REPORT OF CITY ENGINEER. OFFICE OF CITY ENGINEER, CITY HALL, JOHN A. HAVEN, Esq., BOSTON, May 1st, 1874. President of the Cochituate Water Board: SIR,-In compliance with the requirements of the ordinance on Engineer's Department, the following report, upon matters pertaining to water supply, is respectfully submitted :— SUDBURY RIVER AND LAKE COCHITUATE. No water has been drawn from the Sudbury river or Farm pond during the past year, the supply from the lake alone having proved sufficient for all purposes. In fact, as matters now are, no relief can be had from the river, even in case of a deficiency in the Cochituate supply. The monthly average heights of the water surface of the lake, above the bottom of the conduit, will be found in the table on page 38. On Jan. 1st, 1873, the water in Lake Cochituate stood at 12 feet 1 inch above the bottom of the conduit. At the beginning of the previous year there was no water in store, the conduit being then supplied by pumping from a level below its flow line. To maintain the supply, about 1,676,600,000 gallons were turned into the lake from Sudbury river; this, combined with the copious rains of the latter part of the year, brought the water level within about 15 inches of high-water mark at the beginning of 1873. From this date it rose gradually till Jan. 17th, when waste over the dam commenced, and continued till April 23d, the water then standing at 12 feet 111 inches. On May 4th, the stop planks were again removed, and the water allowed to waste, till May 20th. From this time till Aug. 14th it gradually fell, and at the latter date stood at 8 feet 7 inches; on Aug. 27th it stood at 8 feet 9 inches; Oct. 4th, 6 feet 8 inches; Oct. 10th, 7 feet 6 inches; Oct. 19th, 7 feet 3 inches; and on Dec. 31st, 9 feet 9 inches. To secure a flow that will supply the city with the rate of consumption of the past year, there are required from 6 to 71 feet of water above the bottom of the conduit; and, as in September there were less than 7 feet, fears were entertained that a resort to pumping would again be required, but fortunately heavy rains furnished the needed relief. The total waste over the dam for the year has been 2,917,977,000 gallons, equal to an average daily supply of 7,994,460 gallons. Had there been no aid from the Sudbury river the previous year, the waste in 1873 would have been equal to an average daily supply of about 3,400,000 gallons. This waste is due to the want of storage room. The lake is now (May 1st) full, and wasting largely. The town of Natick has obtained an act to take water for a domestic supply from Dug pond, and has recently decided to build works for elevating and distributing it. This will tend to diminish, somewhat, the supply for Boston, though a portion of the water will be received again by the lake in the form of sewage-water; but should a system of sewerage be carried out by the town, it may become necessary to divert even this portion, that the purity of the lake may be maintained. A table will be found on pages 36 and 37, giving, as has been customary, the rainfall on the lake water-shed, amount of water consumed and wasted, rise or fall of the lake-surface, and quantity of water and percentage of fall received into the lake. As has been stated in previous reports, the figures of this table are only approximate. Similar tables have been printed in the annual reports for a number of years past; and as the figures of these tables have lately acquired considerable importance from being quoted and used as a basis of computation in estimating the probable yield of other sources of supply, it is necessary to again call attention to the fact that they are not accurate, and unless used with a knowledge of the nature of their inaccuracy, will lead to fallacious conclusions. In the report of 1863, Mr. Crafts shows that for a number of years previous, the consumption (and consequently the yield of the lake) had been overestimated by a large percentage; and also states his belief, that even the method now used for computing the consumption gives a result considerably in excess. As was said in the last annual report: Although it would cost a considerable sum to provide the means for properly measuring the flow in the conduit, the water at the dam, the average rainfall for the entire water-shed, etc., yet the value of the results to be obtained from reliable measurements would fully warrant the necessary expenditure ; " and the experience of the last twelve months is strongly confirmatory of this opinion. Conduit. On Nov. 19th and 20th, a thorough examination of the interior of the conduit was made by Mr. Wiggin, Clerk of the Water Board, and others, who passed through its entire length from the lake to Chestnut Hill reservoir. A detailed report of this examination, made by Mr. D. W. Cunningham, will be found in City Doc. No. 134, 1873. A number of new and dangerous cracks were discovered; those on the embankment to the west of Charles river were of such alarming character that it was considered imperative they should be repaired at once; accordingly, the water was kept shut off, and a force of masons put at work night and day, until temporary security was ensured. At this point there was found a crack in the bottom, varying in width from 1 to 11⁄2 inch, and 200 feet long, through which an iron rod readily passed and penetrated the gravel filling below. The leakage here must have been considerable, but it did not make its appearance at the surface of the bank, owing to the very porous nature of the material forming it. The repairs made in no way add to the strength of the conduit; the best that could be done was to stop the leakage, and thus remove for a while the danger of undermining the masonry. A new examination has been made this spring (April 14th), which shows that changes in the form of the conduit continue to take place. The crack on the embankment to the west of Charles river, mentioned above, has again opened nearly its whole length, to a width of from to inch. The water in the conduit was drawn down to a less depth than for the examinations of the past two or three years; and the upper reach near the lake was more carefully examined. A number of large springs were found coming up through the masonry of the bottom, and in a number of places the cement was entirely washed from the joints, and the bricks were loose. These springs bring in large quantities of sand; and it is reasonable to suppose that the masonry is slowly undermined and allowed to settle and break up. The bottom, judging from the depth of water at different points, is quite uneven, and the unevenness is probably due to settlements. In former years, when the consumption in the city was much less than now, it was the custom to draw the water out of the conduit a number of times in each year, and to patch up the cracks with cement, or by driving in pine wedges where springs prevented the use of cement. In |