(mile 711), Star Landing (mile 704), Porter Lake (mile 699), Wal histor Bend (mile 678), Delta (mile 652), Dennis Landing (mile 60 knowl Henrico (mile 600), Greenville Harbor Dike (miles 537-535), Hon times chitto (mile 487), Goodrich (mile 460), Hardscrabble-Bondurs Throu (miles 394-392), Goldman's Landing (mile 380) and Morga geolog (mile 278). Fisk o If the river's alinement is good at the point where bank cavi make s threatens a levee, the bank may be economically held by revetme comple work. Alinement is good if the curvature is moderate at the locats have p and also for several miles both upstream and downstream. If mediate river upstream from the location is changing its alinement, the atte navigat on the revetment will shift upstream or downstream and the whas foll will be destroyed by flanking unless extensions up- or down-streat of about as the case may be, are made. It follows that stabilization shou proceed downstream from a fixed point. As a general rule reve concerni ments are successful where used as training works for the maintenan meander of good alinement. When so used they prevent a good alinement fr deteriorating and setting up a series of destructive changes do are near pared a herewith stream. The Mi sible to ha In some situations it has been possible so to improve the alineme of the channel by extensive dredging operations as to remove attack from a caving bank and thereby to save the levee line. Ar such operation involves the pumping and deposition in the rig location of several million cubic yards of sand. With the dreds sand can be moved out of the channel. Sometimes the dredg spoil can be placed where it will serve a useful purpose by direct flow in the channel. The dredge can close chutes and auxilia channels and thus concentrate all flow in the main channel. can cut off points which protrude beyond a good bank alineme any sectio and which give an undesirable direction to currents. By dredgin drawn fro good alinement may be obtained but it cannot be held permanent the river r by dredging alone. The sma seasons of The great main Mississippi River, levee system designed to prote flow scales the alluvial valley from major floods is rapidly approaching comp observe in tion. With the system in its present advanced state, the control origin in a the meander of the river has become the most urgent and diffic the movem and the maintenance of free, easy, and unobstructed navigat bar, and to problem confronting those responsible for the safety of the vall channels from Cairo to the sea. While carried f Station to produ 0 point and crossings crossing b size mea change in lo turbulence men at dow The effect C observed. III. RIVER MEANDER has studied it since the time of its organization. Recently two the banks a River meander is a highly complex phenomenon. The Commissi (b) With the lines of investigation have become possible, viz, determination the geology of the alluvial valley and the use in the Waterw Experiment Station of small streams having movable beds and banks The department of geology of Louisiana State University at Ba In a stre Rouge has made extensive studies of the alluvial deposits in Louisi and of the rivers in that State. The air photographs taken will and meander w Not printed. mapping and those taken for the Department of Agriculture's coeur with control program, together with the logs of thousands of wells drilld) With the for oil and other purposes, made a comprehensive geological exami tion of the alluvial valley and the development of the geologial The follo the laborato are transporte bar where rela history of the river a definite possibility. It was apparent that a knowledge of the past performances of the river in recent geological times might well answer many questions which were obscure. Through the cooperation of the university and its department of geology, and with the approval of the Chief of Engineers, Dr. H. N. Fisk of the university faculty was retained by the commission to make such an examination and report. The work is now approaching completion. The information and conclusions in his report already have proved of great value. Its outstanding contributions of immediate applicability to the engineering of the flood-control and navigation project are the mapping of the courses which the river has followed in its present meander belt, estimated to cover a period of about 2,000 years, the location of clay deposits in old courses which are near the river or have been cut into by it, and the conclusions concerning the poised character of the river and the phenomenon of meander. For use with the commission's report Dr. Fisk has prepared a brief summary of his findings and conclusions which is herewith (appendix II).2 While the geological work has been under way, the commission has carried forward a research program at the Waterways Experiment Station on the meander phenomenon. It has been found practicable to produce small meandering streams which cave their banks, build point and blanket bars, scour in the bends and build up the bars on the crossings during high stages, fill in the bends and scour through the crossing bars on low stages, and in every other respect behave like fullsize meandering rivers. The Mississippi River is of such huge proportions that it is impossible to have hydrographic and bank surveys of sufficient frequency in any section of considerable length to enable definite conclusions to be drawn from the map data concerning causes and effects of changes in the river regimen. The small meandering streams not only reduce the dimensional and flow scales but the time scale as well. This has made it possible to observe in just a few days the effects of what corresponds to many seasons of high and low stages. It has also made it possible to watch the movement of material transported by the stream from its point of origin in a caving bank to the point where it has been deposited on a bar, and to observe the direction of top and bottom currents, the change in location of bank attack with change in stage, the relation of turbulence to bottom scour and the changes which result in river regimen at downstream points from changes occurring further upstream. The effect of slope and volume of flow on meander pattern has been observed. The relations between the character of materials forming the banks and the rate of meander have been investigated. The following conclusions have been drawn from the results of the laboratory research work: (a) In a stream having banks of little cohesion the sands caved out of the banks are transported but a short distance downstream and are laid down on the first bar where relatively low velocities obtain. (b) With the same discharge and slope the most rapid bank caving and meander will occur with bank materials of the least cohesion." (c) With the same bank materials and discharge the most rapid bank caving and meander will occur on the steepest slope. * Not printed. (d) With the same slope and discharge a stream having cohesionless bank 0 stream. pm (e) If the banks of a stream are composed of cohesionless materials, the vention of bank caving by any artificial means will cause the stream to modify characteristics and to approach those of a stream with tough banks. It follows that bank stabilization works, if properly located to reta good river alinement, in combination with dredging can improve bot the low-water navigation channel and the flood-carrying capacity the river. A st during additio require tenance feet. A greater margin of depth under barges will reduce resistance to towing, increas speed, particularly upstream, and increase safety of navigation with the sam power. A greater margin of depth under towboats will increase the efficiency of applic tion of power and, in effect, will increase the pushing power of all towbost designed to operate on a 9-foot depth. New towboats can be designed of greater draft with higher efficiency. They also desire greater stabilization of channels since this will increase the ea and safety of navigation. In general, since most operators on the lower Mississippi serve points on t Ohio, upper Mississippi, or Illinois, they do not expect to load their barges much greater drafts than now is customary unless the upper rivers are given deep channels. be may number This wo 6 month all 18 dr It also follows that the river will regain the length by which it ha no perm or the p system o IV. DESIRES OF NAVIGATION AND FLOOD-CONTROL INTERESTS The riv A public hearing was held by the Commission in Memphis, Tencourage t deteriorat has been Navigation interests desire greater depths in crossings at low rive stages for the following reasons: the natur highways ments can back to av As an e extending Fitler Ben of the 100 existed jus 1933 is also also shown been locate A glance at sive change Caving is a ler Cut-off, Cracraft Cl Fitler Bend In the las have necessi The levee boards in the alluvial valley and their chief enginee and the Delta council desire greater stabilization of channels in orde to retain and if possible to increase (by deepening the channel throug dredging and bank stabilization) the greater flood-carrying capacit which has been obtained in recent years by realinement of the rive They desire also that the river be prevented from destroying t massive levees which have been completed and they believe that th practice of building set-back loops and abandoning the best lands the valley is no longer economically sound. 5 miles of l miles at Ho Kentucky B The cities of Memphis and Vicksburg advocate stabilization of thes river channel in order that harbors may have permanency of location plan, and depth and so that sites on the river may be developed industry with assurance that they will neither be destroyed caving of banks nor left a long distance from the navigation channe by some change in the river's course. 'Not printed. In this sec Construction on the chart. It will tak 100 miles of Between C there are 97. estimates hav W. POSSIBILITIES OF SO MODIFYING THE PROJECT AS TO MEET THE WISHES A study has been made of the channel conditions which obtained during the 9-year period, 1935-43, to determine the approximate additional amount of maintenance dredging which would have been required in each of those years had the project authorized the maintenance of a minimum depth for navigation of 12 feet instead of 9 feet. The study indicates that a minimum channel depth of 12 feet may be maintained through the low-water season by increasing the number of dredges in the maintenance dredging fleet by 9 dredges. This would mean the operation of 18 dredges for a period of about 6 months in years of unfavorable conditions and the maintenance of all 18 dredges in readiness to operate in all years. While such a plan would give navigation the benefits of increased depth, it would create no permanent improvement in the river channel for either navigation or the passage of floods. It would confer no benefits on the levee system or on existing harbors and river terminals, nor would it encourage the location of industries along the river. The river now has the best alinement, the best navigation channel, and the greatest flood-carrying capacity it has ever had. It will deteriorate unless this good alinement is maintained. A huge sum has been invested in the levee system and further improvements in the nature of seepage berms, impervious river-side blankets, and highways on the levees will be made in the future. Such improvements cannot well be made when the levees are subject to being set back to avoid being breached by the river. As an example, attention is invited to the chart herewith (plate 1), extending from Caulk Cut-off (mile 569 above Head of Passes) to Fitler Bend (mile 468 above Head of Passes). The present alinement of the 100 miles of river is shown on the chart. The alinement which existed just before the program of channel realinement was begun in 1933 is also shown. It had a length of 167 miles. On the chart are also shown the former abandoned courses of the river which have been located by Dr. Fisk in his geological examination of the valley. A glance at this map will convince anyone of the probability of extensive changes in river alinement if works are not built to prevent them. Caving is active in Cypress Bend, Choctaw Bend, Miller Bend, Tarpley Cut-off, American Cut-off, Kentucky Bend, Worthington Cut-off, Cracraft Chute, Island 93, Foot of Lake Providence Reach, and in Fitler Bend. In the last 3 years rapidly caving banks within the reach depicted have necessitated emergency set-backs of main line levees as follows: 5 miles of levee at Cypress Bend, 4 miles at Cracraft Chute, and 3 miles at Homochitto. Levees are now threatened at Miller Bend, Kentucky Bend, and below the revetment in Fitler Bend. In this section of the river there are now in place or authorized for construction 21.0 miles of effective bank protection work as shown. on the chart. It will take about 30 miles of new and additional work to hold this 100 miles of river in its present alinement. Between Cairo and Baton Rouge, a river distance of 737 miles, there are 97.5 miles of effective bank revetment in place. Detailed estimates have been made of the amount of stabilization work, which ་ if it could be placed all at once, would be required to hold the riv to its present alinement. The total, in addition to that in ple: amounts to 230 miles. Of course, it would be impossible to pls bank stabilization works at a rate which would hold this great lens of channel on the existing alinement. Several years would be quired to do this amount of work economically with a reasons amount of construction plant and, moreover, availability of fun may be expected to fix the rate of progress. While work is und way in one reach the river will be changing in other reaches. To successful, the work must be done by reaches working downstre in each reach from naturally stable or previously stabilized locatic and in accordance with a carefully worked out plan, the purpose which will be to obtain the best possible alinement through the res under treatment. Thus each stabilized length of bank will serve: a training work to direct the current to the next stabilized bank dow stream. If work is placed in widely separated localities it will pro an uneconomical use of money for much of the work will be flank out by the river, and most all of it will prove to be badly located becau the river will change its position and direction between the scatter works before intermediate works can be placed. The section of the river in which it is most important to preser the existing alinement is that between Mhoon Landing (mile above Head of Passes) and Natchez, Miss. This is the section which the river has been straightened by cut-offs and improvem dredging with a consequent great reduction of flood heights and th elimination of the Eudora floodway in Arkansas and Louisiana fro the project. Stabilization work in this section should be given fir priority. The follo 131. Chan are to be gre something m A general ban That stat Work on any reach should not be begun until funds are in han of casing or in sight to carry it through to completion in a working period cogation until sidered advisable. A 50-mile section of river will require about place and to miles of stabilization works. This would be a reasonable and ec nomical program for a season. For the the ti In recent years, revetment work has been limited to three type articulated concrete, willow fascine mattresses, and sheet asphalthat The sheet asphalt has proved unsuitable in the swifter currents abo valley of the Vicksburg. All three types require investments in floating plant to within narro large to attract contractors to this field for the limited volume The Commis work which could be offered under existing authorizations and apprecessary in priations. As a result all revetment work has been done with hire channel recti Costs consequently are too hig the main M incident to the war, this class of work will cost approximately $700,0 that such st At the present time, with the difficult labor and materials situatia which they of per mile of bank stabilized. The Commission is using precast crete blocks and bucket-placed hot asphaltic concrete separately and in combination for subaqueous work with a view to developir feet at low wa The great another type of revetment which will require a relatively smell inves the country a ment in floating plant for its placement. If a stabilization prograr people in the is adopted and annual appropriations are sufficient to attract contra property valu tors to the field, it is believed that the greater volume of work, com petitive bidding, and the ingenuity of contractors in devising bette and in peace j methods all will tend to improve quality and reduce costs. Stabi location to main that the fore be stabiliza be requi for stab also may A prog of about tion work war. Ju All things should be bank sta $35,000,00 estimate in Docume law by the of caving stabilize th capacity dredging alre |