Diagram M. Mean curve and zone of range of river at Dubuque for eight years. Diagram N. Showing headway under bridges at different stages at Saint Louis, mean of sixteen years. Diagram O. Showing comparative requirements of headway under bridges at different stages at Saint Louis and Rock Island, excluding wintry months. Diagram P. Showing comparative requirements of headway under bridges at different stages at Saint Louis and Quincy for mean of eight years. Diagram Q. Showing comparative requirements of headway under bridges at different Diagram W. Channel piers, Saint Paul elevated highway bridge. Diagram B'. Pier of Rock Island railway and highway draw-bridge. Diagram D. Pier of Quincy railway draw-bridge. Diagram E1. Pier of Louisiana railway draw-bridge. (2) Folded maps: Diagram 1, in five sheets. Valley of the Minnesota and Mississippi rivers a far south as Arkansas; also showing the connection with the basin of Red River and Lake Winnipeg. Diagram 2, in two sheets. Longitudinal section of the Valley of the Mississippi River from the junction of the Minnesota to the junction of the Ohio River, as shown by the bluffs on the right and left banks. Diagram 3. Transverse sections of the Minnesota and Mississippi River Valley, showing our knowledge of depth to bed-rock, &c. Diagram 4. Valley of Mississippi River near Saint Paul. Diagram 5. Saint Paul railway draw-bridge. Diagram 6. Saint Paul elevated highway bridge. Diagram 7. Valley of Mississippi at Hastings. Diagram 8. Hastings railway draw-bridge. Diagram 9. Valley of the Mississippi at Winona. Diagram 10. Winona railway draw-bridge. Diagram 11. Valley of the Mississippi at La Crosse. Diagram 12. La Crosse railway draw-bridge. Diagram 13. Valley of the Mississippi at Prairie du Chien. Diagram 14. Prarie du Chien railway ponton-bridge. Diagram 15. Valley of the Mississippi at Dubuque. Diagram 16. Dubuque railway draw-bridge. Diagram 17. Valley of the Mississippi at Clinton. Diagram 18. Clinton railway draw-bridge. Diagram 19. Valley of the Mississippi at Rock Island. Diagram 20. Rock Island railway and highway draw-bridge. Diagram 21. Valley of the Mississippi at Burlington. Diagram 22. Burlington railway draw-bridge. Diagram 23. Valley of the Mississippi at Keokuk. Diagram 24. Keokuk railway and highway draw-bridge. Diagram 25. Valley of the Mississippi at Quincy and at Hannibal. Diagram 26. Quincy railway draw-bridge. Diagram 27. Hannibal railway and highway draw-bridge. Diagram 28. Valley of the Mississippi at Louisiana. Diagram 29. Louisiana railway draw-bridge. REPORT. CHAPTER I. PREFATORY. Origin and nature of this investigation. References: To Chapter II, on the formation of the Mississippi Valley and depth to "bed-rock;" to Chapter III, a general presentation of Western river-navigation, with discussion of the question of "headway;' to Chapter IV, descriptions of the bridges on the Mississippi; to Chapter V, a history of bridging the navigable Western rivers; to Chapter VI, an account of surveys made, &c.-CONCLUSION RELATIVE TO THE PROPER KIND OF BRIDGE. Origin and nature of this investigation.-This report was authorized by the following provisions contained in section 4 of the act making appro priations for rivers and harbors and other purposes, approved June 23, 1866: For examining and reporting upon the subject of constructing railroad bridges across the Mississippi River, between St. Paul, in Minnesota, and St. Louis, in Missouri, upon such plans as will offer the least impediment to the navigation of the river. Instructions to me from the Chief of Engineers, United States Army, dated August 2, 1866, after assigning other duties to me, say, this "duty is also confided to you, and you will collect all the information pertain ing to it." This enactment in regard to bridging the Mississippi had its origin in a resolution introduced in the Senate (prior to the passage of any act authorizing bridges upon the Mississippi River) by the Hon. Alexander Ramsey, chairman of the Committee on Post-Offices and Post-Roads, and I was instructed to confer with him on my arrival at Saint Paul as one who would furnish me "facilities for procuring much valuable information preliminary to my labors." By him I was furnished with a copy of the debates in Congress on this subject, and taking these as a guide to the nature and extent of the information I was to collect, I probably had a field of investigation more extended than usually falls to an engineer, but in no case have I gone beyond the matters collateral to, if not directly affecting, the strict engineering questions. I have made abstracts of these debates, and give them in Chapter V of this report. It would be a simple matter to report that a bridge giving about 85 feet clear space above high water with spans of 500 or 600 feet (which, in an engineering point of view, are practicable) would offer no obstruc tion to navigation on the Upper Mississippi or elsewhere where vessels are propelled by steam and not by sails, and thus meet the requirement of the act; but it is evident from the debates that the "plans" which shall "offer the least impediment to navigation" must be based not merely upon questions of engineering capabilities. These plans must be within limits of practicability as to cost, and be adapted to the place where needed and to the service required of the bridge. The plans must therefore make reasonable provisions for all the requirements of the case, and the presentation must be accompanied by the facts and other evi dences of practicability and utility. Such is my view of the duty con fided to me, aud it seems implied at least in the instructions to "collect all the information appertaining to it." The passage of several acts authorizing bridges on the Upper Mississippi does not do away with the necessity of this investigation, because the right is reserved by Congress to make such additional legisla tion as the protection of the navigation may be found to require, and there are some bridges built that are not authorized by Congress which may come before it for consideration and action. Investigation is thus as important for the purposes it was ordered, at the present time, as it was at the outset. The necessity of bridging the Mississippi was conceded by every one. The only question was as to the kind of bridge, whether to be low ones with draw openings or continuous and of height sufficient to allow vessels to pass under them. The high bridges were advocated by those interested in the navigation, and opposed by those more concerned in crossing the river, as being impracticable on account of cost. The low bottom-land banks of the Mississippi River and their great width, the opponents of high bridges said, make the high approaches too expensive. Besides this, the bed of the river was stated to be generally of sand to so great a depth that foundations could not be laid upon the underlying rock, the only secure manner of building such high piers. To furnish definite information on these points was evidently one of the objects of the investigation. The Hon. Alexander Ramsey, mover of the resolution, said on April 30, 1866: Survey the whole river and decide, at least as to the future, what should be the character of the bridges there. And in another place: To survey the river, and settle the essential points to be guarded in the construction of these bridges, how, where at the same time the railroads may be accommodated, and the navigation preserved. The kind of survey intended could only be of a very general character, as only $10,000 was provided in the resolution for making it, and it is probably better described by another remark of the Senator: To send out to view the river and furnish us the best information on the subject. It was at first intended that the report should be submitted at the next session of Congress, but the passage at the same session of the acts authorizing all the bridges whose construction had been urged allowed more time. In making it advantage was taken of surveys of the Mississippi, ordered for purposes of improving navigation, and thus a great deal more was done than this appropriation for the special purpose would have permitted. The remainder of this chapter will be given to presenting the manner in which the report is made up and noting some of the most important deductions. Formation of the valley of the Mississippi River and depth to bed rock.— General considerations leading to a knowledge of the general depth of the bed-rock beneath the sand caused me to prepare a map on a scale of six miles to an inch, including the Minnesota River. The drainage of the great basin of Lake Winnipeg appears to have been formerly along this valley. The discussions and conclusions relating to this part of the subject form Chapter II of this report. There seems every reason to believe that the bed-rock can generally be reached for pier foundations by means of the pneumatic process, which has been abundantly em ployed during the period this investigation has been going on at Omaha, Saint Louis, Saint Joseph, and Saint Charles. At the end of the chapter is a table giving the areas of the drainage of all the tributaries to the valley above the mouth of the Ohio. A general presentation of Western river navigation and a discussion of question of headway are given in Chapter III of this report. The interests of navigation, as represented by the Saint Louis Chamber of Commerce, held that no bridge should be built that did not leave a clear head way over the main navigable channel of at least 50 feet at time of extreme high water. There is reason to believe that the extreme high water referred to was that of the highest known, and not of the ordinary high water; for while it is true that during such very great floods business is generally suspended, yet by placing the bridge 50 feet above that level it gave an increased headway for all ordinary floods and for high stages approaching the level of ordinary floods. There has been, so far as I know, no thorough discussion of the subject of relative headway at ordinary stages at different places on the Mississippi. It is obvious enough that 50 feet above extreme high water where the river range is 40 feet and where it is 20 feet is a difference of 10 feet in favor of the first place when the river is at a half stage; that is, there will be 70 feet headway at one place and 60 feet at the other at such time. A different provision in respect to height of high bridges in general seems required. The United States law authorizing the bridge at Saint Louis, however, provided for a headway of about 50 feet at ordinary high water, which stage is about 7 feet lower than extreme high water of 1844. The discussion in Chapter III shows (if we provide on the river above Saint Louis for only the ordinary high water) that an elevation of about 57 feet above ordinary high water will be required to give a headway equivalent to that at Saint Louis. This investigation seems to have established the practical rule for all rivers that equivalent headway at different places requires that the height of the bridges measured from the level half way between high and low water should be the same for all places. This is one of the most important contributions to the subject made by this investigation, and it was essential to reaching it that the observations should have extended over the considerable number of years which it has. A table of rise of water from low to high stages on the Mississippi, Ohio, and Missouri Rivers is given at the end of this chapter. Lengths of spans.-Experience in the interval of time which has elapsed since the investigation began has settled all questions with regard to the practicability of long spans. At Cincinnati there is a railway bridge with a clear span of 500 feet over the channel of the Ohio. It is of the American pattern of horizontal truss, composed of wrought iron, resting upon piers 100 feet above low water. There is also at Cincinnati a railway truss-bridge with one span of 400 feet. At several places there are railway bridges with spans between 300 and 400 feet, and many spans of railway bridges of 300 feet width in the clear. At Louisiana, Mo., there is a railway pivot draw-bridge across the Mississippi of 200 feet clear openings, and propositions are now made by competent builders and engineers to employ two such pivot drawbridges and thus leave one clear opening of 400 feet and two others of 200 feet each side of it. It must be admitted that engineers can make ample provisions for navigation. Accomplished facts leave this no longer a question. Description in detail of the bridges on the Mississippi from Saint Paul to |