« 이전계속 »
themselves when the character of foundation offered is considered, lightness of structure being essential, and cheapness an important item at the present time.
If these proposed structures succeed, and I do not see reasons why they should not, many of our Gulf and lower Atlantic seaboard harbors can be improved in the same way and at less expense than by any other method.
One word in closing in regard to my abandonment of the project submitted to the Chief of Engineers in my letter of
recommending this survey.
This project was based on the supposed existence of a littoral current, constant in direction, and having sufficient velocity to make it effective for maintaining a channel scoured by the tides.
The observations of this survey do not prove the supposition correct, and have caused a change of plan to meet the actual conditions observed. Respectfully submitted,
C. W. HOWELL, Captain of Engineers, L. S. A.
IMPROVEMENT OF GALVESTON HARBOR AND ENTRANCE, TEXAS.
Report of Board of Engineers.
New York, February 2, 1874. GENERAL: I have the honor to transmit herewith
1. The report of the Board of Engineers on Galveston Harbor, Texas, convened at New York City by virtue of Special Orders No. 9, C. S., froin the headquarters Corps of Engineers, January 26, 1874. The estimate by the Board is appended to the report. Very respectfully, your obedient servant,
Z. B. TOWER,
Senior Member of Board. Brig. Gen. A. A. HUMPHREYS,
Chief of Engineers, U. S. A.
ARMY BUILDING, January -, 1874. GENERAL : The Board of Engineers convened by the following order, viz:
[Special Orders No. 9.-Extract.]
HEADQUARTERS CORPS or ENGINEERS,
Washington, D. C., January 26, 1874. 1. A Board of officers of the Corps of Engineers, to consist of Lieut. Col. Z. B. Tower, Lieut. Col. H. G. Wright, Lieut. Col. John Newton, and Captain C. W. Howell, will assemble at New York City, on January 28, 1874, or as soon thereafter as practicable, to consider and report upon the project submitted to this office, December 30, 1873, by Captain Howell, for the improvement of Galveston Harbor and entrance. Captain 11. H. Heuer, Corps of Engineers, will act as recorder. By command of Brigadier-General Humphreys :
Tuos. LINCOLN CASEY,
Major of Engineers.
having assembled as directed, and continued its sessions from day to day till the present, have the honor to submit the following report:
The letter of instructions from your Office of the 26th instant desired the views of the Board “upon the practicability and probable cost of securing a permanently increased depth of water in Galveston Bay and entrance thereto by the plan submitted by Captain Howell, December 30, 1873," and the Board, therefore, confines its report within the limits embraced in those instructions, although its discussions have naturally taken a much wider range.
The question which first presents itself for consideration in the project is, whether it is probable that the two parallel piers proposed by Cap. tain Howell, to extend from Fort Point and Bolivar Point over the outer bar to a depth of 18 feet water, would, if constructed, tend to increase the present depth and permit the ingress of vessels of greater draught than at present to Bolivar Channel, for it is obvious that any increase to the depth over the inner bar leading to the harbor of Galveston would be of no service unless the outer bar be improved, the depths over the two being at present about the same. In other words, vessels which can now pass the outer bar can proceed to the wharves at Galveston.
If the entrance between Fort Point and Bolivar Point were the outlet of a river merely, there might be grave doubts of the success of the plan of improvement presented, and the more so, if the problem were complicated by the existence of littoral currents strong enough to move the sands which compose the coast-line both above and below water. But it will be seen that, in the case before us, the Bay of Galveston (including East and West Bays) constitutes an immense basin or reservoir, which is filled to a certain extent on every flood-tide; this increase of water being discharged on the ebb with a velocity which, if confined by parallel piers and directed upon the bar, could hardly fail of producing an important scouring effect beyond what is now occasioned by the unconfined and wide spread currents. Another advantage of the large interior basin referred to is, that the matter brought down by the rivers is all deposited in the upper portion of the bay, leaving only their waters, cleared of sediment, to pass out over the bar. The bar, therefore, is composed of matter from the Gulf and its shores without appreciable auginentation from the river deposits.
The Board is, therefore, of the opinion that, if piers proposed by Captain Howell were constructed, extending over the bar, the depth of water thereon would be increased in an important degree, though exactly what depth might be looked for cannot be predicted. It is also believed that the inshore extreinity of the pier on the fort Point side of the entrance, from the point where it connects with the bulk head constructed by the city to where it joins the long, straight portion running to the bar, will bave the effect of moving the bar at the Galveston Harbor entrance near to Bolivar Channel, whereby it will, to some extent, be carried off by the main current of the latter. This seems not only likely, but the work will have the effect of extending the extremity of Galveston Island northward, thus re-establishing the condition which existed when the depth over the harbor bar is represented to have been 30 feet. The two piers will therefore have the effect, in the opiniou of the Board, not only of improving the outer bar, but also, incidentally, the inner bar at the entrance to Galveston Harbor.
The letter of instructions before referred to inposes the condition that an increased depth of water shall be 66 permanently” secured. taken literally, this condition cannot, in the opinion of the Board, be fulfilled by the present project, nor by any other known method of im.
provement. Though the proposed piers will not secure an actual permanency of the depth at first attained, unless they should be from time to time extended, or the action of the ebb-current be aided at intervals by dredging or stirring, yet, under the favorable conditions which this locality presents for the application of the pier system, it is believed that the requirements of a practical permanency will, under the conditions before expressed, be fulfilled.
As regards the method of construction proposed by Captain Howell, the Board is compelled to speak with less confidence. The importance of some device for piers or training-walls for the improvement of our harbors, which shall be less costly than those hitherto practiced, is readily recognized. Piers of the length, and other dimensions suited to the case in question, if built of stone, resting upon the easily moved sand, over which they would pass, would involve an outlay which the importance of the port would perhaps not justify, and which would not probably be provided for by Congress. If Captain Howell's plan should succeed-and it is impossible to say that it would not-it will supply the desideratum of a cheap method of construction which might be applied to many other localities where, otherwise, no attempts at improvement would be made in consequence of the necessarily beavy oatlay they would involve. The Board therefore thinks it would be well to make a trial of the device, and would therefore recommend that it be tested by first constructing the inner end of the pier on the Fort Point side, and if found to succeed there, that the pier on the other side be commenced at its shore end, while, at the same time, a length of, say, from 300 to 500 feet be put down near the bar extremity of the same pier to test its efficacy in the most exposed position, the extremities of this de. tached portion being protected from the undermining action of the waves and currents by a suitable apron of bags of concrete or other material. By carrying out the shore end of the pier at the same time as, or before, the experimental portion on the outer bar, some idea can be formed as to the width to be given to the latter to enable it to withstand the violent action in that exposed position. As regards the height to which the piers or training-walls should be carried in order to obtain the desired depth, the Board does not feel able to express an opinion. Even if carried to the height of a single gabion only, an important effect may be expected, and if the action should not be sufficient it may be increased by adding to the height. It is, however, highly important, if not essential, that the gabion should be fitted with covers as well as bottoms, to prevent the scooping out of the sand-filling by the action of the sea in storms. This would necessitate their being filled through a hole left in the cover, by means of a funnel or hopper, or other device.
In a previous part of this report it was stated that the problem of improvement of the outer bar was not complicated by the existence of littoral currents. Such currents do exist, at times, but apparently result from the action of the wind. They run sometimes in one direction, again in the other, and in continued calm weather they are not discoverable. The greatest observed velocity did not exceed half a mile per hour-a velocity which in itself could hardly produce sensible action upon the sands of the bar or of the shoals above or below. The cause which produces the present changes on the bar is doubtless the action of the waves upon the sandy bottom, an action which is very largely increased during the heavy storms to which the coast is exposed. Such storms, when blowing directly or obliquely along the shore in either direction, will doubtless occasion the movement of large quantities of saud along the bottom and in suspension in the water; when directly
on shore this movement will be much less; but the inner bays will be filled to an unusual height with water from the Gulf, which, on the ceasing of the storm, will pour out of the bay and over the bar with great scouring power. Offshore winds drive out the water of the bay, thus producing an effect similar to that which follows the emptying of the surcharged bays after an onshore storm. It is represented that after such action as attends the two cases last mentioned the bar is invariably found in an improved condition.
As regards the works within the bay, designed by Captain Howell for the purpose mainly of increasing the width of the harbor of Galveston, and of improving the bar at its mouth, the Board is of the opinion that nothing should be done till the question of the practicability of permanently improving the outer bar shall have been demonstrated ; and it therefore expresses no opinion thereon. Indeed, it would be impracti. cable to do so without inore information regarding the strength and velocity of the currents than the present survey affords.
A much more extended series of observations would be necessary to a satisfactory conclusion; but these may be readily made whenever favorable results from the works for the improvement of the outer bar shall justify the attempt to improve the inner harbor.
A revised estimate for the two main or outside piers C D and E F is annesed. Respectfully submitted.
Z. B. TOWER,
H. G. WRIGHT,
JOHN NEWTON, Lieut. Col. of Engineers, Breret Major-General.
Generally concurring in the report of the Board, I sign it, reserving explanations and points of dissent, viz:
It is my opinion that such dredging as will be required can be performed by the least expensive method in general use, viz, dragging a harrow through the channel, using a small tug already belonging to the work.
While not positive as to the entire adequacy of the character of coustruction proposed, I yet have more confidence in it than the other members of the Board.
I do not agree with the Board in the increased estimate submitted, but continue in the belief that the estimate submitted with my report should be adequate, provided appropriations for construction be made in time and magnitude to keep work in progress throughout each year, with the largest force that may be employed to advantage.
C. W. HOWELL,
Captain of Engineers, U. 8. A. Brig. Gen. A. A. HUMPHREYS, .
Chief of Engineers, U. S. A. The following is the estimate presented by Capt. C. W. Howell, Corps of Engineers, as the probable cost of the two outer piers CD and E on wbich the estimate of the Board is based :
Feet Length of jetty CD.
20, 800 Length of jetty E F.
16, 200 Total
The number of gabions for both piers placed in two rows and one tier
high is 12,333, at $30 each...
ions, at $30 each...
554, 970 00 58, 114 50
613, 084 50
1,021, 818 50
102, 181 85
Making the total cost of the two piers
Total amount of Captain Howell's estimate...
1, 124,000 35
92, 496 00 308, 320 00
Additions to the above estimates by the Board :
on the supposition that an average of 15 per day throughout the year
be $10.30,832 gabions, at $10 each, $308,320.
Total estimate of Board for the two outer piers, if raised two tiers
211, 461 50 15, 416 00
635, 401 50 1, 124, 000 35
1,759, 401 85
IMPROVEMENT OF REDFISH BAR IN GALVESTON BAY, TEXAS.
This work, for which an appropriation of $10,000 was made June 23, 1874, is but an extension of the work reported on pages 634 and 635 Report of the Chief of Engineers for 1873. The work there reported complete, answered the then existing wants of commerce.
Since, a deeper and wider channel than it afforded through Redfish Bar, has become desirable.
The money now available will be expended in deepening and widening the channel but is not considered sufficient to complete the work.
The work is located in the collection-district of Galveston and near the light-house on Redfish Bar.
Amount in hands of officer and subject to his check July 1, 1873.
868 41 10, 000 00
50 00 10, 018 41
Estimate for completion of the work will be submitted in December next, it being deemed advisable to await the results of the present appropriation before recommending another. Total amount appropriated...
$20,000 00 Total amount expended....