ESCAPE FROM SERIOUS FLOODING

Gisborne Herald, Volume LXXIV, Issue 22374, 5 July 1947, Page 6

ESCAPE FROM SERIOUS FLOODING

SURGE SUBSIDES TIDE MISSES PEAK WAIPAOA’S DISCHARGE EFFECT OF NEW OUTLET Settlers on the Gisborne flats had another narrow escape from serious flooding yesterday afternoon, when the Waipaoa Hirer rose above its natural banks and lapped up almost to the tops of the ilood-banks located at the chief danger-points. _ At the peak of the flooding in the river land-owners were keenly concerned for their crops and stock, and when the level of the river began to drop about 5 p.m. in the vicinity of Patutahi and 'Waerenga-a-hika much relief was felt. There seems to be no doubt that the operation of the training-wall_ and pilot-channel through the sand-spit two miles from the mouth of the Waipaoa River saved the situation. The quick discharge given lo the flood-waters obviated the backing-up of the river s flow, and though there were some minor inundations in the area drained by the Karaua stream, between Manutuke and Muriwai. no serious damage was done at any point along the couise of the Waipaoa , . , . The fact that surf on the beach in the neighbourhood of the river s outlet was moderate also had a bearing on the quick discharge of the flood. The river flowed out fast and smoothiy through the cut and this had a marked effect upon the velocity of the waier for a considerable distance upstream. At the Matawhero bridge, where the main south highway crosses the river, the flood was moving out at high speed throughout the afternoon, the velocity in this section being probably greater than in anv recent storm. The quick movement of the floodwaters cleared the river appreciably before-the effect of the late-afternoon incoming tide was apparent, and there was no meeting of the peaks when the inflowing tide reached its highest point. Rose Over 17ft. Observations taken by two field-staff units under the supervision of Mr. A. D Todd, engineer to the Poverty Bay Catchment Board, indicated that the flood reached its highest level at the Kanakanaia bridge, near Te Karaka, at about midday, when the gauge showed a rise of 17ft. Gin. above normal winter flow. This peak continued until 2 p.m.. after which there was a gradual fall in the level there. At Waerenga-a-hika the peak was recorded at 3 p.m., and was maintained until about 5 p.m These observations confirmed a longstanding conviction on the part of old settlers that in flood-time the peak of water takes about three hours to move between Te Karaka and the chief danger-point in the lower reaches of the Waipaoa River, in the neighbourhood of vVaerenga a-hika and Patutahi. A considerable amount of additional information was gathered by the field units of the Catchment Board's .organisation, and this will be correlated with that secured from a number of voluntary observers who live along the tanks of the Waipaoa in the backcountry areas. The service rendered by tiiese observers yesterday was much appreciated by members of the Catchment Board staff and by the settlers to whom their information was relayed as it became available. Control Measures Settlers in many parts of the district had opportunities yesterday to observe for themselves the effect of river and stream control measures taken within the fast uvo years. Of chief importance was tne construction of the train-ing-wail and pilot-channel at the new outlet of the Waipaoa river, which has had the effect of lowering the level of the flood-waters by at least sft. near the mouth and reducing the danger of flooding throughout a distance of several miles upstream from the outlet. Of secondary importance in the general picture, but hignly valuable in their respective areas, are the measures taken in the Taruheru basin, the Ngatapa stream-bed, and the area drained by me navennam stream. Though work had to be suspended a few weeks ago on the Taruheru drainage scheme, with; only about half of the scheme completed, it was evident yesterday that this project has every likelihood of being an outstanding success. It handled a big volume jof drainage yesferday and cleared up stormwater over a wide area in record time, giving a degree of relief not known for many years. As a sighler on the eventual success of the whole scheme, yesterday’s experience was highly satistory. Ngatapa settlers also noted with interest the rapid clearance of water in the’ Ngatapa stream through the cuts made two years ago to short-circuit the more tortuous bends below the township. In this locality every heavy rain used to create a flood danger which threatened maize and pumpkin crops and frequently resulted in losses of stock, the basin on which the township was sited forming a ponding-area for water which could not escape through the normal bed of the stream. On many occasions the highway was invaded by flood-waters, with consequent damage and delays in transit for traffic. Construction of Cuts Within the past two years the Cook County Council constructed a series of cuts to give the water a more rapid exit from this basin, and the operation of these cuts yesterday left the vicinity of the Ngatapa township comparatively dry. No damage was done to crops, although the rainfall in the catchment area of the Ngatapa stream was exceptionally heavy; and the highway was not even covered by overflow from the stream itself. A "further satisfactory feature was the absence of any hold-up in the flow of the Ngatapa stream in its lower course. When the cuts were made near the township some concern was expressed by settlers on the lower course lest the speedier clearance of the top end would lead to inundations in them area. This concern was removed by yesterday’s experience. Lavennam road settlers likewise found the operation of the flood-gate established last year quite satisfactory, there being no ingress of water from the Waipaoa River even at theheighf of the flood. In past years the drain .had acted as an escape for surplus water from the main stream, which drove up the drain and flooded a substantial area. Yesterday the floodgate held ou.t this water, and though the normal drainage of Lavenham land was checked for a few hours while the Waipaoa was running its peak there was no suggestion of serious flooding. This morning conditions along the Waipaoa River had improved to a marked extent and almost the only problem left by the storm was the accumulation of water in the Ormond Dip, where late yesterday afternoon the depth on the main highway was sufficient to turn back small cars. Large numbers of travellers had to be piloted over this section of the road by the A.A. patrol, and today there was still a sufficient depth of silty water there to constitute a difficulty for the average driver.