Artesian Systems of Heretaunga Plains

Hawke's Bay Tribune, Volume XVII, 1 October 1927, Page 15

Artesian Systems of Heretaunga Plains

SOURCES OF SUPPLY RELATIONSHIP OF POUKAWA LAKE Recently Mr. P. G. Morgan, Government Geologist, visited ...Hawke’s Bay with the view to investigating and reporting on the effect that the lowering of Lake Poukawa and the drainage of the neighbouring ewamps would have on the artesian water supplies at Paki Paki and Hastings. . Mr. Morgan’s report on this subject 1 appeared in the annual report of the Department of Scientific Research and was republished in the Tribune. . There also appeared in the Tribune a letter commenting on Mr. Morgan’s report. .The following is Mr. Henry Hill’s comment on the report and reply to the letter:—

Sir, —I was made aware through the courtesy of your Napier branch and a friend in Hastings of a letter and a report in your issues of the 21st and 22nd respectively, having reference to Poukawa lake and artes ian wells. Why does not vour correspondent “A.B.G.’’ sign his name? One cannot fight "anonoymitv’’ attached to a heap of sawdust. If a writer has an opinion that he can unhold with a reason therefor, let him make it known and sign his name, and good will follw. Clearly “A.B.G.’’ writes without having read anv ot my references to Poukawa lake and the sources of the artesian water in the Heretaunga plain basins. Had he followed the advice given bv Mr P. G. Morgan, ho would have learnt that I made no reference to the drainage of Poukawa lake. With this letter. I am sending a copy of the paper referred to bv Mr Morgan in his report. You are at full liberty to make such excerpts therefrom with reference to Poukawa lake. Paki Paki artesian wells, and to what is said of the sources of the Hawke’s Bay water hearing beds. The paper was published in the proceedings of the New Zealand Institute in 1923, and the facts with reference to Paki Paki. etc., were obtained in a personal visit to the dis triet and by letter from the owners of wells as named in the paper. The information supplied indicates with sufficient clearness, at least to me. that water from Poukawa lake does find its way by underground intervening beds into the artesian system of Hawke's Bay. WATER PERCOLATION. It is useless to talk, or write ior that matter, about the supply of water into the artesian beds merely along a surface channel, such as is sugqqsted. Water does not pass into artesian beds by mere soakage or the cutting of drains. Percolation downwards and horizontal along the inclination of beds may take months, and maybe years to reach a water bearing basin, and it is all nonsense to sui«>ose that so soon as rain begins to fall, it drains into the artesian beds and thus causes a better flowage in wells. 'Mr Morgan, in his report, expresses an opinion as to the probable effects of the drainage of Poukawa lake. 1 do not. Some months ago. when a deputation of Hastings citizens met the Minister and suggested the purchase and drainage of Poukawa lake for settlement and the to sav on the matter; nor has mv opinion altered on the importance and seriousness of the issue raised by me. EFFECT OF DRAINAGE. It is forgotten by many in their desire to obtain Native lands, that soakage of the land has been going on for hundreds of years before the

incoming of the Europeans. Water slowly percolates through the land, and every means employed for draining land lessens the quantity in the adjacent surface beds. Similar processes go on in putting down wells and pits. The land is slowly drained and ultimately desiccation begins. Those who studv water systems are aware of the truth stated here. Hastings possesses --qi-v able well-sinking experts in Mr Liepst and Mr Willan. junr.. and those gentle men know the truth of what is stated here. Lakelets and water basins found here and there over the district are as valuable as the land that surrounds them in providing moisture and limiting extremes of heat in a district where found. EXPERTS DIFFER. Air Liepst does not think that rhe Paki Paki artesian wells are fed in any wav by water from Poukawa. On the other hand, Mr Willan strongly supports the claim, and sends me a sketch illustrating his experiences and results. The tests he has made prove up to the hilt the truth that water is slowly passing along r .he valley at no great depth. I enclose Mr Willan’s letter with diagram to publish. I would add here that Mr Willan has followed for testing purposes ihe whole of the water-bearing areas of the district described in mv various papers. Of course, neither Mr Leipst, Mr Willan nor myself make any reference to the drainage of Poukawa lake. Of the lake I affirm: (a) That percolation naturally proceeds from an elevation of 80 feet above sea level to the waterbearing beds at from 95 to 135 feet in the vicinity of Paki Paki. The latter place is 40 feet below Poukawa. and the water beds as between Poukawa and Paki Paki are' from 95 feet to 135 feet. (b) That should the lake be drained, the physical condition ns io moisture and temperature in the valley will be greatly altered, and the land in course of years will show traces of desiccation. HUMAN NATURE NOTWITHSTANDING. In conclusion. I quote a paragraph from Air Morgan’s letter which I confess I do not like. It is the following : “It needs little knowledge of human nature to predict that if the Poukawa swamp is drained, anv subsequent falling away in the artesian water supplies will be attributed by many persons to the drainage operations. Yet the true causes will be those mentioned above.’’ If drainage of the lake is to bo undertaken and the residents of Paki Paki and district find as a result of such drainage that their artesian

ENCLOSURE 1.-MR WILLAN’S LETTER.

.wqlls ■ have diminished or ceased to flow, I should unhesitatingly refer the cause to the disappearance of the lake, ; Mr Morgan's factors notwithstanding.

Dear Mr Hill, —Please find enclosed letter on Poukawa lake, which appeared in our paper last night. I have drawn a rough sketch showing flow of underground waters as I find them when sinking a well in the valley. At the top end of the lake you can get artesian wells equal to any of our high pressure artesians in the Plain,

The flow of water into the lake underground at the top end is enormous, and I fail to see why it is not running out again as illustrated in my diagramWater does not necessarily have to have a shingle formation for it to per colate through. Around Paki Paki I have drilled wells which produced large flows out of limestone and shale rubble, which I think must have been deposited bv river action from the direction of Poukawa Valley. The fact that the valley narrows at Paki Paki does not alter the fact that in narrow and constricted underground channels water does not run at a greater speed and. thereby draining off a greater quantity of water Tn a given time than if the formation were less permeable. Why some wells do not flow as vou go further up the valley is owing to height above intake and outlet, which of course you fully understand. Theer has been much discussion in Hastings lately regarding artesian supply in connection with the Poukawa lake, and 1 would suggest vou answer some of these critical chans in a good article for our paper. I have given you some data in this letter as I have found it in practice, but should you want more or anything that may occur to vou. I would be pleased to let you have it. Of course, you may not see eye to eve with me. but to me. I cannot discount the Poukawa lake altogether from our artesian system. —Yours faithfully. T. WILLAN. P.S.: Most people consider onlv surface water that drains into rhe lake from streams, springs, etc., but I think that the underground flow from the Otane direction is the most important.—T.W. [The sketch plan, which we are un able to reproduce for printing, shows the direction of the flow of underground water from above Te Auto lake and finishing in the artesian beds at Paki Paki. Mr Willan savs the. data for the plan is derived from the sinking of wells from Paki Paki to Te Ante—Ed. H.8.T.l ENCLOSURE 11. Excerpt from Mr Hill’s paper on Water-conservation and Hawke's Bav Artesian Systems: As for Poukawa lake being the source of supply for the artesian waters of the Heretaunga Plain, it may be of interest to explain the relationship existing between the lake and the plain. Hawke’s Bav ex tending from Portland Island on the north to Cape Kidnappers towards the south, is a part of a land area that was destroyed in part and was otherwise fractured at a period of great volcanic and earthquake activity at the close of the Pliocene and opening of the Pleistocene periods of geological history. The great break about AVaipukurau with the Hatuma lake, and the line of fracture through Otane and Opapa with the series of lakes formed, according to Maori tradition, by Tara and his dogs represent the result of the devastate'.' apd changes brought abcut at that time. Since then the earthbuilding has gone on apace. Only Hatuma lake remains, representing a much larger lake, and the valley between the ranges of hills extending from Waipawa to Napier has been mostly filled bv the washing from the rivers and hills that have taken place. The creek from Poukawa into the plain represents what was at one time a much larger communication, and there can be no doubt tluit water from the lake percolates into the artesian water bearing beds long before they come within the direct limits ot the plain. But what is said of Poukawa applies equally to other vallevs that carry waters to the sea across the plain; hence it follows that there is percolation going on from the Tutaekuri. Ngaruroro, and the Tuki Tuki rivers long before thev enter the limits of the plain, and these sources of supply slowly provide water that is ablp to give a regular quantity of artesian water, sufficient apparently, to meet the full requirements of the district and equivalent, according to my estimate, to an annual rainfall of 7 inches over the entire area of 80,000 acres.