« PreviousContinue »
duce here. The additional draws provided for in the bill to accomplish this object would probably be much more expensive and generally im. practicable.
Section 6.-In line 11, section 6, of the original bill, for “bridge” bas been substituted "span or spans," as there can be no objection to the movement of trains over any portion of the bridge other than the draw. opening. Lines 12 and 13, “or of boats through said draw,” is omitted as unnecessary, such delay being considered of extremely improbable occurrence. The rest of the section is unchanged.
Section 7.—This is section 8 of original bill. An additional requirement is introduced to the effect that the axis of the bridge shall be as nearly as may be at right angles to the current. This is deemed important, to prevent the construction of bridges very oblique to the direction of the current, which are not considered safe for navigation. The pro. hibition of riprap in channel or draw spans is extended to all spans, as experience has shown that its use is never necessary, except as a remedy for improper construction, and its presence always affects the water. way and may unduly increase the velocity of the current at the site of the bridge. This section also requires the removal of this and all other obstructions, under the Secretary of War's direction, by and at the expense of the company or persons owning, controlling, or operating the bridge.
Section 8.-This is a new section intended to regulate the character of the approaches and other parts of the bridge with especial reference to their bearing on the flood discharge of the river.
Section 9.-Is new and covers the case of any bridge erected in the near vicinity of an existing bridge. In this case, if the general requirements were strictly followed, there might result a very serious obstruction to navigation.
Section 10.-This is section 9 of the original bill somewhat amended and enlarged, so as to require the building and maintenance of all such accessory works as may be necessary to overcome, to as great a degree as possible, the obstruction to navigation caused by the construction of bridges. In its present shape the section conforms more closely to existing laws on the subject which it covers.
Sections 11, 12 and 13.-These sections replace numbers 10 and 11 of the original bill. The divisions introduced are the mouths of the Kaw and Platte rivers, instead of the Union Pacific Bridge at Omaha. At the points mentioned the influx of large tributaries modifies very materially the size and volume of the river, and will undoubtedly in the future affect considerably the character of its navigation. Above the Platte River the clear channel-way called for is as small as is considered compatible with the free discharge of the river at high stages, and the height is the same as is required by all recent bridge acts. Between the Platte and the Kaw there is an additional requirement of at least one channel span of not less than 400 feet clear water-way, the height remaining as above. Below the Kaw all spans are to give at least 400 feet clear channel-way, owing to the much greater volume and commercial importance of the river, and the required height is increased 5 feet as the detentions at high stages, due to insufficient height, will be longer, more frequent, and more injurious to navigation than above the Kaw. The lengths of span called for are moderate; in fact, they have been adopted voluntarily in nearly all of the ten bridges which have been built since 1874, owing, it is said, to the saving in cost effected by redncing the number of piers with their costly and difficult foundations.
The Board have omittea the provisions for draw-bridges, as they consider that such structures, daugerous and undesirable in all cases, are entirely inadmissible on the Missouri, where the shifting channels and fierce current require that all possible precautions be taken to prerent bridges from becoming an absolute bar to navigation. This view has been consistently held and urged by the officers in charge of the improvement of this river, and also by the Missouri River Commission. The Board holds that all spans over the water-way should be available for the passage of boats when necessary or desirable, and that these spans should be as long as possible, both for the safety of navigation and for the free discharge of the river at high stages. These conditions can not be complied with in a low bridge. Out of seventeen, the total number of bridges, either built or building over the Missouri, but fom) are low bridges, and all these were constructed prior to 1875. All four are difficult and daugerous of passage, two in fact being well-nigh impassable at high stages, while at the two others navigation has been several times entirely suspended, owing to the shifting of the chanuel from under the draw-spans at low water. Since their construction, ten other bridges have been built, all high, although the alternative of a low bridge was allowed. The motive for this is said to have been economy. It would seem, therefore, altogether unjustifiable to authorize a class of bridges, which, it built, would be a constant menace to navigation and which seem to be rarely demanded even on the score of economy.
Section 14.- This section is a substitute for numbers 12, 13, and 18 of the original bill. The general character of the boats to be accommodated on the Mississippi River above the mouth of the Missouri and on the Illinois River is essentially the same, and the requirements for safe navigation would seem to be about identical. The clear headway required of 55 feet is such as is given by existing high bridges over the Upper Mississippi and is the least height that will accommodate the interests of navigation. The height of pilot houses and other portions of Upper Mississippi steamers have already been reduced to conform to present conditions, and further reduction is impracticable. In many of the bridges over the Upper Mississippi draw-openings of 160 feet and channel or raft spans of 250 feet are provided, but as each bridge furnishes its individual share of obstruction, dimensions heretofore used should not be taken as a guide for future construction. With a view to reducing the expenses of navigation to a minimum, and also owing to the fact that the improvement of navigation has made it possible, the size of rafts has been materially increased of late, and existing bridges are found to be much greater obstructions and to cause more delay and expense than formerly. As the advance in the science of bridge building renders the construction of draw-spans with 200 feet openings and other spans of 350 feet length simple matters, it is thought that the increased dimensions suggested are quite reasonable, and are the least that will properly accommodate present and prospective river traffic.
The section also permits the construction of such inclined bighway bridges as are now in successful use at Dubuque and Saint Paul, and which will doubtless be desired elsewhere in the near future. The orig. inal sections did not permit their construction.
Provision is also made for all cases in which a narrow river, or other causes, may permit a reduction of the requirements without injuring the interests of navigation.
For the Illinois River, where the difficulties of navigation are not so great and where the rafting interest has not to be considered, draw openings of 160 feet are permitted.
The next four sections pertain to the Mississippi below the mouth of the Missouri, over which there is as yet but one bridge, that at Saint Louis. The corresponding sections of the original bill allow draw-bridges to within 8 miles of the Saint Louis Bridge, and below Saint Louis draw spaps in all high bridges are required. These features do not meet with the approval of the Board, and are omitted from the proposed substi. tutes for these sections. The Mississippi, below the junction of the Missouri, partakes mainly of the characteristics of that stream, with the additional feature of greatly increased volume. Instead of the gentle cnrrent and comparatively fixed channels of the Upper Mississippi and Illinois, we find an impetuous current and great instability of channel. Hence, all the objections urged against draw-bridges on the Missouri apply with equal force here, greater, in fact, because the navigation interests are more extensive, great rafts and tows must be provided for, and below Saint Louis the boats employed are much larger. The report of the Board which examined into the question of a bridge recently proposed above the Eads bridge at Saint Louis (Senate Ex. Doc. No. 20, Forty-ninth Congress, second session), gives at length the reasons why low bridges between the mouth of the Missouri and the Eads bridge are considered inadmissible, and in this conclusion the present Board fully concur. The draws called for in high bridges below the Eads bridge the Board consider highly objectionable. Their only object, apparently, would be to enable boats having tall chimneys to get through the bridge without lowering them, at times when the stage of water would not admit of their passing under the fixed spans. But it is only at high stages that any inconvenience from this source would be experienced, and at such times the strong current would render the passage of a heavily-laden boat through a narrow draw opening an extremely hazardous, if not impracticable, operation. On the other hand, the extra cost entailed upon the construction of the bridge by additional piers and expensive draw-spans, would be a beavy and very distasteful item. Therefore, as they consider that the value of these draw-spans to navigation would be little or nothing and the extra cost entailed by their construction unnecessary, they have recommended their omission from the requirements. The Board feel well assured that, by the use of well-known appliances, the upper portions of steam-boat chimneys can be lowered to the level of the pilot-houses, and as the clear head-room they have recommended will pass the pilot-houses of the largest boats on the river, they consider that the slight delay which may accompany this operation of lowering the chimneys will be far less onerous to navigation than the great danger and difficulty which must, of necessity, attend an attempt to pass through a narrow draw opening at high stages of water.
Section 15 corresponds to section 14 of the original bill. The chan. nel-span of not less than 500 feet called for is deemed necessary for the passage of rafts, which are already made up in widths exceeding 400 feet. The other spans over the water-way should be of not less than 400 feet to avoid undue contraction of the water way. The headroom of 55 feet called for is the same as that now required for bridges over the Upper Mississippi River, to which the heights of all up-river boats have been gauged. The southern limit is taken to the northern limit of Saint Louis, so as to embrace in the next section all of the har bornorth of the Eads Bridge.
Section 16 corresponds to section 15 of the original bill. It provides that all spans over the water way of the harbor of Saint Louis, as it will be when its improvement is completed, shall give at least as much accommodation to navigation as do those of the Eads Bridge, and also the same head-room as is given by the bridges over the Upper Mississippi. Any additional spans required to cross the present river-bed may be of less length and height.
Section 17 corresponds to section 16 of the original bill. After passing below Saint Louis, it becomes necessary to provide for larger boats than are employed above that city, and also for the immense grain-tows which go down the river. The Board consider that 500 feet is the least width allowable for any span over the water-way, and that a clear head-room of 65 feet above high-water mark is needed to pass the pilot-houses of the large packets running to Saint Louis. To accommodate the large tows, they consider that a channel-span of 650 feet is the least admissible, and that this width may have to be increased in special cases, at the discretion of tne Board of Engineer Officers elsewhere provided for. To understand the necessity of this great width of span, the size of tows and the manner of handling them must be explained. The diagram annexed to this report shows a tow made up of seven barges and a tow-boat. Each barge is 235 feet long by 41 feet beam, and carries, when the stage of water permits, 50,000 bushels of wbeat, or 1,500 tons of that or other freight. The whole tow, including the steamer, which is firmly fastened to the barges in the position indi'cated, measures 660 feet in length and 205 feet in breadth. The barges, with their apper works or cargo boxes, expose about 15 feet of height above the surface of the water. In descending the stream, if the channel is straight, the tow-boat pushes the tow along, but if the channel is crooked, especially if the current is strong, the limit of capacity of steering by means of the rudders of the steamer is soon reached. When this is the case the engines are reversed and the stern of the boat thrown away from the concave shore. The tow then lies more or less obliquely to the current and is carried on by it, the tow-boat meanwhile, by backing when necessary, preserving a safe distance between the tow and the bank. The degree of obliquity of the tow to the current depends upon the velocity of the latter and the degree of curvature of the channel; in extreme cases it may be absolutely at right angles to the current. This operation is technically known as flanking, and with the tortuous channels and sweeping bends of the lower river is of almost constant occurrence. Owing to the extent of surface exposed to its action, the effect of wind on one of these unwieldly tows is also very great, and for all these reasons it is necessary, to insure safety, that the channel-spans of bridges through which they are expected to pass, should considerably exceed the width of the tows, and in extreme cases even their length, to provide against the contingency of their arriving at the bridge broadside on.
Section 18.–This is section 17 of the original bill. Below the junction of the Ohio the Mississippi is more than doubled in volume, and demands corresponding care in avoiding undue encroachment on its water way. The character of its navigation is also different and demands greater facilities. We meet here not only the large grain tows, already spoken of as leaving Saint Louis, but also the immense coal tows from the Ohio River. Diagrams appended show the arrangement and size of some large coal-tows reported to the Board. The larger of these, that of the Joseph B. Williams, comprises thirty-nine boats and barges, carrying in all 821,640 bushels, or about 32,865 tons of coal The dimensions of this tow were-length, including tow-boat, 1,032 feet; breadth, 256 feet. The other diagram shows a tow of forty-one pieces. It is 904 feet in total length, by 310 feet in breadth, and its cargo con. sists of 764,546 bushels of coal, weighing 30,581 tons.
These are, of course, large tows, but not exceptionally so, and the ten. dency, is to still further increase their dimensions. They are handled in essentially the same manner as already described when speaking of the preceding section, but owing to their great size and weight, and the tortuous course of the stream, the operation of flanking is in almost constant requisition. Owing to the increase in the volume of water, as well as in the demands of navigation, the Board consider it necessary that the length of all spans should be made greater than above Cairo. The clear head-room should also be increased for several reasons. First, on the lower portions of the river, at least, a larger class of boats is used; second, the duration of high water is much longer, the river, at times of flood, remaining for days and even weeks in close proximity to extreme high-water mark, hence detention due to insufficient height would be more frequent and of longer duration; third, the present high-water marks are no safe criterion for the future, since the general leveeing of the river front, now rapidly progressing, is certain to make many cbanges, and will probably result in at least a temporary raising of flood levels. The Board are of the opinion that no spans over the water-way of less than 600 feet should be allowed, and that the clear head-room should not be less than 70 feet above high-water mark. They have left blank the least width of channel-span allowable, since, being evenly divided on the subject, they have been unable to reach a conclusion. Majors Mackenzie and Handbury consider that 700 feet might in cer. tain cases be sufficient, while Lieutenant-Colonel Suter and Major Miller deem 800 feet the least that under any circumstances should be allowed. The Board are, however, unanimous in their opinion that the widths al. lowed by the bill, of 500 feet and 600 feet, are entirely inadequate, and that greater widths even than 809 feet will probably be required for many of the special localities where bridges are most likely to be erected. This matter was carefully considered by the Mississippi River Commission in the case of a proposed bridge at Memphis, and their conclusion and recommendation, based on actual observations on coal tows pass. ing the town, was that a channel-span of at least 1,000 feet clear waterway was required at that place. (See copy of report dated May 14, 1884, hereto appended.)
Section 19 of this bill gives to the Board of Engineers, therein provided for, ample authority to call for such width of channel-span as the necessities of each special case considered may demand.
Section 19 of the original bill is omitted. Its provisions could not be of general application, and are thought to be sufficiently covered by other sections of the bill.
Section 19.-This is section 20 of the original bill, which was founded on the first Ohio River bridge act, approved December 17, 1872. The section has been re-written and is now based on the new Ohio River bridge act, approved February 14, 1883. The additions to this act, not including minor changes, which do not affect the requirements, are that the Secretary of War is given authority, on the recommendation of a Board of Engineers, to refuse permission to construct a bridge in any special locality if it is not a public necessity, or, if erected under the special conditions and circumstances pertaining to the locality, would be an insuperable obstruction to navigation. The new section is also a little more full in its requirements as to accessory works, which experience has shown to be especially necessary in the case of bridges on the Upper Mississippi and Illinois rivers, where the spaus are com