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The total length of the required excavation through them would be (for a channel 24 feet deep and 60 feet wide) about 1,300 yards; the average depth to cut 1.7 feet; and the material to be removed, about 14,700 cubic yards of gravel. The current is not very rapid and in many places the water ripples over the gravel.

2. Ledge Falls. Here a ledge of slate extends across the river and forms its bed for a distance of about 700 feet. The strata have a nearly vertical dip and extend in places, 3 or 4 feet above the water. Over the ledge the river has a greatly increased slope, and an excessively strong and rapid current. At the upper and lower limits of the ledge, the channel between its higher points is, for a few feet, only about 30 feet wide, at which places the water is respectively, 2.3 and 4 feet deep, runs with extreme rapidity, and is very rough, dashing down slopes having about 14 and 2 feet fall in distances of 10 and 30 feet. In the channel the average depth of water on the ledge is 3 feet and the least depth 1 feet. It is roughly estimated that there would here be required the excavation of about 700 cubic yards of solid slate rock.

3. From Ledge Falls to Rocky Rips, a distance of about four and three-quarter miles. Between these two places there is a succession of gravel shoals. The least depth of water on them in the channel is 1 foot; the total length of the required excavation through them about 1,700 yards; its average depth seven-tenths of a foot; and the material to be removed about 8,000 cubic yards of gravel.

The examination of this branch extended only to Rocky Rips. Above these rapids for fully two miles, embracing them and the "Upper" and "Lower" Grindstone Rips, it is obstructed by large masses of slate-ledge and by immense numbers of bowlders of all sizes up to 15 or 20 feet in diameter, its slope is steep; its current very rapid, and the water in places very shallow.

Above the Upper Grindstone Rips there are, I have been informed, occasional long reaches which are comparatively unobstructed. The entire length of the East Branch is said to be about sixty-three miles. It cannot be made navigable further than to Rocky Rips, at least without enormous expense.

THE WEST BRANCH.

Between Medway and Shad Pond, a distance of about ten miles, this stream is obstructed by the following rapids, viz :

Least depth of water in channel, 3 feet; least

1. Nicaton Rips, just above Medway. depth on shoal of bowlders just below, 1 foot.

2. Rocky Beamy Rips, about one and one-half miles above Medway, and one-eighth of a mile long. Least depth of water in channel, 2 feet.

3. Wade Rips. A shoal of bowlders about one-half of a mile long. Least depth of water, for about 200 feet, 14 feet.

4. Burnt Land Rips, about three miles above Medway and about three-fourths of a mile long. Least depth of water in channel, 2 feet.

5. Rocky Rips, about four miles above Medway and about three-fourths of a mile long; least depth of water in channel, 1 foot.

6. Dolby Rips, about five and one-half miles above Medway, and about three-fourths of a mile long; least depth of water, 2 feet.

7. Ledge Falls, about six and one-half miles above Medway, and about 700 yards long; least depth of water, 1 foot.

8. Jerry Brook Rocks, about seven and one-half miles above Medway, and about one mile long; least depth of water, 2 feet.

9. Pond Falls, about one-quarter of a mile below Shad Pond, and about three-fourths of a mile long; least depth of water, 1 foot.

Shad Pond, through which the West Branch flows, is the upper limit of the examination. It has an area of about three-fourths of a mile square.

All of the above rapids, excepting Nicaton, Wade, and Dolby Rips, are, to use the expression, forests of large bowlders, between which the water flows with a very rapid current, and in a very turbulent manner, over a rough and very steeply sloping bed. At Pond Falls, Jerry Brook Rocks, and Ledge Falls, in addition to the bowlders, there are ledges of slate cropping out in the river. The descent of the bed between Shad Pond and Medway must be great.

The West Branch cannot be made navigable above Medway. It contains an immense number of large bowlders. By blasting off the tops of many of them the runuing of logs could be much improved.

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ESTIMATE OF COST OF IMPROVEMENT.

I.-Cost of cutting a channel 75 feet wide and 3 feet deep through the obstructions between Oldtown and Winn.

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Obstructions.

II.-Cost of cutting a channel 60 feet wide and 24 feet deep through the obstructions between

Winn and Medway.

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III.-Cost of cutting a channel 60 feet wide and 24 feet deep through the obstructions between
Medway and Rocky Rips, on the East Branch.

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Add for contingencies and engineering expenses, (say 15 per cent.)....

Aggregate

$122, 018
53, 310
33, 200
208,528
31,279

239, 807

I cannot discover a necessity for the removal of these obstructions by the Government, nor the expediency of the expenditure by it of any such sum of money upon this part of this river for the purpose of improving it for steamboat navigation, cut off, as it is, from tide-water navigation. There are a great number of streams, more or less remote tributaries to the great rivers in the country, for the improvement of which large appropriations could, with as good reason, be expected.

In regard to the expenditure of from $20,000 to $50,000 upon bowlders, chiefly in the West Branch, to improve the running of logs, it is a question whether, with justice, such an expenditure should not be made rather by the lumber interest than by the Government. It would result, probably, in benefit chiefly to a comparatively very small number of persons extensively interested in lumber and owners of large tracts of. land in the lumber region.

The actual descent of the river between different places herein given is taken from a work on the "Water-Power of Maine," by the superintendent of the hydrographic survey of that State.

Respectfully submitted.

W. S. STANTON,
Captain of Engineers, U. S. 4.

Lieut. Col. GEO. THOM,

Corps of Engineers, U. S. A., Portland, Me.

3.-SURVEY OF PORTSMOUTH HARBOR, NEW HAMPSHIRE.

UNITED STATES ENGINEER OFFICE,
Portland, Me., December 13, 1873.

GENERAL: I have the honor to submit the following report on the survey of Portsmouth Harbor, New Hampshire:

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This survey was called for by act of Congress approved March 3, 1873, "making appropriations for the repair, preservation, and completion of certain public works on rivers and harbors, and for other purposes,' and was made under my instructions, in June and July last, by my assistant, Mr. Sophus Haagensen, civil engineer. His report and map of the same, also prepared under my direction, are herewith submitted.

The object of this survey was the building of a breakwater between Gerrish's Island and Wood Island, at the outer entrance of the harbor.

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The site of the proposed breakwater is a ridge or bar connecting these two islands, the shortest distance between them being 1,330 feet at high water and 872 feet at mean low water, while at extreme low water this ridge or bar is uncovered nearly its whole length. This bar consists of coarse shingle, intermixed with large bowlders, covering a ledge which crops out at several places above the 18-foot curve, forming Wood Island, Whale's Back, White Island, Horn Island, and a number of rocky points, dry at half tide, scattered between the high and low water line of Gerrish's Island. The solid and unchanging character of this bar affords a very favorable foundation for the breakwater proposed.

The estimated cost of this work, built of rubble-stone, as shown on the drawing, and for a length of 1,376 feet, is $150,000.

The extent to which the commerce of the country would be promoted by the proposed work, as plainly seen on referring to the accompanying sketch of this harbor, would be very great, in the large increase of safe anchorage ground that would thereby be afforded to the vessels of war connected with the navy yard at this place, as well as to the numerous vessels engaged in the coasting and foreign trade, and in affording a good harbor of refuge, during southeast gales, to fishing and coasting vessels on reaching the outer harbor.

This work would derive increased importance from the fact that this harbor, thus enlarged and improved, would be well protected and commanded by Fort Constitution and Fort McClary and the new batteries now in process of construction on Gerrish's Island and Jerry's Point. Respectfully submitted.

GEO. THOM, Lieut. Col. Engineers, Bvt. Brig. Gen. U. S. A.

Brig. Gen. A. A. HUMPHREYS,

Chief of Engineers U. S. A., Washington, D. C.

UNITED STATES ENGINEER OFFICE,
Portland, Me., November 29, 1873.

GENERAL: In obedience to your instructions of June 25, I proceeded to Fort Constitution, Portsmouth Harbor, New Hampshire, to make a survey such as might be necessary for locating a breakwater between Gerrrish's Island and Wood Island, and making an estimate of the cost thereof.

The field-work was commenced June 28, and finished July 10, 1873.

I have the honor to submit the following report upon this survey, as well as a drawing, comprising a map of the survey, drawn to a scale of 200 feet 1 inch, or 1:2400, showing the location of the proposed breakwater, a map of Portsmouth Harbor, from Whale's Back light to the Narrows, in a scale of 1: 20000, from United States Coast Survey maps, a cross-section of the proposed breakwater, and a length profile through the axis of the same.

The survey was commenced by measuring a base-line on Gerrish's Island, A-B, (794.58 feet long, horizontal distance,) and from this base-line triangulation was extended to various fixed points on Gerrish's and Wood Islands; the location of Whale's Back light (old and new position) and Portsmouth Light was also determined, in order to use those two points, viz, old position of Whale's Back light and Portsmouth light as a base for comparison between the present survey and that of Capt. Howard Stansbury, United States Topographical Engineers, map of Portsmouth Harbor, New Hampshire, 1842-43-44. Details were drawn on the plane-table, and twelve lines of soundings run over the bar between Wood and Gerrish's Islands, the proposed site of the breakwater. Each sounding was located on a certain range by intersecting sights from a plane-table stationed ashore. The soundings were either taken with a 16-foot pole, or with a lead attached to a galvanized-iron chain; no lead-line was used. Numerous borings were made in order to ascertain the character and stability of the foundation of the proposed breakwater.

The soundings are all referred to the plane of mean low water, which is 16 feet below the casemate of Fort Constitution; the tide-staff was placed on the wharf at Fort Constitution; the mean rise and fall of tide here is 8.6 feet.

The site of the proposed breakwater is a high ridge or bar connecting Gerrish's Island and Wood Island; the shortest distance between these two islands is, at high water, 1,330 feet; at mean low water, 872 feet; at extreme low water this bar is uncovered almost its whole length, leaving only a short run close to Wood Island, with not exceeding 24 feet of water in it for a distance of only 200 feet.

This bar consists of coarse shingle, intermixed with heavy bowlders, covering the ledge which is cropping out at numerous places above the 18-foot curve forming Wood Island, Whale's Back, White Island, Horn Island, and a number of rocky points dry at half tide, scattered between the high and low water lines of Gerrish's Island.

A careful comparison of the present survey with that of Capt. Howard Stansbury, United States Topographical Engineers, made thirty years ago, shows no change in the contour-lines, thus indicating that this bar has not been subjected to change during this period; the coarse material of which it is composed, and the easy slopes (line of greatest depression has an outward slope of 1:125, an inward of 1:37) promise a solid foundation and stability to the breakwater which may be built on the bar connecting Wood Island with Gerrish's Island.

The breakwater is proposed to be built of heavy rubble-stone work (riprap) throughout; the top to be 12 feet wide in rep, 16 feet above mean low water, or 7.4 feet above mean high water, which is very nearly the height of the adjoining shores of Gerrish's and Wood Islands, viz: 18.20 feet and 15.05 feet. The outward slope to be 1:2, the inner slope 1: 1. (See Figs. 1 and 2.)

The axis or midline of the top will be a straight line conforming as near as practicable to the line of highest elevation of the bar. Two holes drilled in the slid ledge, one on Gerrish's Island and one on Wood Island, mark this line, the direction of which is N. 39° 6' E., or N. E. & N., true bearing. The distance between these poiuts is 1,398 feet. The rock round the hole on Gerrish's Island is in ref 18.20 feet above mean low water; on Wood Island, 15.05.

The length of the breakwater on top will be 1,376 feet; for a distance of 556 feet the breakwater will rest on solid ledge; for a distance of 820 feet the foundation will be heavy bowlders and coarse shingle.

The estimate cost of the proposed breakwater is as follows: 23,000 cubic yards of riprap work, at $6 per cubic yard.. Contingencies, say.

Total cost of breakwater....

$138,000

12,000

150,000

The advantages to Portsmouth Harbor from this breakwater will be evident from the accompanying map of the harbor, in a scale of 1:20000.

A red dotted line is drawn from Wood Island through the northeast extremity of Great Island, (Fort Constitution ;) the part of the harbor on the northeast side of this line is at present very much exposed during southeasterly blows, especially at high tide, where a direct wave 1,300 feet in width enters the harbor between Wood and Gerrish's Islands, and renders this part of the harbor unsafe as an anchorage-ground. To be safe in a southeast gale, vessels must pass Fort Constitution and anchor up close to the north shore of Great Island, or close to the east shore of Clark's Island. By closing up the gap between Wood and Gerrish's Islands with a breakwater, as now proposed, the above-mentioned area between Wood Island, Fishing Island, and Kittery Point will be perfectly free from undertow, or an addition made to the valuable anchorage-ground of an area covering 612 acres at high water; the part of this area with more than 18 feet of water at mean low water (27 feet at high water) measures 270 acres.

Not only will this large part of the harbor be improved by the proposed breakwater, but the harbor between Fort Constitution and Clark's Island will, during southeast gales, be free from the swell which is at present produced by the spreading of the wave entering the harbor between Gerrish's and Wood Islands.

The building of the proposed breakwater will thus afford efficient protection to the numerous fishing-vessels and coasters using the outer part of Portsmouth Harbor as a harbor of refuge during southeast gales, and increased anchorage-ground will be obtained at a comparatively small expense.

Very respectfully, your obedient servant,

Bvt. Brig. Gen. GEO. THOM,

Lieut. Col. Corps of Engineers, Portland, Me.

SOPHUS HAAGENSEN,
Assistant Engineer.

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