A LOST RIVER

Poverty Bay Herald, Volume LXIII, Issue 19135, 2 October 1936, Page 4

A LOST RIVER

THE GREAT WAIRARAPA COASTLINE SIIBSIDES MR. 11. HILL'S OPINION "The East Coast of the North Island from East Cape to Oastlepoint presents features that imply important physical changes at no distant date," declared the late Mr. H. Hill, 8.A., F.G.S., in the course of a paper read before the Hawke's Bav Philosophical Society in July, 1908. Mr. Hill's observations have an interesting bearing on the subject of the suggested river iiowing under the Poverty Bay flats, claimed to have been located by Mr. J. C. Field, and now engaging the. attention of the Gisborne Borough Council as a possible source of water supply for the town. Originally the East Coast extended much further seaward, according to Mr. Hill, and a large river formerly flowed from Poverty Bay, along the coast south from Gisborne, passing between Mahia and the mainland, thence across what is now Hawke's Bay, and down the district of that name into the Wairarapa. Great Volcanic " activity, he suggested, subsequently caused a large' portion of the coast to disappear and sink beneath the sea.

"Heretaunga Plain is a late formation," declared Mr. Hill, "and the process of growth is still going on as the material is brought down by the rivers. The same could also-be said of the plain area between the mouth of the Wairoa River and Te Kapu, or Frasertown, some 10 miles inland. .So, too, the Poverty Bay plain forms a part of the water area, and both of them occupy the place once occupied by hills that united Young Nick's head with the hills that now bound the coast along what is known as the Kaiti side of Poverty Bav.

"The East Coast between East Cape and Cape Turnagain at one time extended much further seaward. At the time when this condition existed the general slope and river system of the island was very different from what is now the case. The slope was generally to the east by south, and the Ruahine, Kaweka and Titiokura ranges had not then reached their present elevation. The various streams that now constitute the different river systems seem to have formed one river that had its headwaters in the back country to the westward .of Poverty Bay. The river made a bend to the south by west, and proceeded past the Mahia, through Hawke's Bay, south-west to the valley now known' as Heretaunga plain, and thence west by south onward to the. Wairarapa. VOLCANIC ACTIVITY "Towards the close of the pliocene and the opening of the pleistocene periods great and important changes took place. Great volcanic activity was experienced in the interior of this island, and the East Coast was shaken to its foundations. It was during this period of activity that a large portion of the coast disappeared and sank beneath the ocean. Hawke Bay, Heretaunga Gulf. Wairoa Gulf, Poverty Bay and Turanganui Gulf were formed at this time. The great Wairarapa disappeared as a river and the entire aspect of the water drainage was modified. What formerly had been tributaries of a great river now began to form separate basins of their own, and we have the interesting fact that by ordinary earth movements new rivers "and new river systems may be brought into existence and the facies of a country completely changed. "An inspection of the areas, that now form the river basins will supply the fullest evidence of a contemporaneous past in the shingle, pumice, sand and vegetable deposits that are found within them. In Poverty Bay, the Kaiti hills, the lower hills on the" Whataupoko, the hills near Ovmond, Te Karaka, and numerous others abound with facts, to show the state of the country before the present plain and river valley were in existence.

"Similar evidence is forthcoming in the case of the Wairoa, Mohaka and other river basins in Hawke's Bay. At the entrance to the Wairoa and Mohaka Rivers, and on the hills towards Fraserlown and the Wairoa Hospital, shingle and pumiceous deposits occur, and in the inner portion of Cape Kidnappers, sections 200 ft. in vertical height display the same characteristic beds such as are met with, though less developed, in Poverty Bay. To the north-west and south-west of the Kidnappers, through Maraek'akaho. and thence past _ the Gwavas station on to the Ruataniwha plains, the hills both to the right and left are made up solely of the Kidnapper and Poverty Bay shingle series, and these continue through Takapau, Ormondville, Matamau and Dannevirke in varying thickness and extent." RECOVERED FROM THE SEA Mr. Hill went on. to indicate the work that had been done by the rivers that came into existence, following the great subsidence along the coast. "Ruataniwha, Heretaunga, Wairoa, and Poverty Bay plains have all been formed by means of the materials that the several rivers have carried down in flood time," he said. "Slowly the mouths of the rivers have extended seawards as the deltoid areas have grown year by year, and rich lands have taken the place of the once water area, and the same process of growth is going on to-day. The rivers are still carrying down their treasures of material to the lowlands, and these latter are being aided by man's intelligence and industry. Since the formation of the new drainage areas and river systems the 'made land' along the coast, as won from the sea, must amount to over 150,000 acres, and carried a population of about 40,C00 persons. "At the time of subsidence a gulf extended inland of the present Poverty Bay even beyond Kaitaratahi, and into this gulf, which is named Turanganui, several important rivers flowed. As in the case of Heretaunga plain, the rivers were and are great carriers of debris, and the plain as a deltoid! changing area has grown in a manner identical to that of Heretaunga, so that the work of growing is still in progress.'' Mr. Hill's paper was accompanied by various maps rgid one of these is a cross-section showing the bedding of the present Poverty Bay flat from the hills near the school at Te Arai, and the hills over which the road passes to the Waimata Valley. Along the plain is shown the location and depth of artesian wells that have been put down, and also a complete section of one well. The cross-section shows the following wells : —Weston's, S74ft; Makanri, 347 ft. anct 230 ft.; Makaraka, 236 ft.; Taruheru freeing works, 95ft. and 275 ft.