536 



MISSISSIPPI EIVER IMPROVEMENT. 



below. To these general characteristics there are two 

 exceptions, at Rock Island and Keokuk. ... In these 

 localities are found rocky beds, forming rapids which 

 obstruct low-water navigation. Similar formations 

 exist at Fountain Bluff and at the Chain of Rocks be- 

 low St. Louis. At Rock Island a channel four feet 

 deep and two hundred feet wide at extreme low water 

 has been cut in the rock, while at Keokuk has been 

 built a canal, affording a minimum navigation of five 

 feet and a maximum of eight feet. . . . The entire 

 valley, except the sand terraces, is subject to inunda- 

 tion. 



The water is nearly free from suspended 

 matter. There are none of the complications 

 attending the improvement of sedimentary 

 streams. There are lakes and sloughs on both 

 sides of the river, which enable the engineer 

 to control the force he employs in deepening 

 the main channel. 



sand, forming a lake-like expansion and depth above, 

 with slight fall, and a steep, uncertain, and difficult 

 channel below. The most marked example of this is 

 caused by the Chippewa from the head of Lake Pepin 

 down to the Alma. All indications show that the bed 

 is still rising. 



The present condition of the river does not 

 afford a navigable depth of five feet for a suffi- 

 cient part of the year to justify the construc- 

 tion of boats of greater draught. Yet economy 

 in transportation depends upon the capacity of 

 carriers. 



Barges on the upper river, built with a limit of 

 draught of five feet, carry about 12,000 bushels of 

 grain ; while those used below Cairo, when an average 

 depth of eight or nine feet can be obtained for a large 

 part of the year, carry 20,000 bushels on five feet, 

 30,000 on seven feet, and 60,000 on eight to nine feet. 



An economical system of transportation de- 

 mands not less than six feet throughout the 

 channel at all seasons. Even if this depth 

 can be attained with difficulty at Keokuk and 

 Rock Island, two obstructions would not affect 

 transportation so injuriously, provided the rest 

 of the channel for 700 miles were free from 

 danger and delay. The report continues : 



The plan of improvement adopted for this part of 

 the river consists of low- water dams, closing sloughs 

 or side-channels, to augment the flow through the 

 main channel; of spur-dikes, or jetties, or wing- 

 dams, built out from convex snores where the width 

 is too great to direct and concentrate the flow, and 

 produce scour over that part of the bed promising 

 the best channel ; and of revetments to protect such 

 parts of the banks as may be attacked by the direction 

 and concentration given to the current by the dikes. 

 The construction is of layers of stone and of brush, 

 bound into fascines or mats. 



At first these dams were raised only one 

 foot above low water ; they are now built four 

 feet above. They now produce more rapid 

 results to the channel, besides serving to define 

 it, and affording protection against ice. In the 

 opinion of the commission, this system of im- 

 provement is completely successful. Dredging 

 has been occasionally resorted to, where erosion 

 is slow, or landings must be secured in front of 

 towns. 



The results obtained are thus tabulated : 



Practicable depths on bars on (he upper Mississippi 

 River at low water. 



The following local results are more indica- 

 tive, as the appropriations have not permitted 

 work on all the shoals in any one reach: 



The commission approve the system of im- 

 provements now being carried on'in the upper 

 river under Captain Mackenzie, United States 

 engineer. They recommend that the sums ap- 

 propriated be large enough to procure the exten- 

 sive and expensive plant which is durable, and 

 therefore economical ; and that the Des Moines 

 Canal be duly maintained. The progress of 

 the surveys during the year is as follows : 



Triangulation, Illinois River to Ohio River, 

 completed to Powers Island, fifteen miles be- 

 low Cape Girardeau, 205 miles. 



Triangulation below Cairo, completed to 

 Gaines 1 s Landing, seven miles below Arkansas 

 City. 



Precise levels, Illinois River to Ohio River, 

 completed to Cape Girardeau, 190 miles. 



Precise levels, belo\v Cairo, completed to 

 Greenville. 



Topography below Cairo : Survey of Vicks- 

 burg Harbor is completed, and work is resumed 

 near Commerce. 



The Coast and Geodetic Survey report on 

 December 23d and 30th that the following work 

 is complete, or it will be completed by Feb- 

 ruary 1st: 



1 . The triangulation from the Gulf of Mexico to 

 Greenville, Mississippi, a distance of 585 miles ; and 

 that from Helena, Arkansas, to Memphis, Tennessee, 

 a distance of 85 miles. 



2. The line of levels from Carrollton, Louisiana, to 

 Greenville, Mississippi, a distance of 460 miles. 



3. The topography from the Gulf to Donaldson ville, 

 Louisiana, a distance of 195 miles. 



4. The hydrography from the Gulf to Baton Rouge, 

 Louisiana, a distance of 255 miles. 



A leveling party began at Greenville, work- 

 ing down the river, and was below Vicksburg 

 on December 30th, at which time a detach- 

 ment, which began work at Carrollton, Louis- 

 iana, was above Natchez; and the two parties 

 were to meet in January. This is the point of 

 progress reached at the close of 1880 in this 

 work on " the great inland sea." 



