CHARLES RIVER BASIN

The Charles River Basin Commission awarded the contract for building the dam and lock in the Charles River to the Holbrook, Cabot, and Rollins Corporation. The basis of the award was $801,-507.50. In the work so far piles have been driven under the lock in the Boston cofferdam and under the sluices in the Cambridge cofferdam. A few piles also have been driven along the sea wall and in the canals to strengthen them in order that the dredging may be carried to a greater depth.

At the new Cambridge Bridge, farther up the river, the greatest activity at present is in making ready the Cambridge approach. From First street, where a subway is being constructed under the bridge incline, as far back as Third street. Main street is torn up, though a passage for street cars and teaming is still kept open. The work aims to make Main street, beginning at Kendall square, steadily wider and wider until, as it reaches the bridge, it shall have the full width of the bridge structure, 105 feet. This has made it necessary to set back the boiler shops and iron-working establishments on the westerly side of Main street some distance from their old position; but the relocation has been accomplished, and gangs of men are now at work grading and paving that side of the thoroughfare to make it harmonize with the new plans.

On the Boston approach the work has not yet touched Cambridge street anywhere on the landward side of Charles street. It is expected, however, that Cambridge street will be widened in much the same fashion as Main street, and be made to spread out from the corner of Grove street until it reaches the bridge structure with the desired width of 105 feet.

As a result of the attempt to improve the basin, the Longwood bridge and the low railroad bridge beside it has been raised under authority of an act passed by the legislature of 1904. A new and wider bridge will also be built connecting Boylston street, Cambridge, with Harvard street, Allston, thus affording a better approach to Soldiers Field. The act authorizing this bridge was also passed by the legislature of 1904.

As previously announced the dam is being built on the present site of the Craigie bridge, and its total length when completed will be 1300 feet, the width varying from 340 to 490 feet. It will consist of two masonry retaining walls on pile foundations, the space between them being filled with earth to a depth of from 15 to 50 feet. The height of the dam will be 21 feet above mean low water, about the present level of the street at the Cambridge end of Craigie bridge.

On the lower side of the dam there will be a roadway 85 feet wide, and on the upper side a park or embankment of 6 3-4 acres. There will also be an esplanade constructed by the City of Boston, extending from Charles Bank park to Charlesgate East, making a drive and walks in the rear of Brimmer and Beacon streets. On the Cambridge side an embankment park, for which the land has already been purchased, will come nearly to the dam. The contract calls for the completion of the work by July 15, 1908.

The calculations for the work are as follows: earth excavation, 340,000 cubic yards; masonry, 43,825 cubic yards; filling, 390,000 cubic yards; piling, 470,000 linear feet; pine lumber, 235,000 feet; spruce lumber, 550,000 feet; riff raff, 9, 700 tons. There will be two locks in the dam, the larger being 350 feet in length and 45 feet wide, and of sufficient depth to allow a vessel drawing 16 feet of water to pass through at low tide. The smaller lock will be suitable for launches and row boats. Eight sluices will be provided, and in emergencies the smaller lock will be used as a flood-sluice for letting water out of the basin. There will also be outlets for marginal conduits, through which all sewage overflow, which now goes into the basin in times of heavy rain storms, will be carried down to tide water. At present about 1800 feet of the marginal conduits on the Boston side has been completed.

The dam will maintain a basin 8 miles long, and will affect the level of the water as far as the dam at Watertown. There will be 17 1-2 miles of shore-line, nearly all of which will be devoted to park purposes, the land having been purchased by the Metropolitan Park Commission and the City of Cambridge. The level of the basin will be about 2 feet below the present mean high tide level. Part of the engineering scheme for the construction of the dam provides for a temporary shut-off which will establish the level of the basin at about the same level as the permanent structure. The terms of the contract call for the completion of this shut-off dam by August 1, 1907.

The commission in charge of the work consists of President H. S. Pritchett of the Massachusetts Institute of Technology, Hon. H. D. Yerxa, and Hon. J. B. Holden L.'71. H. A. Miller is chief engineer.