THE CITY ENGINEER ON THE WAINUI WATERWORKS
Following is a copy of the report submitted by the Engineer to the City Council on the Wainui waterworks:—
“Gentlemen— I have the honour to report the result of my inspection of the concrete race at Wainui-o-mata on Sunday last, the 27th instant. I went through the race from one end to the other, and found that the race for about three-fourths of its length will require repairs, and in several places there are cracks on the bottom, in the angles, and at the side, and the whole of this length will require to be rendered on the bottom in cement.
Just between the first and second tunnels from the well, for a distance of about 40 feet, the bottom and middle parts of the race have cracked, and this portion has sunk in consequence, caused by the subsiding of the ground, the race having over filling placed in a gully; and to give the Council an idea of the work, I might mention that before repairs could be effected, the water lying in the bottom of the race was washed out through it, and I noticed wherever there was filling under the race, there were the largest cracks.
On the bottom of the race through the tunnels the rendering appears to have altogether disappeared. The more serious of these leaks were temporarily repaired by Monday morning, and the water was turned on again to the city at 6 p.m.; but in order to thoroughly repair the race, it will be necessary to shut off the water from Wainui-o-mata for at least a fortnight.
In order to show the difficulty of detecting the leaks where the cracks occurred in the race, it is only necessary to point out that those occurred where there are gullies in which water is flowing at all periods of the year, and a pipe drain was placed under the race in order to carry off the water from these gullies, and it was into these pipes that the water from the crack was flowing, and so escaped detection until the fine weather set in and the streams became almost dried up. Then it was found that more water was coming through the pipes than was flowing down the stream, and the leaks were consequently discovered.
With reference to the water flowing from the sluice tunnel, which is about four chains long and three feet in diameter, I may mention that this has always leaked owing to the defective sluice-valve at the inlet, which allows the water to come over the top of the valve, and this can only be remedied by having a proper sluice valve of cast-iron, with gun metal facings and frame. The custodian and I went through the tunnel and found the water was coming not only through the sluice valve, but also into the concrete tunnel, through holes in the sides, in at least a dozen different places, showing that the water was percolating through the main wall and along the line of the tunnel, so there would be very little use in trying to block up the outlet of the tunnel, and nothing can be done until the reservoir is emptied.
It has always been considered that the flow of the Wainui-o-mata River would of itself be sufficient at all times to keep the well full, so there was very little provision made for storage, and this has proved to be sufficient until the last three weeks, as during the whole of last summer there was a wash of water either over the by-wash at the well, or over the main by-wash; but during the last three weeks the summer flow of the river has not been sufficient to keep the well full, showing that there is either a greater consumption in the city or that the summer flow is much less.
And having gained the experience by this season’s drought that the summer flow of the Wainui-o-mata River, at its lowest, is not sufficient to keep the well supplied, and thus maintain the pressure to reach the higher levels of the city, I beg to recommend that as soon as possible the 30in mains be extended from the bottom of the well to a point in the reservoir at a level of about 2ft above the inlet to the sluice tunnel, thus utilising the present basin and making it into a storage reservoir.
By this means, if the basin were cleaned out, about 20ft in depth of water could be stored instead of only 5ft as at present. Another advantage of this would be that the waste over the by-wash at the well would be prevented. I estimate the cost of the work as suggested at £7000.
Since the temporary repairs have been effected the reservoir has become full and the water is running to waste over the main by-wash, and there is no likelihood of there being any scarcity of water at Wainui-o-mata this season.
With all due respect I would like to mention that the recommendation for cutting off the water from Wainui-o-mata was not made by me for the purpose of repairing the race; but, as stated in my report, for the purpose of giving the reservoir a chance to fill up, and thus enable the well to be kept supplied, which the then flow of the river was not capable of doing; and I then took the advantage of the opportunity offered to make a thorough examination of the condition of the race.
I also beg to report that Mr J. R. George, the manager of the gasworks, has kindly lent me some mains which, together with what we have in store, will be sufficient to connect the main from Karori Reservoir with that from the distributing basin, so there will be no necessity to call for tenders for the same. I expect to have the connection made by tomorrow week.
In conclusion, in justice to myself, I would like to state that the concrete race and sluice tunnel were passed and taken over before I assumed office, and the only portion of the Wainui-o-mata waterworks with which I have been concerned was the repair to a portion of the main wall which had been washed away just previous to my arrival in the Colony, forming the cushion wall, and laying the 3-24in sluice pipes, which work was satisfactorily performed by the contractor, Mr J. Saunders.
—B. Loughrey, City Surveyor.”
We understand the Public Works Committee referred the report to the Inquiry Committee appointed to deal with the matter.
Tags: Newspaper Water Race Waterworks
