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THE SECRETARY OF WAR,
A report upon the survey of the harbor of Mobile.
IN THE SENATE OF THE UNITED STATES,
March 17, 1880. Ordered, that the letter of the Secretary of War, in reference to Mobile Bay, be transmitted to the House of Representatives for its consideration. Attest:
JNO. C. BURCH,
IN THE HOUSE OF REPRESENTATIVES.
MARCH 22, 1880.-Referred to the Committee on Commerce and ordered to be printed.
Washington City, March 13, 1880. The Secretary of War has the honor to transmit to the United States Senate a letter from the Chief of Engineers, dated the 11th instant, and accompanying copy of report of Capt. A. N. Damrell, Corps of Engineers, upon a survey of Mobile Harbor, Alabama, made in compliance with the provisions of the river and harbor act of June 18, 1878.
Secretary of War. The PRESIDENT
of the United States Senate.
OFFICE OF THE CHIEF OF ENGINEERS,
UNITED STATES ARMY,
Washington, D. C., March 11, 1880. SIR: I have the honor to submit herewith a copy of a report to this office from Capt A. N. Damrell, Corps of Engineers, of the results of a survey of Mobile Harbor, Alabama, with a view to its further improvement, to comply with provisions of the river and harbor act of June 18, 1878, making appropriation for tests, surveys, and borings to ascertain the practicability of deepening the ship channel leading from the lower anchorage to 22 feet or to any less depth above 13 feet.
A preliminary report submitted in January, 1879, will be found in Senate Ex. Doc. No. 38, Forty-fifth Congress, third session. Very respectfully, your obedient servant,
H. G. WRIGHT, Chief of Engineers, Brigadier and Brevet Major General. Hon. ALEXANDER RAMSEY,
Secretary of War.
SURVEY OF MOBILE HARBOR, ALABAMA, WITH
The act approved June 18, 1878, directed the amount appropriated, $10,000, to be applied to making tests, surveys, and borings to determine whether the ship channel now leading from the lower anchorage in Mobile Bay can be deepened so as to admit vessels drawing 22 feet, or any less draught above 13 feet, to the wharves of the city of Mobile.
Preparatory work was commenced, under this act, on the 12th of July, 1878, and the field work on the 15th of August. A preliminary report was made on the 7th of January, 1879, which is contained in Senate Ex. Doc. No. 38, Forty-fifth Congress, third session. The work was termi. nated on the 1st of September, 1879, and the final report commenced.
During this time, in addition to the labor of collecting outfit and organizing, soundings were made from a point in Mobile River opposite Beauregard street, near the upper limit of the city of Mobile, down the river, and through the channel dredged under Congressional appropriations from 1871 to 1877; also throughout Garrow's Bend (just below Choctaw Point) and down the western shore of the bay to Alabama Port (the nearest point on the mainland to deep water); thence to the 18-foot curve in the lower anchorage; across the upper end of the bay, across the lower end or entrance, and at various other points.
Borings were made, at intervals of 2,000 feet, from a point in Mobile River opposite Government street, near the center of the city front, down the present channel, beyond "Dog River" Bar, and from there, at intervals of a mile, about, to the 18-foot curve at the lower anchorage, a distance (total) of about 27 miles. Other borings were made along the western shore. All of them were made to a depth of 26 feet. A line of levels was run from Cedar Point (the extreme southern point of the western mainland) up to the Mobile and Montgomery Railroad bridge, across Mobile River (above the city), a distance of about 46 miles.
Triangulation was carried over the entrance of Mobile Bay, including Coffee, Dixie, Sand, and Pelican islands, east end of Dauphin Island, and Mobile Point, over that portion of the bay included between the
eastern and western shores, the obstructions on the south, and the mouths of the Mobile, Tensas, Spanish, Apalachee, and Blakeley rivers on the north, and throughout the whole length of the Mobile River.
Cross-sections and current observations were taken of all the above rivers, and of all their important tributaries, inlets, and outlets, where practicable.
Samples of water were obtained at various times, localities, an depths, in rivers and bay, and tested for sediment.
The usual office work, plotting notes, arrangements and study of data, consumed the remainder of the time.
The results obtained from the work are as follows:
The tide-gauge observations indicated a total average rise and fall of 3 feet in the bay; that the tidal current tends towards the eastern shore, the river discharge being principally carried along the western shore. (As further evidence of this, the eastern shore is comparatively free from, while the western is covered with, accumulations of drift from the rivers.)
At the cut-off in the Alabama River, about 70 miles above the head of the bay, tidal observations indicated a rise of 0.77 foot.
The soundings showed that the old dredged channel has maintained the depth obtained in 1877, and that there is now a good channel of 13 feet depth way through.
The following is a list of vessels drawing 13 feet and over, that arrived at and departed from Mobile during ten months, without meeting any difficulty in the cut, with the high tides for the corresponding dates, as indicated by the tide gauges, the average mean low-tide reading being 7'2" :
The banks of the cut were also found generally unchanged.
The water in Mobile River, below Beauregard street, has about the same depth for navigable purposes as in 1871, except at its mouth, where
the depth appears to be increasing on the east bank, at Pinto Point, and decreasing on the west bank, at Choctaw Point, outside of the dredged channel, however. In Garrow's Bend the water is shoaling rapidly in toward the shore, probably caused by the jetties constructed by State authority there in 1872. Generally speaking, no material changes were found in the body of the bay. The borings everywhere indicated about the same condition of the bottom for the same depths. Sand mixed with mud and shells to a depth of about 14 feet, and below this to the depth of 26 feet, the extent of the borings, a stiff tenacious clay, hard on top and softer below. The same formation was found on the bluff banks of the western shore, the clay being from 12 to 15 feet from the surface or about the water level. The line of levels indicated a fall of only 0.75 of a foot in 46 miles.
The principal features shown by the triangulation is the extensive changes that have taken place since 1856, the date of the last Coast Survey chart; 1st, at the entrance of the bay in the formation of the two islands," Coffee” and “Dixie,” to the east of Sand Island, and on the opposite side of the main ship-channel, the change in form and extent of Sand Island, the large diminution in area of Pelican Island, the washing away of the northerly beaches of Dauphin Island and Mobile Point, and the deposit on the corresponding south beaches.
2d. At the head of the bay in the extension of the river mouths and their bars to the southward. The cross-sections and current observations indicate an aggregate discharge of over 100,000 cubic feet per second by the rivers into the bay.
The sediment observations give 100 grains of sediment to the cubic foot of water as the average amount in the rivers, and decomposed veg. etable matter as the principal component.
Before stating the conclusions arrived at, or opinion formed, I would state, it was not considered the intent of Congress to restrict the survey to a study of only a single project, although that idea might seem to be conveyed by the wording of the act, and, therefore, all were considered which had at different times been suggested (so far as I could learn) or occurred to me, for the relief of the commerce of this port, as follows:
I. Making a harbor on the south of Dauphin Island and connecting it with Mobile by rail.
II. Making a harbor on the north side of Dauphin Island with railroad connection.
III. Making a harbor at Alabama Port with same connections.
V. Damming all but one river, improving that one, and directing its discharge into the bay with the expectation of its scouring its way to deep water.
VI. Using the tidal current for scouring a channel by training its flow between the entrance and upper end of the bay between parallel walls.
VII. Dredging a channel through the bay, following the line of deepest water, and carrying the dredged material to a safe distance.
VIII. Dredging and scouring a channel through the bay by damming all but one outlet, contracted to a proper width, and training the flow between artificial parallel banks to deep water or tidal channel, and dredging out or stirring up all material that would not scour.
The first four projects are not believed to be desirable by themselves (although the last should, and probably will at some future time, be carried out by private enterprise, and would be of great importance in connection with the work recommended), and this was considered so apparent
on account of the evident cost, direct and indirect, in necessary construction and depreciation of values in the present city, that they are passed over with mere mention.
The fifth project would not, in my opinion, prove successful. The sixth, I think, could be carried out to a successful conclusion, but the cost would be very great.
The seventh project is a continuation of the one that has been persistently followed since 1827, by which the water has been deepened from a minimum depth in Choctaw Pass of 5 feet 6 inches, and on Dog River Bar of 8 to 13 feet throughout. The success of this plan so far proves the sagacity of the various engineers who have advocated it, and I can see no good reason why it cannot be carried still farther, in obtaining still greater depths, and be equally successful.
The eighth project is a combination of the two principal ones which have been continually agitated since 1827.
Each one has had many strong and able believers, who have asserted the superiority of one or the other method, verbally or in print.
The great objection urged, heretofore, against the dredging system has been, that a cut made in the middle of a large shoal bay, receiving annually from its tributaries immense quantities of sediment, and traversed by a complicated system of river and tidal currents, due to winds, tides, and river discharges, would rapidly fill up. This argument has been disproved by the facts to the present time.
The principal objections to the scouring system, or combined scouring and dredging, has been the great cost of training the flow of river water through the bay a sufficient distance to accomplish the desired result, the perishable nature of such training walls, if built of such materials as could be obtained at a reasonable expenditure, and the probable formation of a bar at the ends of the dikes or jetties.
As the scouring power of the large volume of water daily discharged by the various rivers into Mobile Bay seemed generally to be recognized by all engineers who have written or expressed opinions in the matter, a portion of the time consumed in the survey was devoted, and a great deal of study given, to ascertain if there was any way to utilize this force that would be free from the objections mentioned, with results as fol
The river water can be all emptied into Mobile Bay through one mouth of proper cross-section at Choctaw Point, either by damming all outlets but Mobile River, at their heads or at their mouths, at a coinparatively small cost. Thence through the bay parallel walls would have to be constructed to near a point where the tidal current sweeping by their ends would be strong enough to prevent the formation of a bar. There is such a point, and, therefore, the last objection has no weight. To reduce the force of the others, it is suggested they might be built of brush and piles, of which there is an unlimited supply, of easy access, along the whole length of the western shore below Dog River Point, to be covered first with material excavated from the bottom with a dredgeboat, and afterwards in the more exposed parts with stone ballast from vessels arriving, or from quarries up the river, and that the channel be carried so near the western shore that but one strong dike need be built of the full extent; the length of the other being materially reduced by the portion of the western shore which might be utilized, and the cost of such as had to be built reduced to a minimum, by the fact that as it would not be exposed to rough water a simple inexpensive construction
The amount that would be removed by scour, and the amount that would