set-back is not a permanent cure of the trouble. There are many points where the river is now near the third successive levee location made within the past 15 or 20 years. Moreover, a set-back sacrifices the highest and best land. The river makes as much land as it destroys but what it makes is a sand bar across the channel from the set-back. The accretion will not be fit for cultivation in a lifetime and can never be protected at any reasonable cost. Each set-back is a local retreat of considerable magnitude. But in the aggregate, over a term of years, the results are almost unbelievable. For example, the lower Yazoo levee district has about the same length of levee line now, 178 miles, that it had when the district was organized. But none of the existing levee is on the original location-and since 1880 the district has lost 305 miles of levee which have been replaced by set-backs.

Hebra

At the present time four large set-backs of main Mississippi River levees and six set-backs of Arkansas River levees in the alluvial valley below Pine Bluff are under construction. These set-backs will cost $4,700,000. The main-line levees are now threatened at other points where the river is already too close to them to make it certain that measures for the prevention of a breach can be taken in time. The proximity of the river to the levee and the rapid rate of bank caving at Francis (mile 610) in the Yazoo Basin where a set-back has only recently been completed are causes of anxiety. A somewhat similar situation also exists at Fitler (mile 469), also in the Yazoo Basin. Other points where the river is already too close to the main-line levee are Island No. 8 (mile 917), Island No. 9 (mile 913), Cow Island

97001-44