There is also presented a hydrograph record of the river for four years past which indicates the conditions ordinarily met with as regards river stages at various times of year.

In the balancing of interests between the traffic on the river and that across the bridges, it is believed to be fair and just that for boats of excessive size and height the navigation of the river above a 15-foot stage be eliminated from the problem; (1) because of the comparatively small number of these boats; (2) because of the questionable necessity of having such high boats at all; (3) because of the period of the year when these extreme stages are reached; (4) because these periods of time are so limited in length; (5) because of the generally accompanying swift currents, and (6) because of the oft-times accompanying dangerous floating drift and floating ice.

As to the height of vessels, it is to be noted that the great bulk of navigation under the bridges is not through traffic, but is simply movements about in the lower stretch of the river which forms part of the harbor of Pittsburgh. The commodities moved are nearly all sand, gravel and coal in barges, which loads are almost invariably taken up stream while the downward movement is mostly of empty barges. These barges are mostly moved by harbor tugs. The harbor tugs actually in use are from 22 to 27 feet high, averaging about 24 feet.

The heights of the Monongahela standard towboats vary from 24 to 32 feet, averaging about 28 feet. Out of a list of 28 such boats but 5 exceed 28 feet in height.

The few packet boats running on the river are of moderate height and can be accommodated in the harbor under the bridges at ordinary river stages. The amount of business that could be done by a few packet boats of extreme and unnecessary height is so small that to raise the bridges to a sufficient height to accommodate it would place an entirely unjustifiable tax and inconvenience upon the far greater business interest of the city concerned in crossing the river.

The following tables show the average number of days per annum during which various types of existing vessels would be prevented from navigation by bridges of various assumed heights above the Davis Island Pool:

In drawing conclusions from the above table, as a basis for plans governing the expenditure of millions of dollars in construction and the permanent establishment of conditions of navigation and of traffic over the bridges and the enormous business interests concerned, it is important to bear in mind that the types of vessels here considered are antiquated, and can undoubtedly be materially changed in many particulars to the benefit of all interests.

As bearing directly on this question of boats and bridges, attention is invited to the following extract from the report of Hon. D. S. Alexander, chairman of the River and Harbor Committee of the United States House of Representatives, in submitting for action of the House the last River and Harbor bill on February 11th, 1910:

Modern Type of Boats for Non-tidal Rivers.—"The British Government has been designing shallow-draft boats for use on the Nile, and the German and Austrian governments have been working along similar lines with reference to methods of transportation on the Rhine, the Danube, the Elbe and other waterways. The boats designed have been very successful, having been used in connection with modern loading and unloading appliances. On our western rivers little change has been made in the design of towboats, barges, etc., since 1860, and it is believed that a design embodying the best points of modern vessels, with modern machinery and cargo handling devices, might lead to a marked increase in the traffic on the non-tidal rivers of the United States, especially after permanently improved channels are available.

"It is believed that the appropriation of $500,000 to be expended in the purchase of plant for use in connection with the work of improvement of the river will also provide for experiments to be carried on by the Government which will result in improving the present type of river freight carriers; and also that these tests can be made in no other way, since the expenditures and uncertainties involved preclude the use of private capital for the purpose. As a result of the tests or experiments it is hoped that a large saving to the country at large may accrue from decreased costs of transportation, and that a type of carrier may be developed which will also reduce the cost of all bridges across navigable streams due to lessened requirements in the matter of head room."

This report of Colonel Alexander, the very able Chairman of the River and Harbor Committee of the House of Representatives, is worthy of serious consideration. Such an investigation and experiments to determine the best type of carriers to use on the river seems certain to be provided for and may result in clearly demonstrating that no necessity exists for raising the Allegheny bridges at all, in accordance with the possibility outlined by the closing paragraph of Colonel Alexander's report above. The appropriation of $500,000 as recommended by Colonel Alexander is included in the River and Harbor bill which has passed the House of Representatives and Senate. There is every probability that it will become a law.

A vast amount of water traffic is carried on inland waterways all over the world under fixed bridges with far less head room than is provided for under the Allegheny River bridges. It is customary in other parts of the country and the world to establish for rivers a minimum head room for bridges at a high navigable stage, which stage is considerably lower than the maximum or even the ordinary high flood stage. For instance, in the new barge canal being built by the State of New York at a cost of $108,000,000 the minimum head room under all stationary bridges is fixed at 15½ feet at the high navigable stage of the water. The high navigable stage is based chiefly upon what is a safe navigable stage, taking everything into consideration. It is by no means a very high stage. As this canal runs through the canalized Mohawk, Oneida, Oswego, Seneca and Clyde rivers, the situation is comparable with that on the Allegheny. The depth of the canal at low water is to be 12 feet, so it is seen that the clear head room is but about 25 per cent greater than the minimum depth of the water. The boats must be made to fit the bridges, and not the bridges to fit the boats. It is estimated that the amount of traffic which will pass through these canals about 450 miles long and under these 15½-foot bridges will be about 20,000,000 tons annually, many times the amount making use of the Allegheny River. The present Erie, Champlain and Oswego canals in the State of New York, which have been in operation for about 80 years, are crossed by several hundred bridges giving a clear head room of 13 feet. No complaint about this head room is known to exist, notwithstanding that steam vessels are largely used for navigation purposes on the canals. The boats have to be made to fit the bridges and not the bridges to fit the boats.

At Paris, the river Seine running through the city carries a very large amount of business. Annually about 20,000,000 passengers, and about 11,000,000 tons of freight are carried on boats of various kinds. There are 36 bridges which span the river and must be passed by the water-borne traffic. The clear head room under these bridges at the highest navigable water varies from 11.25 feet to 21.88 feet. By highest navigable water is meant the stage of water when by reason of floods or currents, navigation ceases. This Paris water-borne freight traffic on the Seine amounts to fully 7 times that of the Allegheny River and passes under 5 times as many bridges, with minimum available head room at high navigable stages just about one half that under the present bridges over the Allegheny at a 15-foot stage. The conditions of navigation on the Seine at Paris are practically the same as those on the Allegheny at Pittsburgh. In Paris the boats are made to fit the bridges and not the bridges to fit the boats.

From these and many other illustrations that could be given it is evident that it is not universally or even commonly considered necessary or advisable to sacrifice business interests crossing the bridges to navigation interests using the waterways, to any such extent as that demanded by the navigation interests of the Allegheny River.

Conclusions as to Clearance Heights.—Disregarding for the moment the question of the time when changes in the present bridges should be required, it is believed, after very careful consideration, that the conditions brought out by our study of the problem would best be met by fixing the elevation for a substantial portion of each bridge in the center at a clear height above the pool level of substantially 37 feet, or 28 feet above the river at a 15-foot stage at each bridge. It is believed that this elevation will give fair, justifiable and all really needed accommodations to the navigation interests. This height can be attained without extravagant and unjustifiable expense and inconvenience to the business interests involved in crossing the river, and while it cannot be hoped that it would be satisfactory to the extreme advocates of river and harbor interests, it ought to satisfy those who are able and willing to give proper and fair consideration to other interests than their own. There are no reasonable navigation demands, with bridges at this elevation, that cannot be met if the water-borne commerce be conducted with vessels of the best modern accepted type and not of extreme or unnecessary height.

Piers and Channels.—For the benefit of the navigation interests there are certain changes in some of the bridges over the Allegheny that should be made without question. These relate to the location of piers and location and width of the navigable channels.

At the extreme mouth of the Allegheny River a new bridge, the North Side Point bridge, has been approved by the War Department and is to be built. This is to have one central pier dividing the river into two channels.

A short distance above this North Side Point bridge is situated the Sixth Street bridge, in some respects the most important highway structure crossing the river. This bridge now corresponds to the North Side Point bridge in having a central pier and dividing the river into two main channels of ample width of over 400 feet.

The next bridge, the Seventh Street bridge, also has now a central pier with channels about 320 feet width on each side of it. The next bridge up the river, that at Ninth Street, has shorter spans, with the piers so unfortunately located as to be decidedly obstructive. As this bridge is of relatively light construction it is possible that the heavy and constantly increasing traffic which it is called upon to bear will before long necessitate its reconstruction anyway, and it will not be unreasonable to require it to be rebuilt with fewer piers properly located to conform to the plan adopted for the Sixth Street and Seventh Street bridges.

As a permanent arrangement of piers for the above three bridges either of two logical plans may be adopted. The first is to retain the existing two-spans center-pier arrangement of the Sixth Street and Seventh Street bridges, conforming to the center pier plan required by the United States Engineers for the new North Side Point bridge, and reconstruct the Ninth Street bridge upon the same general plan. The other is to reconstruct all three bridges with two piers and three spans each, as recommended by the local office of the United States Engineers. The first or central pier plan has the merit of economy of construction in that it involves the construction of no new piers for the Sixth Street and Seventh Street bridges, and permits the continued use of the existing superstructures of the Sixth Street and Seventh Street bridges by simply raising them to the elevation that may be decided upon and ordered. So far as we can ascertain, in view of the center pier plan adopted for the North Side Point bridge, the advantage to navigation appears to lie on the side of adhering to a center pier plan for these bridges also. On the other hand, there is no doubt that three-span bridges could be made more agreeable in appearance than two-span bridges. But the possible gain in appearance alone does not appear sufficient to justify the adoption of three spans.

The next bridge above Ninth Street is that of the Pittsburgh, Fort Wayne and Chicago Railroad. This has been constructed with two main piers providing one main central channel 337.5 feet wide and three other piers giving four channels from 155 to 163 feet wide. Owing to the bend in the river at the bridge and the distance above the Ninth Street bridge, there is no valid objection to this single main central channel at the railroad bridge connecting either with two channels divided by the central piers of the bridges below, or with a central channel if those bridges should be reconstructed on the three-span plan.

The Sixteenth Street bridge has been constructed with 3 piers dividing the river into 4 channels of about 150 feet each; the clear head room beneath it is less than that now given by the bridges below it. The best arrangement to be made with this bridge is to require it to be rebuilt without the central pier, leaving a central channel about 320 feet in width between the two side piers to correspond with the railroad bridge just below it. It is an old, covered, wooden bridge, in poor physical condition, and, as previously noted, it is probable that it must be raised anyhow in connection with eliminating railroad grade crossings on the approaches.

The Thirtieth Street bridge has its piers properly spaced to leave a central channel 285 feet in clear width and no changes are required in pier and channel location at this bridge.

The Thirty-third Street or Pittsburgh Junction Railroad bridge of the Baltimore and Ohio System has 3 piers, giving a main central channel of 232 feet wide, with side channels 195 feet wide, and on the Herrs Island side of 150 feet. No change is needed in the location of the piers and channels at this bridge.

The Forty-third Street bridge is built with 3 piers, making 4 channels each of about 160 feet wide. It gives less clear head room at high river stages than most of the lower river bridges. It is an old wooden bridge, in poor physical condition. The best arrangement for this bridge is to treat it as the Sixteenth Street bridge, and to require it to be rebuilt, omitting the central pier and leaving a central channel about 300 feet wide, to correspond with the bridges below it. The elimination of railroad grade crossings on the approaches to this bridge is already a pressing public need and must soon result in its raising or reconstruction at a higher level.

Considerations against Requiring Changes in Bridges To Be Made at Present.—The following important questions, having a direct bearing upon the proper design of permanent bridges across the Allegheny River, are now under consideration:

1. The Flood Commission is getting data for studying the question of a protective embankment along the river front, and of the proper grades of streets and bridge approaches in the region subject to inundation. The design of such flood-protection works should have important bearing upon the grade, location and design of the permanent bridge abutments. This Commission is also studying the question of impounding the flood waters of the Allegheny and Monongahela Rivers in their upper valleys, which may result in materially lessening the height and velocity of floods in the harbor of Pittsburgh, and consequently, simplify the bridge and navigation problems of the harbor.

2. The question of the best routes for surface cars and rapid transit lines crossing the Allegheny River is now being studied for the City as a part of a comprehensive plan for traction improvements. The result of these studies might readily affect the design of the new bridges.

3. The government experiments recommended by Colonel Alexander of the River and Harbor Committee and authorized in the River and Harbor bill just passed by Congress and providing for the development of a more economical and efficient type of river-boats, requiring less head room than the present antiquated types, may soon show results that would have a decided influence in determining the reasonable clearance heights of bridges.

4. Attention is also invited to the fact that the people of Pittsburgh have voted to expend about $7,000,000 in certain public improvements. Among these are the cutting down of the "Hump," an obstructive hill in the city's midst, widening some streets and filling certain other streets in the North Side and West End that are flooded at high river stages. The material from the "Hump" in the vicinity of the Court House is to be hauled to these North Side streets across the lower Allegheny bridges under question. The work is of great magnitude and it will take at least two years to complete it. Any material alteration to the bridges such as proposed by the Board of Engineers will require a long time to be carried into effect. While this bridge work would be under way, the transportation of the material excavated from the "Hump" and the filling up of the low grade streets of the North Side would have to cease or would be carried on with great difficulty and inconvenience to other traffic. This would tie up the whole work while it is in progress, causing material injury to the city, for it is to be extremely annoying and bothersome while it is in progress, and the longer this period is strung out the worse it will be.

For all of the above reasons we believe that to precipitate the actual reconstruction of the bridges at this time would be most undesirable for the city and prejudicial to the best results, in the long run, for all concerned.

RECOMMENDATIONS

In conclusion we beg to recommend as follows: 1. That the Sixteenth Street and Forty-third Street bridges, which are obstructions to navigation on account of their pier locations, narrow channels, and exceptionally low clearance height, be required to be rebuilt with their piers so located as to give channels conforming to the neighboring bridges, and that their elevation be fixed with regard to eliminating the railroad grade crossings on their approaches, but the minimum clearance shall be fixed in accordance with the closing paragraph below.

2. That the Ninth Street bridge should be rebuilt as soon as practicable with a center pier and two wide spans conforming to those of the Sixth Street and Seventh Street bridges. The design of the new Ninth Street bridge, however, should not be finally determined and erection begun until a definite plan for comprehensive improvements in the traction system between the two sides of the river has been decided upon. Unless new circumstances develop before the construction of this bridge is begun that materially affect the problem of clearance height, the elevation should be fixed in accordance with the closing paragraph below.

3. That all questions pertaining to changing the elevation of the Sixth Street, Seventh Street, Fort Wayne, Thirtieth Street and Junction Railroad bridges be deferred to await the report of the Pittsburgh Flood Commission and the resultant action; to await the report on a comprehensive plan for traction improvements; to await the completion of the work projected by the City in cutting down some streets and filling others; and to await the results of investigation of river-boat design and construction provided for in the River and Harbor bill just passed by Congress.

4. That, if it is deemed essential and necessary at present to decide upon the elevation to which all Allegheny River bridges must be made to conform, this elevation be fixed so that there shall be a clear head room of substantially 37 feet above pool level, varied so as to give at each bridge a clear head room of 28 feet when the river is at a 15-foot flood stage. This height to be maintained over the entire main span where there is a central span and for 180 feet on each side of the central pier where there is a central pier.

We have the honor to be, very respectfully,

Your obedient servants,

Thomas W. Symons,
Col. Corps Engineers U. S. A., retired,

Frederick Law Olmsted.

APPENDIX I

Amount and Importance of Bridge Traffic.—Highway Bridges.—The following table gives the records of counts made in the fall of 1909, and spring of 1910 on the various bridges over the Allegheny River:

Assuming that the average number of vehicles per day and the average tonnage per day are the same throughout the year as during the periods of counting, we deduce the following results:

Railroad Bridges.—The bridge carrying the heaviest traffic is that of the Pittsburgh, Fort Wayne and Chicago Railroad, a part of the Pennsylvania System, which forms one of the links in the main line of this railroad system between the East and West. Across this bridge are carried each year about 2,750,000 passengers, 32,000 tons of mail, and 53,000,000 tons of freight and general railroad traffic, besides about 2,135,000 pedestrians,[42] making it one of the greatest throats of commerce in the country. This is a double deck bridge of 4 tracks, 2 tracks on each deck, with a wide footway on the lower deck. It is to be noted that the amount of traffic passing over this bridge is about 25 times as much as that which floats on the water beneath it, and is far higher in quality and value per ton.

The other railroad bridge crossing the river within the city limits is the Thirty-third Street viaduct of the Baltimore and Ohio Railroad. This is a link in the Baltimore and Ohio Railroad between the East and the West and carries an enormous traffic amounting each year to about 217,000 passengers and 24,330,000 tons of freight, express and other trains.

Uniting this with the traffic over the Fort Wayne bridge of the Pennsylvania we have crossing the Allegheny River on the two railroad bridges a gross amount of 77,330,000 tons, and 5,102,000 passengers and pedestrians, with a value of tonnage traffic estimated at approximately $4,957,000,000.

APPENDIX II

Amount and Importance of River Traffic.—The following statistics were obtained from the United States Engineers' office and show the number of boats, net tonnage and number of passengers passing Dam No. 1 in the Allegheny River during the year 1909:

The following are statistics of counts taken in 1909 at the different bridges:

Assuming that the ratio between the number of vessels during any given period and the total for the year is the same at all bridges as at Dam No. 1; and assuming that the relative number of different kinds of vessels are the same at all bridges; and further assuming that the average weight of cargo is the same at all bridges as recorded at Dam No. 1, we reach the estimates of total traffic under the bridges given in Table No. 3.

The largest total, that passing under the Ninth Street bridge, is without doubt somewhat less than the total traffic on the river, and a careful study of the figures would seem to indicate that the total water-borne traffic of the Allegheny River in 1909 amounted to about one and three-quarter (1¾) million tons of cargo or three and one-half (3½) million tons gross displacement, including cargoes, barges, tugs and all vessels.

The water-borne commerce on this river is of the cheapest character, consisting almost entirely of sand and gravel dredged from the rivers and coal floated down the Monongahela and delivered along the shores. All this sand, gravel and coal is carried in low-lying barges or scows moved by tugs or towboats.

A small amount of package freight comes in and leaves by packet boats.

The average value of the freight based on prices prevailing in 1910 is about $3 a ton. The average value of the carriers is about $65 a ton. As there is a slightly greater weight of freight than carrier, an average of $30 per ton would be a fair estimate of the value of freight and carriers. The total value of the water-borne traffic of the Allegheny River for the year under the various bridges would, therefore, be about $105,000,000.

The passenger traffic on the river is so small that it may be considered negligible. It is estimated at 35,000, largely pleasure traffic in small boats.

About one-third as much tonnage goes through Lock No. 2 as through Lock No. 1, and about one-sixteenth as much goes through Lock No. 3 as through Lock No. 1. There is no navigation on the river above the third pool. It is claimed, however, that with the further canalization of the river above Dam No. 3 and the raising of the bridges this traffic would be greatly increased. It is to be hoped that there will be a considerable increase, but there are distinct limitations on the probable amount of the increase. The Monongahela has a larger and more highly favored local territory to draw upon for freight than the Allegheny so that under the best of conditions, with every possible improvement of navigation, the traffic on the Allegheny can never be expected to approach that upon the Monongahela.

The total amount of freight of all kinds passing Dam No. 1 on the Monongahela in 1909, was 5,417,873, or a little more than ten times the amount on the Allegheny, while the tonnage passing over the Allegheny bridges is thirty times greater than the tonnage on the Allegheny River.[44] Yet, if conceivably the traffic on the Allegheny should equal that now on the Monongahela, it would still be only one-third that over the Allegheny bridges.

Since the figures for the present traffic over the Allegheny River bridges are used for comparison with the present river traffic, and since the former must continue to grow steadily with the growth of the Pittsburgh industrial district, it seems quite clear that no conceivable growth in the latter can seriously affect the overwhelming predominance of the bridge traffic in amount and value.[44]