Statement of boulder-work on the Minnesota River, to accompany the report of Captain E. Bell, United States inspector. 28 28 Johnson's Reef, about two and a half miles below Brown's, at the island. 29 1871. Reef opposite Helverson's, one mile below Brown's 14 Boulder Point to Sacred Heart Creek, 12 miles from Yellow Medicine. COLONEL: According to instructions contained in your letter of June 15, I have the honor to submit the following report of operations for the improvement of the Illinois River, during the year ending June 30, 1871: ORIGINAL PLAN. At the beginning of the year work was in progress under the contract of F. D. Van Wagenen, with Lieutenant Colonel and Brevet Major General J. H. Wilson, for dredging between the town of Henry and Copperas Creek, under instructions to prepare a bottom for a 7-foot navigation, after a proposed lock and dam at Copperas Creek should be completed. According to those instructions, the theoretical plane of excavation was parallel to the surface of the supposed pool of the dam, and therefore nearly a horizontal plane; the allowed slope being 0.25 of a foot to the mile. Referred to the low-water surface of the river, the depth to result from the excavation would vary from 5.2 feet at Crow Creek Bar, to 2.0 feet at Coon Valley Island, where the supposed plane of 7 feet ceased to cut the bottom. According to the plan, the immediate interests of the present navigation were of secondary consideration, and the principal object being connected with a scheme whose execution was a contingent event, did not commend itself to popular favor, and exposed those prosecuting it to adverse criticism, as wasting money at points where no difficulty in navigation ever existed. The original programme was strictly adhered to until July, 1870, when it was decided to so change the order of execution as first to remove those bars which were giving most trouble to navigation, which being done, criticism was silenced; and the low stage of water compelling the removal of the bars to a greater depth than was designed, the result has been a benefit to navigation, and a reasonable expectation of permanence secured, which would not have followed the carrying out of the original scheme. Experience quickly justified the opinion that it was impracticable to make a permanent bottom to a grade arbitrarily fixed, in cases where the removal of a few inches only was required. The material being sand, lies in transverse ridges or reefs; consequently a cut of less than half a foot would do no more than level off the crests of the ridges, which, in running water, would very quickly be replaced; for this reason it was deemed best to confine the dredging to the bars, from which a sufficient quantity was to be taken to afford material to effect changes in the area of flow, to confine the water to the channel, and to lower the grade below the prescribed plane, so that the crests of the inevitable reefs should be below that plane. In consequence of these necessary modifications, no dredging was done below Kingston, and the grade was lowered at Lick Creek, Tamarsh Island, and Dutchman's Bars; the last two localities have been designated in former reports as one bar-"Kingston Flats." The above-described modifications being made, the work was carried out without sacrificing any important part of the original intention, while affording a decidedly better channel for present use, which promises to be permanent. PROGRESS DURING FISCAL YEAR. The progress of the work up to the date of the last report had been slow, but by additions to the working equipage, and other expedients, the rate was increased, and good progress made during this latter half of 1870. In the spring of 1871 work was continued under this contract until June 16, when it was suspended on account of supposed exhaustion of the appropriation. A later examination discovered an available balance, and work is now in progress upon the points left incomplete at that date. The result of the work under this appropriation has been to afford a channel of 5 feet from Henry to Peoria, thirty-seven miles, and a further extension of fifteen miles, with a depth of 4 feet, and a bottom for a 7-foot navigation is now prepared, reaching to Copperas Creek, if the dam be raised six inches higher than first proposed. But as the construction of that dam at an early date is very improbable, and as sev eral bars are left, which will now be considered serious obstacles, they will be included in the estimate of further work required. PROVISIONS FOR FUTURE PROGRESS. In August last I was directed to submit a scheme for the expenditure of $100,000, appropriated by Congress at the session of 1869-70. ENGINEERING. Failing to be convinced of the necessity of so costly an improvement as that by locks and dams, and in view of the fact that in any case the execution of that plan was uncertain, I favored a project in which the present benefit was the leading object. Previous to submitting the project, the commissioners for the State of Illinois proposed essentially the same, which, being adopted, renders the work of the United States and that of the State distinct, but not conflicting. The project contemplates the prosecution of the work on the part of the United States, with a view to make an open channel navigation, with a minimum depth of 4 feet, by dredging and constructing dams to control the water, which, if means are promptly provided, can be done in two years. The limit just mentioned, of 4 feet, we know can be secured at moderate cost, and maintained at about the same expense as for maintenance and attendance of the five locks and dams proposed; and this depth will amply satisfy any possible demand upon the river until the enlarged canal, talked of but not in progress, is ready for use. In carrying out the scheme, it was decided not to let the work in sections, to be entirely completed up to the proposed standard, but to classify the bars according to their character as obstructions, and to remove them in the order of classification. For the removal of the first class, including all having less than 2.5 feet at lowest stage, proposals were invited by advertisement, dated September 6, 1870. Profiting by experience, it was also decided to protect the work from deteriorations by making the excavation 6 inches below the line of 4 feet draught, limiting the excavation to those portions of the shoal where the original depth was less than 4 feet. In making location of the lines of proposed channels, the natural channel is taken as a guide, unless both economy and convenience in use suggest a change. In all cases, the lines are either tangent or very flat curves. As it was important to have the curves conform to the shape of the natural banks, a laborious investigation was made to determine the curve that would satisfy the condition, resulting in a formula which closely follows the banks, and is also very convenient in use. The formula is for a 'n2 + n polar curve, in which the radius vector=a+ c, in which a is assumed as a round number greater than the width of the river, and e determined by equations of condition that the curve is to pass through three selected points, as deposit of excavated material is intended to aid in confining the current to the channel at all stages below a mean. The limits of deposit-ground are also defined by curves of the same species. As the method has been tested by a year's experience, during which the river has passed its ordinary variations of stage without, in any case, developing any tendency to fill up the excavated channels, it is hoped that the labor spent in elaborating the method was not in vain. Under the first contract dredging alone could be done; therefore I was unable to fully carry out what I thought desirable in the way of protecting the works. The latter contract provides for some cases, and I am satisfied, from the success so far attending them, that it would be well to increase the item of protection still further. PROGRESS DURING THE YEAR. Up to the close of the year the work done by F. D. Van Wagenen was located at the following places: Which represents the total cost of improving fifty-two miles of river, which is now complete. The work mentioned above as done at Henry lock was planned and directed by the engineer of the lock, Mr. D. C. Jenne. FUTURE PROGRESS PROVIDED FOR-WORK. For the expenditure of the appropriation made in 1870, a contract was made October 18, 1870, with James T. Hayden, who, after the delay necessary to build the required boats, reported ready for work January 2, 1871, since which date work has progressed, except when suspended for repairs and other frequent mishaps. The contractor being notified to increase bis force, has made arrangements to do so, but the additional machinery has not yet arrived upon the work. With the expected increase, the completion of his contract within the next fiscal year is assured. Under this contract, the following work has been done : The last two items were incomplete at the close of the year. 14,506 35 The existing contract covers the following bars, for which the means now available will be ample, in addition to the above: 1. Moore's Island. 2. Naples Flats. 3. Big Blue River. SURVEYS AND RESURVEYS. During the past year no extended surveys have been made. A change in the method of conducting them puts it in the power of the regular engineer party employed to lay out and direct the work, to make very elaborate surveys, which heretofore required a large party; and now the soundings are taken immediately in advance of the dredging, therefore the only surveys have been of the bars worked on. A large amount of material on hand at the beginning of the year has been worked up and plotted on the several scales required for working and record sheets. In working up the results of the surveys of June, 1870, my attention was drawn to the numerous errors made in reading and recording depths measured by hand, and the failure to develop the shape of the bottom by detached surroundings; also, it was found a very laborious matter to test the excavated channel for lumps and ridges. These considerations led me to study the problem of mechanical sounding under the conditions noted; the result was a machine working on the principle of the pantagraph, recording a continuous profile of the ground passed over, which, being applied to the system of pontons already in use, gave satisfactory results, and after being fully tested, the machine was purchased for the Government on your recommendation.. The machine not only gives better results than hand labor, but greatly reduces the expense for field and office work. Tested both by crossings, duplications, and by comparison with rod soundings, the results are always correct. WORK REQUIRED TO COMPLETE THE IMPROVEMENT. Whatever may be said in favor of a slack-water improvement, in connection with the enlargement of the Illinois and Michigan Canal, considered as a military or naval measure, or in view of a possible development of commerce over the line, there can be no dispute that, until the canal is complete, an open channel of 4 feet depth is ample to satisfy the trade, and, as a canal project would be the work of many years, it is my opinion that to foster the trade by opening and maintaining a good channel equal to the present canal is all that can now reasonably be asked of the General Government. Former reports, recommending a much more costly improvement, contain arguments which may safely be referred to, to justify a less expensive one, such as is now in progress, and which can be completed according to the following estimate, covering the entire river now unimproved: ESTIMATE. The estimate is made for a channel 150 feet wide and 44 feet deep in excavation, with dams to confine the water when required. |