Reclamation Works

Hawke's Bay Tribune, Volume XIII, Issue 282, 14 November 1923, Page 5

Reclamation Works

Mr. G. Nelson’s Scheme DIVERSION OF RIVERS. ADDRESS TO BOARD. In connection with his scheme for reclaiming the waste land around Napier, Mr. Geo. Nelson (reclamation engineer) yesterday addressed the Napier Barbour Board as follows:— THE VARIOUS AREASThe area concerned in those proposals is bounded on the east by the sea Ijeach, on the west by th© Grcenmcadows hills, on the south by a line drawn from Redcliffe to Waitangi, on the north and It embraces, and is bounded by, the limits of the Ahuriri lagoon and the lowlands adjoining it. Excluded from the area are all lands not liable to lie flooded. The whole area concerned has a common interest in river control, and its boundaries may, presumably, be regarded as ceter minous with those of that portion the Rivers Board district lying north of the Redcliffe-Waitangi line. These lands are interested in the river diversion proposal. The drainage district comprises all those lands within the area concerned which will be benefited bv the provision of improved drainage facilities. The reclamation area may lib defined as that portion of the drainage district which has little or no economic value in its present condition. NEED FOR DR AINAGE AUTHORITY

Before the work can progress, it will b<‘ necessary to take fcteps to put these several classes of lands under tribute according as, and in proportion to the benefits which they derive from the proposed expenditure. As matters stand the Board may carry out drainage works of great benefit to neighbours without being able to recover any part of the cost from the owners of the lands so benefited. It is a position which demands immediate attention. In the meantime. I am proceeding on the assumption that such body as may be constituted the authority for the main drainage of these lands will take over the assets and liabilities of this Board in respect to its main drainage works. The Awatoto canal now being excavated, is one of such works. The time expended on main drainage.works has been kept separate and I will ask the secretary to keep an account of it. METHODS EMPLOYED.

The method followed by Gooddall, . Carr, Kennedy and Co. and this Board hag been by the construction of works, more or less suitably designed, to promote the deposit of alluvium upon the low lands, and thus raise them to a ’ level enabling drainage. The best ex_ : ample of this method was that afforded r by Kennedy and Co. when dealing with the 300 acres now known as Napier South. This area was formed into a i settling basin by means of the earthwork embankment which was thrown around it. The Tutaekuri river was ’ diverted from its course along Riverbend road and turned into the settling 1 basin at its south-east end. At the 1 north-west end of the basin a portion 1 of the enclosure took the form of n • stone weir, over which the river water, ■ now deprived of its silt by the process of sedimentation, was permitted tc escape. The distinction between this method and that since employed by the ' Board is that, whereas the syndicate, • by the completeness of their arrangements, entrapped the whole of the ■ available silt passing under Meeanee bridge, the Board’s intake works con- • sisted merely of overflow cuts. Th<' great bulk of the silt flowed past these ’ down the river ? to be deposited in the • lagoon, some m the Inner Harbour, and the balance in the roadstead. 1 am aware that there are some who, enthused by the success that attended the operations of the syndicate, advocate the thorough treatment of out I lowlands on similar lines. The silting method has its ad van tages I admit. It suits the duckhunters and would provide a job for me and my children into the tenth generation. I was engineer to the syndicate from the latter part of 1900 till early in 1906—throughout practically the whole of the construction period. Speaking with the authority thus acquired, I say unhesitatingly that you should abandon the method as soon as you can. METHOD TO BE PURSUED. This problem must be tackled, as all problems in civil engineering are tackled, on economic lines. Apart* irom the areas which will be taken in from time to time from building sites, we cannot afford to reclaim our lowlands unless at a cost justified by their value for farming purposes. The method universally employed for reclaiming lowlands, at a cost within the limits thus imposed, is by draining them. The typical procedure is to cut a contoijr canal to carry the run-off from the ground already high enough to afford natural drainage. This channel would be tidal, and its effective level for drainage purposes would be mean sea level. Picture this canal as n ring running on a contour say four feet above mean sea level enclosing say 4000 acres. Picture within this another ring canal, embracing say 2700 acres, drained through a sluice which would exclude the tide water and be opened for only a couple of hours when the tide is out. The function of this canal would be of course to drain 'the annular space between it and the outer one. Its water level would depend on the tide range. We may tentatively put it at ISin. below mean sea level. It would drain the land lying below the 4ft. contour and above the 21ft. contour. Within the inner ring is all land loss than 2|ft. above mean sea level. It would bo drained by pumps which would keep the water down to n level about sft. below mean sea level. It will thus bo seen that, under the arrangements outlined, there are throe drainage levels:— (1) Naturally drained. (2) Sluice drained. (3) Pump drained. < The arrangement outlined is merely 1 typical. When the results of the topo_ graphical survey are available and the areas falling within the several levels < accurately computed, the various possibilities will be thoroughly examined. 1 What has been said so far refers to the reclamation of lowlands for farming. These lands will be well drained and suitable for building upon, but, if public sentiment demands tnat they bo raised, they con be lifted with spoil excavated and deposited by suction ■ dredges. The inner harbour basin can i furnish enough material to raise not less than 1500 acres, and, to raise the remainder, lakes can be excavated a? ’ and where required, MAIN FEATURES.

Th© main features of my proposals are:—

fl) Tlie diversion of the Ngaruroro and Tutaekuri by means of a joint channel discharging into the sea at Waitangi, • (2) An embankment across the southern end of the Ahuriri lagoon from north of Parke Island to Westshort (including provision for the passage of the tidewater to and from the remainder of the lagoon). (3) The drainage of fill lowlands south of this embankment by means of ditches and canals drained down to a fresh water lake to be formed in the lagoon to the oast and north of Parke Island, the water level in such lake to be maintained at a suitable low level by one or other of the means indicated, or by a combination of such means.

(4) The construction of certain ma., avenues for road traffic to and from Napier. (5) The reclamation by means of spoil excavated from the harbour basin of an area of several hundred acres immediately on the south side of the Parke Island-Westshore embankment, such area to be developed as a seaside resort (6) The layout and sale of garden suburbs from time to time. (7) The reservation as an industrial area of certain lands adjacent to the Port. (8) Generous provision for the recreation <>f the people. (9) Lands not otherwise required to be brought into condition as soon as possible and Jet as small farms. (10) To compensate for the reduction in area of th. Ahuriri lagoon by tne excavation of channels designed to secure a fu’br fill of what remains, the spoil from such <*hannels to he deposited upon adjacent beaches or islands, which will be planted and otherwise improved in due courseIMMEDIATE PROSPECTS. The whole of the Awatoto block and part of the Richmond block, about 800 in all, should be (available for settlement next year. Pending the diversion of the river to Waitangi, the silr. can be used to raise the general level of the area, between Parke island and the Westshore embankment. Th< “South West Pass” referred to in my report will greatly assist the process. Ar earlv work in this locality will probably bo the construction of a rubble wall thrown out from the south, ern end of the Westshore bridge for a distance of about 40 chains in a northwesterly direction. The immediate function of this work will be to prevent river silt lining carried into the harbour on the ebb tide. It Hl] later form part of the proposed embankment. When the Waikaka has completed the excavation of the new pass she can continue the development of the scheme in this localitv.