5

H.—34

Malvern Water-race. —This water-race receives its supply from the River Kowai, which is a tributary of the Waimakariri Eiver. The head-works consist of a concrete weir or dam across the bed of the river, which raises the water about 10ft. above its normal height. The bed of the river is a mass of moving shingle, and in order to prevent this from getting into the water-race, a tunnel forty-six chains in length is constructed at right angles to the bed of the river, through a high terrace forming the right bank of the river, and is lined with concrete and brick. At the entrance of this tunnel two bywash-gates in the weir are placed close to the sluice-intake gate, which is set iu concrete at the mouth of the tunnel. These bywash-gates carry away all the surplus water in the river in ordinary weather, and prevent the shingle accumulating at the entrance-gate of the tunnel, and also act as regulating-gates for keeping the water up to a certain level. The entrance-gates at the mouth of the tunnel are fitted with screw-lifts, so as to gauge the quantity of water to be admitted. During floods the surplus water that cannot pass through the bywash-gates goes over the top of the weir. At the lower end of the tunnel the water flows in an open conduit for ten miles, where it is divided into two main branches, the first branch being twelve miles in length, at the end of which the water is again divided into five branches. The second branch is twenty-two miles in length, and from it at intervals four branch races are taken, which are in the aggregate twenty-nine miles in length; the total length of the main and branch supplies being ninety-one miles. The water from these branch supplies is conveyed in distributing-channels, which form an aggregate length of about five hundred miles, and carry the water through almost every section of land in the district. The dimensions of the water-races are as follows : Main supply, 14ft. wide, capable of carrying water lft. deep; No. 1 Branch, Bft. wide by lft. deep for twelve miles, afterwards 6ft. wide by lft. deep; No. 2 Branch, Bft. wide by lft. deep for the first seven miles, a.nd 6ft. wide by lft. deep for the remainder of the distance. The branch races are all 2ft. wide by lft. deep. The fall or inclination from the head-works in the main race is 30ft., No. 1 Branch 37^ft., and No. 2 Branch 40ft. per mile. The fall in the branch races is various, according to the direction in which they extend : those flowing in a southerly direction have about 25ft., and those flowing in an easterly direction about 15ft. per mile. Concrete falls, with aprons of grouted boulders, are placed at regular intervals in the main race, and similar falls made of wood are constructed across No. 1 and No. 2 Branches, to reduce the velocity of the current, which is limited to about 3ft. per second. The carrying capacity of the tunnel and main race, with the first two branches, is calculated at 18,000,000ga1. of water in twenty-four hours, or 12,500ga1. per minute. A flow through the headworks of 7,400ga1. per minute has been found sufficient for all requirements in ordinary weather ; but during the prevailing north-west winds, when the season is hot and dry, it requires about 8,600ga1. per minute to provide for increased percolation and evaporation. The area of the district which is watered by this supply is 102,813 acres. The district is divided into blocks of land, containing about fifteen hundred acres each, and each block is entitled to receive and be supplied with a separate gauge, which is taken from the main or branch supplies according to the circumstances of the case ; but a supply is not granted until the necessary application-form is signed by the proprietors of the land within the block proposed to be watered, in accordance with the water-race by-laws of the county. The total cost of these works was about £20,460. Oreendale Water-race. —The supply of water for this race is taken from the Hawkins Eiver, which is a tributary of the Selwyn Eiver. The head-works consist of a concrete chamber 6ft. square, into which a supply of water is led, by means of a sluice-box, from the river. From this tank or chamber earthenware pipes are laid for about two chains into an open ditch. The water is gauged by means of a sluice-gate in the chamber, which is worked with a screw-lift. The dimensions of the main channel are 2ft. wide, capable of carrying water lft. deep, and from the end of the main channel there are two branches. The water is simply allowed to flow in a sinuous course through the land to be benefited by means of the main race and the two branches, which nearly run through the whole district; the length of the channels being twenty-two miles, and the fall averaging about 30ft. per mile. The carrying capacity of the main and branch races is calculated to be l;850gal. per minute, but the quantity of water ordinarily flowing is about 750ga1. per minute. There are no gauges in use except in the head-works. The cost of the head-works and the first three miles of the race was £202, the remainder of it being constructed by the proprietors of the land. The area of land watered is 10,400 acres. Waireka Water-race. —This is a race similar to the Greendale Water-race. The supply is taken from the Selwyn Eiver by having a wooden culvert laid in the ground for about 84ft. in length, and connected with the river at the upper end and with an open channel at the lower end, a sluice-gate being fixed at the inlet end of the box to admit and regulate the water into the open channel. The main channel is 2ft. wide and lft. deep for the first mile and a half, and lft. 6in. wide by lft. deep for the next mile and a half. The distributing-channels are only in course of construction, but when completed will be about twenty miles in length. The cost of the head-works and first 2 miles 10 chains of water-race was £158 ; the remainder of the distance has to be constructed by the proprietors of the land that the supply will benefit. The area of the district that this supply will water is 6,178 acres. Hororata Water race. —There are two water-supplies in the Hororata District, which comprise about ninety-six miles of main channels. No. 1 supply is thirty miles long, in two branches, and has a carrying capacity of 700gal. of water per minute. No. 2 supply, including branches, is sixtysix miles long, and has a carrying capacity of 4,200ga1. of water per minute. Fifteen miles of branch races are under contract for construction, and fifty miles additional are proposed to be constructed. The dimensions of the channels vary according to the quantity of water they are required to carry, the main channels having a fall of fin. and lin. per chain respectively. The branch races or channels follow the natural inclination or slope of the ground, having a minimum fall of lin. and a maximum fall of 2in. per chain ; and the general depth of the water in the races is one-half the breadth of the bottom, the slopes on the sides being 1 in 1; and the grade, fall, or inclination allowed being sufficient to give a velocity to the current of from 1-Jfty. to 3ft. per second.