NOTE.-Number of cubic yards of brush mattress work placed in jetty, 71,657.3. Statement showing number of days of favorable weather and the number of mattresses placed

during the year.

Six mattresses were lost by breaking loose from tow of tug Cynthia, owing to heavy sea running. None have been lost from jetty.

REPAIRS TO PLANT.

Tug Cynthia was hauled out twice, hull cleaned, and machinery overhauled; tug Molyneux was hauled out, and hull and machinery repaired; placing-barge was hauled out, and hull repaired.

The plant, with the exception of barges 2, 3, and 4, which require some attention to their sheathing, is in good condition for constant and efficient service.

Respectfully,

Maj. S. M. MANSFIELD,

Corps of Engineers.

W. A. HINKLE,

Superintendent.

REPORT OF MR. H. C. RIPLEY, ASSISTANT ENGINEER.

UNITED STATES ENGINEER OFFICE,
Galveston, Tex., August 21, 1883.

SIR: I have the honor to submit the following report relating to the survey of Galveston Harbor, Texas:

The survey was commenced on the 12th of May, and concluded on the 21st of July ultimo, having been prosecuted during favorable weather and at such times as not to interfere with more important work. The actual time consumed in the hydrographic work was forty-nine and one-half hours, embraced in portions of twelve days. The area covered is 16 square miles, extending from near the quarantine station, in Galveston channel, to the Gulf, and embracing the inner and outer bars.

The accompanying tracing shows a plot of the survey, together with a sectional elevation of the south jetty as constructed up to June 30, 1883.

Comparing this survey with that of June, 1882, we note the following changes, all depths referring to the plane of mean low tide: There has been a deepening at that point in Galveston Channel west of the Fort Point light-house, where a shoal had formed, arresting the 18-foot contours, so that now there is a least depth of 18 feet. There has also been a deepening on the site of the inner bar, which can now be crossed with a least depth of 25 feet, there being as much as 274 feet depth between it and the shoal above mentioned.

In Bolivar Channel little change is to be noted inside of the 18-foot contour. There is an undoubted tendency, however, to straighten the southward deflection existing at its outer end.

At the extreme point of the bight the 18-foot contour has moved to the north and east about 800 feet. Farther north this contour has moved eastward from 400 feet to 1,500 feet, and on the north side of the channel for a short distance from its eastern end it has moved south from 200 feet to 500 feet.

These movements, however, are effected with a slight change in depth, on account of the nearly level bottom; but as we approach the crest of the bar, following the line of the axis of Bolivar Channel nearly, we find a bight of the 16-foot contour to have advanced fully 1,500 feet, showing a scour in places of over 3 feet depth.

In the jetty channel at the shoalest point there has been a deepening of 14 feet, so that there is now a least channel depth of 13 feet, and a width of 1,000 feet from the jetty to the 12-foot contour north of it. Aside from the deepening in the jetty channel, the depth on the crest of the bar remains practically unchanged; the bar, however, has moved gulfward some 300 feet, and the area between the 12-foot contours has diminished in width a perceptible amount.

South of the jetty for the outer 2 miles but little change has occurred; the same trench exists close to the jetty, which at a point about 1 mile from the outer end of the jetty has widened somewhat; this is obviously caused by the escape of water through the gap in the upper courses of the jetty at this place.

Nearer the shore the shoals have somewhat changed in position and shape; the 8-foot contour outside of the first shoal met has moved shorewards about 500 feet, except in a narrow ridge near the jetty, where it has pushed out about 1,200 feet.

The swash channel has greatly diminished in both width and depth, and an accretion of some 200 feet has been made to the shore, in addition to numerous ridges, which have made their appearance above the water surface.

Along the north face of the jetty, where it crosses the shoal near the Fort Point light, a trench has been excavated by the overfall of water which comes in through the swash channel, and which is deflected from its accustomed route by the building up of the inner end of the jetty. That portion of this shoal lying north of the jetty has been depressed on the north and west, and extended on the east, the 6-foot contour having advanced eastward nearly 1,000 feet. The eastward advance of this shoal has so much encroached upon the channel, which crossed the line of the jetty about 1 mile east of Fort Point light, that it would seem to be only a matter of a few months' time when this channel will be entirely filled.

5455-E 83-68

The shoal south of the light-vessel has changed very little. The northwest c has been depressed slightly, and northeast corner extended about an equal am At the east end the 12-foot contour has moved west. At one point this move amounts to 500 feet. At the time of the previous survey the movement of this was in the opposite direction, and it is believed that it will resume its east advance when the gap in the jetty at this point is closed.

The area north of Bolivar Channel was not covered by the survey of last; Comparing it, therefore, with the survey finished in February, 1881, we find tha shoal extending out along the north side of the channel has experienced no į change. Its western limit embraced in this survey has been narrowed somewha the enlargement of the swash channel at that point, and its eastern end has m to the north, an amount corresponding nearly with the northward movement of. var Channel at its eastern extermity.

The 8-foot contour has moved easterly, inclosing a narrow ridge for a distanc fully 2,500 feet.

The 12-foot contour to the north has moved out about 400 feet.

Between the 12-foot and 18-foot contours a remarkable shoaling has occurred, 18-foot contour having moved gulfward at one point over 2,000 feet. There is i evidence of a trench for much of the distance along the line of the Bolivar Gabionn but where it was deepest it has greatly shoaled, and in places no evidence of a tre remains. The shoal which crosses the swash-channels south of the gabionnade has creased in width 500 feet, and has moved southwestward a like amount. The no side of Bolivar Channel, between the 8-foot and 20-foot contours, seems to posse remarkable degree of permanency.

Altogether the changes for the past year, or indeed for the two years past, consider the magnitude of the jetty already constructed, are very slight, and indicate rat the direction towards which changes are tending than any very important res accomplished.

The straightening of Bolivar Channel at its outer end is evidence of the supp which the current in that channel gets from the jetty in its efforts towards a strai passage into the Gulf in opposition to the littoral current, which tends to deflect it the southward.

The gulfward movement of the bar, without a corresponding increase in depth up its crest, would seem to indicate the importance of an early and rapid construction the north jetty.

The changes thus far do not seem to warrant the expectation of a much grea increase in depth in the present jetty channel, but the indications seem to point t new channel at a much greater distance from the jetty and more nearly on the p longation of the axis of Bolivar Channel.

The closing of the gap in the third and fourth courses of the south jetty will doubtedly hasten this result by diminishing to a great extent the cross-current on bar, which is produced by the littoral current.

In conclusion, I desire to express my indebtedness to Lieut. W. L. Fisk, Corps Engineers, Mr. J. M. Picton, assistant engineer, and Mr. H. J. Condron, for valua assistance in the conduct of the survey and construction of the chart.