Tulsi, in the island of Salsette, five miles south-west of Bhandup station on the Peninsula railway, three miles north of Vehar, and: about two miles south of the Kanheri caves, has an artificial lake and water-works, which provide part of the water-supply of the city of Bombay. The lake lies in a narrow valley surrounded by hills, whose steep wooded slopes rise about 800 feet above the level of the water. It has an area of 331 acres and a gathering-ground of about 1450 acres. When full, its surface is 452.50 feet above the Bombay Town Hall datura and 37236 feet above mean sea level. The water can be drawn off to a depth 53.14 feet below the highest level, the difference representing 1949 million gallons of water. It is estimated to supply 160,000 of the population of Bombay with a daily allowance of thirty-five gallons a head.

From the engineer's house, on a knoll about 200 feet above the water near the centre of the rugged north bank, Tulsi and the entire length of Vehar stretch southward like one great lake crossed by a bar of woodland. From the north-west and from the north-east two rugged ranges of teak and brushwood-covered hills, from 500 to 800 feet high, draw together with a rapid curve. As they come near each other, the hills fall to the lake with graceful outline, and again rise in two wooded knolls which are separated by a low belt of deep forest. On the further side of this belt of wood the wild hills and forests of Tulsi give place to the woody islets and the low eastern bank of Vehar, and, beyond Vehar, dim rice-fields and salt wastes stretch to the chimneys and towers and the sea-girt palm-groves of Bombay.

In [Contributed by Mr. J. W. Smith, C.E,, Resident Engineer, Bombay Municipality.] 1865 a commission appointed to enquire into the Vehar water-supply, reported that it was not enough to meet the wants of the growing population of Bombay, and recommended further surveys. The surveys were made by Mr. Russel Aitken, executive engineer to the Municipality, and they occupied about two years and a half. Mr. Aitken proposed several schemes for new reservoirs, and one of these was the Tulsi project. His idea was to throw a dam across the river Tassu just below the village of Tulsi, and cut oft' its waters from the Kanheri valley and turn them south into the Vehar lake. Government appointed a second commission to consider the proposed schemes. In July 1869, the commission recommended the adoption of the Tulsi scheme as an auxiliary supply to Vehar. At the same time they noticed that the scheme would yield only temporary relief, and suggested that further surveys should be undertaken to find a low level reservoir from which water could be brought by a covered masonry conduit to Bombay. Additional surveys were undertaken by Captain, now Colonel, Tulloch, R. E., then executive engineer to the Municipality.

Meanwhile, the short rainfall of 1871 caused much distress in Bombay, and Dr. Thomas Blaney urged the necessity of carrying out the Tulsi project as an auxiliary to Vehar. His proposal was adopted in November 1871. In April 1872, with the approval of Government, the works were begun under the control of Mr. Rienzi Walton, C.E. They consisted of a masonry dam across the river Tassu, of a tunnel under the ridge that divides Tulsi from Vehar, and of an open cutting or channel from the dam to the northern mouth of the tunnel.

Northwards from the upper end of Vehar, the ground gradually rises to Tulsi. At a short distance from Tulsi the ascent is steep, and then the slope falls in the opposite direction towards the Kanheri valley. Here the Tassu takes its rise, and, following the slope of the ground, flows west down the Kanheri valley, away from Vehar. A masonry dam was accordingly built at the lowest end of the Tulsi lake, and an open cutting and tunnel made to carry the water back to Vehar. The dam is a fine piece of engineering. It is 600 feet long, and at one part is eighty feet high. The thickness at the base of the highest part is fifty feet and the width at six feet below the top nineteen feet. The additional six feet of height, which has been recently added, consists of a supplemental wall six feet thick at the base and two feet thick at the top. The level of the top of the supplemental wall is 456 feet above Town Hall down or 375-86 feet above mean sea level. The form of the original section was suggested by Professor W. J. Macquorn Rankine of the University of Glasgow. The works, exclusive of the supplemental wall, were completed by June 1874, at a cost of 45,000 (Rs. 4,50,000).

The want of sufficient pressure to supply the higher parts of Bombay was found greatly to mar the completeness of the Vehar scheme. To remedy this it was agreed that the Tulsi lake, instead of being auxiliary to Vehar, should be made an independent source of supply. The further works required for this purpose were begun early in 1877. They consisted of a dam on the ridge between Tulsi and Vehar, a waste-weir, an outlet tower, and a twenty-four inch main from Tulsi to Bombay. This dam of earth, with a puddle wall in the middle, was 1463 feet long, and had an extreme width of 160 and a mean width of 123.5 feet, the area of the whole site occupied by the dam being about 20,000 square yards. The dam has been recently raised; and, in carrying out the work, the length has been increased to 1537 feet, the extreme width to 232 feet, the mean width to 148 feet, and the site occupied to about 24,000 square yards. The maximum height of the dam is now twenty-eight feet, and the uniform width on the top is eighteen feet. The level of the top is 458.50 feet above Town Hall datum. The puddle wall is ten feet thick at the bottom and eight feet thick at the top. The slopes on both sides are three to one, and they, together with the top, are protected with stone pitching. The waste-weir, which is near the west end of the new dam, is in the solid rock, at the level of 443.50 feet above Town Hall datum. By means of planking let into grooved iron standards built into a masonry wall that runs across the narrowest part of the weir, the level is raised to 452.50 feet. In case of need the planking can be easily removed and the level of the water rapidly lowered. The water-way at its narrowest part is 138 feet wide. The banks are protected on both sides by masonry walls.

The outlet tower is built of ashlar masonry on a foundation of natural rock at the meeting of the open cutting and the tunnel. The water enters the tower through four cast-iron tubular bends forty-eight inches in diameter, placed 438.50, 42500, 411.33, and 39936 feet above the Town Hall datum. The bends are closed by heavy ball valves actuated from the platform of the tower. When open the valves are covered with strainers of fine copper-wire gauze. At the bottom of the tower is the up-turned end of a forty-two inch cast-iron pipe which runs through the tunnel, and, as it leaves, divides into two twenty-four inch pipes. One of these is continued about 100 feet and ends in the bottom of the ravine. The other is carried along the west side of the Vehar lake by Marol, Shahar, Koli-Kalyan, and Bandra, over the creek between Salsette and Bombay at the side of the Baroda railway. It then follows the line of rail to Mahim and Dadar, crosses the flats to Mahalakshmi, and, passing over Khambala hill by the new Pedder road and to the top of Malabar hill by the new Gibbs road, ends at the Malabar hill reservoir, eighteen miles from Tulsi. For a great part of the distance the main is laid on a low embankment with many small bridges. It is divided into several sections by sluice valves over which sluice houses have been built. These works were designed by Mr. Rienzi Walton, C.E., executive engineer to the Municipality, and most of them were carried out by Messrs. Scott McClelland & Co., contractors, represented by Mr. John Campbell. The outlay, including the supplemental wall on the masonry dam, and the raising of the earthen dam and the waste-weir, has been about 337,000 (Rs. 33,70,000).

The works were opened and Tulsi water first admitted into Bombay on March 15th 1879, by His Excellency Sir Richard Temple, Bart., G.C.S.I., Governor of Bombay. The ceremony took place on the ridge at Malabar hill, near a reservoir which has been designed by Mr. Rienzi Walton to regulate the outturn, prevent varying pressure in the main, and ensure a supply of water in case of accidents to the main. Filter beds will be attached to the reservoir, and it will probably be partially covered. From the reservoir, distribution mains are laid over Malabar hill, but the chief main runs down the steep eastern face of the hill to Chaupati, and supplies various parts of the city. The water, by means of a by-pass, can be made to flow straight from the supply main into the distribution mains. Connections have been made between the Tulsi and Vehar distribution mains, so that the water from either lake can be turned into them at pleasure.

The internal length of the Malabar hill reservoir is 735 feet, its mean width 296 feet, and its area five acres. The depth of water is nineteen feet three inches. After allowing for divisional walls and inlet and outlet arrangements, the capacity is about twenty-five million gallons. The level of the surface of the water is 256 feet above Town Hall datum. The outlay will be about 37,500 (Rs. 3,75,000). This includes the cost of Pedder road over the ridge of Khambala hill and Gibbs road from Gowalia tank road to the ridge of Malabar hill, along which roads the supply main has been brought by a direct route from Mahalakshmi. These thoroughfares were much needed, and have proved very useful. Part of the Gibbs road consists of a handsome masonry viaduct, which crosses the steep path up which the Parsis carry their dead to the Towers of Silence.