APPENDIXES

TO THE

REPORT OF THE CHIEF OF ENGINEERS,

UNITED STATES ARMY.

FORTIFICATIONS, Etc.

APPENDIX No. 1.

REPORT OF THE BOARD OF ENGINEERS ON THE MEANS FOR PROTECTING THE SITE OF THE FORT AT SANDY HOOK FROM EROSION BY THE SEA.

OFFICE OF BOARD OF ENGINEERS FOR
FORTIFICATIONS AND FOR RIVER AND
HARBOR IMPROVEMENTS, &c.,

New York, November 18, 1881. GENERAL: The Board to whom was referred, from the Office of the Chief of Engineers, by indorsement of August 12, 1881, the consideration of the oscillations of the shore line at Sandy Hook, N. J., with the inquiry whether the fort at Sandy Hook is in such danger by reason of these changes as to warrant the large expenditure which would be required for the protection of the site, have the honor to report:

The papers sent from the Office of the Chief of Engineers for the consideration of the Board were:

1. Letter, with sketches, from General Benham, in charge, to the Chief of Engineers, January 14, 1878.

2. Letter from same to same (with sketches), December 13, 1878. 3. Letter, with inclosure and three photographs, from Capt. W. S. Staring, Ordnance Department, of June 11, 1881, to Lieut. Col. T. G. Baylor, commanding Ordnance Proving Ground at Sandy Hook.

4. Letter from General Benham to the Chief of Engineers of August 12, 1881, in reference to the above.

5. Letters from same to same of August 13, 1881.

General Benham, at the request of the Board, furnished tracings exhibiting the shore lines from 1778 to 1878, inclusive, and also caused the shore line to be taken October 5, 1881, by which means the Board are in possession of the latest data in reference to encroachments upon the high-water line.

Reference is made to tracings A, B, C, sent herewith.

It appears that the rate of movement of the point of the Hook northward was, from 1778 to 1819, 550 feet, at the yearly rate of 13 feet. From 1819 to 1835, 1,150 feet, at the yearly rate of 64 feet.

From 1835 to 1844, 650 feet, at the yearly rate of 72 feet.

From 1844 to 1856, a retrograde movement southward of 450 feet, at the yearly rate of 37 feet.

From 1856 to 1864, a movement again northward of 670 feet, at the yearly rate of 84 feet.

From 1864 to 1868, 170 feet, at the yearly rate of 43 feet.

And, finally, a retrograde movement southward, from 1868 to 1881, of 710 feet, at the yearly rate of 55 feet.

Directing attention now to the beach east of the fort, the following distances from the northeast and the southeast salients to the line of high-water are compiled from the records:

Owing to the small amount of funds available for the shore protection, work was necessarily confined to the construction of short jetties, which, although useful in an emergency to cover an exposed point, will be found useless as a solution of the general problem of preservation whenever the causes tending to wear away the site of the fort are in full activity and continue in operation for a term of years.

In the appendix to the Coast Survey Report of 1857 will be found a report of the advisory council to the commissioners on the preservation of New York Harbor from encroachment. This report, signed by General Totten, Chief Engineer, U. S. A., and Professor Bache, Superintendent of the Coast Survey, treats, among other matters, of the progressive developments to the northward of the point of Sandy Hook. They say.

Various causes were assigned for this growth, and minute observations of the tides and currents were made by the Coast Survey, under the immediate direction of the superintendent, by sub-assistant Heury Mitchell, under the authority of the commissioners to test the various suppositions.

From these observations it was determined that on both sides of Sandy Hook, on the ocean side and on that of Sandy Hook Bay, there prevail during the ebb and flood tides northward currents tending to carry the sand on both the outer and inner shores to the northward. In the False Hook Channel this current prevails for seven hours out of the twelve. On the inside the northwardly current prevails for eleven hours out of the twelve.

With regard to the relative moving power of these currents, as compared with that of the opposite currents in the same localities, Professor Bache, in Appendix No. 27 of the Report of the Coast Survey, 1858,

stated that for a current station situated near the upper end and about mid-width of the False Hook Channel, the northwardly current was superior in that respect to the opposite in the ratio of 5 to 1, and that for the shore, on the side of Sandy Hook Bay, the ratio was 45 to 1.

Returning to the report of the advisory council it states that at the meeting of the outside and inside northwardly currents their motion is lost, and the sand which they transported is deposited.

These currents during the time they are opposed to the proper direc tion of the ebb and flood currents are eddy currents, and are produced by the draught of the main channel.

The report also states that the outside northwardly current had not only carried the materials of the New Jersey coast northward, but it had diminished very much the area of the shoals known as the False Hook and Outer Middle Ground; had deepened the bar at the southern end of the False Hook Channel from 21 to 22 feet; had, according to Mr. Boschke, deepened the channel by 14 foot, and had removed the bulkhead which, in 1836, closed the northern end of False Hook Channel, giving 30 feet water where there had been twenty years previously but 13 feet; and also that the inlets near Shrewsbury had been closed, due to the same northward drift.

In the same report is given the computation of Mr. Boschke that in twenty years 1,500,000 cubic yards of sand had been removed from the False Hook Channel; that about 1,000,000 cubic yards of sand had been transported from the Outer Middle and False Hook shoals, of which half a million had been redeposited at the northern end. Thus 2,000,000 of cubic yards of sand had been transported towards the point of Sandy Hook, the main ship-channel, and the southern part of the bar, from this locality alone; bounded on one side by Sandy Hook shore and on the other by the outside of the Outer Middle and False Hook shoals.

During the same period the average depth of the main ship-channel had changed but little, and by Mr. Boschke's estimate but 95,000 yards had been deposited in it. The growth of the Hook had added about 2,500,000 to this encroachment, representing with the deposit in the main channel more than the excavation from the False Hook Channel. The wear from the inside of the Hook during the same period amounted to 100,000 yards.

The council also concluded that the sand from False Hook Channel did not at once reach the bar.

As at that time the point of Sandy Hook was rapidly moving to the northward, the question as it then appeared to be was to arrest this 'movement when it should become excessive.

The council also reported that in the twenty years preceding 3,000,000 cubic yards were known to have been removed from the channels at the outlet, and that in the shifting of the shoals 54,000,000 cubic yards had been carried inward. (In fact, referring to Mr. Boschke's paper in the Supplement of the Coast Survey Report of 1857, a short calculation will show that 54,000,000 cubic yards of the shoals were carried an average distance of 1,655 feet.) They also stated that all the shoals except Flynn's Knoll had moved to the northeast, while that one had moved to the northwest by west, and also a general deepening of the channels had taken place.

The state of things the Board is now asked to provide for is the reverse of the preceding problem. The point of Sandy Hook, instead of moving to the northward by an increase more or less rapid, has, since 1868, receded for a distance of 710 feet, and the northeast salient, together with

the whole east front, is now at distances from high-water mark varying from 210 to 410 feet.

The advisory council recommended strongly a physical survey of New York Harbor for the purpose of determining the causes of the changes in the bottom which the hydrographic surveys made for their service had exhibited, and also as a means of comparison with future physical surveys. The Board has, however, been unable to find the records of any physical survey of the bar and neighborhood of Sandy Hook having a bearing upon the question submitted to them, with the exception of the physical survey made over a limited area about the year 1857 in the neighborhood of Sandy Hook, and to which reference has repeatedly been made in former portions of this report.

Besides the records of the advance and receding of the shore line north of the fort, and to the east, as delineated on tracings A, B, and C, the additional information concerning the locality in question is confined to tracing D, which exhibits the changes in the 18-foot contours of False Hook, Flynn's Knoll, and along the shore of the Hook.

With the scanty stock of data supplied from existing records it is impossible for the Board to determine with a certainty sufficient to carry conviction to their own minds all the causes of the growth and decrease of Sandy Hook, or the limits of these changes. There are, however, some significant facts exhibited which will go far towards the formation of the opinions which the Board are required to give upon the points submitted.

The axis of the northward growth of Sandy Hook, as shown on tracing A, has generally been along a line directed northwest, from the northwest salient of the fort. Since 1868, the date from which the point began to recede, this axis has inclined more to the westward, so that at the present time it has a direction nearly west, and the point of the Hook has consequently made a notable encroachment upon the inside channel. The Board is not in possession of data sufficient, except in a general way, to assign the causes of this change.

The causes affecting the magnitude of the Hook are the currents of the main, of the False Hook, and of the inside channels; to these must be added the action of the waves which stir up the sand of the beach and of the bottom, moving it by their own power of translation, as well as delivering it over to the transporting power of the currents. The resultant of these causes has generally had a tendancy to incline the axis of the mass of sand lying north of the fort to the west of north. A deflection westward of the northerly currents of the inside of the Hook would materially assist in this operation, as also slight changes' in the direction of the currents of the Main and False Hook Channels, and in this connection it is probable that the wharf at Sandy Hook has had some effect by deflecting the northerly currents of the inside channel more towards the west. The receding of the point of the Hook to the southward is due to waves and to the eroding action of the currents of the main channel.

The encroachments on the beach to the east of the fort are due to the waves and to the currents of the False Hook, which find less work in widening that channel at the expense of the beach than in deepening it; and it is found that the 18 foot curve of that channel has in late years encroached westwardly upon the beach.

It cannot be assumed that the changes in the beach north and east of the fort have been caused by a diminution in the periodical amounts of sand transported by waves and currents, for such supposition would

be inconsistent with the fact of the general maintenance in equilibrium of the channels and shoals of the bar.

The sand in circulation has been mostly thrown up by the waves and so brought under the action of the currents, for otherwise the growth of the point of the Hook, if made exclusively at the expense of the peninsula, would have before this absorbed entire portions of it, and have much attenuated its present dimensions.

The present projection into the inside channel of the point of the Hook may be the beginning of a formation similiar to the projection at the Horse Shoe and at the Cove.

It is evident that without the accurate knowledge, which could only be furnished by an extensive physical survey, it would be unwise to attempt to place a limit to the progress of encroachment upon the beach, encroachments which have already been so great since 1868 that their continuance for a few years would seriously endanger the fort.

It is not supposed that the fort is in any immediate danger, but it seems probable that the encroachments on the east shore will continue if not arrested. It appears from the shore line records that the short jetties, before their total or partial destruction, notwithstanding the limited lengths given them, were, under ordinary conditions, efficacious in arresting beach abrasion, helping rather to build up the beach by holding sand-drift. Those that still exist, even in their present condition, are to a certain extent useful.

The beach south of Jetty 1, including that portion protected by Nos. 6 and 2, has extended seaward largely since 1872, proving the excellent effect of the system in that locality. The next three in order in a northerly direction, 1, 4, and 5, constructed of concrete, though still in place, are much injured, their top portions having been carried away by stormwaves, in consequence of which even smaller waves have penetrated beyond the jetties, washing away the bluff behind their shore ends. Jetties 7, 8, and 3, built of perishable materials, have been almost entirely destroyed.

Five hundred feet of the triangular bulkhead remain out of the 1,250 feet constructed originally to extend from Jetty 1 (see tracing C) nearly to Jetty 8.

Jetties 1, 4, and 5, should be repaired during the summer months by raising them with concrete, made of the best possible material, above storm-tides, at least on their inner ends, and they should be extended into the sand bluffs, and perhaps be further aided by shore protection so as to prevent the possibility of the storm-breakers turning them. To take the place of Jetties 3, 8, and 7, it is proposed at or near position of former Jetty 8, to construct another, extending sufficiently far into the sea (to the 6-foot curve for example), to arrest the currents of the False Hook Channel, strong in this locality. This position is assigned the new pier for the reason that it will there best protect the most exposed part of the fort.

Should necessity arise for a second jetty of similar length, the prolongation of No. 4 might effect the object desired.

However, it is not intended here to prescribe definitely any new jetty except the first named, as the conditions of the problem may be subject to changes which can only be properly studied when they shall have arisen. The proposed short jetty, or jetties, may be constructed of concrete next the shore, and of large stone supported on rafts or mattresses of brush for the greater and outer portion. Stone would be more economical if proper appliances for landing and depositing it were provided.