THREAT TO WORKS:

Rotorua Morning Post, Volume 1, Issue 185, 30 March 1932, Page 5

THREAT TO WORKS:

INVESTLGATIONS BY WELL - KNOWN ROTORUA - DIVINER DANGEROUS P O TENTI ALITIE S A highly disquietirig statement and one which, if Mr; Thompson's investigations are correct, has a very grave bearing upoh the whole stability of the Arapuni hydro-electric umdertaking, was made to a "Post" reprSsen- ' J tative yesterday hy Mr. A. G. - Thompson the well-knowri water diviner of Rotorua, who hSs recently returned from investigations made at the works; t : Mr. Thompson states defiriitely, and is prepared to stake his reputation upon the assertion, that a large underground stream', "a second Waikato" iii volume, sweeps almost under the powerhouse, while a large subterranean "fountain head" or up-rush of water with underground streams radiating from it, may prove a grave source of danger when the ? tremendous pressure of the water rushing through the head- > race is released. According to Mr. Thompsori, jthe main stream is not more than 1^0 feet below the surface at the p'owefhouse, arid iis quite possihly respoiisible for the Mysteribus vihratibri which has made it unsafe to u'se ori'e of the turbines. Another sigriiiie'ant fact is that, according to Mr. Thbmpson's plotting of the course of the stream, it follows the same line as the recent earth crack which developed at the penstocks, arid necessitated a hold-up in the wofk 'and extensive strengthening operatioris. Mr. Thompson's rbputaUori as 'a sucCessful diviner is well known iri the Rotdfua district, and his outstanding suCcess in corinection with the underground streams which thf eat'eried the bororigh sewefage pumpirig station is still fresh iri the pfiblic mind. In view of these facts, arid iri view also of the undbubted poteritialities of danger and serious damagb which exist if Mr. Thompsori's assertions are correct, his stateinent's undoubtedly merit the inost v serious attention, and at the very least, thb most careful and independent irivestigation to determine their truth. Tests Carried Out Mr. Thompson's investigations were made in company with a prominent engineer, and it has since heen ascertained that certain horing tests hrive been made which 'have definitely established the existence of .underground water at spots marked by him. Mr. Thompson's t contention is that the scouring action bf a large body cf underground water may at any time precipitate troubTe, whfie he also suggests that the weakening ' of ihe ground in the vicinity of the "glory hole" where the headrace waters sweep dowh a slope on their returri to the river, may, despite the concrete strengthening work which has been carried out, result iri a serious erosiori wlrch might possibly cause grave trouble at the penstocks. ".-;V ? *'■ * • • ♦ -k- ' Course of Stream The course of the main underground stream, according to Mr. Thompson, vuns at right angles to the Waikato River and the headrace, and passes within six or severi yards of the near eorner of the power-station. It is significant, he states, that the turbine which is at present proving unsatisfactory, is the one most adjaeent to the course of the stream, . and he suggests that the vibratioh ih the machine which has puzzled the experts may conceivably he due to the fact that the scouring of the underground river is weakening the concrete foundations upon which it was set. In order to prevent this vibration, the turbine was placed upon a sobd block sunk well down, but if Mr. Thompson's hypothesis is correct, ft would be possible for the ground beneath this block to he undermined aiiii weakened by the passage of the underground water. A theory suggested to explain the vibration was that a vacuum was created by the out-rush of water from the' penstock tunnqls, but if this theory was tenable, ; it would he logical to assume that all of the turbines, and not one only, would be affected. In any case, it is definitely known that the particular turbine which has heen causlrig trouble will not be used when the works commence to ojierate. Line of Crack. From the power-house, Mr; Thompl son states, the course of the i stfeani follows along 'the line of ! the recent crack to the penstocks and i crosses the headrace at a considerable i depth. ' : When he conducted his investigations, Mr. Thompson drbve pegs. above certain spots where he' considered } water should he fofind, and he states p that subsequently boring tests have , proved the truth of his theory. The l pegs were driven ori the other side j of the race beyond the penstocks> but j so far as he knew no tests had been ' ; made between the penstocks and the power-house. t - Precipitate Trouble. * At one spot, Mr. Thompson states, the stream flows under the penstock tunnels which run from the headrace to the power-house, and while it dp- ^ pears to be at a considefably greater depth at this spot than nearer the tiver, there is still a danger that any . earth tremor or undue scouring in the L stream may precipitate trouhle.'hy l" undermining the tunnels or fhe $owerhouse. e In this connection, Mr. Thompson considers that a heavy damming of r the stream may have beeri resfion,e sible for the ahpearance arid variaw tioris in level of the "mystery lake" l(i a large lagoon of water tvhiqh appeared in the hills at the hack of. Mt. •ri Maungatautere during the operations at Arapuni. He states that' so far 'as 3f he can determine, the underground ig streani flows froni the directiori in t- ' ' (Continued ori Page 3)

UNDERGROUND R!VE?f «*/ (Continued) ;; which this lake appeared, and sug,'gests that it may conceivably have been formed by the damming of the •stream, and the forcing of its waters •up some earth fissure which connect;;ed with the depression where the lake ;'now lies. The appearance of this • -sheet of water aroused considerable "curiosity, and it is possibie that if Mr. Thompson's assertions are proved, the Tsecret of its cnmmrtion with Aia- ' .puni may be explained. • . p" ? . Underground Fountain Head Another source of potential dang.,er, Mr. Thompson states, is adjacent to the "glory hole," the artificial " waterfall over which the millions of gallons from the headrace will rush ..when the water is released. ' . Mr. Thompson states that he went very carefully over this ground, and . is convinced that at a considerable ' depth, at a spot about a cha'n from " the edge of the "glory hole," there is p. tremendous up-rush of water . from a "fountain head" or large subterranean spring. This "fountain head" is a centre point for a number of smaller underground streams ; which radiate from it, and have had the effect of considerably weakening the ground in this vicinity. » This weakening, Mr. Thompson states, may have been further accentuated by the construction of the tunnels which were built on the recommendation of Professor Hornell to carry away the seepage water. It was considered that ' this seepage emanated from the lake or the river and while to a certain extent this is ' probably correct, Mr. Thompson contends that to an even larger degree the underground streams are respon- , sible for the excessive moisture which is weakening the ground.

i The danger at this point, he states, » may come when the water is released through the headrace and the tremendous pressure which it will exercise makes itself felt. A great deal of concrete strengthening work has be^n carried out at the race as a safegua~*d against tlr's contingency, but with t^e pressure of the water above, and the unsuspected weakness brought about ~ by the presence of the underground 7* water courses, there is a grave poscubility, in Mr. Thompson's opinicn, that a portion cf the underground ♦ structure may give way and a dangerous scouring commence. This scour- - ing might auite easily be unsuspected beneath the waters of the race, until •» irrenarable damage was caused by a " . sudden breakage. With the tremendous erosive force of the water, it I would be possibie for the scouring to extend to such an extent that it woukl undermine the stability of the spiT- - way wlrch sfands between the pemmd uu waters from the lake, and their •j release.

Stake ReputaFon Mr. Thompson stated that he was definitely convinced that his investigations, if tested, would be proved to be correct. As a layman, he cor.ld venture no oninion upon the exact extent to which tbe presence of the^e undererround streams would affect the . stability of the scheme :n general. hui it app°ared to h:m that there was an « urgent necessity to invest:gate tl'is new development and ascertain what could be done to safeguard the pch tion. He was certain of the presen-e " of these large bodies of underground water, and was prepared to stake his reputat'on that careful and inderevdept tests would establish the truth of his inwQC"'"iTat:o.ns.