report of October 15, although there are certain points of difference, as will appear from the fact that the board found it necessary to reconmend some modifications of the plan.

There are four essential points upon which the advocates and opponents of the proposed bridge disagree. These points were all considered in the former report of the board, but as they embrace substantially all the questions treated of in the communications under consideration, a more extended notice of them appears proper in this place, and will, perhaps, afford the most direct means of accomplishing the object of this report. These points are: 1st. The width of the draw; 2d. The double-draw system; 3d. The height of the bridge; and, 4th. The effect of the piers upon the ice.

1st. As to the width of the draw, the advocates of the bridge claim in general terms that 70 feet is wide enough for the purposes of navi gation, while the protest, numerously signed, and forwarded by the Hon. Leonard Myers, states that "Few tugs will risk the passage of the draw and be responsible for the safety of the vessel they may be towing, unless the distance between the piers is at least 125 feet. The passage, as a general thing, must be made with the tide, which is about three miles per hour, and the speed of the tug must be from three to six miles faster in order to use the rudders effectively, thus making the chances for collision with the piers almost a certainty, if the piers are less than 125 feet apart. If there should be any wind at the time of passage, the

chances for collision will be increased.”

The exact width of draw required for this particular case, is a ques tion which could hardly be decided even by expert pilots, without at least one trial under the circumstances supposed to exist. And the board, therefore, finds it extremely difficult to decide upon a proper width, especially since the widening of the draw diminishes the width of the clear water-way of the main channel, and thus increases the difficulty to be apprehended from floating ice.

The board is of opinion that the minimum width of 85 feet, recommended in its report, will not be too great under the circumstances, and considering the great length of the piers and splay at the ends, and that they are to present smooth planked surfaces in the opening of the draw, it would seem that, except in extreme cases of wind or tide, and, of course, unavoidable accident to machinery, a skillful pilot should be able to tow any of the class of vessels which now pass above the proposed site of the bridge, through such an opening in safety.

It is thought, however, that the results of numerous special investigations of the widths of draws on western rivers may require the Depart ment to make considerable change in the width proposed for this draw, and it will be seen, from what follows, that if the opinions of the board were not limited to the consideration of this special project for a bridge, it might recommend that the draw be entirely dispensed with.

2d. The double-draw system is not specially approved by any of the foregoing communications advocating the bridge, although it is indorsed by implication.

In regard to this feature of the bridge, the protest already quoted says: "The arrangement by which one of the draws will be closed while the vessel is passing, will effectually prevent any attempt to pass. The captain of a vessel must know to a certainty that all the draws will be open when he approaches the bridge, as there will be no time to stop when he reaches it, and there would be no room to swing, in case the anchor is dropped."

The common practice at draw-bridges is to begin to open the draw

long before the vessel reaches it; in fact, many times the distance between the draws in the proposed bridge must be allowed in order to avoid accident, even when the machinery of the draw is in complete working order. With three draws, each liable to get out of order, it would be extremely dangerous for a vessel to attempt a passage unless, as above stated, all the draws were seen to be open. By suitable arrangements for the purpose, and taking sufficient time, a vessel could be warped through as they go through canal-locks; but this would be an obstruction to the navigation of the river, and the bridge company would be obliged to open all the draws at once, or nearly so, since they would have no legal right to delay vessels in order to keep up continuous travel across the bridge.

The board, therefore, only considered this question as one relating to the convenience of the bridge company, and that it might safely be left for experience to demonstrate whether the draws could be operated as set forth in the specifications of the project.

3d. In regard to the height of the bridge, the protest forwarded by the Hon. Leonard Myers states: "The height of the bridge above the water is only 90 feet at the highest place;" and, in the last paragraph, same paper, "To avoid all difficulties, it is suggested that the bridge be made as high as the East River Bridge at New York, as the same character of vessels will pass here."

The resolutions of port wardens also "protest against the building of any bridge across the Delaware River, unless the height of such bridge will allow all vessels to pass under free of obstruction."

The height referred to as the extreme height of the bridge, 90 feet, is the height over the main or western channel. And from the foregoing it will appear, that if this height could be increased to 135 feet, the height of the East River Bridge, the objection as to height would be removed, and the draw could be entirely dispensed with. But to accomplish this and preserve the present grades and curvature of the structure, the height near the middle of the bridge, which is now 111 feet, would be increased to nearly 160 feet, and each of the approaches would require an extension of about 900 feet, as shown by the annexed diagram. As the increase in height, if practicable, would remove all the foregoing objections, it becomes proper to inquire how such a radical change would affect the interests of the bridge company, or whether it would be reasonable to require them to make such a change.

Referring to the diagram, A, A, A, floor-line of bridge, as designed, distorted two and one-half times as high as it should be for the horizontal distances represented, B, B. B.

Floor-line of bridge raised so as to give a clear height of 135 feet at the middle of the main channel, and dispensing with the draw altogether. C C. Floor-line which might be adopted, giving a clear height of 135 feet as before, but dispensing with all the piers except the two represented by dotted lines.

This last form is, of course, obtained at the expense of symmetry, but the grades would be no steeper than those designed, and there would be required but two piers, one of greatly reduced height, in the waterway, in place of the eight now required-the two draw-piers, as now designed, consisting of three piers each, and there being two other piers in the eastern channel.

This arrangement will also leave the western channel entirely unobstructed, as the first pier would stand upon the shoal north of Smith's Island, which is entirely out of the way of navigation, and could have no appreciable effect upon the regimen of the river.

The grade of the approaches, although longer, would be no steeper than at present, and would be very much shorter than by the second method of gaining sufficient height.

HORIZONTAL SCALE, 1 INCH = 1000 FEET.

VERTICAL

DO. 1 INCH = 400____DO.

DIAGRAM.

B

B

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16

SECTION OF RIVER BED

The height over the eastern channel would be greatly diminished, but the navigation of this channel is pronounced, by those familiar with the locality, to be of trifling importance as compared with that of the western channel.

The length of spans required would be increased to about 1,000 feet which has been demonstrated to be entirely feasible, and it may be added that this was about the length proposed for the bridge at the first meeting of the board, the spans being shortened and increased in number in order to remove the draw from the shoal near Smith's Island to deeper water along the main channel.

4th. The question of ice is thus set forth in the protest:

But the introduction of piers in the channel, between Smith's Island or the bar and Philadelphia, is one of the most objectionable features of the draw. Now, whether the piers may be 70 or 125 feet apart on one side of a channel, now too narrow in winter, it will certainly stop the ice earlier, below the bridge as well as above it, and close the navigation when it was before open. Before the river is closed, the floating ice generally accumulates and floats along the western side of the island where it is proposed to place the piers, making it impossible for either iceboats or tugs to tow a vessel through the draws with safety.

Allusion is also made to the effect of a pier of the Camden water-works, which is stated to have hastened the closing of the river by ice at that point, and which it is thought will increase the difficulty experienced from the draw-piers of the proposed bridge.

That these piers will tend to close the river by ice cannot be doubted; but, in the opinion of the board, such effect is too remote and uncertain to constitute a valid obstruction as contemplated by the law. It is presumed that Congress is aware that all piers in navigable rivers tend to hasten the closing of those rivers by ice, and yet numerous bridges have been authorized across such rivers, requiring many piers, and producing in some caces ice-dams of formidable dimensions.

It is probable that good ice-breakers, aided by the rise and fall of tide, will prevent the ice from adhering, to any very great extent, to the piers or damming up against them.

The rate at which the river closes up will doubtless determine to a great extent the amount of influence exerted by the piers. For example, the entire river might close up in one or two days, which would allow but little time for the piers to operate, while, on the other hand, should the river just barely freeze over without the piers, it might close up entirely with their assistance, so as to obstruct navigation for several weeks.

The effect of removing the draw-piers entirely, as already proposed, would of course place this question, beyond a doubt, on the side of safety.

I. C. WOODRUFF, Lieutenant Colonel of Engineers.

J. D. KURTZ,

Lieutenant Colonel of Engineers.
W. R. KING,

Captain of Engineers.

R 23.

OFFICE OF THE CHIEF OF ENGINEERS,

Washington, D. C., May 3, 1871.

SIR: In my letter of the 22d December last, transmitting the report of a board of engineer officers convened to consider the plans of the bridge authorized by act of Congress of April 6, 1870, to be built across the Delaware River, between Philadelphia and Camden, I stated that after careful examination of the subject, the conclusion I had reached was that a bridge built according to the plan as then proposed by the bridge company would seriously obstruct the navigation of the river, but that such modifications could be made as to obviate the most serious objections brought against it, and that the company should be notified to submit another project.

The company having done so, the same board of engineer officers was directed in March last to re-convene, to consider and report upon such modified project as might be submitted, and I now have the honor to transmit their report, with accompanying papers, from which it appears that the bridge company has presented two modified plans, differing but little from each other, in which the draw system is dispensed with, and the elevation of the bridge increased.

The greatest height of 135 feet is, however, attained at a point near Smith's Island, instead of over the middle of the main channel.

But as this elevation is attained at a point where the depth of water is 25 feet at low water, it is thought that this difference is not a serious objection to the plan, and the board is therefore clearly of opinion that neither of the plans now proposed will obstruct, impair, or injuriously modify the navigation of the river.

Very respectfully, your obedient servant,

A. A. HUMPHREYS, Brigadier General and Chief of Engineers.

Hon. W. W. BELKNAP,

Secretary of War.

The plan which requires the bridge to be built with two whole spans and two half spans is approved, and the Chief of Engineers will notify the bridge company accordingly.

WM. W. BELKNAP,

Secretary of War.

WAR DEPARTMENT, May 20, 1871.

R 24.

PHILADELPHIA, PENNSYLVANIA, April 29, 1871.

The board of engineers constituted by Special Orders No. 40, dated Headquarters Corps of Engineers, May 6, 1870, and re-convened by Special Orders No. 33, March 21, 1871, "to consider and report upon the modified project for the bridge across. the Delaware River, between Philadelphia and Camden," having completed the examination of the project, respectfully submits the following report:

A brief account of the previous action of the board will perhaps afford the most direct means of explaining the nature of the modified project now proposed. At the first meeting of the board, in May, 1870, it was found and reported that the project was in a very crude and undigested state. The location and details were not fixed upon, soundings not taken, drawings and specifications defective, and considerable time was necessary to enable the engineer of the bridge company to supply these deficiencies.

At the second meeting of the board, in October, 1870, the project was found in a more matured state, the drawings and other information called for by the board having been procured. The board reported that, with certain modifications, as the widening of the draw, and requiring of the bridge company to keep all the draws open at a time, if found necessary, the bridge would conform to the requirements of the law.

At the third meeting, in December, 1870, the board having been re-convened “to consider certain communications received since their report of October 15," the board found but four essential points on which the advocates and opponents of the bridge differed, viz:

1st. The width of the draw.

2d. The double-draw system.

3d. The height of the bridge, and

4th. The effect of the piers upon the ice.

It was reported that the first three of these differences could be entirely removed, and the fourth greatly diminished, by increasing the height of the bridge over the main channel to 135 feet, and dispensing with the draws altogether.

At the fourth or present meeting of the board, the engineer of the bridge company presented two projects based upon these suggestions, differing but slightly from each other, and the level of the roadway being in both cases nearly like that called the unsymmetrical form in the report last mentioned, the chief point of difference being that the height of 135 feet is attained at a point near Smith's Island instead of over the middle of the main channel. As this elevation of the bridge is attained at a point where the depth of water is 25 feet at low water, it is thought that this difference is not a serious objection to the plans proposed.

The board is, therefore, clearly of opinion that neither of the plans