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HAVE the honor to submit the following project for the flood control of the Mississippi River in its alluvial valley.

The plan is a comprehensive one, providing for the maximum flood predicted as possible, and for future expansion to meet changing conditions. It includes a spillway above New Orleans, diversion floodways in the Atchafalaya and Tensas Basins, a river bank floodway from Cairo, Illinois, to New Madrid, Missouri, together with strengthening and a moderate raising of existing levees. It is designed to prevent any material increase in flood stages. Channel stabilization and navigation improvement are included. Exclusive of rights of way, incidental drainage works, and damages, if any, recommended to be borne by local authorities, the estimated cost of flood control works is $185,400,000, and of channel stabilization and mapping $111,000,000; a total of $296,400,000. The distribution of cost must be determined by law. The suggestion is made that a distribution by which the cost of flood control works in general is borne 80 per cent by the Federal Government and 20 per cent by the Valley States, and the entire cost of channel stabilization is borne by the United States, would accord with the fiscal policy of the President and the precedents established by Congress.

This is a copy of that part of this report in which the plan is presented.-The Editor.

The reorganization of the Mississippi River Commission, Federal control over structures within natural floodways, and the comprehensive mapping of the alluvial valley are also recommended. Flood control of tributaries will be reported upon after the completion of surveys already authorized by Congress.

The control of Mississippi floods by reservoirs is shown to be too costly to warrant their construction. Their development for local benefits is discussed. Other suggested schemes, including levees of sufficient height to contain the maximum possible flood, are discussed, but found inadvisable.

ESSENTIAL FEATURES

The recommended plan fundamentally differs from the present project in that it limits the amount of flood water carried in the main river to its safe capacity and sends the surplus water through lateral floodways. tial features and their functions are:

Its essen

Floodways from Cairo to New Madrid, from the Arkansas River through the Tensas Basin in the Red River, and from the Red through the Atchafalaya Basin to the Gulf of Mexico. These will relieve the main channel of the water it cannot carry and lower the floods to stages at which the levees can carry them.

A controlled spillway to hold the levels down to safe stages at and near New Orleans.

Local setting back of the levees in the main river at bottle necks to increase its carrying capacity and reduce its flood heights.

Greater protection against crevasses by strengthening the levee by reducing flood heights through the increased widths of channel afforded by floodways, spillways and setbacks, and by moderately raising the levees where needed to meet predicted flood stages.

The progressive revetment of caving banks to protect the foundation of the levees and to stabilize the river both for flood control and navigation.

Improved navigation channels for river traffic, not less than 300 feet wide and 9 feet deep, to be obtained by dredging and draining works where necessary between Cairo and New Orleans.

The estimated construction cost of the complete plan is $296,400,000, and it can be advantageously executed in approximately ten years.

The project recommended gives the maximum of results for the minimum of cost. It recognizes the interests and protects the rights of those who will be chiefly benefited and of the taxpayers who furnish the funds. Complete flood control embodying the cheapest practicable reservoir system would be much more expensive.

The plan heretofore pursued has been the construction of levees high enough and strong enough to confine all of the flood waters within the river channels. The levees that have been constructed are not sufficiently high for such floods as are now predicted. The cost of raising and strengthening them sufficiently to carry extreme floods would greatly exceed the cost of the plan proposed. Furthermore, the extent of the disaster which follows a crevasse

increases greatly as the flood is forced to higher stages by confinement wholly within the levee system. The loss of life and property in the recent great. flood in the alluvial valley followed the breaking of the levees which reclaimed the land for the use of man. This reclamation had been pushed so far that insufficient room was left in the river for the passage of the unprecedented volume of flood water. The levees must be strengthened, but a halt must be called on further material increase in their heights and the consequent threat to the inhabitants of the areas they are built to protect.

Man must not try to restrict the Mississippi River too much in extreme floods. The river will break any plan which does this. It must have the room it needs, and to accord with its nature must have the extra room laterally. In its original state the river had only one low water channel until it reached the flat land near the Gulf, but in flood it overflowed an area 50 miles wide, which is really its natural flood bed. The water which cannot be carried in the main channel with the levee at reasonable height must be diverted and carried laterally. Some additional capacity can be obtained in the main river by local setbacks of the levees. As a general setback is not practicable the remainder must be supplied by floodways paralleling the general course of the river.

The plan recommended provides the requisite space for the passage of floods. and levees of adequate strength to withstand them, so that should a flood recur of the magnitude of the flood just experienced, the maximum of record, it would be passed out to the Gulf without danger to life in the alluvial valley, and without damage to property except in the floodways allotted for its passage. Controlling side levees limit the area of the floodways, and protect

Should Divine Providence ever send a flood of the maximum predicted by meteorological and flood experts as a remote probability, but not beyond the bounds of ultimate possibility, the floodways provided in the plan are still normally adequate for its passage without having its predicted heights exceed those of the strengthened levees. The plan is designed to be both simple and comprehensive, flexible and adequate to prevent a calamity such as that of 1927 from happening again as the result of any flood past or predicted. It is capable of modification or expansion, if desirable, to further accommodate an increasing population and its property.

FLOOD CONTROL OF TRIBUTARIES

Plans for the flood control of the tributaries will be developed as funds become available in accordance with an act passed at the last session of Congress. It is impracticable to present such plans at this time, because of lack of data and time. Congress recognized the need for further data when at its last session it enacted a law in the River and Harbor Act, approved January 21, 1927, authorizing and directing surveys by the Corps of Engineers of a large number of rivers, including the tributaries of the Mississippi, to determine the best use of their water resources. Flood control, power, irrigation, drainage, navigation and water supply must all be considered. This act was designed to promote the harmonious and coördinate development of all our water resources. Work on these surveys will require several years and will be expedited as funds are made available in future appropriation bills. Much work which has been done in arriving at the present alluvial valley project, particularly that done in the

when the tributary studies are undertaken. Many reservoirs on the tributaries which would be of little help to the Mississippi will be of great value in the control of floods on the tributaries as well as for other uses.

For the above reasons, only the lower courses of such tributaries as are directly connected with the flood control of the Mississippi in the alluvial valley are included in the plan herein. The other parts of the tributaries will be reported on as soon as practicable as contemplated by the Act of Congress referred to above.

DESCRIPTION OF PLAN FOR FLOOD CONTROL OF Alluvial VaLLEY The details of the plan by which the surplus water will be carried with safety vary in different parts of the river. The alluvial valley of the river may be considered in three principal sections; the northern, comprising the St. Francis Basin on the west side of the river; the middle, including the Yazoo Basin on the east, and the Tensas Basin on the west, running on the east from near Memphis to Vicksburg and on the west from the Arkansas River to the Red River; and the southern, or Louisiana Section, from the Red River to the Gulf of Mexico.

The portion of the alluvial valley from Cape Girardeau, the northern limit of the alluvial valley, to Cairo, can be protected by a slight increase in the size of the levees. The serious problem begins at Cairo at the confluence of the Ohio and the Mississippi. From here to New Madrid the main levee on the west bank chokes the river unduly and should be set back sufficiently to lower the head of water at Cairo by 6 feet in an extreme flood. The existing river bank levee will be retained, but lowered 5 feet. The floodway between the new and the old

levees will be capable of cultivation at all times excepting in floods greater than that of 1922.

An estimate is included for removing part of the dike on the Tiptonville Ridge to reduce the backwater area at the mouth of St. Johns Bayou to the minimum practicable.

From New Madrid south to the mouth of the Arkansas, the levees will be raised moderately. Local setbacks will be made below Helena and at other bottlenecks where necessary to restore greater cross sections in the main river. These modified works are designed to carry the highest predicted flood, except that it may be found expedient not to raise the levees opposite the backwater areas of the St. Francis and White Rivers. In this event, if a possible superflood should come, it may cause a crevasse in the levees at these points, increasing somewhat the height and acreage of backwater area, but doing comparatively little harm.

From the mouth of the Arkansas to the Old River, at the mouth of the Red, extreme floods cannot be carried between levees of the Mississippi without dangerous increase in their heights. A floodway for excess floods is provided down the Boeuf River, on the west side of the river. Excess water cannot be carried through the section on the east side, since it would be forced back into the main river by the high lands on the east bank below Vicksburg and have to be carried thence for 160 miles between the main river levees to the mouth of the Red River. The entrance to the floodway is closed by a safety plug section of the levee, at present grade, which is located at Cypress Creek, near the mouth of the Arkansas. To ensure their safety until this section opens, the levees of the Mississippi, from the Arkansas to the Red, will be raised about 3 feet. To prevent flood waters

from entering the Tensas Basin, except into the floodway during high floods, the levees on the south side of the Arkansas will be strengthened and raised about 3 feet as far upstream as necessary.

The section at the head of the floodway will protect the land within the floodway levees against any flood up to one of the magnitude of the 1922 flood. A flood of a magnitude somewhere between that of 1922 and of 1927 will break it, turning the excess water down the floodway, which will carry it safely to the backwater area at the mouth of the Red River.

Below the Red River, setbacks of the levees will be made at critical places in the main river, to insure the better discharge of flood waters, but the carrying capacity of the main river cannot be increased materially without unwarranted hazard to life and property in the state of Louisiana. At the city of New Orleans, an increase in levee height is considered unsafe, aside from the great cost of raising the levees and the wharves built upon them. To afford proper protection to New Orleans, with its population of nearly half a million and property value of over a billion dollars, a special floodway upstream from the city is essential. The most practicable location is on the east side of the river, discharging into Lake Pontchartrain. A controlled spillway at Bonnet Carré will limit the discharge through this floodway to that necessary for the protection of the city.

At high floods it is also necessary to divert down the Atchafalaya Basin the flood waters in excess of the discharge capacity between the levees of the Mississippi. This is accomplished by strengthening and raising the levees on the main river 3 feet for the necessary distance to assure their safety until levees at the head of the Atchafalaya