OVER THE SPILLWAY

Evening Post, Volume 105, Issue 4, 6 January 1928, Page 8

OVER THE SPILLWAY

DIVERTED WAIKATO A THRILLING SPECTACLE PIERCE EROSION The Waikato Biver has been successfully diverted from its old bed at Arapuni to tho elevated channel from which tho water, descending through pipes, will reach the turbines of the coming big power station. By midnight on 31st December the Waikato River "first-footed" the creek unknown to fame as Waiteti, and great was the surprise of the creek, says the "Taranaki Herald." Greater it was when, 12 hours later, its bed had been consumed by the river, and greater still, five hours later, when this old river in a new course had cut a channel chains wide and fathoms deep. A little before midnight on the last ! night of the year the water, banked up for 18 miles by the Arapuni dam, lapped over the spillway and by morning was running just over 12in above the weir. No seepage of any moment- had taken place above the power house site, and the total flow below or around the dam (including old springs) was not more than the insignificant quantity of ono cusec. The new river, passing over tho spillway, reached the top of the new cataract, without erosion and leaped down to the flat, a distance of 70ft from the top of the cataract, as the beginning of a new Huka Falls and Atiamuri Rapids combined, and found its way to tho old bed two and a half miles downstream from the dam, by the farthest and best course. What it did on that course was- the spectacle of the day and of the job, if one forgets the two explosions at the diversion tunnel., Suffice it to say that in one hour it eroded more spoil than was sluiced out of the head-race in a year, and that in 24 hours it was well into its second million of cubic yards. And all this with about onethird, of the volume of the river. CLOSING THE GATES. The partial closing of the foot-thick steel gates began on 2nd December, and since then the water has been backing up behind the dam, which from crest to deepest point is 215 feet deep. The lake thus formed—Arapuni lake, as it must in future appear on all maps—is now about three-eighths of a mile wide for about four miles, and is a lovely stretch of blue water, upon which various kinds of boats have already ventured. WILD LIFE DISTURBED. Many slips of pumice have 'occurred on the banks, and in shallows where the heads of manuka bushes are.,, still above water, frogs croak en_lcssly against such wanton interference with Nature. A forfeman states that as the swampy portion of the head race was being submerged he saw rats, which abound in the scrub, chasing dislodged frogs and actually diving after them in the water. Furthermore, rabbits driven away from their burrows by the water tried to run back to them when dogs chased them. Leaving fact, one may perhaps continue in legend. The Maoris, it seems, remained convinced that the taniwha still lived in the river and would upset the scheme ono way or another, and so sure were they of tho existence of the monster that they had a distaste against coming down from the quarry by launch. BEFORE ITS TIME. By 11 p.m. on 31st December, the lake, stretching back 18 miles into the hills and holding 5,000,000,000 cubic feet of water, was beginning to lap over the spillway. Thanks to some rain in the previous week, it was about 36 hours ahead of schedule. By morning it was running one foot deep over the weir, the position then roughly being that one-third of the flow was going through the tunnel, one-third over the spillway, and one-third to storage. Below the spillway the stream races to a cataract which finally leaps past a huge boulder, taking a leap of 30ft or 40ft to tho flat, where a lagoon has formed. When the whole flow of water goes over, it will make a double fall, with the boulder in the middle, and what will happen to the boulder then will be of great interest. That boulder may cost a tremendous amount of money should it wash away and lead to erosion up toward the spillway. That is a matter for fte future, however. DISAPPEARING ACRES. Fromthe spillway to the point where the new river is desired to enter the old course the distance is one and threequarter miles. Beneath the falls it widened out into a large lagoon, and then took th old Waiteti Creek channel which meandered along the north side of the flat and entered the river at the most northerly point possible. When the flow began there were three falls eight feet high on the way. By noon, so great was the erosion, there were none. Through the flat, which, except for odd rocks and banks of boulders, appears to be one mass of pumice, it had cut a channel in places two "chains wide and ten feet deep. Falls from the banks continued endlessly, and acres disappeared, in an hour. At one point rock on each side held the stream, which ripped through it like the Waikato of the. gorge, to exert its fury against the sandbanks below. Toward the old river course it took the turning to the north, as was intended, and made banks 25 feet high. But tho pressure at the turning point ate into the 40ft bank that separated the river. Great slips came down, and suddenly, after 4 p.m., it broke through and for the remaining hours of daylight the few spectators had a sight that has never before been seen in the Dominion. First, the water fell into the old course over a bank Bft high. This bank crumbled before one's eyes. In an hour and a half it had gone through the horseshoe stage and had been eaten into a channel four chains long and about eight feet deep. Rocks rumbled down and ti-tree floated away, often in an upright position. It was a spectacle that the ordinary man would have regarded as incredible from hearsay. Tho south bank was at least 40ft high, and it began to slide away at the rate of feet a minute. At dusk the local people went home and, as they sank to sleep upwards of two miles away, heard a sound that was like wind in high trees, with the rolling stones producing'the effect of a rumbling freight train. IN THE MORNING. In the morning the gap was not a few chains wide, but between 200 and 300 yards, with another 100 yards of the high bank on the south menaced. The chance was terrific. The current had left the north side, had passed away from a boulder bank in its earlier course, and was still ripping away the bank on the south which, as tho bank of the old river, might have been expected to contain rock. The effect of it all had been to fill the old course with silt, and in consequence tho water from the diversion tunnel banked up to a height of at least 15 feet. To help to clear the silt, and also to reduce the amount of debris going down to clog tho screens at Horahora, the gates were opened a little during the night. A RUBBISH "MAT." The Public Works authorities had anticipated that a considerable amount of &£__: ____4 te ____*_d __w__*_-_»

from tho erosion of tho new course, even though the scrub along the Waiteti banks had been burned. They had j prepared for it by constructing a boom of wire and slats floated by oil drums, by which it was hoped to divert this matter from the head race at Horahora. They had not expected, however, that many acres of standing scrub would be shifted, and toward the end of the afternoon the boom was not equal to the demands, when additional men had to be assembled at Arapuni and sent down to help to keep the screens clear. By 10 p.m. the task got beyond them, and the station had to be partially closed down. This happened several times during the night, when it. ">vas stated the "rubbish" formed a mat along the screens that a man could walk on. However, Auckland power was fed back, and with constant cleaning tho station was kept going. Arapuni had given a number of thrills since it began, but that of Sunday and Monday, when the new course i was eroded in such a remarkable manner, was the most spectacular. It might bo said that the Waikato or its taniwha has had' its final protest, and that in duo time, thanks chiefly to a remarkable low degree of percolation from tho head race, it will soon submit to the toil of the turbines. Should it yet succeed in keeping a high-water level at the power-house site, the job of the Public Works Department will be difficult and long.