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the smallest angle of which is about 30 or 40 degrees. When in place in the river, the small angle points upstream, one side lying horizontally on the bottom. On the other side, that is now in an inclined position, there lies a layer of brush, held with the butts at the bottom of the river, and their tops pointing obliquely toward the surface and downstream. In this position the dike bears a striking resemblance to the abattis used in fortification work and from this resemblance they are sometimes called abattis dikes.

It was not expected that this form of dike would be found to be suitable for general use as a standard type for contraction work. but it was planned to use it in special localities and for special pur poses only. The principal use intended for it was to aid and hasten the building of the bars along the low-water channel crossing, thus narrowing the channel and consequently deepening it. It was thought that in this way the effects of dredging could be greatly increased, and in some places the necessity of dredging avoided. These dikes were planned to be of small cost and of such light construction that they would not become serious obstructions should a change of conditions afterwards leave them in a navigable channel.

Dikes of this character have been built during the seasons of 1898, 1899, and 1900, and have all been located within the limits of the First district. This work has not, however, been always under the charge of the First and Second district officers. In 1898 the work was started under the First and Second district officer, then Captain Patrick, Corps of Engineers. The next year it was transferred to the office of the secretary, again Captain Patrick, his duties having been changed. In 1900 this work was transferred back to the care of the First and Second district officer. Under these circumstances, and to make the history continuous, the work during the entire three years will be described here.

The details of the construction of these dikes are shown on Plate XVIII. They are composed of triangular frames, each consisting of bottom and top timbers and a rear strut, and usually of an additional intermediate strut. The frames thus constructed are placed at about 6 or 7-foot intervals and are held together by longitudinal stringers and poles, the stringers being placed at the top of both struts and at the bottom of the rear one. The longitudinal poles rest on and are lashed with wire to the bottom timbers, one of them being placed as closely as possible into the angle of the triangle. To give the dike longitudinal stiffness, diagonal braces are placed in

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the plane of the rear struts. On the longitudinal poles and the lower rear stringer, and wired to them, lies a layer of "ground" poles placed transversely and spaced some distance apart. The butts of these poles lie in the angle of the dike, while their tops project well to the rear. On these projecting tops there is placed a thin layer of brush held down with poles and wired; the whole construction of poles and brush forming an apron mat to prevent damage to scour. On the butts of these ground poles there is placed a layer of brush, and on this the stone ballast, needed for sinking the dike. This is placed as far forward as possible in a triangular pile, the amount required being from one-fifth to one-third of a ton per linear foot of dike. In the plane of the upper sides of the triangle is placed the really effective part of the dike, the brush screen, the brush of which projects well above the frame. This brush rests on and is spiked to the forward longitudinal and the ground poles, and is wired to the stringers where it crosses them. To assist in holding the brush in place, a longitudinal binder pole is placed along the front of the dike near the bottom. In some of the early structures other binder poles were placed in front of the brush screen, but these have proved to be unnecessary and are liable to catch drift, and they are now omitted. In the earlier dikes the brush was spaced some distance apart, but this left the dike so open that in the later construction it has been placed as close together as it will lie without forcing. When placed thus, the natural irregularities and crookedness of the brush are such as to leave ample space between them. In all the dikes made up to the present time the brush has been used as it comes, without topping, but these bushy tops are bent over and down by the current and their own weight and frequently break where the brush crosses the upper stringer. Consequently, it is expected in future construction to top the brush and to use poles in place of it.

These frame dikes as above described are constructed on ordinary mat barges provided with launching ways, two barges being used, lashed together end to end, as in this way about 250 feet of dike can be built continuous, this being a convenient length for the sections. The barges are prepared for the dikes by lashing on the ways three lines of longitudinal poles, and on these the dikes, as above described, are constructed, the bottom timbers of the frames being wired firmly to these longitudinal poles. By cutting the lashings fastening these longitudinal poles to the ways the dike can be allowed to slide off and into the water. This process of cutting the

lashings, however, taxes some little time and as I steine
the whole dike would be free at one time, there was introllets
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future.

During the construction of these dikes the barges are mort fne bank at the most consentent place, and when the weton ite is ready they are toxed to the proper place. Premions to me) D of single anchor piles has been driven about 50 feet above the de sired location of the dike, the interval between the pile being j feet or more, depending upon the depth of water and the spongi of current. Each pile has fastened to it, at such a distance from the lower end as to be at the bottom of the river when the pile is dama several wire strands long enough to reach the dike, the love ol of the strandes being coiled up and hung on the top of the pos until needed. In addition to this line of anchor piles a line of mooring piles is driven farther upstream. two piles for eact wTVE. to hold the barges in place during preparation for sinking. All pules before being driven are sawed about half through, so that when they are no longer needed they can be broken off near the hot tom of the river by pushing against them with a steamboat. This does away with the possibility of their becoming an obstruction to navigation.

As soon as the section has been towed to place, and has been properly aligned, the strands are brought from the piles, all slack hauled up and their ends securely fastened to the dike. In deep water with strong current one cable is used to every frame, but for shoal water or slack current fewer of these are necessary. The mat barge meanwhile is held in place by lines from each end of it to the mooring piles, and the section is prevented from prematurely sliding off by being firmly fastened to the ways and by the chocks. When everything is ready to launch, the wire ties are cut, and when all are removed the signal is given to loosen the chocks and let go the holding lines, and the current floats the barge downstream, allowing the section of dike to float off. This is done very quickly, the sections usually diving down in such a way that the base becomes nearly perpendicular, but they quickly right themselves as soon as the current begins to press against them. In the first dike built the attempt was made to lower the sections down slowly by

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neans of slip lines, but this experiment was not repeated, as it nearly resulted in disaster to the barges as well as to the section. When once this heavy mass started to move nothing could hold it, and it was only by quickly throwing the ends of the slip lines from the kevils that damage was averted.

In order to keep the sections under observation after being sunk, gage poles, marked in feet and tenths, are fastened at each end of the section perpendicular to its base. From observations of these it has been found that, though the sections dive down perpendicularly on being launched, they quickly right themselves. For a short while afterwards they lie flat on the bottom, but later they begin to sink at the upstream side on account of the scour there. This scour usually continued for from twenty-four to thirty-six hours and then ceased. It has at times amounted to as much as 4 feet. One feature especially noticeable is that as soon as a section of dike is placed a deep hole begins to scour out around its exposed end, and unless this is stopped that end will continue to settle for a longer time.

As it is manifestly impossible to place two separate sections in close contact, and as it was feared that scour through the interval might undermine and injure the ends of these sections, it was at first decided to place the separate sections in echelon instead of in line; that is, each section is retired a short distance below the preceding one and is drawn inshore, so as to lap it by several feet. This method was used in 1898 and 1899 and prevented the damage feared, but the current through this gap had a tendency to cut out a depression in rear of the more advanced section, and in 1900 another arrangement was made. During construction all the work above the ground poles was omitted for several feet from the outer end of each section, and on these ground poles was made a sort of mattress. When the dike was sunk, this mattress prevented or diminished the cutting of the deep holes above mentioned. When the next section was ready, it was placed on the same line as the preceding section, as close to it as possible, and with its inshore end resting on this mattress. There was thus left a small opening between the sections, but with a mattresed bottom. This arrangement has worked very well, and no damage has been caused by scour through these gaps. When the outer end of the dike is reached, a small fascine mattress is first sunk to prevent the cutting of a deep hole at this place, and on this mat the end of the last section is placed.

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When the dike abuts against a high bank it as Desser
the bank for some distance up and down stream graingoa,
gentle slope and carrying the structure of the like at least e
the way up the slope. When the dike abuts against av
must be continued on the bar, at least for some distans vs.
somewhat similar structure, rising at least as high as the top
dike in the water. In some cases it has been found negre
carry the dike all the way across the dry bar and up t
bank.

Structures of this character have been built at four lo
Point Pleasant, in 1898 and 1899; Cherokee, in 1899 and 190
Ashport Bar (Plum Point Reach), in 1900; Elmot Bar P
Point Reach), in 1900. These will now be described:

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SEASON OF 1898

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Post Peasant.--Point Pleasant is situated on the right bank of the river, 80 miles below Cairo and 10 miles below New Madrid. From New Madrid to Point Pleasant the river is straight, and in this straight reach the river has wandered here and there, someTinies cutting away one bank and sometimes the other, with the result that the river has become quite wide. This widening causes, at buch water, a deposit of material, and this deposit has taken the form or a mareber of middle bars, through which the low water has hod to cut are own channel. The channel has shifted in place from Yo To Yer and for veral years it has been necessary, in order To obrem a patase de

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