50 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Feb. 



ON DKEDGING BARS OF RIVERS. 

 By a. C. Jones, Engineer. 



Having seen in the American newspapers several projects for deepen- 

 ing the water, or removing the bars at the passes of the Mississippi river, I 

 am induced to give a sketch of what was done by the United States steam 

 dredger Balize, as I am firmly convinced that the only feasible plan for im- 

 proving the passes is by dredging. First removing all the lumps in the ship 

 channel, and then deepening the bar by carrying it away as raised. It is 

 idle to talk of damming, ploughing, or dragging, as these projects would never 

 enter the brain of any person that was conversant with the ditiiculties to be 

 encountered. 



An impression exists that the bars consist of soft mud, and are easily re- 

 moved. This is erroneous, for the bars are hard, and studded with mud 

 lumps, which are forced by some subterranean agency through the bottom, 

 and up sometimes as high as ten feet above the surface of the water. These 

 lump consists of a compact clay (alumine,) of the consistence of cheese, and 

 the surface receives a fine polish when cut with a sharp knife. The action 

 of the water has very little effect on the lumps, (some have perpendicular 

 sides,) except during severe storms, when the tops are washed oft' to the sm-- 

 face of the water. When the surface is slightly inclined, it is generally 

 covered with innumerable clay pebbles, the fragments of the lumps taking 

 that form by the action of waves on them. 



For a perfect understanding, I will give a short history of the Dredger 

 from her commencement. The boat was built by John Vaughan, at Ken- 

 sington, in a substantial manner, and the engine and dredge machinery, by 

 Messrs. Levi Morris and Co. ;* all being fair specimens of Philadelphia work- 

 manship. The whole being under the immediate direction of Captain Andrew 

 Talcott, United States corps of Engineers. The machinery for one side being 

 so far completed as to make a partial trial in the dock ; all bidding fair to 

 perform well. The boat was hurried otFin the early part of January, 1838, 

 before the full completion of her machinery, through fear of being detained 

 by ice. The Balize did not prove to be a good sea boat, owing to the pecu- 

 liar distribution of the machinery on board, and in consequence of the rough- 

 ness of the sea, caused considerable rolling ■, the boilers being cylindrical, 

 and on the guards, at times, it was difficult to keep the water at the proper 

 height. I found great benefit in knowing the level of the water, by the use 

 of my gauge tube, as described in the Journal ; the ordinary gauge cocks 

 giving incorrect results, especially when foaming. The boat drawing nearly 

 two feet more water than her proper draught, made the passage long. 



I may mention here that I found the carbonate of lime in the boilers in- 

 crease in quantity, in a given time, as we proceeded South, although the pre- 

 caution of cleansing the boilers at the stopping places, and constant blowing, 

 was strictly attended to during the voyage. 



On the arrival of the boat at the North East pass, it, and all the force, was 

 put in requisition to assist the corps of engineers in the survey which was 

 then going on ; and it was late in the season before all the necessary fi.\tures 

 were completed to commence dredging. After several trials, it was found 

 that the chain being part of cast iron, (although proved to a strain of twenty- 

 seven tons, at Philadelphia,) frequently broke, owing to the hardness of the 

 bottom, coupled with the great size of the buckets, the contents of each 

 being one cubic yard. New chains were immediately ordered, but owing to 

 shipwreck, and other causes, the chain for one side, although first made, did 

 not arrive until eight months after. On the receipt of chains for one side, 

 numerous experiments were tried at difterent parts of the bar, perfecting the 

 machinery, and driUing the men. In November, orders were received to 

 proceed with the dredger to Red river, to remove a bai' at the mouth of the 

 Ghute — prior to our arrival, the pent up water had cut a channel of sufficient 

 depth. The only obstacle was an island of mud, 140 feet long, and 50 feet 

 at its greatest breadth ; the whole being two feet above the surface of the 

 water. The dredger was moored alongside, and operated on it with the 

 buckets of one side, and in 23 working hours, one-half of the island was re- 

 moved down to 13 feet water. As the particles of mud were only carried 

 away by the current, the same mud was raised by the buckets several times, 

 and as many of them came up heaped, so as to contain two cubic yards, it 



* As a proof of the excellence of the workmanship of the engine, I will 

 give one example. When I left the boat, the key of the connecting rod, at 

 the cross head end, remained as driven when steam was first ajjphed to the 

 engine, it not having been required to alter it. 



was computed that the dredge raised the enormous quantity of 600 cubic 

 yards per hour,t which is far surpassing any other machine in the world. 



The Balize then removed back to her station, at the North East Pass, and 

 proceeded to cut away a mud island, or lump, standing in the centre of the 

 main channel, at the mouth of the Pass. The weather being stormy, the sea 

 forced us to abandon the lump, after making several partial days work on it, 

 and we then operated at the head of the bar proper, which extends five- 

 eighths of a mile from the sea ; this enabled us to work in smoother water. 

 The bar being formed of alternate strata of sand and deposit from the river, 

 making the bottom hard ; and as the buckets were designed for soft mud, 

 their size prevented their acting well — but with this disadvantage, 1500 cubic 

 yards have been conveyed away by the hoppers, without extra exertions, in 

 eight hours working. 



On the 5th of March, we again moored alongside of the island which we 

 previously worked on, and commenced working actively at it, when the sea 

 would permit. The subduing it was necessarily a slow operation, its size 

 being about 350 feet by 150, at its greatest breadth ; the top being almost 

 at the surface of the water, with nearly perpendicular sides. The dredge was 

 a long time cutting at it with the buckets of one side before any mud could 

 be raised by those of the other side, to be conveyed away by the hoppers. 



On the 5th of April we had cut and removed nearly half of the lump dowa 

 to 13 feet water, the boat was then shifted to the north side of it, and on the 

 12th the dredger (drawing 8 feet water) passed over the top of the lump, 

 operating with both sides and filling two hoppers at the same time. 



On the 17th of -\pril, 1839, orders were received to stop dredging and lay 

 the fleet up, the appropriation being expended. A few thousand dollars more 

 would have removed this lump from the channel, as the smoothness of the 

 sea at this season of the year admitted of nearly constant working — subse- 

 quently the fleet was ordered to Mobile and there laid up. 



The principal diflSculties encountered in our operations were, 1st, in placing 

 the machinery from the want of correct knowledge of the bottom — for al- 

 though several partial surveys had been made by difl'crent persons from 1S20 

 down, and inquiries from shipmasters and others supposed to be conversant 

 with the actual state of the bars, yet their reports left the impression that 

 the north east bar was soft mud and easily removed ; as this proved to be 

 incorrect, the consequence was that niimerous alterations had to be made as 

 experience pointed out. 



2nd. The operations being on the margin of the Gulf of Mexico, great loss 

 of time was experienced from the prevalence of easterly gales, which blowing 

 against the current of the river caused considerable sea, the depth of cutting 

 being from 13 to 15 feet, the force of the sea had a great effect in deranging 

 the machinery. 



3rd. In conveying the mud away from the dredger often considerable time 

 was lost by the hoppers not discharging their load (100 cubic yards) owing 

 to the mass beco.niing compact. 



A great loss of working time was also owing to the tow boat frequently 

 getting aground and blundering iu bringing the receiving vessels to, and tak- 

 ing them from, the dredger, all these, coupled with the general inexperience 

 attending works of this kind and magnitude, and being distant over 100 

 miles from the nearest workshops, prevented a successful beginning; but the 

 latter part of the operation, owing to the perfection arising from practice, 

 was highly successful, and will bear a comparison with any other dredging 

 operation. 



In connexion with the foregoing, I give yon the mean of a number of ex- 

 periments made with the engine at Mobile, during the month of June, 1839, 

 these may be relied on as correct, although differing from some of the theo- 

 retical properties of expansion. I was unable to give higher speeds to the 

 wheels on account of bringing home the anchors, the boat being moored in 

 the stream. 



The horizontal cyUnder is 19J inches in diameter, and 7 feet stroke, and 

 works either by a whole stroke eccentric or a -| cam, the exhaust either way 

 being the whole stroke. Each wheel is of the double form, 18 feet 7 inches 

 in diameter ; extreme length of the bucket 6 feet 10 inches ; each section has 

 12 buckets 21 inches deep. 



The shaft has two fly wheels and couplings to admit of the engine being 

 worked independent of the wheels. 



The time for experimenting was chosen when there was little or no current, 

 the engine being in perfect order, and working with httle friction. 



' That there may be no doubt of this, I will state that tight buckets were 

 raised per minute. 



8 X 1 X 60 = 480 cubic yards, even measure. The bucliets being tept heaped, 

 600 yards is a safe estimate. 



