the dam and preclude the possibility of further undermining. The scouring seems to have reached its limit in depth. Very little, if any, increase has occurred at any point for several months, and there has been decided shoaling in many places.

It had been suggested that some widening of the mattress foundations, and also that some perpendicular jetties to the dam, would be advisable. One jetty, of about 100 feet length and 40 feet width, was placed without producing any app irent effect. It is evident that the scouring is caused by the overfall of the water and not by parallel currents.

The widening of the foundations by mattresses was not resorted to, as, after the scouring on each side of the dam had occurred, the expense of such work would be nearly or quite as great as the filling the slopes with riprap, while the efficiency would be much more doubtful. The following sectional diagram illustrates the present general condition of the dam, the effect of the scouring by the overfall of the water, and the method of completion proposed.

The forces to be contended with in the closure of the New Inlet are well illustrated by the fact that in the present imperfect state of the dam the water on the river side, toward the last of the ebb-tide, has several times been observed to be 2 feet higher than on the sea side. When the water is completely shut off by the dam, the difference at certain times will probably amount to 3 feet. The flood-currents are apparently as strong as the ebb, but the difference in level cannot be so nearly determined till the dam is completed to high-water. From a comparison of tidal observations made in 1876 and 1877 with those made since the partial completion of the dam, there appears good reason for the opinion expressed in former reports that the range of the tides will be increased rather than diminished in the river at Federal Point and above by the closure of the New Inlet, thus adding a vast force to the scouring power at the mouth by the increase of the volume of water.

The disturbing forces of the New Inlet tides explained in former reports will also be removed. These are especially powerful in the vicinity of the New Inlet and the Horseshoe Channel. The good effect of the partial closure is already apparent. The available depth in the Horseshoe Channel has increased fully one foot since the dam was begun. A reference to the sketch of this vicinity which is annexed hereto will show that good results should be expected. The main flood after the full closure will no longer be met near the Horseshoe Channel by the inlet flood, nor the main ebb-currents be diverted and disturbed by those of the inlet.

The primal fact which lies at the foundation of the great deleterious influence of the New Inlet as well as of the difficulty of closure, is that the average time of the tides at the natural entrance and on the sea side of the New Inlet dam, when finished, will be nearly simultaneous, while the same on the river side of the dam will average fully an hour behind. There is, therefore, or will be during more than half the time of each tide, an alternating average difference of at least 1 foot, in level, which is varied at different periods of the tide and with different tides and winds.

As the volume of the New Inlet tide, though large in itself, is small compared with the overwhelming tides of the entrance, there has been some approximation to the effect which may be conceived to be produced by the interposition and sudden removal of the complete dam, at the times of these differences of level.

The effect of the partial closure of the New Inlet is already apparent at the natural entrance. It is believed that the “ Rip" of the western channel was never so long in so good a condition. It has been reliable for fully 9 feet depth at mean low-water since October 1, 1877. At the present time the shoalest soundings are 104 feet, excepting for a distance not exceeding 60 feet on soft sand.

The effect at the Bald Head Channel is less apparent but not less real. Since the coast survey of 1872, the distance across the bar, from 12 to 12 feet depth at mean lowwater, has diminished from 2,400 to 1,200 feet, and the deep water is pushing in a direct line across the bar. It is very unfortunate that funds have not been available to assist in the process. It is probable that this process and its incompletion accounts for the slight shoaling on the bar which has occurred during the year. The shoalest soundings are now 9 feet at mean low-water for very short distances (in two places) on shifting sands.

No great permanent changes have occurred in the shore-lines of Federal Point. During the prevalence of strong southwest winds, and a course of high tides in August, 1877, a tendency to flank the dam at Federal Point was experienced. This was promptly checked by stone filling, and the dam was made much more secure thereby. A line of sheet-piling was also driven from the end of the dam to the high mound at the quarters. The sand has formed a ridge over it above the highest tides. The general surface of the land has risen.

Some abrasions have occurred, but they have been followed by accretion, and there has been a general advance of the crest and low-water lines.

Considerable changes have occurred in the shore-lines of Zeke's Island, especially on the easterly side and near the dam. The low-water line has advanced about 300

ORIGINAL BOTTOM

feet for a distance of more than a quarter of a mile. The crest line has made a less advance.

There has been a general growth of the island excepting near its connection with Smith's Island. In this vicinity there has always been alternate accretion and abrasion on the sea side. The old superstructure of the connecting works was thoroughly worm-eaten, so that little force beyond the buoyancy of the water was required to move it. About 150 feet in length was washed out by the storm of September 17, 1876, as per last report.

During the past two months a new breach has been made in it of about 300 feet in length, a little northerly of the other, so that the water passes freely at half tides. As the foundation stone and timbers are intact, there is no immediate danger of a thorough breach. It is intended to repair these breaches as soon as funds are available.

The ultimate strength of the work will be increased by the washing of a large amount of sand from the sea side, and filling the deep water on the bay or river side. The long narrow sand-beach of Smith's Island which separates the sea from the bay has improved in condition during the year, although the "swashes" across the beach, some 3 and 4 miles from the head of the island, remain open.

At the beginning of the year the spring tides washed over several miles of this beach. During the year it has risen above the highest tides excepting at the swashes. These have now an aggregate width of about 2,950 feet at high-water. This embraces the middle ground between the first two "swashes," which is bare at about half tide, and about 1,400 feet in length. The southerly swash, originally about 800 feet in width at high-water, has diminished to less than 200 feet.

The process of shoaling in the rear of the "swashes" has continued throughout the year. There is but little doubt of their ultimate closure by natural causes and of the growth of a large area of marsh or grass lands, thus forming the best defense against future breaches and repeating former experience, and especially of the great breaches of 1857.

By reference to the surveys of Lieutenant Glynn of 1839, it appears that the long narrow sand-beach was bordered with but very little marsh. Comparison with subsequent surveys shows its growth in the rear of the several breaches, and especially of the great breaches of 1857. It is to be noticed that these breaches cause a more rapid recession of the general line of the beach.

The present breaches are so remote from the river and channels and the New Inlet, and so little influenced by its closure, that no immediate danger can be apprehended from them. Therefore no expenditure is recommended for their closure during the coming year unless there be more unfavorable developments.

No great changes in the shore-line of Bald Head Point and the opposite point of Oak Island have occurred during the year. The southwestern shore of Bald Head Point has receded and there has been some advance northward and eastward. The width from point to point remains about the same.

The new cut behind the Horseshoe Channel near Snow's Marsh has remained in the same condition during the year. The shoaling at the upper end destroys its utility for more than 8 feet draught at low-water. A reference to the annexed sketch will show the remedy proposed.

It is apparent from the general shape and condition of the river and channel, as well as from observations, that the prevailing tidal currents both of the ebb and flood, and especially the ebb, cross the upper or shoaled portion of the cut obliquely, and will do so after the complete closure of the New Inlet. This is the cause of the shoaling, the bottom being sandy.

It is not believed to be practicable at any reasonable expense to divert the main currents through the cut, but by giving the upper end of it a new direction above Snow's Marsh parallel with the prevailing currents, extending it to the 12-foot pocket, which is very nearly connected with the main channel of 12 feet depth at low-water (as may easily be done by a very small amount of dredging), a good and reliable subsidiary channel may be obtained of 12 feet depth at low-water, much more reliable and permanent than the Horseshoe Channel, as that will always be more subject to cross, changeable, and opposing currents, which are the source of its changes and deterioration.

The channel thus obtained will more than justify all the expense thus far incurred by dredging it, and the comparatively small expense proposed to make it available. The new dredged channel at the "Logs," near Campbell's Island, retains its depth of 12 feet at low-water. It is only 130 feet in width, and it should be widened to make it more serviceable.

The exhaustive hydrographic survey of the river between New Inlet, Snow's Marsh, the deep water above Federal Point and below Price's Creek light house, has been completed and the map projected on a scale of 200 feet to an inch.

A like survey of the New Inlet extending over the whole basin and to deep water over the shoals has also been made, and the maps projected on a scale of 400 feet to an

A thorough survey of the Bald Head and western channels of the natural entrance has been made, and projected on a scale of bo:

The triangulation in preparation for a complete hydrographic survey of the river connecting the above surveys has been made.

Reconnaissances and examinations have been made and reported from time to time of Federal Point, Zeke's and Smith's Islands, Bald Head Point, &c.

The tug James T. Easton, and the crew of the same, have been very useful in these surveys, and very little extra labor has been employed on them. The tug was laid up under the care of a watchman and the crew discharged December 31, 1877. Some repairs will be required to put her in running order.

The suction-dredge Woodbury has been laid up under the care of a watchman during the year. Her hull and machinery have necessarily suffered some from decay and rust. Her boiler is known to be worthless. The machinery and pumping apparatus are in reasonably good condition.

Simultaneous tidal observations have been taken, especially at Smithville, Federal Point, and Wilmington. They have not been taken with a view to determine the absolute average range of the tides so much as their relative movements and ranges at the several places.

Some of the comparative results of these observations are shown below. These tidal observations will, on comparison with future observations which may be made at the same places after closing the New Inlet, show the effect of that work on the tidal movements.

From 184 simultaneous observations, each of high and adjacent low-water in 1876 and 1877, and 71 similar observations of the same from February 11, 1878, to May 30, 1878, since the partial closure of the New Inlet, the following results appear:

One hundred and eighty-four observations in 1876 and 1877.

Comparative results of twenty-eight simultaneous observations of high-water and adjacent lowwater, from April 22, 1878, to May 30, 1878.

The tides observed in 1876 and 1877 give about the average range at Smithville. Those observed in 1878 give less than the average, because more of the larger tides were omitted.

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