Details of Charles River Dam.

The Charles River Basin Commission has advertised for bids on its contract for the dam which is to turn the Charles river into a freshwater basin unaffected by the tides. The dam will be built on the present site of Craigie bridge, and its total length will be 1300 feet, the width varying from 140 to 490 feet. It will consist of two masonry retaining walls on pole foundations, the space between them being filled with earth to a depth of from 15 to 50 feet. At the ends 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 contracts call for completion of the work by July, 1908.

The engineers of the Commission have made the following calculations: earth excavation, 340,000 cubic yards; filling, 400,000 cubic yards; concrete masonry, 41,000 cubic yards; piling, 490,000 linear feet; pine lumber, 1,100,000 feet; spruce lumber, 550,000 feet; riprap, 10,000 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 be also 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.

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.

The benefits of the basin will be realized much sooner than was anticipated by the petitioners who secured the legislative act authorizing the work. 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. Rowing men of the present Freshman class, therefore, will be able to enjoy, for a year at least, the advantages of the greater depth of water and the absence of tidal currents, which, in the spring and fall create much rough water when flowing against the prevailing winds.

As a result of the proposed improvements o the basin, plans for the improvement of the bridges below the University boathouse have been definitely arranged. The Longwood bridge and the low railroad bride beside it will both be raised under authority of an act passed this year by the last state legislature. A new and wider bridge will 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