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At many dams there is a temporary bridge above the wickets from watch they are raised. This is probably the better method, but in a wide river it would probably cause some delay in getting the wickets up, wless a considerable force of laborers were kept on hand to expedite operations. Two or three men are all that are employed in France to manage a lock and movable dam.
Assuming then a method of improvement by movable dains on the Chanoine plan, we require the following constructions:
1. A movable dam of Chanoine wickets divided into navigable pass and weir.
2. A lock large enough to pass an ordinary coal-fleet through in one lockage.
The dams should hare a vertical height of 12 feet, that being as far as present experience goes, about the greatest practicable Leight of a morable dam. The lift from one pool to the next will be 6 feet, and there will be a minimum depth of 6 feet below each dam, thus securing a 6-foot navigation at all times.
I have already chosen the approximate position for a suflicient number of dams to make a 6-foot navigation at all seasons between Pitts: burgh and Wheeling. I do not think it advisable to make an estimate at present for extending this work below Wheeling. The sites and length of dams are as follows:
Where two lengths are given in the above list, the dam rests on an island, and there are two channels to be closed.
The width of navigable pass is an indetermined quantity. Coal-fleets are generally four barges or 100 feet in width, but at times they have a width of five barges, (120 feet,) or even of six barges, (144 feet.) As they will have the smooth wall of the lock to guide them into the pass, I think it will be quite safe to limit its width to 250 feet. The rest would be weir and Brunot chute, should the latter prove a success, or weir only if the contrary.
Experience in France shows that the locks should be large enough to pass a coal-fleet, either ascending or descending, at ove lockage. An average fleet has ten barges, (130 by 24 feet,) one fuel-flat, (100 by 22 feet,) and one steamboat, (230 by 48 teet.) The barges could pass two abreast if the locks were 50 feet wide, three abreast if they were 75 feet, four abreast if they were 100 feet wide. The first size is, however, too small for packet-steamboats which require from 60 to 80 feet, and the last-named size is too wide to be closed by the ordinary lock gate. The width of the lock must therefore be 75 feet.
To hold such a coal.fleet as I have described above, the available length of lock must be 620 feet, and this should be increased to 630 to give play for the gates, and to avoid a tight fit.
The lock should therefore be built with a length between miter-sills of 630 feet, a width of 75 feet, and an ordinary lift of 6 feet, but with strength enough to sustain a pressure of 10 feet, wbich would bappen should the lower pool be emptied in low-water.
This length may seem excessive, but the advantage of passing a fleet at one lockage is very great, and the increase of cost is not in proportion to the length of lock. The most expensive parts of a lock are the gates and the masonry around them, and these cost the same in all locks of the same width and lift, regardless of their length. The difference between a short and a long lock of the same width and lift is only the cost of the extra length of chamber wall, and this is the cheapest masonry about the lock. The fleets on the Seine are somewhat smaller than those on the Ohio, though their larger barges have almost exactly the same dimensions as Ohio coal-barges. (See Ex. Doc. No. 127, II. of R., 43d Cong, 1st sess., page 5l.) To pass one of these fleets at a single lockage, the lock-chambers on the Upper Seine have a width of 10 feet, and an available length of from 591 to 615 feet.
In order to avoid delay and waste of water when a single steamboat wishes to pass through, the locks should have extra gates at the middle, so that the whole length of lock need not be used unless occasion called for it. This will add somewhat to the expense, but I believe that the advantages of diminishing the amount of water needed lor lockage during very low stages, and of expediting the passage of packet-boats, will be wortb obtaining.
The cost of such a lock as I bave described, would be, in round numbers, $200,000. The cost of 13 such locks will therefore be about $2,600,000.
These figures will be somewbat modified when a detailed estimate can be prepared. A special party is now at work definitely locating the proposed dams tbat I have approximately located above, and making borings to determine the character of foundation at each site. This information will be embodied in the report ordered for the Senate Committee on Transportation, and will somewhat modify the approximate estimate herewith presented.
The cost of the movable dams will be:
These estimates for the dams have been carefully prepared under my direction by Lieutenant Maban, by using the itemized bills of materials prepared from actual construction in France, and are believed to be qnite accurate. No account has been taken of the Brunot chute, which, if successful, will replace a part of the weir. It would, however, increase the cost of a dam.
A morable dain of the average length of 1,473 feet will then cost as follows: 230 feet of pass, at $344 per foot.
$50,000 1,273 feet of weir, at $227 per foos.
Total for one inovable dam
374, 971 Thirteen movable dams without locks will therefore cost.
4,874, 623 The cost of a single lock with movable dam will be...
574, 971 And the whole cost of this improvement from Pittsburgh to Wheeling. 7, 474, 62.5
Iu beginning this work we should first build the locks, as during the coustruction of the dains they will answer as waste-treirs, and will also
keep open a passage for navigation. I think that at as early a date as possible this work should be simultaneously begun at all points between Pittsburgh and Wheeling, because it will take all of two seasons to build these locks, and their construction must precede that of the dains. There is no doubt whatever of the absolute necessity of using locks in any rational plan for improving the Upper Ohio so as to secure a 6-foot navigation. Whatever changes may be made in the details of the dams, the locks must be the same. For this part of the improvement of the Ohio, I therefore now ask for.. $2, 600,000 Engineering an<l contingencies of lock-construction, 5 per cent..
130,000 Besides this special sum, I request the following: To complete snag-boat..
$35,000 To keep dredges at work 9 months, at $3,000..
27,000 For six months' service of snag-boat, at $3,000.
18,000 For improvmg Lower Ohio by dikes.
170,000 Office expenses.
20,000 Total ........
3,000,000 I have not thought it necessary to attempt detailed estimates on the dikes for the Ohio below the Falls, as this work is so dependent on un. foreseen contingencies that such estimates are of little value., The bars that are in most need of improvement are Portland, Flint Island, Puppy Creek, Scuffletown, Three-Mile Island, Shawneetown, Treadwater, foot of Cumberland Island, and the Grand Chain.
percentage due ou contracts not yet completed)
26, 675 96 150, 000 00 207, 286 47
194.883 84 3,000,000 00
IMPROVEMENT OF THE OHIO RIVER BELOW THE FALLS.
UNITED STATES ENGINEER OFFICE,
Cincinnati, Ohio, November 30, 1873. GENERAL: In reply to your letters of September 1 and October 1, I would submit the following in regard to the improvement of the Ohio below the falls so as to secure a depth of 5 feet at low water. gret that I have been absent on duty so much lately, and have been so buss on board-reports, that I have been unable to take up the subject earlier; but as I gave my views at length in my testimony before the Senate Committee on Transportatios, for whose information (as I was informed these questions were asked, I trust that the delay was not been injurious.
The first question in your letter of September 1, reads as follows:
Please inform this Office whether you are prepared to submit a project forimproving the Lower Obio River, from Louisville to Cairo, so as to atford a depth of not less thau 5 feet at the lowest stage of water known. If not, please state what additional inforination you require to enable you to prepare such a plau.
In reply I would state that the only plan which I am at present prepared to recommend is the one now in use throughout the whole river,
and that is the concentration of the currents by dikes or wing-dams, and the closing of all but one channel where there are two or more. Whether this method will secure five feet during dead low. water I cannot no :v tell, but I am rather of opinion that it will not. It is possible that we might secure four feet, but experience alone will answer this question. I should state that no work was done on the Lower Ohio by Mr. Roberts, and that I have only commenced the work this season, and consequently have too little experience in this matter to give a positive reply. The dikes at French and Henderson Islands are both under way, but it is not likely that either will be finished this season. The latter was commenced first, and its effect was so quickly felt that there was no trouble at this bar during this summer's low water. But the mere fact of boats being able to cross this bar does not show the maximum that could bave been brought over, as during the low-water season there was only 20 inches on French Island bar, (the work at that time had not begun there,) aud from two to three feet on some others, and therefore all boats were run ing very light. Last year I commenced work at Cumberland Dam and at Evansville dike, but the object in view at each of these places was the changing of old channels, and not their deepeving, and, besides, both of these works are unfinished.
One great difficulty in improving this part of the river is that the coal-fleets that start from Louisville for southern markets are much larger than those that come from Pittsburgh to Louisville, and this fact, together with the lack of definiteness in land-marks in the river below the Falls, makes it dangerous to recluce the channel-width below 600 feet, and of course the same depth cannot be expected in a wide as in a narrow channel.
There is another point on which reasoning is of little avail, and experience alone is to be trusted. That is, whether or not the sands that are swept throngh narrow artificial channels will not form below, and the practical result be simply a change of position of the bar, without increase of depth. If the work formerly done on the Ohio had been kept in good condition, and carefully observed and reported upon, we should now be able to settle this matter; but our records are unfortunately defective, and the old works have themselves been so degraded that they now exercise no perceptible influence on the bars. I bave in this office all the records about the Lower Ohio that I could secure in the Department or elsewhere, and I herewith present, in chronological order, a summary of all the opinions on the effect of dains and dikes in the Lower Obio which I could gather from the records.
The earliest report on file in this Office, which records the results of work on the Lower Ohio, is by Colonel Long, in reference to the dike at Henderson Island. His report is in the shape of marginal notes on the drawings which he forwarded to the Department. On his “Sketch No. V," a copy of which I send herewith, there is the following note. The remarks in brackets and the italicizing are mine:
From the diagram now before us it will be perceived that the bed of the river has undergone a material change since the commencement of our operations,
A portion of the sand accumulated above the dam during the freshet before mentioned [ winter of 1824-25] contributed to form the circular bar at the lower extremity of the dam, across the outward margin of which the depth of water is only three feet as represented in the sketch. A large quantity of sand previously situated in the bed of the river above the dam, was now distributed over the space between the dam and the dry-bar below, occasioning the shoal presented in that part of the river. The elevation of the bar above the dam, with the exception of the channel contiguous thereto, remained about the same as it was at the commencement of the work this year, although its position approximated considerably nearer to the island.
The general depth of water in this part of the river, at the time alluded to, was from 21 to 3 feet, but owing to subsidence of 18 inches, which took place during the progress of the work, its depth was now only about one-half that abore mentioned. The position and depths of the channel, occasioned by the dam, are indicated by the drawing, in which are inscribed a series of soundings, corresponding to the depth of water actually found in the channel at this very low stage of the river. At the lower extremity of the channel the depth is only 3 feet for a distance of 12 or 15 yards; but the sand is bere exceedingly loose and yielding, the current setting strongly across it, and daily rendering the channel deeper and broader. It is not expected that the channel occasioned by the lam will continne to occupy the position it now has longer than the present season, for the following reasons: The next freshet will probably bring down a large body of sand from above, and deposit it immediately above and below the clam in such a muer as to form a bar rising to the top of the dam throughout its whole length; sich being the event, the most elevated part of the bar will be that portion of it situated contiguous to the dam, so that when the river subsides, the water, instead of being drawn off through a channel adjacent to the dam, as is now the case, will pass over a less elevated part of the bar at a considerable distance above it. Should the result forove as here stated, there can be little doubt either of the efficiency or permanency of the work, for it will then be protected from the undermining intuence of the current, and secured from the shocks of floating ice and drift of every description to which it would otherwise be exposed.
I woulil particularly call attention to the following points on the sketch : The limited depth of water across the bar, the narrowness of the channel indicated, and the shoal formed below the dike.
Captain R. Delafield, Engineers, in his report, dated January 16, 1833, (Doc. No. 66,) states as follows about the work on the Lower Olio:
The last class of works [deepening the water on the bars] has now been so far tested as to renderno longer doubtful tlie success of removing the bars from their present position, and to this period entirely accomplishing the object iu view of giving a permanent and unchangeable 34 and 4 foot channel-way.
With a judicious location of the daws, I am Diore fully confirmed in the belief that permanency may be secured to all such works, and that removing the bar from one point shall not form another in mediately below. This is the only doubt as to the eutire success of the works of this class.
The results thus far have been satisfactory. Last year two of the most difficult and shoalest bars were dammed, as shown by tigures 1 and 2 accompanying this report.
On the Scuttletown Bar (Fig. 2) there was formerly but 18 to 20 inches water at the low stage of the river. Since the dams have been constructed there is four feet, and no injurious formation below it, all the sands baving apparently been deposited under the lee and edily made by the dam, and the channel contined within permanent banks.
A reference to Fig. 2, No. 8, of my report of 1831, will exhibit the position of the shoals at that time, and the present sketch (Fig. 2) will give an idea of the change effected by constructing the dams.
Fig. 1 is a sket i of another system of dams constructed last year, that have been productive of satisfactory results at the Sister Islands. In this case, as the previous ones, the sands washed from the bars have been deposited under the leo of the clams. Fig. t, No. 12, of the report of 1831, exhibits what was then supposedl to be the position of the shoals at that time, and the sketch accompanying this report (Fig. 1) the present position of the slioals, If these two figures are correct, a very great change has been maile in the whole best of the river, proving the facility with which the channel may be deflected in any direction, and the necessity of having surveys for each and every one of these bars, to judge properly of the effect produced.
I append to this report copies of Captain Delafield's maps of the bars at French Island, Scuffletown, and the Sisters, the work being then under way at the first-named place, but tinished at the other two. He shows a depth at French Island of 24 feet, at Scuffletown of 4 feet, and at The Sisters of 31 feet.
There are on file in this office sketches of the dams at French Island, Scuffletown, Three Mile, and The Sisters, made by Lient. A. II. Bowman, Engineers, in 1835, in connection with some maps of work on the Cumberland, These sketches have neither scale nor soundings, and the repport that probably accompanied them is not on file in this oflice.
Capt. R. E. Lee, Engineers, in bis inspection report to the Chief Engi.