1

bottom, and the space to the sand-rock filled with 8 to 10 inches in depth of stone and then run full of soft cement, so proceeding to the top, finishing the upper layers with brick, the grouting under the bottom of the sills filled between them to their tops, and the whole floor was covered with 4-inch plank, and timber placed over these plank, gained into the posts, to resist any upward pressure from beneath.

To secure perfect faces of sand-rock the width of the tunnel varied greatly, being from 10 to 90 feet, while its height was very constant, being about 16 feet. Whenever more than 20 feet wide, walls were constructed of heavy masonry to support the limestone overhead.

This plan was adopted for the reasons that it cost much less than a solid plug; could be put in in very much less time, and when in was available and, in fact, indispensable for drainage for the leakage while the Government work was in progress, and also to protect it from any damage from springs, as in all cases where any springs were found they were all incased in iron pipes and allowed to flow into the tunnel to prevent washing, and were outside the same.

Eight hundred feet of this lining has been finished in a very thorough manner, and a temporary bulk-head of timber put in about 600 feet from the lower end, in which there is an aperture sufficient for drainage.

The plan for preserving the timber is to put a bulk-head at the mouth of the tunnel, flowing it full of water, with outlet sufficient to remove

pressure.

Having this base of 800 feet for a bulk-head, the water can be held in perfect safety after the whole work is completed. This bulk-head is the next work that, in the opinion of the committee, should be done. In putting this in it is proposed to build of first-class masonry, extended across and connected with the sides of the tunnel in the most substantial manner, through which an iron tube is to be placed on a level with the bottom of the tunnel, provided with an iron gate sufficient to take off all the leakage from work in progress above. This, in case of break at the head of the ledge, will prove of vital importance in stopping the current of water, until such time as the same can again be stopped where it occurs.

The plan of this committee for the work above this bulk-head is as follows: To excavate all the débris from the breaks in the bed of the river between the islands, cutting out the sides and bottom, as within the tunnel, to the solid sandstone, then proceed with timber, plank, and filling of stone and grout next the sandstone on each side and on the bottom; this lining to be extended up as near to the head of the ledge on the west side of Nicollet Island as possible, and on the east side until connected with the walls now in at the head of the ledge there; a sewer to be constructed on the bottom, extending up to the Government work, of sufficient size for drainage purposes, then the whole basin between Hennepin and Nicollet Islands, and along the sides of Nicollet Island, to be filled with the best quality of gravel for puddling level with the surface of the limestone, and well secured with riprap. At the head of the ledge and in the bed of the river above all excavations and holes in the sandstone, caused by piers, logs, or any other cause that now exist, to be filled with best gravel and heavily riprapped, forming, in fact, a new bed to the river above the limestone.

It is estimated that the cost of completing the main bulk-head, the lining above the same, the building of the sewer and puddling with gravel up to the head of the ledge, will cost about $90,000, and the puddling and riprap in the bed of the river about $25,000.

We regard this work as indispensable to the preservation of the falls, and of the greatest immediate necessity. We also regard it as necessarily preliminary to the successful prosecution of the more elaborate work undertaken by the Government.

We further represent that the funds provided for this work have been nearly exhausted, and respectfully ask that the Government appropriation be devoted to the prosecution of the tunnel-lining and puddling the basin, and also the permanent bulk-head.

When all of this work has been completed, and the roll-dams contemplated in the plan of the apron have been built so as to cover the limestone with a sufficient depth of water to prevent the action of frost on the bed of the river, we think that the immediate danger to the falls will have been guarded against.

Having the utmost confidence in the executive ability of Mr. J. T. Stevens, who has had charge of the work on the apron and on the tunnel, we would respectfully and most earnestly recommend that he be continued in charge of the work, under the direction of the United States engineer in charge.

Attached, marked "A," find diagram of cross-sections of tunnel.
All of which is respectfully submitted.

S. W. FARNHAM,
R. J. BALDWIN,

S. H. CHUTE,

WILLIAM D. HALE,

Board of Construction.

H. T. WELLS,

O. A. PRAY,

PARIS GIBSON,

M. W. GETCHELL,
Union Committee.

D. MORRISON.

W. D. WASHBURN.
J. S. PILLSBURY.
RICHARD CHUTE.
W. W. EASTMAN.
GEO. A. CAMP.

GEO. H. KEITH.

JAMES A. LOVEJOY.
S. C. GALE.

H 15.

IMPROVING MINNESOTA RIVER.

SAINT PAUL, MINNESOTA, July, 1872.

COLONEL: I have the honor to submit the following report of operations for the improvement of the Minnesota River for the fiscal year ending June 30, 1872.

On the 1st of September, 1871, the contractor, Mr. S. A. Hooper, commenced the work of removing the bowlders that were left from our last winter's work, from the channel of the river between the mouth of Yellow Medicine River and Sacred Heart Reef. The river was at an excellent stage for our work, there being not more than eight inches of water on some of the reefs we encountered. The work progressed favor

ably, and on the 22d of September we had removed all of the bowlders, making a straight and wide channel through all the reefs between the mouth of the Yellow Medicine River and Sacred Heart Reef.

On the 23d of September we began work on the Sacred Heart Reef and continued the work at this point until the 12th of October, when the contractor suspended operations to prepare for his winter campaign and until the ice was strong enough for his men to work upon. The bowlders in Sacred Heart Reef were all removed except four, which were left until later in the season.

While the contractor was making his preparations for winter, I made a reconnaissance of the river to a point seven miles below Fort Ridgely, and found a great many bowlders and snags, also overhanging trees on the banks, and logs, which will soon form dangerous obstructions in the river.

On the 11th of December, 1871, we commenced work again on the bowlders remaining at Sacred Heart Reef and continued the work down the river, removing bowlders only, as far as Fort Ridgely. At this place I received a letter from you stating that our appropriation was nearly exbausted, and I stopped work on the 25th of January, 1872.

The year's work has been confined to the removal of bowlders, and the channel of the river, from the mouth of the Yellow Medicine to Fort Ridgely, a distance of seventy miles, is in an excellent condition as regards bowlders. There are a number of snags remaining between Sacred Heart Creek and Fort Ridgely, which we could not remove on account of the small amount of the appropriation left unexpended. I send herewith a statement showing the number of yards of bowlders removed.

All of which is respectfully submitted.

Your most obedient servant,

Col. J. N. MACOMB,

EDWIN BELL,

United States Inspector of Work.

Corps of Engineers, U. S. A., Rock Island, Illinois.

Statement of bowlder-work on the Minnesota River, to accompany the report of Captain E. Bell,

United States inspector.