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The accompanying letter (marked D) shows the object of the examination of this river, and the commerce of the river that would be benefited by an improvement of the same. Respectfully submitted.

GEO. THOM,
Colonel of Engineers,

But. Brig. Gen., U. S. A. Brig. Gen. H. G. WRIGHT,

Chief of Engineers, U. 8. A.

REPORTS OF MR. SOPHUS HAAGENSEN, ASSISTANT ENGINEER.

A.

UNITED STATES ENGINEER OFFICE,

Boston, Mass., December 3, 1881. GENERAL: I have the honor to report upon the examination of Merrimac River between the head of Mitchell's Falls, below Lawrence, Mass., to Manchester, N. H., made in pursuance of your written instructions dated July 27, 1881.

I first visited the offices of the water-power companies on the river, in Lawrence, Lowell, and Manchester, to learn what surveys were already in existence that would throw any light upon the present examination and facilitate the work.

I found that complete shore line surveys for the purpose of determining flowage lines had been made, embracing the whole length of the river in question (50 miles); also levels connecting with those of the United States Engineers at the miter sill of the lower lock in Lawrence to Pawtucket Dam at Lowell.

As the hydraulic engineers of the water-power companies generously allowed the government the gratuitous use of this information, you decided that in addition to the copying of said surveys a general hydrographic survey of the river should be made with more minute examinations of the obstructions met with; also independent levelings of the falls above Lowell mill-pond up to Manchester, as well as the establishment of gauges and benches for future reference. This work I commenced on August 10, and completed it October 4. The maps copied were as follows:

In the office of Essex Company, Lawrence, Mass.: 1. Map of river from head of Mitchell's Falls to lower locks, Lawrence, with horizontal

contours (1 foot equidistant) of parts of the bottom, by H.-F. Mills, 1876. Scale,

1:2400. 2. Map of river from lower locks, Lawrence, to Lawrence Dam, with horizontal con

tours (1 foot equidistant) of the bottom, by H. F. Mills. Scale, 1:1200. 3. Maps of shore and flowage lines between Lawrence and Lowell (in six sheets).

Scale, 1:3000. 4 Map of shore and flowage lines between Lawrence and Lowell. Scale, 1:12000. 5. Protile of river slope between head of Mitchell's Falls and Pawtucket Dam. Divers

scales.

In the office of Proprietors' Locks and Canals, Lowell, Mass. : 6. (a) Shore lines of upper part of Hunt's Falls, by A. H. Howland, 1871. Scale,

1:600.

(b) Cross-section of same. Scale, 1:300, 1:120. 7. Merrimac River, between Pawtucket Falls and Cromwell's Falls (Lowell mill-pond),

by U. A. Boyden, 1840. Scale, 1:4800.

In the office of Amoskeag Company, Manchester, N. H.: 8. Merrimac River, from Cromwell's Falls to Manchester, N. H., by A. M. Chapin),

1865. Scale, 1:9600. Besides minor plans and printed maps obtained, as well as gauge observations at

Lowell and Lawrence, records of freshets, heights, &c. My own investigations consisted of a thorough soundiug of the river, in which the sounding boat was run on lines from shore to shore perpendicular to the axis of the stream, soundings being taken at equal intervals of time and recorded. Gauge observations were made at the same time. The iutervals between the lines of sounding vary from 600 feet to 100 feet (and even less), according to the depth met with, the shoaler portions being covered more closely than the deep basips.

The lines of sounding were tied to a continuous chain measurement of the shore.

Material was thus collected for the construction of a complete bydrographic map of the river.

*

In the several falls special examinations were made, the details of which have been reported to yon from time to time.

Obstructions to navigation in the shape of bowlders, points of ledges, &c., were examined, and, where practicable, measured. As the river was low during the work and special examiuations as far as possible made at times when little or no mill-water was running, it is believed that most of the sunken rocks requiring removal have been noticed.

Levelings in Hunt's Falls * connect with the zero of Essex Company, and of proprietors' locks and canals' scales of heights throngh the upper and lower monuments (respectively at the head and foot of Hunt's Falls), established by Commissioners to determine the rights of flowage by the Lawrence Dam at certain stages of the river.

Above Pawtucket Dam, levels commence at the foot of Cromwell's Falls (where the Lowell mill-pond ends), 174 miles above Lowell, and they were carried continuonsly up to the top of Amoskeag Dam in Manchester, a distance of 14 miles ; they were checked by releveling from Amoskeag Dam to the starting point;t they also connect with the Amoskeag base. It was not deemed advisable to ascertain by spirit level the fall of the river on the Lowell mill-pond, involving the running of 354 miles of level lines. For the purposes of navigation this part of the river is practically level. For the sake of referring the heights above Cromwell's Falls to the United States Engineers datum plane, the surface of the mill-pond has been considered horizontal on Sunday, September 16, 1881, at 2 p. m., the most favorable opportunity which presented itself. Should these 354 miles of levels be run, it is possible that a correction (the adding of a constant) will have to be applied to the heights above Cromwell's Falls, as given on the accompanying drawing No. II.

The slope of the river, represented in profile on this map, has been constructed from simultaneous observations on the gauges established, and corresponds to the average height prevailing during the survey (mill-water running), and I have called it the stage of ordinary low-water with mill-water running.

Map No. II gives, besides the slope of the river, the heights of gauges, bench-marks, &c. ; also the location of the various obstructions referred to in the estimate. The heights are drawn to scale 1:100; the horizontal distances have for the sake of clearness not been drawn to scale, but are stated in number at the foot of the sheet.

The working up of the first-mentioned eight sets of maps to a nniform scale, and the plotting of the hydrographic survey thereupon, has not been attempted on account of the limited time; only in places where improvements are needed have the soundings been plotted, especially so below Lawrence, at Gage's Ferry Shoal, and at Andover Bar, and between Lawrence and Lowell in Hunt's Falls, and adjoining parts of Merrimac and Concord rivers.

The map of Hunt's Falls (No. 1), with proposed improvements, has been already forwarded to you with a special report dated November 9, 1881.

In other parts of the river the notes only have been referred to, so as to report intelligently upon the channel.

The navigation of Merrimac River above Haverhill, Mass., has, since the opening of the channels through Mitchell's Falls, been practicable to the head of those falls for craft drawing 44 feet of water in ordinary low-water with mill-water running.

To further extend this channel to the locks in Lawrence, it is only necessary to deepen it at two places, namely, Gage's Ferry Shoal and Andover Bar, and to remove a small quantity of rocks at a comparatively slight expense (soe special report herewith of October 15, marked B).

Since the opening of the channel through Mitchell's Upper Falls the effect of the tide is perceptibly felt above, in the difference of velocities during ebb and flood, so that tidewater now virtually extends to Lawrence.

To carry navigation above Lawrence a fall of 314 feet has to be overcome from the Jower lock to the mill-pond above Lawrence Dam. The locks in Lawrence Canal are 20 feet wide, 100 feet long, and they admit 2.6 feet draught over the miter sill of the lower lock; should this condition be altered either by lowering the miter sill to the requisite depth or by building a new lock in front of the present one with its miter sill at the proper grade, there are yet many impediments to the navigation of such craft as could be navigated above the Lawrence Dam. The streets in Lawrence, the gas and water mains cross the canal on bridges which leave only 3 feet space between them and the canal level. To provide these bridges with suitable draws, and to carry the gas and water in syphons below the canal bottom, will be so expensive that the question arises whether it would not be more profitable to construct a new canal and locks on the south side of the river.

Above Lawrence Dam there is no obstruction in the form of shoals or bars to a 4-foot channel as far as Hunt's Falls; only scattered rocks need be removed, beginning 7 miles above Lawrence Dam.

*This set of levels check with Commissioners' levels witbin 0.03 foot. + Checking within 0.09 foot.

At Hunt's Falls, 9 miles above Lawrence Dam, there is a fall of 11 feet to overcome in a length of 5,700 feet. Different plans of making these falls navigable have been discussed in special report dated November 9, 1881. Considering the immense value of the water power in Lowell, and tbat any works built in the river for the purpose of procuring slackwater navigation would tend to reduce the area of cross-section, and thus damage the water power by raising the river, it appears to me the most feasible way to excavate straight channels through the chutes in Hunt's Falls, and by stationary engines on the shore to hanl the vessels or barges over the falls.

Above Hunt's Falls there is a fine basin with deep water in the city of Lowell; it extends for about a mile to a distance of 11 miles from Lawrence Dam ; three-fourths mile beyond is the Pawtucket Dam and the Lowell mill-pond, the surface of which is 365 feet above the basin !elow.

To further extend navigation above the Pawtucket Dam in Lowell, the Pawtucket Canal is available for craft drawing 3 feet and of 12 feet width, the lock chambers being 100 feet long. This canal is entered by the Concord River, which joins the Merrimac directly above Hunt's Falls. Between the entrance to Pawtucket Canal and the month of Concord River there are still some slight rapids where additional excavation would have to be done to make a channel 3 feet dieep.

As the same difficulties exist in the Pawtucket Canal as in the Lawrence Canal, in regard to streets, water and gas mains crossing the canal at a low grade, it is perhaps worth considering whether a new set of locks and a canal from the head of the basin three-fourths mile below Pawtucket Dam to the mill-pond above could not be so located as to avoid the cost of changing existing bridges, streets, &c., in Lowell; and at the same time provide for greater width of lock chamber than 12 feet, which is the minimum width the present laws of Massachusetts oblige the canal company to maintain. The depth of 3 feet which the Pawtucket Canal Company maintains in the Jocks might in a new canal be increased to continue 4-foot navigation above Lowell to Nashua, N. H., where the channel is deep enongh now.

Between Lowell and Nashua the river is deep and there is no less depth in the channel than 8 feet on this distance of 134 miles. The opportunities for traffic by water between these two cities compare favorably with those vetween Newburyport and Haverhill, and very little improvement is needed to make it safe. Opposite Tyng's Island, about 41 miles above Lowell, we meet with the Old Wiscassee Dam, which is now submerged and has from 1 to 2 feet of water over it; but a passage has been cleared through it, 10 feet deep, which only needs to be properly buoyed out. Some rocks and a point of ledge below this old dam require removal.

A short distance above Tyngsborough Bridge, about 64 miles from Lowell, bowlders need removal.

Two ledges and a rock below Nashua should also be removed to make this part of the river safe to navigate.

Above Nashua the channel becomes shoaler and the rocks more frequent; 44 miles above Nashua (or 174 iniles above Pawtucket Dam) the smooth water of Lowell millpond ends and a series of falls and rips commence, which continue up to Manchester, N. H., with intervening pools.

The rise on this part of the river is as follows:

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From foot of Cromwell's Falls to foot of Moore's Falls
Fruto foot of Moore's Falls to foot of Little Cobass Falls.
From foot of Little Cohass Falls to foot of Goff's Falls.
From foot of Goff's Falls to foot of Short Falls
From foot of Short Falls to foot of Griffin's Falls
From foot of Griffin's Falls to foot of Merrill's Falls
From foot of Merrill's Falls to head of Merrill's Falls.
From foot of Cromwell's Falls (elev. 93.01) to head of Merrill's Falls (elev. 126.17).

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I. t., from Manchester, the river falls 331 feet in 13 miles.

The top of Amoskeag Dam (elevation 177.99) is again 51.82 feet above the head of Merrill's Falls.

It is not practicable to make these several falls navigable by excavation of chandels in the rapids. Cromwell's Falls, and perhaps Short Falls, might, by a large outlay of money, be treated so that stationary engines could help barges through the rapids. The only practicable way is to restore slackwater navigation on this part of the river by means of locks and wing-walls parallel to the shore, transferring the upper levels to the locks at the lower levels.

The river, before the building of the railways, was navigated from Boston via the old Middlesex Canal to Lowell, thence to Manchester and above to Concord, N. H.

Remains of the locks and wing-walls, by which the falls were then overcome, still exist in the river, and the present project contemplates their restoration, with little or no change in location. The canal-boats at that time were 8 feet wide, 80 feet long, and the dimensions of the locks were suited to admit these boats. If restored, the locks should be 20 feet wide and 100 feet long, allowing a draught of 3 feet, for which the following estimate has been made. The locks were formerly built of granite, in a very solid manner, and some of the old lock-walls are yet in a good state of preservation, especially so in Griffin's Falls. The wing-walls and dams were made of crib. work, and are now nearly all razed to the low-water line. The locks should be rebuilt in solid granite masonry, the stone doweled together. To build the wing-walls and dams of solid granite inasonry would secure permanent works; but the cost of it would be so greatly in excess of crib-work (excess estinated at $690,000) that it is thought crib-work for the wing-walls and dams (where the latter are needed) would answer the prrpose, if damage done by ice freshets was promptly repaired.

To secure a navigable channel 3 feet deep between the falls it will be necessary to remove a great many bowlders in places specified in the following estimate.

In Cromwell's Falls the wing-wall should be carried a distance of 900 feet from the entrance to the lock (to B 13), and there cross the river as a dam, instead of being carried through the upper part of the falls for an additional distance of 21,000 feet.

The bar above Ram Rock, between Little Cohass Falls and Goff's Falls, is one of the worst places in the river; if a dam could be built at Little Cohass Falls, the water could be raised sufficiently on the bar to give 3 feet navigation; but this would, at the same time, back the water up at least 1 foot (more at high stages of the river) in front of the mills on Great Cohass Brook; and the damage to this water power would probably exceed the cost of clearing an artiticial channel through the bar, which consists of heavy bowlders, and no doubt would maintain its depth if excavated. The estimate has been made for such a channel.

At Goff's Falls ledges run across the river; at the most favorable place to pass the ledge, and directly above the proposed lock site, its elevation is 115.56, while the water level of the pool above is only 14 feet higher (117.06). A channel through this ledge would be very expensive, and as the river channel' between Goff's Falls and Short Falls is shallow, it will be preferable to raise the level above Goff's Falls by closing up the gaps between the ledges by dams having a least elevation of 118.56.

At the head of Baker's Island, above Griffin's Falls, the navigation is again difficolt; here a shifting gravel bar obstructs the passage; there is, however, depth enough in the gulley, but this is narrow and may change its location through the bar. It should be watched, and its location marked by buoys or shore. ranges.

Between Merrill's Falls, in the city of Manchester, and the head of navigation, near the new iron bridge (McGregor Bridge), is still a small fall of about one-half a foot, caused by the rocky bar below Factory Bridge. A channel can be cleared here by the removal of bowlders.

The estimated cost of the various improvements is given below in tabular form.

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Estimated cost of making the channel of Merrimao River navigable between Mitchell's Falls, below Lawrence, Mass., and Manchester, N. H.

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BETWEEN MITCHELL'S FALLS AND LAWRENCE.
Ledge below Gage's Ferry.
Gage's Ferry Shoal.
Ledge above Gage's Ferry
Ledge in mid-channel.
Andover Bar
Bowlder at Spicket River

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Bowlders in channel below Hunt's Falls.
Channel in Hunt's Falls, Lower Chute
Channel in Hunt's Falls, Upper Chute.
Channel at mouth of Concord River

BETWEEN LOWELL, MASS., AND NASHUA, N. H.
Rocks below Wiscassee Dam
Ledge at Wiscassee Dam...
Rocks at Tyngsborough Bridge.
Ledge above Little's Station.
Pierce's Ledge
Rock below Nashua

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Locks and crib

work.

Ledge.

Obstructions.

Price per cubic

yard.

Canal wall.

Cubio yards.

Locks.

BETWEEN LAWRENCE AND LOWELL.

.

BETWEEN NASHUA AND MANCHESTER, N. H.
Rocks near Hill's Ferry
Salmon Walls
Old Darrah
Rocks off Whiting's Point

..

92
84
116
500

.

5 00
5 00
5 00
5 00

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